Gallery, Projects and General => Project Logs => Topic started by: sorveltaja on March 23, 2020, 08:24:37 PM

Title: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 23, 2020, 08:24:37 PM
So this is going to be an attempt to make sense, of what kind of simple circuits could be used with analog hexaphonic guitar pickup.
I felt that it isn't fair to clog the optical pickup thread with this subject, so here we are.

But to the point. To get started, I'm aiming for outputs, that have more harmonics in them, than the plain square waves, that the pickups produce(there are clips on the optical pickup -thread).

Here is the first circuit, that I have already simulated, and tested on breadboard:


That waveform isn't in sawtooth form, that I was after earlier, as it was used on many analog synthesisers. It sounds like this(saved from the simulator, but the breadboarded circuit sounds practically same): (

It has one drawback in it, though. The fundamental frequency of the output is input divided by 8(In this case the input frequency was 1000Hz, and output was 125Hz).
There was only one thing, that I could think of, to multiply the input by 8, to get the input and output frequencies to match - 4046 pll(phase locked loop).

As the form of the input is square wave, it wasn't problem. That 4046(standard version) requires input to be close to the supply voltage, which was 9 volts.
The amplifying circuits of the optical pickups provide enough output, so that the 4046 is able to track the input signal.

I'm not too good on drawing schematics, but here is the circuit, as it was breadboarded(10k resistors on the right present resistor network):


In practice, it seems to work.

Then, after some searching on the net about "staircase generator", I found something like this, kind of "sampler" that is based on 4051(8-channel multiplexer):


It sounds like this: (

For some reason, it also has fundamental output frequency, that is divided by 8. The 10k resistor network might not be necessary, but the point is, that the resistors on the 4051's outputs could be replaced with trimmer pots, to adjust the combined output to make arbitrary waveforms.

I haven't breadboaded that yet, but what the heck, there is only one way to find out.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 24, 2020, 05:59:41 PM
The 4051-based idea of arbitrary waveform 'generator' is now tested on the breadboard, and it works. The circuit:


And same on the breadboard:


The stepped output waveform is easily modified with trimpots. As there are 8 outputs, there are also 8 adjustable steps in the wave. Triangle-ish one:


And same after filtering:


One thing, that I noticed, when looking the combined waveforms on the scope, is that it couldn't track them too well. All kinds of wiggling happened. Maybe the produced waveforms are more complex, than they look.

But on the other hand, I think I'm going to build(at least) two or three of those 4051-based contraptions. Perhaps some with fixed waveforms. For the adjustable ones, some kind of futuristic, retro indicators would be nice to have, to visualise the form of the wave without the need of using scope. Something like 8x8 Led matrix comes to mind. But we'll see.

As mentioned before, that circuit also divides the input frequency by 8, and therefore needs 4046 and 4017 before it, to multiply the input frequency first by 8.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 25, 2020, 11:17:32 PM
So now I'm hooked into testing/making a visual waveform indicator for that 4051-based generator. As usual, the simpler it is, the better it is.

One possible candidate is something like this:


I already have the two 3914's(actually from an ancient led-oscilloscope project) and 4017's on my shelf. Plenty of leds also(from the same scope project).

I tried to simulate the above circuit, but the results were very quirky and useless. That's why I'm not a big fan of simulations. Certain rules must be obeyed, or the result is garbage.
So not much of  'diy circuit bending' allowed.

Usually at that point I move straight on to breadboarding, but this time both boards are occupied by other circuits, that are still under testing. Jolly good(

But no matter what, I'm going to test that circuit above, to see if it's clumsy or useful in practice.

In fact, even if there are several of those 4051-based devices, only one "plugin"- 'display unit' is actually required. After all, they need visual indicator only, when adjusting the waveform. Multiple, permanent displays would be a lot nicer, though.

In the end, a spin-off of the recent brain hickup was to make a steampunk-like, victorian style, mechanical indicators for each of the trimpots, that are used to adjust the waveform.
All the gears and stuff.. some of them could be rather easily printed out... and the end result would be - bulky.

And other than that, I had an idea of using the pickup's outputs to control some kind of mechanical devices. Sort of like Mellotron(, that has a tape loop for each keys of the keyboard. Very heavy yes, and the tape technology is getting rare these days.

Instead, for more precise(like industrial) response, stepper motors could be used to rattle whatever objects, or what the heck, even plain cheapo small electric motors for more "organic" sound.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 27, 2020, 11:03:34 PM
Led matrix isn't easy to breadboard, so I decided to build one, for 10x8 leds. Last two rows will be added tomorrow, and rest of the wiring:


So far, all the rows seem to work, as expected. Needless to say, that it's rather tedious to build things like that. Local suppliers have a very limited selections of the led displays, so one should see what's available on Ebay. But for now, I'll skip that option.

On the other hand, what could be better, than recycling components, that have gathered dust for years on the shelf?

What comes to that 10x8 led matrix, if the idea, that I'm after, works, it could be used as a single display for something, like three 4051-based generators. Not really multitasking, but for one generator at a time, when checking/adjusting the waveform.

While scavenging leds from the old led-oscilloscope project(it had 16x10 leds), I got an idea, that the 8-step waveform generator could be extended to have 16 steps for finer adjustment. Probably not worth doubling the parts count, as it could still sound the same as 8-step one does.

After all, using simple filter(s) to alter the stepped waveforms could be easier to deal with.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 28, 2020, 09:10:03 PM
So the led matrix is built, and the circuit is breadboarded:


The led "display" shows different waveforms, but not exactly in a way, that I was after.

As on the oscilloscope, there should be a trigger function, which keeps the waveform from wandering back and forth. It is possible to do, by adjusting the 4017's frequency, but the "triggering" depends also on 3914's input signals frequency.

One might wonder, why I'm so eager to add a visual indicator for that 4051(8-channel multiplexer)-based waveform generator. It's simply because I just love all the bells and whistles it could be a lot easier to remember, what kind of set of adjustments sounds good or bad.

Like a connection between aural and visual 'image'. For example, a guitarist, that uses one or more effect pedals, has an image in his mind, of what his favourite sound 'looks' on those pedals in a form of settings.

Currently, the 4051-based circuit is on the breadboard, and has 10k multiturn trimpot for each channel. Dirt simple option could be to use slide potentiometers instead, for a good visual reference.

Although the slide pots tend to be quite pricey(at least the decent ones), I consider that as a plan b, if that led display-based idea fails.


Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 29, 2020, 09:47:55 PM
Well, I did tinker with that led display, and it was hours of fun, but to make it usable.. too much of a hassle.

Now it's time to get back to actual sound making circuits. Next thing is going to be to test, how these can be used, instead of 10k trimpots(to adjust 4051's output levels to form the waves):


They are 45mm ones from Velleman's graphic equaliser kit, that I once built, but never used.

Circuitry for a single 4051-based generator will (most probably)include:

- 4046 pll and 4017, to multiply the input frequency first by 8, so the input and output frequencies are the same
- 4040 to make the 4051 to do the 'multiplexing'
- buffer for the combined waveform output(not sure about that yet)

So I'll stick with that composition for now.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 30, 2020, 07:19:05 PM
Test setup with slide pots:


Although the pots are logarithmic(audio), they already feel a lot more natural, when adjusting the waveform. Almost like kind of an audio mixer. But instead, they adjust steps of the waveform. If it was an audio mixer, log pots should be perfect for it.

But is it(an audio mixer), as its output is audible, but the signal is made of dc voltage? Beats me, as there are plenty of different elements in project like this, of which I can't make any sense at all.
So after all, linear slide pots would be a better option for a visual reference of the waveform, and I'll probably order some in the future.

It's been a while, since I tested how the built(or breadboarded) circuitry actually sounds like, when using a guitar/hex pickup as a signal source. Basic external 'effect' circuits already sit on the breadboard, so it should be good to go.

All kinds of crazy ideas keep popping up, one of them is to control the 4051's stepped waveform with light, by using ldr's(light dependent resistors) instead of pots. Then whatever light source, and some simple rotating mechanical contraption, to create shadows for the ldr's to modulate the waveform, without added complex electronics, that is usually involved.

In the end, the amount of possible options is vast. All that is left, is to choose all one of them(at a time).

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on March 31, 2020, 08:17:30 PM
This time a bit about 4017-4046 -based frequency multiplier, like it's wired on the breadboard:


4017(decade counter) divides its input frequency by 2 to 10, depending of how it's wired. On the above pic it's wired to divide by 8.

Quite straightforward, when compared to 4046 (phase locked loop), that does the exact opposite - frequency multiplying, by the factor, that 4017 divides it. 4046's output frequency is then input * 8.

That output is then fed to 4051-based stepped waveform generator, and as it is 8-channel multiplexer, it's output frequency is divided by 8(took me a while to figure that out).

Anyways, that 4046 needs some 'tuning', to get it to work on a desired frequency range. It's easier to do that on higher frequencies, but under 100Hz it gets finicky.
On a guitar(using standard tuning), lowest frequency is about 82Hz(e).

It's not a problem to get the 4046 to track even lower frequencies, but, lower the needed minimum frequency, the narrower the range. There might well be more 'advanced' ways(meaning, that I should understand, what I'm reading) to expand the lower frequency ranges, but, again, simpler it is, the better.

After some fiddling, the above circuit now works from ~80 to ~300Hz, using 9V supply. That should be enough for the three thickest strings(e-a-d), if played on the 12th fret, or lower.

When adjusting, or 'tuning' the 4046, using first potentiometers, makes it a lot easier. But not so on capacitors, as the variable ones seem to be on the picofarad range only(as far as I know).

Then I got this idea of making sort of adjustable capacitor board, by using a rotary, or other switches for the range of 1 to 470 nanofarad. After all, it could make dialing between different values more sensible, instead of having dozens of capacitors, that need to be plugged in and out one by one.

Don't know yet, how to achieve that, though. Maybe it's good enough subject for the next sub-project.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 01, 2020, 06:51:36 PM
Today I got an idea of using 4017(decade counter) as a simpler, single chip alternative to 4051-4040 based waveform generator, as its outputs are sequenced similar way.

It doesn't need a counter chip to do the sequencing, so I breadboarded it, and it worked... sort of. It made stepped waveforms, but when adjusting one step up, others moved around.
I guess its outputs needs to be buffered before they go to the potentiometers, or something like that. Overly simple idea wasn't so simple anymore.

