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Diy optical pickup for guitar -- is it possible?
sorveltaja:
The new 90 degree mech/optical setup is ready for testing, for the thinnest string(0,25mm). For the reflective material, I glued aluminum foil to thin cardboard, so that it's easier to handle, and to cut to suitable size.
Then it was tested with the previously mentioned test-setup. Again, the input ---> output -results were close to mirror-like surface. But when looking that aluminum foil, it doesn't seem that 'mirrorish', though.
It could be carefully polished, but I'm thinking of replacing it with thicker brass, or aluminum, which should be a lot easier to polish, although they should be sawed and filed to the size.
Bit of work, but not a big deal.
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The cover with alu foil glued in. There were thinner legs on the front side, but I managed to snap couple of them out, while sanding the upper surface(it was printed upside down).
But the overall construction feels rigid enough without them, so I snipped rest of them away also:
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I certainly hope, that this setup, even with cover in place, works, as it feels somehow very 'natural', without the feeling, that something is protruding between the strings:
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After some testing with the thinnest string(without schmitt trigger), there was output, but it wasn't easy to locate the factors involved(as I have a nasty habit of starting at the hardest point available ).
But after all, it looks promising enough for this setup; so the next step will be the thickest string, that has a lot more output to boot, to hopefully get a bigger picture, of how that setup works.
sorveltaja:
The cover is now ready for testing all the strings:
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Aluminum foil was replaced with 0,25mm brass. The brass sheet was first treated with dremel and polishing compound, and after that, the pieces were sawed with a fret saw to size.
Bit of filing to remove any burrs, and that's it.
There is one thing though, when handling polished brass like that. To avoid any fingerprints on that shiny surface, straight after polishing, I covered it with a tape.
After sawing and filing, it was peeled off, before gluing the pieces in place.
Although the brass surfaces on the above picture might look like mirrors, they are actually quite 'shady'. But, after all, if aluminum foil performs well enough, polished, more solid metal surface should do even better. So fortunately, no need to go crazy with the polishing.
With this mech/optical setup, there are a lot of options to test. One being like this, where the distance, and angle between sender/receiver could be altered, while still using that very same 'base platform':
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At this point, when the amplifier circuit is completed(although not perfect, but good enough for now), as well as the schmitt trigger one, a very basic kind of 'foundation' finally exists.
With that in mind, it allows one to dive more into other factors of testing, like producing a stable signal from the string(s), that could be a lot more easier to measure, than simply plucking the strings.
One of the reader mentioned earlier something, that reminded me of a 'sustainer', that is used to input the string(s) signals, and fed back to the speaker-like 'exciter'(under the strings), to make them 'sustain', or ring constantly.
I'm considering of making that kind of sustainer for a single string use, that could be fed with open string's fundamental frequency with a function generator.
One heck of a side project, but the concept isn't actually new for me.
sorveltaja:
It seems, that the 'resonator' to make the string(s) constantly ringing, while adjusting/measuring output of the pickups, doesn't need to be that complicated, as I expected.
Using small 8ohm speaker and function generator, I tested, what could be the position, to get the strings to respond to speaker signal.
So far, at end of the neck, where the guitar's headstock usually is, turned out to be the best location. My guitar is a decapitated version, so it doesn't have a headstock, but I managed to tape the speaker so, that it doesn't touch the strings:
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That way the speaker makes the neck and body resonating, and therefore, also the strings. I guess, that it would help to have a headstock, with a mass in it to make the neck resonate even more.
Even that small speaker works, although a bit bigger one could help with higher frequencies, that the thinnest strings use.
I have another small 8 ohm speaker, and maybe I'll add it in series or parallel with the one already in use, to hopefully get some extra resonating power.
As one could expect, thicker strings resonate/vibrate a lot easier, than the thinner ones, which require the speaker(s) to be driven harder.
I'm not sure, if driving the speaker(s) straight from the function generator is a wise thing to do, for a long time period. To play it safe, I'm going to breadboard one of the 386- based amps to drive them:
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Some things, of how to get the strings to respond to the fed signal: the signal itself should be in sine wave -form, as the wooden parts of the guitar do not seem to respond to (somewhat unnatural) square/rectangular waves that well.
Also, the signal feeding the speaker(s) should be 'tuned' for each string's fundamental frequency, to get them to resonate. That is, when testing one string at a time.
Although the setup is fairly simple, a sine wave generator, that has an option for fine tuning for the frequency, is highly recommended.
sorveltaja:
I tested the x200 gain configuration of the 386-amp, to drive the speaker, and it clips and distorts the fed sine wave, even at very low levels, making it useless for the purpose.
So next is going to be the mildest, x20 version.
I have also looked a way to improve the way, of how the vibration is transferred to the guitar body. There is a thing called 'vibrating speaker', which could be made using a sacrificial speaker.
As I have one, that's what I did:
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I did cut the cone on the edges, and hot-glued random, printed left-over t-piece to the center of it. As the piece, that holds the strings, is made of aluminum, I used superglue to attach the assembly to it. Removal is easy, just knock it out.
It works bit better now. I have only three thickest string's pickups in the guitar so far(need to prepare rest of them also), but for them, the signal is more than enough. One of those strings, when tuned in, actually starts to buzz like sitar string, and the signal, that is fed, must be turned down, to get cleaner output. All that by abusing using only the function generator to feed the speaker.
As always, plenty of testings ahead, before usable end-results.
sorveltaja:
Some observations, while testing. First the overall base setup for all the strings:
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To avoid confusion about the guitar strings(with a standard tuning), they go from thickest to thinnest; e-a-d-g-b-e. Basically just a bunch of different gauge steel/nylon wires, in certain order.
But so far, some results of the three tested setups; first one seems to work on four of the thickest strings(e-a-d-g). That setup doesn't give strong enough output for the second thinnest string(b), though.
Second one is a bit of a mystery, as instead of increasing the output, when cover(with reflective surfaces facing the strings) is on, the output disappears(b-string).
Third one, again tested on a b-string, seems to be a step to the right direction, as it provides more output, when using the cover.
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Distances/angles between the optical components on those setups are only arbitrary, but I think still a very good way to get a hunch, of how they behave, and affect the overall output.
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