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Cheapo guitar sustainer/feedbacker
sorveltaja:
Steve, yeah it indeed is. Especially, when tweaking the user interface to suit. I admit being very picky about it, as everything unnecessary should be either removed or simplified to the core, in the name of utility.
At this point, almost all of it is accomplished.
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What comes to the main project, I've been looking for a source for tactile transducers in my country. Only one, that I was able to find, is 58mm, 25W one. Pretty bulky for this purpose.
Other ones available are 'bass shakers'. Not sure how they would work as an exciter for the sustainer, as there are higher harmonics involved also.
Although my current setup with 2.5W amp and 8ohm 0,25W speaker works, the speaker, as it has a moving cone, makes it rather fragile for extented use.
So, next thing to do is to see what ebay has to offer. I have never used tactile transducers, so I'm not quite sure, what size, or power rating to look for.
In the spirit of this forum, I'd rather like to try and build my own version of tactile transducer. I haven't found much info on the net about it, or perhaps I used wrong words, when searching.
WeldingRod:
Laziest is copying the "buttkicker" brand bass shaker. Round magnet in a slippery tube, set up where its magnetically centered. A big winding either exerts an up or down force, depending on polarity. Should be scalable to small size.
Look for the cross section halfway down.
https://thebuttkicker.com/company/
Sent from my SM-G892A using Tapatalk
sorveltaja:
WeldingRod, thanks for the tip. That's the principle, that I'm going to use as a starting point.
First test coil:
Coil has 0.2mm wire, and to get approximately 8 ohms, about 15 meters of it was used. To get more practical view, I modeled the coil to fit to that size of bobbin.
Finished coil has resistance of ~9 ohms.
That coil was used to test, how it works with 12x3 round neomagnet, that is glued behind the guitar's headstock. It showed signs of life, so next step is to concentrate to the 'tactile' part.
Basically it's like a solenoid, that is controlled by audio signal. The moving part (in this case neomagnet), while vibrating, needs to have something, that prevents it from rattling against the bobbin. Some kind of diaphragm. For that, I'm going to test the 1mm thick rubber sheet, that is under the coil in the above pic.
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To get back to previous setup with a small speaker, it's probably the easiest, non-intrusive way to get acoustic feedback from the strings. At first I aimed to clean, undistorted signal to feed the exciter(speaker), but it would require a lot more power, and perhaps (too) big exciter.
So far, conclusion is, that small speaker works because the amp distorts heavily, creating overtones and harmonics. That particular amp was/is used with 3 volts, that is way below its 'normal' value. It alone produces plenty of distortion.
And no, it's not necessarily suitable for battery use, as it draws 60-70mA at 3 volts.
In the meantime, I think it would be fair to make raw samples, of how it responds to chords and single notes.
sorveltaja:
In the past week, I've been testing different size coils and magnets for the exciter, but none of them works like the small speaker. There seems to be all kinds of unwanted resonant peaks involved. Also it appears, that I'm not that good at making an efficient coil-magnet device.
As the speaker works at quite low amplifier supply voltage, I'll stick to it. Simpler it is, better it is.
Obviously the guitar itself has its own resonance frequencies, as well as that speaker. That's the reason, why I use super tone control between guitar and the sustainer.
Finally I got myself together, and recorded a sample, while turning the knobs. It's unedited, though:
http://www.elisanet.fi/kz1706/sustainer/Sustainer_test_2.mp3
Haven't done much with the previously mentioned pedal yet, so next on to it.
sorveltaja:
Time for an update. Finding usable range for the led/ldr-optoisolators(which control the frequency of the super tone control) isn't as easy as I thought.
Main problem is perhaps, that the freq. control for the stc was originally a dual 10k pot, and the ldr's, that I have, have resistance range from about 100 ohms to over 30M.
I guess that's the reason, why the effective range is so tiny, 10k vs 30M. I tested different resistor values in paraller with ldr, but it didn't have the effect, that I was looking for.
Next thing was to try the voltage divider. It's a bit better, but still the usable range is quite narrow. I'm not exactly sure, what other factors are involved.
But anyways, a block diagram of the current setup:
On the left is the pedal section, having 317-based adjustable regulator, that gives ~2.5V output. It controls the stc's optoisolators. Reason for that extra optoisolator, is that instead of six wires, only one coaxial cable is needed for the pedal connection.
As the usable range of the optoisolators is narrow, very little current is needed to drive the pedal's led(~20uA). I have no idea, why that is, but 9V battery could well be enough for it.
317's, that I have, seem to keep the voltage level constant, until the supply voltage drops below 5V.
On the right side is the 2.5W amp. I happened to find 8ohm 0.5W speaker, while going through the shelves. It works better than the 8ohm 0.25W one, that I used before. It's not much larger, but has more mass in it. Conclusion: the size of the speaker isn't critical. But small ones (~50mm dia.) are cheap, and appear to fit in the headstock, without sticking out too much.
Also the amplifier can be about anything, as long as the speaker can handle it. It really doesn't take tens of watts to make the guitar's strings 'sing'.
In the end, what comes to narrow range of the optoisos, there might be a workaround in a mechanical form.
When the pedal is moved up an down to block/unblock the led's light, the ratio of the movement... yeah, sounds easy, but we'll see, as I have a nasty habit making simple things complicated
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