Next I'll be drawing pcb for the 4017-4046 freq. multiplier, and 4051-4040, which so far seem to work, as expected. I ordered 60mm linear slide pots, and the plan is to stack the pcb under them.
There should be plenty of room for other possible circuits also, like filters and such, but we'll see.

To get back to that previously mentioned 'variable' capacitor board, I had this in my mind, where caps could be added one by one, in parallel(to add capacitance).


But naah, I can't figure out, how to do it that way. Then on to the net to see, what kind of devices are available. Decade resistor boxes, also some capacitor ones, but not really anything dirt and cheap enough for diy purposes.

Actually, just minutes ago, when writing this, this half-baked idea popped out of thin air:


So then I thought: hmm, why not use 45 caps instead of 9, to make steps from 0 to 90nf ?

Using the same pattern, first select hundreds, then tens, and then ones, if needed. Three 10-step rotary switches for that perhaps. Definitely not as pocket friendly, as the potentiometers are.
135 caps for the range from 1 to 999nf. Plus three rotary switches. Plus I have no clue, does it work in practice.

Price of the components shouldn't be too prohibitive, if the aim is to use that contraption for lo-fi audio, or other such things.

I have one old rotary switch somewhere, if memory serves. If I manage to find it, I'll do some testings with say, 6 cap sets, using probably other switches too.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 03, 2020, 09:07:47 PM
Almost finished new board for frequency multiplier 4046-4017 and waveform generator 4040-4051:


I used headers for the parts, that adjust the capture range of the 4046, so they can be changed, if needed. Longer headers on the left are for slider pot connections(and also for future testings with something like ldr's).

Sometimes I wonder, why on cmos counter chips(like ones used here), the outputs are in awkward order. Should need hair-thin pcb traces to get them all to the same side in order, and even then, some of them cross each other.

On the other hand, that shouldn't be a problem, if one was able to make two-sided pcb's. I have some in my shelf, but haven't yet got that far, to start testing different methods/techniques.
Could very well be worth it, because I just hate using many jumper wires for a pcb, like above. Lots of room for stupid mistakes.

But otherwise, it's time to take a peek, what's on the to-do list.

- to make an audio mixer, that can handle wide variety of signals, and -levels.

- to make 4049(Hex Inverting Buffer) -based fuzz unit(s). Let's be honest, certain kind of distortion adds plenty of texture to the overall soundscape, if desired.
What I mean by certain kind of distortion is, that 4049-chip, when configured as a linear amplifier, clips the input signal gently, very much like tube amps do.

It must be one of the few of the logic chips, if not the only one, that can be (ab)used that way. As far as I know, one of the first ones to notice that, was Graig Anderton(author of still excellent book Electronic Projects For Musicians), back in the seventies.
So no wonder, that it's used in some of the commercial "tube sound" effect pedals.

- to add some kind of (possibly modulable/envelope) filters for the outputs

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 05, 2020, 07:35:46 PM
Current circuitry had one stubborn bug in it, but finally I managed to stomp it out without using bug spray(

Circuit with correction in red:


Now it works, as it should. 1M pot on the right side will probably replace the 100k resistor, to make 4046's tracking speed adjustable. That together with 100n capacitor(can be anything from say, 10n to 10uF) provides the "timing" for it.

As mentioned before, 4046 has plenty of options, of how to make it sound/behave. In the past, I once found(accidentally) a combination for 'portamento' -like effect.
Back then, I used guitar with standard monophonic electromagnetic pickup, as a signal input. In certain frequency range, it sounded like a Theremin(, that 'slides' between notes.
Outside of that range it just went nuts, and sounded like farting bagpipe. If memory serves, I recorded that. Not sure if it still exist on the hard drive, though.

But yes, I'm eagerly waiting for the ordered linear slide pots to arrive, to make an enclosure for them, with that circuitry, to get them in more usable form.

I have almost finished a simple mixer also(project 18 from the earlier mentioned Craig Anderton's book ), which currently has only three channels(I ran out of several components), but should be enough for starters.

Originally it had 4739 dual op-amp, but luckily there is an updated version of that pcb(and some other projects too), that uses 5532 dual op-amp instead:

While scavenging 10k pots from the abandoned projects, I found almost intact adsr-device. I wondered, why the heck have I built that for. In short, adsr stands for attack-decay-sustain-release.
Mostly used with sequencers, and other rhythm-based things(as far as I know).

After some searching on the net, it seems to be a part of many analog synth setups. When looking the pcb with magnifying glass, there it was: Yusynth adsr:

I'm not sure, if it's usable with all the other recently built stuff, but we'll see.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 07, 2020, 07:01:47 PM
Not much of a progress, as I'm still waiting for those linear pots. In the meantime, the mixer now has an enclosure:


For now, I'll probably use two 9V batteries to power it, to keep amount of running wires as low as possible, as it needs bipolar supply.

After I manage to make few more devices to form a 'basic' effect setup, then it could be sensible to gather them in one single, larger 'panel', where connections between devices could be made by using patch cables. A bit like an oversimplified version of this(


I have one of those 80's cassette player enclosures ready for that. As can be seen, it was once used for a project, that never happened:


Another one is this stereo graphic equaliser, which should still be in working order:


It could have its uses, as a part of the effects board, as it is now. But if not, again one enclosure more, to use for something like a vocoder. After all, it has been gathering dust for last 15 or so years.

So the overall possible scenario might look rather ambitious, but I don't care too much about that. One step ahead, at a time, and sometimes(in my case often) two steps back.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 09, 2020, 07:16:37 PM
Circuitry with linear slide pots:


It has a skeleton 'enclosure', as I'm not yet sure about possible additions. 1M pot on the left is for 4046's tracking speed, but it needs one of the timing capacitors to be  "variable" also. It needs to be tested, which cap values are most usable, though. Then rotary switch to select between them.

This current circuitry's output should be made ready to be fed to more than one devices, like mixer, filters, or echo/delay simultaneously. So It might need a buffer/splitter for its output. There is a project 26, 'Spluffer' in the Craig Anderton's book, which does exactly that. 

Once I get the mixer together, then could be a time for a bit of break in building, and trying to figure out, how the hex pickup setup works/sounds with this circuitry, that is monophonic after all, meaning, that it should handle single notes(like on single string) just fine, in the range of 80-300Hz, with current 4046 configuration.

So it should be good to use with thickest string(e) output to accompany other strings. But we'll see, how that turns out in practice, as there are already many(so far uncertain) factors involved.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 10, 2020, 05:36:12 PM
Today, when testing the mixer, using function generator and a scope, I found it to be mesmerising to watch the waveform to morph from one shape to other, as I turned the mixer's knobs.
Yes, I'm easily amused by things like that(

But anyways, there were only two waveforms to play with, and I haven't even yet listened, how they sound, when mixed together. Should be hours/days/weeks of fun. Especially, when third waveform/source, or filter is added to the mix.

All the stuff are almost ready for aural testings. If(when) that works out as expected, then it's time for replacing the tiny, battery powered audio amp with some kind of headphone setup, to hear the nuances better.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: AdeV on April 10, 2020, 05:53:06 PM
I have to say - this is a fascinating project, even if I haven't got a clue what most of what you're doing is...! Lots of good circuity stuff though :)

A question - what software did you use to produce that circuit layout? I've used kicad for all my recent attempts at circuit board making, but I think that it's more suitable for producing layouts for commercial operations, given the default track width is, if I recall correctly, just 0.25mm wide... which looks great on the design, and usually vanishes when I try to etch it!

Also, have you heard of Martin Molin's (Wintergatan) "Marble Machine MMX"? It's nothing like your project, but is similar insofar as being a musician building an engineering device - in this case, a musical instrument played by dropping marbles... it's quite the adventure (I suggest starting with some of the early videos, then maybe jumping ahead a bit, as there's around 120 mostly weekly updates by now!) Here's a link to the full playlist: MMX playlist (
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 10, 2020, 07:34:13 PM
Ade, thanks for the heads up.

I'm using Rhinoceros to draw the pcb layouts. Tracks can have any width, but I've used mostly the "beefy" 1,8mm ones, as they seem to transfer rather well. Sometimes, if some pcb has very thin traces, I just re-draw it to have thicker ones.

I guess all that could be done with something like 2d-vector software perhaps? I wish I could recommend something, but as I've used Rhino for pretty much everything, from 3d-modeling to 2d-stuff for years, I haven't looked for the alternatives. Ideas anyone?

I haven't heard of Martin Molin before, but will check it out. Thanks for the link :beer:.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 11, 2020, 10:10:14 PM
I was going to test the hex pickup today, with the step waveform generator. I had completely forgotten, that it has a very quirky power connector, that needed to be wanked around to make a contact.
Like wallwart ones, that has a center hole in the plug. Both the plug, and socket are brand new, so perhaps they are of different size.

But yeah, that bugger ended the testing session effectively( Instead of feeling like flattened pancake, I'll get armed with the trusty stomping shoes.

I'm thinking of ordering mono jack -type connectors instead. Also the whole power supply scenario needs to be replaced with something more 'universal', or 'centered', having several regulated 5 and 9 volt outputs, and (possibly variable)split power supply outputs for 15-18 volts too.

Hmm. So many plugs and sockets, and wires. Maybe it would be a better idea to gather all, so far built circuitry, including power supplies, in a one larger box, that was mentioned earlier.
So that will be the subject of the next sub-project.

Other than that, I've been trying to find an article, that is about building 8-channel vocoder. I used to have copy of that article in printed form, but can't find it anymore. If memory serves, it was originally in Keyboard magazine. Even online search didn't give any usable results, although when I get to the mood for searching something, if it exist online, I tend to find it.

Anyways, I built that vocoder in the past, using perfboard. Apparently it didn't survive, having wildly running wires around, and all that stuff. But it was good fun to play with.

I'll have to admit, that having a vocoder is an obsession for me, as it could be used in so many more ways, than just 'talking' instrument. For those interested, Kraftwerk is one of the first/most well-known groups, that used variations of it to make the "robot" voices. It was used also by Walter/Wendy Carlos in movie Clockwork Orange's soundtrack. Cylons from Battlestar Galactica, and so on.

