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Cheapo guitar sustainer/feedbacker

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Another audio effects project? really? But yeah, nothing else has appeared, after finishing the scalloped guitar, so it's time to open a new can of worms.

Bit of background about this one: As far as I know, there has been commercial sustainers in different forms available for a long time. Lots of diy-versions are on the net also.

So, what is sustainer, and what is it's purpose? It simply imitates really loud guitar amplifier, that produces acoustic feedback, making the guitar, and its strings to vibrate more wildly.

I guess, that most of us don't have a luxury of cranking the amp to ear-bleeding levels. That's when the sustainer enters the room. No loud amplifiers are required.

In general, there are two types of sustainers: most widely used ones, that look like a guitar pickup, and fit in the same cavity. They use electromagnetic means to excite the strings. Major trademark is, I guess, 'Sustainiac'.

Other one uses electro-acoustic way to achieve the results. A transducer is fastened to the guitar's headstock, making the guitar's neck vibrate, which then excites the strings. Trademark for that is 'Sustain-Man'.

Obviously, on both systems, there is a guitar pickup, that feeds the exciter circuit.

To get the project started, I'll focus on the latter, electro-acoustic one, as it's way more simpler to approach, since it doesn't require winding of exciter coil.

When I was adjusting the hexaphonic pickups in one of the previous project, I used a small speaker(8 ohms, 0.25watts) to make the strings vibrate, one by one.

That same speaker at this moment, on the right side:


Although not necessary, I reduced it's outer diameter a bit. Also the printed parts might not be necessary at all. Then I glued M8 nut to the center with hot glue. Next I added a neodymium magnet to it, so that it sticks nicely to one of the tuning machines:


Amplifier used is a Velleman's 2.5 watt one, that I had laying around:


For this purpose, 2.5 watts is way too much, and I ended using that amp at 3 volts, instead of 9-15 volts. Otherwise nasty rattlings appear, when it clips/establishes feedback loop.
Also I have no desire to fry that speaker.

In the end, I have tested that 'exciter' on the guitar, and yes, it seems to have something in it. Actually at the lower voltage supply level, the feedback is more pleasant.

Next thing to do, is to make some audio samples, then probably breadboard a 386-based amplifier for further testing. But we'll see.

Love your projects!  :coffee:

First test audio sample:

I used an old Zoom multieffect pedal to add a bit of reverb and also a hint of compression.

Connections at the moment: guitar--> sustainer amp, and Zoom. So far the guitar signal is split between them, using a 1-in, 2-out stereo plug adapter.
Guitar pickups used are passive ones, and it would be a better idea to use an op-amp based, buffered splitter instead.

One thing that I've noticed so far, is that the feedback loops are kind of 'fixed', and therefore are bit too predictable for my liking. But then again, the source of vibration is in fixed position in the guitar's headstock.

Commercial units apparently have settings/switches for the fundamental, and harmonic frequencies of the sustainer. As far as I can guess, there is probably some sort of phase differences involved between the guitar pickups and the exciter coil, which then allows the player to choose, which one is desirable.

After all, I wonder, why those commercial ones don't have an effect loop options in them. At least, if there were such, they aren't much advertised, or perhaps I'm totally missing something.

What I mean by that, is simply adding some kind of subtle, pulsating/modulating element to the signal path, to possibly make it more lively.
I have some possible ideas, how to achieve thing like that, so testings ahead.   


Audio projects are very interesting. I have a few I will be attempting shortly...

Keep it up. Love the inspiration.


So I've done some testings, using the zoom's effects between guitar and the sustainer. It (zoom)has several modulating effects, and for some reason, only the phase shifter appears to give a sort of effect, that I'm after. That phase shifter is quite lacking, but still.
Makes me wonder, does it really modulate/shift the phase of the signal, or is it just imitating. Shouldn't be too difficult to check that out with function generator and scope.

I tried to record the audio results, but guitar's signal was very weak, due to the lack of the buffer for the pickups.
As always, I have a habit of tinkering with everything else first, and only then consider building something, that is an essential basic block, when starting project like this   

Anyways, if there is something about involving the phase shifter with the sustainer, I have an analog one, that I built as a past project. It needs an enclosure, and some wiring, to get it in more usable form, though.


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