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Diy optical pickup for guitar -- is it possible?
WeldingRod:
Capacitor to ground on the pot mounting nut...
Sent from my SM-G892A using Tapatalk
sorveltaja:
WeldingRod, that's a good idea, but the pots are trimmers, and don't have mounting nuts in them. But on the other hand, it could be worth testing, if at first replacing one of them with actual pot, that has a metal cover and mounting nut, affects the noise level... hmm, we'll see.
The noise gate, that I've been tinkering with, is based on the circuit on the left(source: https://sound-au.com/project145.htm):
Although it is for switching, it could be abused used as a sort of 'automated volume pot', by substituting the Vctl input with an audio signal.
To drive the led, I've been using breadboaded circuit like this:
Component values on the above pic aren't necessarily same anymore, as I change them during testing, to see the differences.
So far, after plenty of adjustments, it seems to be almost usable. Drawback is, that it decreases the overall signal levels from the strings/pickups also.
To simplify its construction, instead of using each string to drive its own led, could be to drive all the leds with a single input from the traditional electromagnetic pickup.
Might seem odd, but actually there is no need create individual volume envelopes for each string/pickup, as the whole point is to use the device only for polyphonic(chords) purpose.
Monophonic stuff(like solos) could then be done by using plain old electromagnetic pickup, as needed.
To get back to the noise problem, quickest and dirtiest workaround is possibly to use a foot pedal/switch to control/kill the output, once the chords fade out.
I'm not sure, if I should even mention one of my mad mood ideas. But here it goes, anyways. The thing would be to use 4046-based phase locked loop(pll) -circuits for each string, to track the frequencies.
When the frequency is stable enough(like after plucking the string), the pll can lock to it, providing 'yes' -signal to a certain pin.
After that plucked note fades out, noise takes over. If the noise is random enough, the pll just wanders, and can't lock to it, providing 'no' -signal to that very same pin.
But in the end, I haven't yet tested, of how the externally installed circuitry sounds, with all the noises. Time to find that out.
sorveltaja:
Time for an audio testing, and the result, although rough and noisy, wasn't as hopeless as I expected. Again, raw output from the schmitt triggers recorded to laptop:
testi_2.mp3.zip
All the six strings were plucked to form the chords/sounds, and to mask the noises. If partial chords were plucked, noises from 'idling' strings/pickups would mask them.
It seems, that every string/pickup needs their own, individual noise gates. That previous 'touching the amp boards trim pots with finger' -trick doesn't work anymore, as all the pickups are connected.
Infact, it makes the noise problem even worse.
As mentioned before, I'm willing to keep the current setup, as it's so much easier to move around, and to work with, as all the circuitry is in an external enclosure, and the cables between it and the guitar are secured with strain relief clamps.
So, on to the noise problem. I'm going to test an optoisolator-, and 4046(pll) -based ideas.
sorveltaja:
After trying out some stuff about reducing the noise levels, I finally got this frustrated feeling in my stubborn head, that I'm beating a dead(or actually very noisy and farty) horse.
It's time to ditch the 386-based amp board, no matter what. When shortly testing two of the pickups with only the phototransistor amp-thingy(that are also in front of the 386-ic's), noise levels were already many times lower:
The above circuit will likely still be a part of the forthcoming circuitry. It seems to (probably) have enough output on its own, to feed the schmitt triggers. More testing with thinner strings is needed to confirm that, though.
On the other hand, the mechanical setup appears to work, as expected, apart from two of the thickest strings(e-a).
They are thick enough to almost cover the entire ir-beams from sender to receiver(which have 1,5mm diameter 'eyes'), providing erratic, octave-doubling effects.
Their optical components might need to be replaced with 3mm ones, but, as always, one thing at a time.
sorveltaja:
When looking an alternative for the 386-based amps, I ended up testing a 4049(Hex Inverting Buffer and Converter)-based one (source http://electro-music.com/forum/topic-51275.html).
Although the schematic on that page uses two stages, I cropped the second one out, to see if the thing works with fewer parts:
After breadboarding, and some usual tests with thickest, and thinnest strings outputs, and with schmitt triggers, yes, it seems to be working. Not only that, but it's also a lot more responsive to gain adjustment, than the 386-amps were.
Nice thing about that 4049-chip is, that it has all the needed six 'amps' in a single 16-pin chip.
There is one serious precaution, though. I almost fried the chip(it got very hot), when forgetting to connect unused inputs to the ground(or to +, as the datasheet says).
As before, the noise wasn't much of a problem, when testing one string/pickup at a time... I'm not expecting wonders, as there is a big chance, that combined pickup outputs combine the noises also.
One possible way to minimise that, would be to mount the circuitry again, in the guitar. If that single-4049-chip-amp stuff works, the whole circuitry could then take a lot less room, than the previous 386-amp one did.
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