Fortunately, there are other versions to build. Possible candidates are the Elektor, Okita, and Mfos(music from outer space) ones.

Besides all that, easy shortcut could be to buy one of the digital ones, that have reasonable price tag, but in my case, no way Jose. There just isn't easy ways to modify/abuse that kind of devices.



Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 12, 2020, 06:16:35 PM
The 8-channel vocoder, that I mentioned earlier, I found stuff about it on my hard drive. What makes it better, is that it's so much simpler, than any other ones that I've checked so far.

I'm going to draw the pcb using this image, as I haven't found any better images of it:


Length of that pcb is about 430mm. Too big for me to make, so I'll divide it to 3 or 4 parts.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 13, 2020, 06:49:24 PM
The vocoder pcb almost redrawn:


It has some tight spots, that needs to be taken care of, though.

I'm redrawing the component designators also, as the image is too blurred to be (possibly)transferred to the component side of the pcb(haven't done that before, but well see):


As can be seen, it's Paia Vocoder. Originally it was published as a project in Keyboard Magazine by Craig Anderton, in the 80's.

There doesn't seem to be too much info about it on the net, as many of the builders seem to look for fancier, 12, 14, 18, or even 24 channel ones(
I have a feeling, that this humble, 8-channel one is overlooked. One reason for that could be, that the actual kit on the Paia website is out of stock.

But on to the pcb itself. As mentioned before, it will be divided to 3, 4 or 5 parts, and probably stacked together, to make it a whole lot narrower.

Of course there is one major factor, of how to verify, that the redrawn pcb actually works, as it should? I'll be doing some checkings/comparisons with component designators, and what not, before dividing it into smaller parts.

It uses 5 x 4136, and 1 x 301 -op-amps, which are fortunately available from my local supplier. It also uses 4 x 570 or 571 compander chips, that I already have in my shelf. Rest of the parts are resistors, pots, caps, switches, and connectors.

It requires bipolar -15/+15V supply, which takes us back to the previously mentioned need to make a more 'universal' power supply.

After all, I have to remind myself(all the time) to take only one step at a time.


Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 14, 2020, 05:48:44 PM
Divided vocoder pcb:


I decided to use 75 x 100mm pcb's as they are already available in that size. Cutting the pcb is something, that I've never managed to do properly.

On the other hand, I have only used 1,6mm boards, and have scored them to get cleaner results, but they seem to be too thick for that, and the edges tear. Maybe 0,8mm ones, which I'm going to order next, are more suitable for the 'score and snap'.

While reading through the vocoder's assembly and user manual, there is a mention about "clarifying mod". It uses 4 x 084 op-amps, and some resistors, so I'll order parts for that too.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 16, 2020, 06:40:10 PM
While waiting for the ordered parts, I made a 15V split power supply pcb:

It needs an ac wall wart to power it. I have only one, that is for 12V. I was ready to order 15V one, but then thought: hold on, doesn't dc wall warts have already an ac output in them, that is rectified by using diodes to make dc voltage?

So I had to look, what I have in my boxes of 'stuff'. Surprisingly, there was 15V/500mA dc adapter, that didn't seem to belong to any device, that I use. I managed to open its enclosure, and took some measurements with multimeter. Yep, it could perhaps be used for the purpose.

Only two wires needed for straight ac output. Actually I'm going to use its dc wires for that, as they have a nice strain relief clamp already. No extra wires or holes needed.

But there is one very serious precaution, though: to do something like that, one must be extra careful, as there is live 220V(in Europe) involved, when that adapter is connected to mains.

Disclaimer: If in any doubt, don't do it. If one still insist doing it, that one takes full responsibility, of what he's doing.

Only once I've had 220V shock, and yes, it was indeed very nasty, so I'll do my best to avoid messing with it.

But enough of that. The 15V split psu will be a 'master' one, that feeds lower ones(like devices, that have 9V regulator in them). But we'll see, what comes out.

When looking inside of that previously mentioned ex-tape recorder enclosure, there was dust and a phase shifter:


I doubt, if it's still in working order, after two decades, due to corrosion of the pcb traces. As can be seen, two ic's are configured to substitute original op-amps(super-rare 4739's). White blocks are diy optoisolators(led/ldr), to replace original Clairex CLM6000's(that were probably never available outside US, but what do I know).

Quite a mess, that is worth only for looting socketed ic's, pots and switches.

I'm considering of rebuilding that, but what comes to optoisolators, they need some fiddling(when using ordinary leds and ldr's) to get them to the 'working range'.
Or just re-use the components inside white blocks, and look, what kind of mods I did use back then, to get them to work.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: on April 17, 2020, 02:31:25 AM
They're not cheap, but still available -
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 17, 2020, 07:15:14 PM
Seadog, yes quite a price for single led/ldr -pair. One way, at a fraction of the cost, is to make ones using a heat shrinking tube.

If memory serves, it wasn't that difficult to get ordinary led/ldr pairs to work, as required in that phase shifter. In schematic, there is a 470k resistor in parallel with ldr, and 200 ohms current limiting one in series with led. The circuit itself:


Playing with those two resistor values should do the trick. Nowadays the leds are much more brighter(and/or efficient?), so they need to be tamed down, to fit for the rest of the circuitry.
Ldr's responses (could) vary between maker/model, so some tinkering with them also, I guess.

More about that, when I get to building the actual device.

Ordered parts came today, so I managed to finish the 15V split power supply circuitry. I also did the previously mentioned ac-mod for the 15V dc wall wart.
I'll have to admit, that I got a bit nervous, when testing those out. I had already a box of fuses, and some other measures of precaution, just in case, that something goes horribly wrong.

But it went well, and they work nicely together. Fortunately there are very rare occasions, where I have to do projects like that.

Next thing to do is either:

- print an enclosure for that split power supply(not sure yet of its final assembly, though)
- build that phase shifter
- build the vocoder
- drink few more beers(

Somehow I have again this familiar feeling, that I'll have to start with the most complex one, that is vocoder(well maybe not that complex, but considering its parts count).

Yep, vocoder it'll be.

In the end, I think I should provide some audio clips every now and then, considering so far built devices/circuitry. But easily accessible/usable audio recording interface is still missing.
I'm thinking something like a usb-based ones. But we'll see.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 18, 2020, 06:49:05 PM
The pcb for the vocoder needs thorough cross-checking, using the schematic(down-sized to fit for the page):


Luckily most of it is repeated 'blocks', like op-amp and compander sections in the middle. Only the component values vary between them. But still, tedious task to do, so I'm expecting to take a break of it at some point, and do something else, like building the phase shifter.

What comes to the previously mentioned audio recording interface, there seems to be a lot of those usb-based soundcards.

Without knowing too much about them, something like Behringer U-Phoria UMC22 could do the job for 39 euros, but it's currently out of stock on local supplier:

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 19, 2020, 08:38:47 PM
Cross-checking that vocoder pcb is indeed very slow thing to do. I had to restart from the beginning a few times, to find better ways to approach it, and perhaps learn something in the way.
So far I've found several missing traces, and errors, when compared to previously drawed one, using that blurry image.

But after all, no matter how long it takes, I guess it could be worth the effort. If not, there are always plenty of other vocoders to choose from.

In the meantime, I have also had some ideas, like making the filter sections 'variable', using headers for their capacitors. Originally the cap values are for 200, 400, 600, 950, 1300, 2200, 3000, and 4900 Hz. But we'll see, once I get there.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 20, 2020, 05:24:02 PM
Oh boy, what a job to do! Time flies, when you're having fun(or so they say). Now the vocoder pcb should match the schematic:


Next step is to verify, how well they match... only one way to find that out. Yes, by building it.

But now it's good time to take a break of it, although some traces perhaps need to be beefed up. For now, I'll leave it there.

I'll start building the phase shifter, by redrawing its pcb, as it has too thin traces, overly big pads, and some too tight spots, for my liking. I've already added letters to the bottom(like in the original pcb), to make building more straightforward:


That is the updated version of the original pcb, found at

Then salvaging all the reusable parts from the old phase shifter, printing 'housings' for led/ldr -pairs, and so on.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 21, 2020, 06:20:06 PM
The phase shifter pcb is finally in etching bath. It took 6 or 7 times, to get all the traces to transfer. Usually it works right away, but this is a bit bigger pcb(100 x 93mm), than most ones, that I have previously made.

As I use flat iron, as a part of transfer, it just needed more heat and pressure to be distributed, than smaller ones. Fingers crossed, that the traces stand one more time the heat, when soldering, as I already roasted that pcb so many times.

Anyways, once it seemed good to go, I dropped it in etching bath, and only then noticed, that the trace pattern was mirrored(
That is one bugger of a trap, where I fall every now and then. But yes, it was (again) one of those moments of "Play it again Sam, one more time, but please, not backwards this time".

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: PekkaNF on April 22, 2020, 05:30:38 AM
Play it again Sam gone Leslie Nielsen?

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 22, 2020, 06:28:26 PM
^^Just like that :D

But yeah, holes for the phase shifter pcb are now drilled. There are some fractures in only few traces, that needs to be checked, if they need to be patched, though.

Vocoder pcb images are also ready for transfer. Should make a good practicing on that size(100 x 75mm), as there are five of them.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 23, 2020, 08:27:39 PM
The phase shifter board with almost all components:


IC's, some switches, and pots are to be added. Optoisolators need to be made, and the resistors parallel with ldr's, and resistors in series with leds need also be tested, and modified, if needed.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 24, 2020, 07:04:47 PM
Today was a 'wire hassle' -day. I'm glad that it's almost done:


I tested the circuitry shortly with variable psu, as usual, slowly increasing voltage, and the current limit, while observing, to make sure, that if something goes wrong, there is less chance to damage the components.

So far, no smoke or sparks. Almost there, but still some stuff to do. To be honest, I'm looking forward to get a break from building, and do aural testings instead.


Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 25, 2020, 08:47:33 PM
Not much progress today, except making first optoisolator for testing. Components used:


The leds are white, very bright(actually painfully bright, once they get some 'juice') ones. Ldr's are 'hermetically' sealed ones. There is no specific reason, why I chose to use those exact components.
They are just a part of the optical component stock, that I gathered back in the early phase of the 'optical hex pickup' -project.

