Author Topic: Extending the soundscape of a hexaphonic guitar pickup  (Read 311 times)

Offline sorveltaja

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Extending the soundscape of a hexaphonic guitar pickup
« 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):

http://www.elisanet.fi/kz1706/optical_pup/4040_testi.mp3

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:

http://www.elisanet.fi/kz1706/optical_pup/4051_testi.mp3

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.



 

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #1 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.



Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #2 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(https://en.wikipedia.org/wiki/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.


Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #3 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.

   

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #4 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.


 


Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #5 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.


Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #6 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).



Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #7 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.

Offline sorveltaja

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Re: Extending the soundscape of a hexaphonic guitar pickup
« Reply #8 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.