Author Topic: Extending the soundscape of a hexaphonic guitar pickup  (Read 4080 times)

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #25 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 http://www.generalguitargadgets.com/effects-projects/extras/epfm-book/

Then salvaging all the reusable parts from the old phase shifter, printing 'housings' for led/ldr -pairs, and so on.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #26 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".

 

Offline PekkaNF

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #27 on: April 22, 2020, 05:30:38 AM »
Play it again Sam gone Leslie Nielsen?


Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #28 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.



Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #29 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.




Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #30 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.

   




Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #31 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.

 




Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #32 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. 

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #33 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:

http://www.elisanet.fi/kz1706/optical_pup/phase_shifter_testi_1.mp3

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.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #34 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.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #35 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.



   

 

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #36 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.








Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #37 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.





   

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #38 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.




Offline Sea.dog

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #39 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.

Offline BillTodd

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #40 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 :-)
Bill

Offline awemawson

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #41 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.
Andrew Mawson
East Sussex

Offline awemawson

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #42 on: July 28, 2020, 08:20:25 AM »
Picture as promised (of the IC leg straighteners)
Andrew Mawson
East Sussex

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #43 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.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #44 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.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #45 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.


Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #46 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.




Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #47 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.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #48 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. 

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #49 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.