Printed enclosure for the led and ldr:


They are secured in place with few drops of super glue. Then some heat shrink tube to keep the ambient light out:


Both ends need to be sealed also, using just about anything, that is thick enough, and opaque. As I have some black acrylic paint, that's what it'll be.

What comes to testing that optoisolator with the rest of the circuitry, I think the led part of it should be quite straightforward. There is an adjustable LFO(low frequency oscillator (running at ~0,2 - ~8Hz)) that drives it, and the involved series resistor needs to be adjusted to make the led to pulse so, that it fades completely, when the lfo wave hits the 'bottom'.

At this point, when thinking about it, when the lfo wave hits its highest spot, the leds, that I'm using, should glow very brightly(remember, this circuit was originally published ~40 years ago!), which shouldn't be a problem, unless that led starts to draw excess current. But we'll see.

The ldr -part(having a parallel resistor) is somewhat more difficult to imagine(at least for me), but in the end, it should be about adjusting its response, to fit the range of led's brightness variation.


Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 26, 2020, 08:07:01 PM
It seems, that the resistors for led and ldr might not need to be modified that much, if at all. For my surprise, the led already pulses in a way it should do.

So I listened to the output, and there was an audible pulsing effect. It was rather lacking, as I tested the circuitry with only one(of four) optoisolator, and sine/rectangular waves. The lfo and optoisolator -part of the schematic:


As can be seen, there is already a limiting resistor(R6) at the output of the lfo(IC3A), that drives the leds. There is also an option to use an external source for modulating the leds(feeding it to pad P, while pad N is disconnected).

Now rest of the optoisolators are finished, and soldered to the board. Only few resistors(for leds and ldr's) needs to be added, and the circuitry should be completed.

If all goes well, then it's finally time for (lengthy)audio testings. 
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 27, 2020, 09:09:08 PM
After playing with different settings for a good few hours, the phase shifter seems to be working now, as it should. A very primitive audio clip, where 50Hz rectangular wave was used as an input source: (

There are two things, that needs to be modified(not required, but for my personal taste), though. One is to increase the value of the capacitor(C9), to lower the speed range of the Lfo(IC3A, which drives/pulses the leds).

Another one is to alter the range of the 'offset' -control. I'm not sure, how to explain it clearly, but here it goes anyways: the Lfo wave, that modulates leds, has a very narrow 'effective area', where the phasing effect is audible, while rest of it is 'dead zone', where nothing happens. So that very 'effective area' is passed way too quickly.

What I'm after, is to make whole Lfo range 'effective'.

This waveform(internal, part of the circuitry), that drives leds, is triangular. I tested using the external source(function generator) with triangle, and also sine wave, but still similar results.

Then came the idea of testing the leds with plain dc, instead of pulsing waveforms. That way it was a lot easier to 'browse' through the Lfo range. As a result, the effective range is indeed very narrow, within 0,5 volts(of several volts range).

And of course, what a bummer, as I forgot to write down resulting numbers, while testing.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 29, 2020, 07:32:10 PM
Today I simulated the Lfo part of the schematic, with different values for R27, R7, and R6:


I managed to get quite good results, but when I did the same modification in practice, they didn't work at all, as expected.
My aim was to bring the triangle wave, that IC3A(which modulates the optoisolators leds) makes, between 2,40 - 2,80V, because that's where the effective range seems to be.

I tested with function generator's triangle wave, having 0,40V with 2,40V offset, and that's where it sounded the best, without gaping dead zones.

When doing the mod to the circuitry, it messed the Lfo speed settings also. It's not worth to restore the original resistors, as with them, it was already too quirky. I think it's time to ditch the included Lfo section, and use something, more usable instead.

After searching alternatives from the net, there is something, but not quite what am looking for: A simple, variable speed triangle Lfo, with adjustable dc bias.

On the other hand, I already have built that step waveform generator(the one with slide pots), which shouldn't need bias adjustment, just some filtering to make a decent triangle waves, at needed 'biased' voltage level. Might well be worth testing.

If it works for modulating the leds, then build another, simplified version(without 'divide-by-8' -section), that uses multiturn trimpots for finer step level adjustments.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on April 30, 2020, 09:13:56 PM
Today, I restored the original resistor values(R7, R6 and R27) for the Lfo, because I had completely forgotten to test, how changing the resistors, that are in parallel with Ldr's, affect their range.

But nothing usable came up with that, so the original resistor values(R33 - R36) remain the same(470k). 

I haven't yet found a simple alternative triangle/sine lfo, that has an adjustable bias in it. So that must be one of the tough ones to implement, as the ones I've found so far, are way too complex.

The base circuit of the phase shifter works as it should, except the Lfo section. After all, the device could still be used as it is, even though being 'lacklustre'. But we'll see.

Different approach for an alternative Lfo could be to try and make one, that is electromechanical, like a pair of led/ldr, that has a rotating disc(with holes/patterns) between them.
Not sure, how the most usable, 'effective range' could be achieved by using contraption like that, though.

But the involved factors(like motor speed, brightness of the led) should be a lot more easier to comprehend(at least for me), than using only electronic components.


Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 19, 2020, 05:11:23 PM
So, after quite a long hickup, it's time to get back to the project. The phase shifter, that I was working with back in the april, is still at the same stage. It should be usable, but still needs some tweaking and testing.

As there was period of weeks, when my ability to concentrate was practically lost, this is also an attempt to get the 'mojo' back.

To get my feet wet again, there is that vocoder-thingy. I already have all the needed components in my shelf, plus the pcb's are also etched, drilled, and ready to go:

Probably not the most simplest project, as there is also a 'clarifier mod' for that vocoder involved. But what the heck, I'll give it a shot.

The hex pickup system was removed from that guitar, to get room for the ordinary guitar humbucker pickup. But I'm quite sure, that it's just temporary, as that hex pickup system has that specific sound, that I'm after.

But after all, it's just a matter of having a dedicated guitar for it. As a matter of fact, that guitar was hacked together from bits and pieces, so it isn't necessarily the most playable one, but for now, it's adequate enough for that purpose.

As an off topic ramble, I might order my first ever decent electric guitar, once I get the tax return next month. If that goes, as expected, the old carcass has the hex pickup system installed back in it permanently.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 23, 2020, 05:33:37 PM
The vocoder pcb's are almost populated:


Between the boards is a two-sided, printed 'clip', that holds them nice and tight together. It could well be a permanent holder(probably needs to be extended on both ends, to have holes for screws).
Also it takes the strain off the to-be-soldered connecting wires, making the boards a lot easier to handle together, when the outboard wiring mayhem hassle begins.

Once all wiring is done, and all goes as expected, plan is to stack two pairs of the boards, to make the whole pcb footprint narrower. When all 5 boards are placed one after another, the cumulative width is just too excessive, being about 550mm.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 27, 2020, 08:06:00 PM
Wiring hassle before and after, using rather hi-tech building platform:


I have omitted some switches and plugs(right channel and effect loop), as they might not be necessary in testing phase. Lots of unshielded wires running around, so we'll see if the noise becomes a problem.

Currently I don't have enough shielded cable for all the wiring, so only audio plug wires are shielded.

Next I'm planning to draw and print some kind of gadget, that makes bending the IC legs hopefully easier. When the IC is new, the legs are usually spread out too much to be pressed to the socket.
Bending and aligning the legs one by one is just pain in the arse to do, especially, if there are more than one IC involved.

After that, I think it could be time press the IC's into the sockets. That is always preferably done only after all the soldering is done, but in this case, none of the IC's (4136 quad op-amps, 571 companders, and one single op-amp) are cmos-based, which could be very sensitive to static electricity.

As mentioned before, there is a mod, that clarifies the overall operation of this vocoder(buffering the input level pots). It adds even more wires, and althoug there are simple and clear instructions, first I have to get my head around, of how to connect it to the main circuitry.
Warning: babbling ahead.

As usual, when building this kind of lengthy project, there are always times, when I think that "why bother, buy something commercial instead, that works right away". 
One example of it is a stomp-box size Boss VO-1 Vocoder, under 200 euros, that seems to do all the tricks and even more(based on youtube videos about it).

I have a sneaky suspicion, that it(and also other ones in that price range) is based on dsp(digital signal processing) technology. So its behaviour is pre-programmed, and can hardly be altered.

What comes to commercial analog vocoders(stand-alone units, not the keyboard-embedded ones), they tend to be bloody expensive(if one can find/afford one these days). At least I would never dare to modify anything like that.

But again, this is about analog signal processing, as it has some... quite different aspects/dimensions in it.

Most lamest example, that I can think of, was back in the 90's, when I had a cheapo start-o-caster(my first guitar, now long gone), and Dunlop's Cry Baby wah pedal. Yes, expected sounds were there.

For some unknown reason, I decided to connect the cables in reverse/backwards to the wah pedal. Of course, there was no direct guitar output, but instead bird-like sounds, depending of the guitars volume/tone settings/wah pedal position.

That very same effect can be heard on one of the Jimi Hendrix's Electric Ladyland track. I don't claim to have enough intelligence/creativity to find that effect; it was pure coincidence.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: on July 28, 2020, 05:37:26 AM
When I played with ICs I used to grip the end of the package and press the legs onto the bench thereby straightening all of legs on one side. The alternative is to make a carrier that you press the IC into, package first, which closes the legs. You can then use it to position the IC over socket and then press it in. I'm enjoying this build and understand exactly why you want to build it rather than buy a ready made product that doesn't have the flexibility that you can add to yours. In addition, the satisfaction you'll fell when it's finished can't be bought.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: BillTodd on July 28, 2020, 06:32:34 AM
This is like a trip down memory lane for me ,  I was doing something not so different 45 years ago :-)
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: awemawson on July 28, 2020, 06:58:07 AM
I still have some IC 'leg straighteners' consisting of a jig and some bearing races that progressively form the legs to the correct spacing for a socket. I'll take a picture later when I'm in the workshop.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: awemawson on July 28, 2020, 08:20:25 AM
Picture as promised (of the IC leg straighteners)
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 28, 2020, 06:16:47 PM
Thanks for the replies, guys. Awemawson, that's an interesting idea of the leg straightener. Haven't seen those before. Shouldn't be too hard to make one.

Another way could be like this, that has printed/machined block with a 'pocket' to fit the IC in:

Then the legs are pressed, using vice:

That block might not be necessary, but it limits the legs from bending too much. It seems to work quite well, at least on 14 and 16 pin ones, and the IC's pop nicely into sockets.

