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.
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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.
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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.