On the other hand, I finally got my head around of how that mod should be connected to the main circuit:

Now that it's done, moment of truth gets closer. All the needed basic wiring is done, except power connections(three wires for the main boards, and two for the mod board).

The main circuitry(pcb's) is yet to be verified. As far as I know, most of the builders of this device have built it using the kit, that was available on the Paia website(not sure, if they still make that kit, as it's been out of stock for a long time).

Plan is to start testing as soon as the power wirings are done.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 29, 2020, 03:32:41 PM
Well, first testings are done. No smoke or sparks so far, but the device behaves strangely. All kinds of odd distorted sounds, but not the actual vocoder-effect.

There could well be error(s) in the pcb layouts, that I traced myself. Or bad soldering, like bridges between traces. Or just about anything.

So the tedious part of stomping bugs is about to begin. After checking the solderings, and if they are ok, is to use an audio probe, to follow, how far the input signal goes, before it starts to distort/clip.

But yes, it is always a gamble to build something using pcb layouts, that aren't verified by any other builder(s).

I had some success building a working, but rather complex as a whole(at least for me) circuitry for the hex pickup, but it was divided in so many 'blocks', which were built one at a time, and tested, before even planning the next one.

Easy to say afterwards, but I should have done same with this project also. When one is stubborn like me, learning takes time.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 31, 2020, 05:36:22 AM
When checking solderings, there was only one bridge. But then I found multiple errors also. They were easy to fix, by adding a solder bridges to pairs of IC legs.

Still no cigar. Finding bugs by using an audio probe seems to be more difficult as I expected, as there are too many interactions with pots/knobs, and switches involved, which affect the results.

So I think it's not worth of the effort. What I'm going to do, is to crop all the extras(stereo-, loop send/receive, fuzz, and bypass options) out of the schematic/circuitry, making it a lot easier to make sense of the signal paths.

Then start from scratch, using same method as mentioned before; divide circuitry to blocks. Breadboarding first, and only after certain block is tested and working, draw a pcb for it, and build it.

I already have all the needed IC's, pots, and jacks. Some caps and resistors could be scavenged from the already built circuitry.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on July 31, 2020, 04:23:12 PM
Today I did some drawing, of how the blocks could be breadboarded. Both the instrument- and microphone input stages consist only single amp. So does the output stage.

The heart of the device is between:


On the left side is one of the bandpass filter pairs, which share the same component values. In total there are 8 pairs of them, for 200, 400, 600, 950, 1300, 2200, 3000 and 4900 Hz. Obviously different frequencies require also different capacitor values. Other than that, all the pairs are identical, and use the same pcb layout. Should make easier to build the blocks one by one.

Plan is to make separate pcb's for each pair, so that they could be handled like 'modules'. 

For those I'm going to use dual op-amps, instead of quad ones used in that already built circuit. I happened to find more than enough duals from my shelves, and also few single op-amps, that I'll use for input- and output stages.

On the right side is one of the 571 dual companders. I might have used one or two in some projects in the past, but never actually fiddled with them. But now there is a good chance to hopefully make sense, of how they work, at least during testings.

So here we go again, and next on to the breadboarding.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 02, 2020, 02:47:51 PM
Both input stages were breadboarded, and tested. I did draw pcb's also:


So I printed the transfers, did some ironing, etched the boards, and drilled the holes. Only after that, I noticed that they were reversed...  Sometimes the printed transfers need to be mirrored but not this time. The way, that I draw the layouts, they should be printed as they look on the screen. If there is some text in them, only that should be mirrored.

To keep the project going, I made new ones using non-mirrored transfers, and now the boards are in etching bath.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 03, 2020, 03:01:33 PM
Today was spent mostly by drawing new layouts for buffers(the 'clarifier' mod for the vocoder):



First is the old layout. Second is the new one, divided to two separate boards. Both have only one input, and 8 outputs. I thought that it would be more handy to gather the outputs together, so headers will be used. There are no ground connections in the buffer boards, as was mentioned by the builder of the mod.

As can be seen, there are no other components than quad op-amps and a few jumpers, so I didn't bother to breadboard it. If the IC's are fine, it just should work. 
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 04, 2020, 06:17:36 PM
Input and buffer boards almost finished:


Only one of them doesn't have a header, being mic input board, as it was the first one that I did draw and build, and didn't consider of using headers.

But after that, I got back to my senses, as using them(headers) should minimise the wiring hassle between stages. That way, testing of the 'modules' is also a lot simpler thing to do.

Next thing to do, is to add necessary wires for the boards, and test them together. If that goes well, then on to the bandpass filters.

In the end, today I got the tax return, and ordered hopefully a good guitar. It's a "buy a pig in a poke" gamble, so we'll see about that, once it arrives.

If it's good enough, it means, that I can dedicate the old 'frankenstein' -guitar solely for the hex pickup system, which was used on that build thread.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 05, 2020, 05:50:19 PM
Today I've been mostly scratching my head, about how to draw a 'bus board' for the blocks:


Idea for that came from the Elector vocoder. I'll draw 3d-model of all the boards(blocks), as they are built.
Usually on more complex projects like this, it's the best way for me to make sense, by 'simulating' the objects, that have actual physical dimensions.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 07, 2020, 06:53:25 PM
Boards are almost ready for transfers:

( (

First is one of the eight band pass filters, and second is one of the four companders. I did some double-checking, and it's worth the effort, as there were some obvious errors.
Now they should have been sorted out.

When taking a break of the drawing/checking, I got seriously distracted, when looking at some other vocoder schematics. They have some nice extra features, such as separate level adjustments, inputs/outputs for each BPF/channel, which could then be cross-linked in any order, using patch cables, to make it behave like ministry of silly walks.

But back to reality. At this stage, that kind of options would make the process a lot more complex. After all, the idea is to first build a bare bone -version(as I have already cropped all the extras out of the layout/schematic) of the vocoder, to get a grasp of how this specific breed(Paia) works.

I haven't yet found a way to draw the 'bus board', or 'motherboard', where all the blocks could then be inserted using headers. It's probably because at the moment I don't have too much of circuit board to spend.

I have a bad habit of drawing the layouts basing of what I currently have on the shelf. Yes, it's unnecessary subconscious limiting factor.

When going back to the hex pickup -project, there were numerous versions of different layouts/schematics/stages, to get closer to the desired results.

So I think, that part of the learning is about remembering, and revisiting the ideas, that once worked. For me, at least, it requires some deep digging, to access that mindset again.

But enough of that jabbering. I'm going to place an order for the components/stuff, that might be needed in the project, plus some more. This time the circuit boards will be 0,8mm ones, as they are easier to cut, than previous 1,6mm ones.

In the end, off-topic, as always. The new guitar, that I ordered, should arrive next monday. Can't wait to get my hands on it. If it's as good as expected(no broken neck due to transport, or other major defects), then it's time to restore the hex pickup-hassle back to the old guitar.

It was very easy to disassemble, but takes plenty of testings(and cigarettes) to get it back in working order. But the sound, that it gives, should make it worth the efforts.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 08, 2020, 05:18:44 PM
Bus boarding in process:


Really good concentrating exercise, I must say. I started by adding power connection traces, but soon noted, that It's better to leave them last. That way the signal paths have traces with less jumper wires.

Whole layout is about 260mm long, so it is too big for me to make it in one piece. Once the drawing is done, I'll divide it to 3 or 4 parts, which could then be connected together using pins and headers.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 09, 2020, 06:26:52 PM
Drawing of the bus boards first version is almost finished:


At this stage, I think I'll probably use angled female headers for bus board connections. At least it should make testing of the separate boards easier, by using the same wires as on the breadboarding.

If testing goes ok, they could then be connected together by adding male pin headers between them. For that, I'm going to order longer ones, as the ones I have in shelf, are too short.

But first things first. Next I'm going to build one of the band pass filter boards, to verify that the layout works. Then same for one of the compander boards.
The rest of those 'blocks' use same layouts, but the component values differ.

As the essence of the vocoder forms, lo-fi audio samples are on their way.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 12, 2020, 08:08:44 PM
Today some cross-checkings:



First are the band pass filter sections, and then the compander ones. It is important to connect them in certain order as 'pairs'.

Bus boards were also checked, but building them comes later, once the numerous 'sub-blocks' are built, and tested.


Few words about current side project. Monday I got the ordered guitar, and oh boy, it needed plenty of adjustments to make its playability better. Not only that, but one part needs no other than machining.

I dont even remember, when was the last time, that I milled a tough-ass steel part. Luckily I have some carbide bits for that.

But yeah, that guitar, as it arrived, wasn't really user friendly, although it's on the mid price range. I have a feeling, that there lurks a quite decent instrument, once it has the loving care it needs.

I'm aware, that there are some strict rules, concidering the warranty. But meh, it's mine. Once it entered my apartment, it sure ain't leaving any time soon.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 16, 2020, 06:48:36 PM
Finally, first ones ready for testing:


I think I'll start with band pass filter(on the right side). With component values that it has, the 'peak' should be at ~4900hz.

Then the compander board, which, to my understanding, acts like a dual channel... something. As it is now configured, one channel's output level controls the other channels output/gain/level.

Still, there is something about it, that I can't get my head around. Maybe it's simpler than that. But we'll see, once I start testings tomorrow.   

Regular off-topic ramble:

This week, I've been mostly fiddling with the new guitar, to make the best out of it. All the most tedious things are almost done, of which worst was trying to mill the locking nut, that had convex surface at the bottom, when it should have been straight.

Even with carbide milling bit, it was just too much for my small, humble mill. (Obvious) conclusion was, that the part is hardened, or is made of some grade of stainless steel(which I doubt in this price range).

Anyways, quite a lot of material(~1mm) needed to be removed, and the only way I could think of, was to replace the carbide bit with a 20mm diamond wheel, and humiliate that tough part by taking tiny shaves at a time.

Hours later, major pain in the rump -stuff was done. But yeah, now the bottom of the locking nut is straight, and allows a lot easier way to adjust the height of it, by using shims.

It's a part of the Floyd Rose tremolo system, which, when properly adjusted, keeps the instrument in tune, no matter how much string bending, or whammy bar is used.

That's one of the main reasons, why I have wanted a decent guitar with that kind of hardware for years.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 18, 2020, 04:43:19 PM
Testing of the first boards was rather quick. Band pass filter has its peak at ~5000Hz, which I found out just by dialing the signal generator's frequency, until max.voltage was reached.
I used a scope to see the results, although same might be done using a multimeter.

Compander was tested by feeding sine wave to both inputs, of which one is for microphone, and other is for instrument(keyboard/guitar/synth, you name it).

When trying to clarify/simplify(at least for myself) of how the vocoder actually works, it's actually quite simple principle: microphone signal controls the instruments signal.
Both inputs have identical band pass filter -sections.

In practice, let's take a keyboard, that plays a sustained chord, which is then fed to the instrument input. Then some words/singing in the microphone input.
When the vocalist says 'boo', or 'ess' in the mic, that signal goes through the band pass filters, and tells the instrument side to let through only the very same frequencies of that keyboard chord.

But enough of that. After some etching and drilling, rest of the boards are on the making. Compander boards are already populated, but again, I had to cram some components in, due to making the layouts/boards as small as a stamp (


Band pass filter boards ready for the parts. I managed to salvage all the needed components from the previously built boards:


If and when all the 'blocks' are built, tested and working, then the aural testing -fun should be a bit closer. Some bus boarding, and other supplies need to be ordered before that, though.   

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: awemawson on August 18, 2020, 05:31:19 PM
Surely those electrolytics donít need to be 250 volt working   Rated at a lower voltage theyíd be much smaller and your board less crowded.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 19, 2020, 09:10:45 PM
That's a good point. I haven't paid too much attention for the voltage ratings.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 20, 2020, 05:46:14 PM
Band pass filter -boards are now finished, and tested. Regardless of the clumsy looking capacitors, they work as expexted:


Bus board for companders. I'll make the rest for others, once the ordered pc boards arrive:


Generally, the paper(magazine, or whatever I have at the moment) that I use for the trace transfers, gives acceptable results, but could be better.

Lots of pitting, and tiny fractures in the traces. To this day, it hasn't really been too big of a problem, but I always have to check the continuity of the traces. Once drilling is done, I clean the board thoroughly, and spray a protective 'solder-active' lacquer, to prevent future corrosion of possible weak points.

Yes. there are 'press-n-peel', and UV-based products, which could be a good choice for verified pcb layouts. But for highly experimental, 'trial and error' -stuff, they tend to be rather costly.

There are lots of different ways to do the cheapo laser printed diy-transfers on the net, but it all depends of the paper and/or the method, that is used. For example, if one sees a video on Youtube about the subject, it doesn't mean that same kind of paper is used on mags/adverts around the world.

So far, I've found, that there are at least three ways to adapt the process for one's currently available paper types: ironing, water-acetone method, or combination of both.
None of the previously mentioned methods produce perfect results; but after some practice, they should get the job done adequately.

After all, the point is to not be too dependent on certain commercial brands/products, as they come and go.

Maybe it's time to end this off-topic-ish ramble for now.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: awemawson on August 21, 2020, 02:41:43 AM
Years ago there was a thing called a Dalo Pen, that had a thick ink that was resistant to ferric chloride etchant. A bit of a pain to use but a very quick way of making simple PCBs

They were very expensive but I found that Layout Blue was etch resistant so I refilled marker pens with it.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: RussellT on August 21, 2020, 05:35:12 AM
I've tried a few of the internet methods using photo paper etc, but I decided that buying the press and peel paper wasn't as expensive as wasting copper clad board.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: vtsteam on August 21, 2020, 10:12:20 AM
Pretty amazing project sorveltaja, and extremely well detailed.  :jaw:  :coffee:  :beer:
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 21, 2020, 03:57:36 PM
Awemawson, yes I use Decon Dalo pens occasionally to patch weak/broken transfer traces. There is a small story, considering the Dalo pens: back in the 90's I went to electronics shop, and wanted one of them, although being expensive. When all the stuff was paid, sales person did put them in the plastic bag.

After some months went by, and there was need to use the pen, I opened the box, and it was full of Dalo pens... dozen or more of them. I thought of returning them, to be fair, but didn't have the receipt anymore.

I still have some of them left, good as brand new. Bit of a history, as that seems to be discontinued product.

Russell, thanks for the suggestion. When thinking of it, Press-and-Peel(or UV-method) could well work better, when the traces are really thin, and high precision is required, like on the layouts, that use smd(surface mount device) ic's/components.

Vtsteam, thanks for the heads up. It is my aim to document the project(s) as well, as I can. That way it makes more sense to me, of what I'm doing. Hopefully it makes projects like this easier to approach, even if one doesn't have a massive experience in electronics(me neither), but is still interested in experimenting.

In the end, the compander bus board is now finished, and connections tested:


The four pin header on the right side is for the op-amp -board(to be done), that sets the output level using a pot. The pot on the upper side is to adjust the 'vocoder threshold'.

At this stage, further testings have to wait, until rest of the bus boards are made. Otherwise the results(and amount of wires needed to connect all together) might end up being a great confusion.

Ordered pc boards should arrive in next monday. All the 'blocks' are finished, except the output op-amp. Next onto that.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 22, 2020, 07:33:23 PM
It is always a positive surprise, when ordered stuff arrives earlier than expected. That's what happened, and now the project is at this stage:


Some wirings and the output op-amp board needs to be made. After that, it's finally time to find out, how all those circuits works together.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 24, 2020, 06:26:41 PM
Today i've been mostly testing the vocoder, as a separate blocks, and as a whole. Everything should work, but there is no actual vocoder effect. I don't expect to get the sound of full blown 24-channel one, as this has only 8 channels.

Still, there should be clearly audible effect, like on this video of the same Paia vocoder. Demo starts at ~1.10:

Companders work, although they give rather odd waveforms. Not sure why that is. Maybe that's the part of them, that I can't get my head around.

Band pass filters work. To be sure, I did also some aural testing on each of them, using a signal generator's 'random noise'(not really random, more like a loop, which can be heard at a low frequency like 1Hz). They all have different, distinct audio ranges.

One thing that came to mind, was to replace the companders with something simpler, like Led-Ldr(Light dependent resistor) pairs. After a bit of search on the net, conclusion was, that they aren't generally used for a vocoder.
All the diy -designs, or versions that I'm aware of, use IC-based solutions for that.

The Led-Ldr pairs are used on some diy compressors, phase shifters and so on. Of course the linearity isn't at the same level with the IC-based 'level adjustment' -devices.

Despite of all that, I think it's worth of testing, how they could possibly work for this purpose. The form will probably be like on an envelope follower from Craig Anderton's "Electronic projects for musicians":


Basically, the above Led-Ldr envelope follower works as follows: an audio signal is fed to the input, and goes through the op-amp(IC1), which drives the Led portions of the optoisolators(OI1 and OI2), so that the leds light up, roughly following the input signal's amplitude. Amount of that light tells the Ldr, how much it can 'open', by lowering its resistance.

So, plan is to start by cropping the above schematic's parts count to bare minimum.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 25, 2020, 05:10:44 PM
To see, if the compander bus board could be used for led-ldr pairs, I made adapters for the pin headers, so that it's easier to connect the breadboard to the rest of the circuitry:


I did roll some temporary optoisolators to test the concept. They aren't lightproof, and need to be covered with something like a cardboard box, when testing. I had to order more ldr's, as it is probably better to have the same model for all the eight pairs:


First I connected some leds to compander bus boards' header pins(which are connected to band pass filter's(bpf) outputs), and it was like a christmas tree. Frequency sweep from 0 to 6000Hz showed, how each channel responded to certain frequencies. Adjustable gain, first stages(for mic and instrument) had expected results; when turning the gain down, leds dimmed correspondingly.

So far, it looks like the bpf's outputs itself might have enough drive to make the leds light up at the usable levels.

One part of me tells that the signals should be buffered, before they hit the leds, but not yet; only if there are several, noticeable impacts to the rest of the circuitry, then it should be done.

Version 0.1 layout of the possible compander-replacing led-ldr portion:


Mic input signals drive the leds, and should ideally be in a dc form. Diodes do some rectifying by allowing only positive peaks of the ac-form audio waves to pass through, and then the 47uF caps smooth out rest of the signals.

Instrument input signals go through the ldr's, that act like variable potentiometers. Again, microphone's signal controls the intrument's signal output level.

As can be seen in the above layout, 'outputs' of the ldr's are fed to the final stage, being an op-amp. They are simply tied together, which shouldn't work, as all of them will fight against each other, to get a place in the sun. Buffering seems to be the key, and is added later on, if definitely needed.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 26, 2020, 05:46:55 PM
First aural test, using previously mentioned circuit. Currently 5 of 8 channels are connected:


Resulting audio, rather muted and distorted, with little of an eq added to clarify:

Audio files used to drive the vocoder: a sample from an audiobook "Gods of Mars"(freely available from for mic input. For instrument input, an audio file, using the hex pickup, recorded back when I made final adjustments for it.

It's very tricky to get the adjustments to the point, where the effect is most clearly audible. Changes in input signal levels affect the result also.

I'm thinking of testing the inputs by using compressed audio signals, to get more stable action. First it could be done by compressing the audio file's signals, and if it helps the overall performance, then build a compressor for each input. But we'll see.

After all, I am very much surprised, of how that rudely simple concept, where I just threw some components to breadboard, gives signs of life. Absolutely worth further testings.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: vtsteam on August 26, 2020, 10:11:25 PM
Amazing. And fascinating. Beautifully presented.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 27, 2020, 04:52:48 PM
Vtsteam, thanks.

The ordered ldr's arrived, and now all the 8 channels are connected. First sample was made using the same hex pickup track, to feed the instrument input. Control input (Mic) was fed with 2Hz(120bpm) square wave. Raw output, so there was no post audio processing(who needs a drum machine, sequencer, or a keyboard anymore): ( 

This one was made by feeding the same clip from previously mentioned audio book(speech) for mic input, and 50Hz square wave for the instrument input(or was it vice versa). But anyways, that required some heavy eq'ing afterwards, but still lacks the definition: (

So far, as this vocoder is a bare-bone version, it has already exceeded my expectations, by opening a whole new audio landscape for experimenting.

Some aspects, that need to be worked on:

Compressing the signals in audio files by using an audio editing software(like Audacity), especially speech, is more complicated, than it seems.
I'm not an audio engineer, and just fiddled with some settings, but it's way too easy to add unwanted distortion to the original signal, by 'ballparking'.

Another way to approach the problem, could be to use a soft-clipping circuit, to squeeze the speech signal between certain values, and adding needed harmonic content to it at the same time.
To realize that, something like 4049 cmos ic(which is known for its properties to clip in tube-like manner).

I should have some of those ic's in the shelf to boot, so it's going to be one of the subjects of forthcoming testings.

Then there is one thing, that I noticed earlier: the band pass filters don't have equal output levels, even at their fundamental, or 'peak' frequency ranges. I have no idea, if that is what they are supposed to be, but I'm going to find out, if they could be 'leveled' in a simple way, like using trimpots, that I have.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 28, 2020, 07:44:01 PM
Not so much of an aural testing today. Instead I've been drawing a breadboard version of a compressor, that uses led-ldr pair for gain control. If it makes noticeable improvement for speech processing, more about it later.

I also measured outputs of the band pass filters, one by one. 0.1 volt sine wave was used, at each one's peak frequency. Power supply at -15/+15 volts. Results:


Quite a lot of deviation, to say at least. I started modding with the 560p one, to add more gain for it. Schematic of the mic-instrument pair:


First I removed resistors Ra and Rb(both 4.7k), and replaced them with 10k multiturn trimpots. Still not enough, so I detached one end of the Rc and Rd(2.2M each), and added 2.2M resistors in series with them. Then I was able to get the max. output to 12.0 volts, which might be enough for now.

I just don't understand, why there is so much deviation between bpf's outputs. 560pf one had 072 dual op-amp, and I replaced it with 082, to make sure, that the ic is working, but still same results.
Those bpf's have identical components, besides frequency setting capacitors.

Modifications are quite simple to make. On the right side is modded one:



Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 30, 2020, 07:13:11 PM
Each of the band pass filters were adjusted to have ~12 volts(p-p) outputs. It alone made audible improvement to the overall output.

Just today I read from some forum, that this(Paia) vocoder, has an inherent property in form of deviation of the bpf outputs. When I was measuring the compander's output levels, it wasn't so dramatic, so that could the reason, why the designer of this device(Craig Anderton) did let them be, as they are.

But now it's been taken care of, and the previously mentioned compressor for speech signals may not be necessary at this point.

Optocoupler pair, as a module, and built one(1 of 4):


There were two odd things, that I stumbled upon. First one was, that I had to swap mic/instrument connections for the led-ldr pairs 2-4-6-8. Otherwise they wouldn't give any output. Probably some logic error in the bus boards. I didn't want to spend too much time to find them(errors), instead it was easy to fix the problem, when they were on the breadboard.

Second one was utterly strange. When I built the above led-ldr pair as a module, there was usual testings, to see if it works, as expected. Procedure was this: feed a low frequency square wave(1Hz) to the led inputs, and higher one(audio range) freq. signal to ldr's. That way I expected to see, how the slowly flashing led turns on and off the signal, that goes through the ldr.

No such thing. The signal went through the ldr, and the flashing led did affect it only barely visible amount, when looking at the scope. I used signal generator for the signals, and dialed the levels up and down, but no visible reaction.

There I was, thinking: "bugger! this doesn't work!". Then I did the same tests with 'previously aurally tested and working' -setup, that was on the breadboard. Exactly similar results.

My conclusion was, based on level measurements, that it shouldn't work, but when connected to the rest of the circuitry, and listening to the output, it works, for some reason.

There must be some 'plan 9 from outer phase' -audiochemical processes going on.

But seriously, the way they work, isn't obvious(at least for me). I would most probably have skipped the whole concept, if I was counting on my skills to find out, what's happening, just by looking at the numbers or curves.

In the end, no off-topic ramble this time.

Makes one wonder, why the optoisolators aren't used on diy-vocoders(as far, as I'm aware of).
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on August 31, 2020, 08:07:59 PM
All the optocoupler boards are finished, and the whole device works, as expected. Now it's time to look, what needs to be added/modded, to get the most out of it.

First one is simple; 100k potentiometers(left from the arbitrary waveform generator -project) between bpf- and optocoupler boards, to adjust each channels levels individually:


It works like an equaliser, but has rather subtle effect. That is probably because the leds on the optocouplers could use more 'juice', to make the ldr's more reactive/responsive. The outputs of the band pass filters, although their gains are cranked close to the max, are still lacking the grunt. But then again, they weren't originally designed to drive leds...

I discovered a possible trick to increase their current levels, while testing earlier with a single potentiometer. So far, I can't tell, what the cost will be(like roasted op-amps, and such).

As always, there is only one way to find out.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 01, 2020, 08:31:50 PM
The previously mentioned trick to increase the current levels for the leds didn't work well at all. Leds flashed a lot brighter, but the audio output was not usable, being heavily distorted and muddy.

There I was, reminded of the thing, that everything doesn't have to go to eleven(like Spinal Tap). I encountered the very same thing, when building the electronics for the hex pickup.

In fact, the band pass filter's gain levels are so high, that the output op-amp clips/distorts way too easily. Maybe just replacing it with a pot(and perhaps with a buffer(which has a unity gain)) could be enough, as the output seems to be already 'hot' enough, to need any amplification.
But the idea of using the 100k pots between bpf's and optocouplers seems to work quite well, when inspected and listened closer.

It is true, what I've been reading about analog vocoders: it takes a lot of effort to get a grasp, how to operate the bugger, to suit one's taste(or get whatever usable effects).
Not an object for me, as I tend to go to extremes, when testing/abusing such diy-built devices.

Partly off-topic philosophising:

When I got my first stereo system, some time went by, and I read that an equaliser would improve the listening experience. So I bought one(that I still have).

At first, when turning the knobs up an down, I wondered: "where is the beef?". Again, after some time, I started to notice slight differences in sound quality, when playing with the knobs.

Eventually that eq became an essential part of the stereo system. The key is to develop the hearing,

Same seems to apply to this device also: Hearing/ear training. Instead of turning the knobs to eleven, there are subtle things, of which the secrets are made of.

In the end, I have ideas about extending this vocoders range of usability further, by adding something like 4046-phase locked loops for each channel. We'll see about that.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 02, 2020, 07:30:51 PM
I can now see, why there is a fuzz option for the instrument input, in the original schematic. It adds, when used very sparingly, a bit more harmonic content. So I breadboarded the 'tube sound fuzz':


It uses a 4049 cmos hex Inverting Buffer -ic:


I left the R6(10M) out of the circuit, as only very mild portion of fuzz is needed. Actually finding a sweet spot could be easier to dial in, if a multiturn pot was used insted for R5(1M).
They seem to cost at least five times more, than ordinary pots, so I rather look for other options. One could be to use gears to increase the ratio of rotation.

I have some plastic gears from printers etc. and also guitar tuning machines, that use brass/steel worm gears. Printing the gears with small teeth, like mod 0.5, and expecting them to mesh smoothly, isn't too good idea, as I found out on one of the past projects. In future it could be done, once the entry level printers develop enough.

Certain level of precision is preferable, so perhaps the guitar tuning machines(having something like 8-12 ratios) would be more than plenty. They also take less room, than similar ratios done with spur gears. I have a feeling, that it will be the next 'sub-project'.

In the end, an audio sample, where the fuzz was used for instrument signal: (

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 03, 2020, 08:39:43 PM
Today, after finding this video, I got stuck in the idea for printing the reduction gears for the pot, after all:

As can be seen, fewer and bigger gear teeth are used. There is a link to Thingiverse for the 3d model in the video description.

There seems to be quite a lot of slack between them, which could probably be adjusted in the slicer settings. Haven't got much into that, so I rather redraw/modify the gears using 3d software.

When there are sun- planet-, and ring gears involved, trying to figure out the gear ratios makes me feel dizzy, so it's better to just print out some samples, and see, how it works.
Nothing critical about the gear ratios, so any result, that 'feels' good enough for the purpose, is worth testing with actual potentiometer.

At first, I'll be using simplified tooth shapes for sketching:


This will be a short sideproject, to see, if the concept is relatively easily implemented, as I don't feel like delving into it too deeply at this point.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 04, 2020, 08:45:47 PM
The "potentiometer gear reducer" -side project goes on: I noticed, that gears with straight teeth don't work so well in this case, so helical ones would be better.

Test setup for gears with 45 degree angle:


Idea came from this:


Printed parts:


So far, it seems to work as expected. For now, tolerances are bit tight, but it's just a matter of playing with the offsets of the gear profiles.

Also, as the gears are helical, they tend to 'climb' up or down, while turning back and forth. Some sort of support structure needs to be added to keep them in place.

Currently the footprint, or outer diameter of whole thing is 30mm.   

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: on September 05, 2020, 06:57:44 AM
I'd suggest printing them as Herringbone gears which have no side thrust. The downside is that the outer would need to be split so that it could be assembled from each side and then joined at the separation line. Or maybe the gears could be printed as two halves that come together with pegs to engage them. They'll still require some means of gluing or a snap-together fitting so that they don't part company in one direction.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 05, 2020, 07:35:31 PM
Seadog, thanks for the idea! I tested it and it works very well to keep the gears in place.

Assembling the thing, yes, it's a bit of dowside, but somehow I managed to cram the gears together.

With the gear sizes, that I've tested do far, the reduction ratio is close to 4(by eyeballing, while rotating). Sun gear has 5, planet gears 8, and ring gear has 22 teeth.

To simplify the thing, I guess only one planet gear(blue one) might be enough, as there aren't much of forces involved. With small, printed gears, there seems to be always hideous tight spots, so reducing the gear count is an attempt to minimise that: 


If more gear reduction is needed, there would be room for that also:


To get less wobbly action, the sun gear should probably use a metal rod(2mm in this case), attached to the green part.

As an alternative for using gears, plain friction based one, as on a picture on the previous post, should make the desingn a lot more easier to build. Using the steel balls would require very tight tolerances, and is therefore beyond the scope.

Again, one possible option could be to use something like rubber as a material for the planet gear, which otherwise causes the tight spots.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: Joules on September 06, 2020, 01:05:42 AM
I think you are getting confused with the ball bearing pot.   They are no more precise to make than a 3 legged stool, the use of 3 bearings (the items of precision) allow the shaft to self centre, a bearing pot can slip.  It relies on two conical surfaces to work, the shaft is tensioned to maintain friction.  As the shaft and cone wear, the ratio of turns also changes, slightly.  Do you want repeatable location (geared) or high resolution of motion, the two are not the same.

The tight spots in prints will always be present in a cartesian printed part, they canít produce accurate round components.  The best you can hope to achieve in extruded filament is using a delta printer as they have no XY backlash, but plenty of other setting issues.   Resin printers seem to produce some of the most accurate gears I have seen as they have such high resolution and consistent blob size.

Reducing your nozzle diameter, will also allow more accurate parts to be printed, but a higher level of printer tuning is also required.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 06, 2020, 07:42:03 PM
Joules, that's interesting. I thought that the ball mating outer metal surface had similar form, like on ball bearing. Thanks for clarifying.

What my aim to achieve with this, is simply to make it easier to find sweet spots, which seems to occur at rather narrow ranges of a 1M pot.
It's a case of listening for the audio output, so the actual resistant value isn't important.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: Joules on September 07, 2020, 05:19:04 AM

For the benefit of anyone struggling with how this works, the parts contacting the balls need to be metal, but the rest could be 3D printed, such as the carrier that holds the balls and transfers their motion onward.   I know this form of reduction drive from telescope fine focus controls.  The drive can be configured push or pull by the direction of the cones, this is in fact the opposite to the potentiometer in question, only low load applications need apply   8-)
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 07, 2020, 07:21:04 PM
Joules, thanks again. I'm thinking of making one(or more) at some point. Currently I have only 4mm bearing balls on my shelf, which would make the thing too small for my paws to build.

At least 8mm ones would be easier to handle, so I'll order a bunch of them, and other sizes too. But yeah, it'll be fascinating project to get into. Although the working principle is quite simple, it would require its own, separate building thread. 

In the meantime, some temporary (and bulkier in size) two-gear based solution will be used. Once I get to the point of building the enclosure for the vocoder, smaller is better, as I don't know yet, how many more pots/knobs/plugs it will have in its front panel.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 08, 2020, 09:01:23 PM
To get back to the original subject, it's time for another audio sample. First is the original, that has tango on the left channel, and steam train on the right: (

The very same audio file was fed through the vocoder: (

To get the actual effect, both inputs (mic and instrument) should have signals, that have common frequencies(like above). I've tested both the tango and train tracks separately with animal sounds, like birds, horse, chicken and crow. Not much common frequencies between them.

One trick could be to slow down, or to speed up either of the channel's signal, to get them to the same frequency range. But that's just a tip of an iceberg of possibilities.

Current to-do list: build the fuzz, as it's working well with the vocoder.
Build the 'Super tone control', that has separate high- band- and lowpass controls in it:


It should add more flexibility for tone shaping of the input signals. If it does well, I'll build another one for the output also.

In the end, the enclosure, being an empty cassette deck, would be a lot better to work with, than the current cardboard mock-up. Also it would have its own +15/-15V power supply, instead of using the bench psu with wires and clips. In other words: a developing stand-alone unit.


Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 09, 2020, 09:06:27 PM
For testing the vocoder effects between different audio samples, there is an easy way, using Audacity's(free audio editing software) vocoder, which I discovered just recently.

I tried it with the same tango-steamtrain audio sample, that was previously posted. With default settings, similar effect is there, but has somewhat different 'pronouncing', when compared to the analog device.

Today the ordered bearing balls arrived(for the potentiometer 'gear' reducer). There doesn't seem to be 3d-models of them available on the net, so why not make one.
So far, I have fiddled with different ball sizes to see, what the approximate ratios could be. Printing the ball mating surfaces/objects might work, or then not.

Preferably the ball mating surfaces should be machined out of metal, but I'd like to find out, if there are simpler ways to achieve acceptable results, without using the lathe. 
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: Joules on September 10, 2020, 03:39:18 AM
I will refrain from commenting further on the bearing surfaces, at the beginning of this project I didnít belive the optical pick ups would work.


Well done on that.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 10, 2020, 09:34:22 PM
I didn't believe either, when I started that pickup project. There I was wondering: "nobody have done this, as far as I know, so it shouldn't work". Then I needed a proof, of why it shouldn't work.

That's how the project started, by just doing against one's better judgement. At some point, the 'shouldn't' changed to 'could', and later on to 'would'.

Don't know, if that makes any sense, but it seems to be the pattern, that I've noticed, when looking back to the recent, experimental builds.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: Joules on September 11, 2020, 01:27:18 AM
Makes lots of sense, if you ever saw my 3D printed ball nut for the insane.  It started out as theoretical, proved impossible, til I got a 0.3mm nozzle.   Hence my suggestion for your small gear, good to see people push the boundaries and change our thinking and understanding on the way.

I know I said I wouldn't, but....   You might consider 3D printed press tooling.  Cut up some steel beer cans to make discs with holes in.    They could be pressed to form conical surfaces for your prints, allowing a metal surface for bearing contact, without machining.  Press tooling makes good sense as you potentially have multiple parts to make, assuming you have an Arbor press or the likes of.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 11, 2020, 08:09:16 PM
Measuring, how to fit the vocoder into the enclosure. Bit tight, so the slide pots between band pass filters and optoisolators can go, for now. If needed, they could be added afterwards:


I've had a far-fetched idea of adding some kind of an audio analyser to the setup, having an led bar display for each channel, to show and hold the peaks of average values of say, 5 sec. audio samples, to get the 'profiles' of certain sample's frequencies.

In practice, I guess it would get too complicated, if only analog components were used. An alternative could be to use one of those cheapo pocket size oscilloscopes instead.

Getting/testing smaller nozzle has been on my to-do list for a while, so we'll see, once the current projects give room for it.

What comes to conical metal(or other material) surfaces, there is a slight chance, that they might not be necessary, as I noticed today, when fiddling with different configurations. Also the tension spring might not be needed. It seems that only the centerpiece, or 'sun gear', that rotates the bearing balls(planets), needs to be made of metal, having smooth surface.

Printed outer ring turned out to be adequate for testing(although smoother/machined surface would be better). Once there is sufficient amount of tension between the parts, they rotate just like planetary gears do.
Almost too simple, so there must be some serious obstacles ahead. To find out, what they are, I'll start a separate thread about the subject soon.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: WeldingRod on September 11, 2020, 10:09:04 PM
Loving the cardboard aided design ;-)
That's how I did the guitar amp box with my son!

Sent from my SM-G892A using Tapatalk

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: BillTodd on September 12, 2020, 09:31:17 AM
I've had a far-fetched idea of adding some kind of an audio analyser to the setup, having an led bar display for each channel, to show and hold the peaks of average values of say, 5 sec. audio samples, to get the 'profiles' of certain sample's frequencies.

Can you program a PIC micro? (specifically 16F877)

I have a few 101 segment bar graph VFD devices and drivers (I think I'm out of PCBs but the gerbers are in the zip file) . Happy to donate one to the cause if you can use it :-)
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 12, 2020, 08:55:50 PM
WeldingRod, yes, delightful and universal prototyping material.

Bill, I appreciate the generous offer. Only problem is, that I don't know how to program in assembly langue. Back in the eighties I had the Sinclair Spectrum, which had an option to use assembler(was that same as assembly language?). Although I was fascinated by its sheer speed(sample programs from books and magazines), when compared to ones written in basic, I never understood its construction.

Later on, when internet started to grow, there were more info and samples of it available, but still I ended up scratching my head. So far, basic is the only language, that I can comprehend, and write simple math programs. I remember trying out some basic to assembler(or to machine code) translators at one point, but back then the results weren't too spectacular.

Since then, I haven't looked much into it, so in these days, more robust ways to do the translating could be available. As far as I know, there are also Basic Stamp -systems available, but as they don't seem to be as popular, as PIC-based ones, the prices are prohibitive, especially, if one needs several of them for separate projects.

Apart from the "language barrier", an interesting subject.

Today I managed to almost finish the fuzz and super tone control for the vocoder:


Again, the fuzz pcb layout was mirrored, which I noticed(again), while soldering the corner legs of the ic socket(

Anyways, It was a breeze to make a corrected one, as the board is so small.

The way, that the fuzz works with the vocoder is already tested, when it was on the breadboard. The super tone control will have to wait, until the vocoder itself is fitted into the enclosure.

The plan is to use as few switches as possible, to avoid unnecessary wiring hassle, when compared to the original, Paia version.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: RussellT on September 14, 2020, 12:22:26 PM
You could try Mikrobasic for PIC.

I've used it a bit - seems to work well.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 14, 2020, 07:04:21 PM
Russell, thanks for the tip. I downloaded the demo, but haven't tried it yet.

Now the vocoder has an enclosure, although carboard is still in use for front panel:


There will be at least 7 pots more and one switch, once the fuzz and super tone control are installed. Then plug for the headphones, so the output doesn't need to be connected to the pc's soundcard, while testing.
Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: RussellT on September 15, 2020, 01:41:32 PM
Russell, thanks for the tip. I downloaded the demo, but haven't tried it yet.
The free version is only limited by size of program - and the limit still gives you a lot of scope.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 17, 2020, 07:20:50 PM
Today more cardboarding:


Before putting the tone control and fuzz into the vocoder enclosure, it's easier to first test different combinations, to see, how they work. Knobs need to be printed, and power supply wirings added.

Title: Re: Extending the soundscape of a hexaphonic guitar pickup
Post by: sorveltaja on September 21, 2020, 08:30:00 PM
Tone control and fuzz are now tested and working. Haven't used them with the vocoder yet, as I got bitten by the "guitar repair/mod" -bug.

The new guitar, that I have, needs some minor fret leveling to get the strings lower, without too much string buzz. It should be done right at the first shot, so I'm going to practice the techniques, using the old crappy Ibanez, which requires a lot more fretwork anyways, to be playable.

Then came also the idea to scallop the fretboard of that old bugger. It's something that has haunted me for years. If I mess it up, no harm done. If successful, I have probably given it a whole new life.

But yeah, I'll get back to testing the vocoder with its new companions every now and then.

In the end, I'll install the hex pickup system back to the guitar, that was used for testing it. Before that, there is some rewiring to do, to make it a bit easier.