Gallery, Projects and General > Project Logs
Diy optical pickup for guitar -- is it possible?
sorveltaja:
When testing breadboarded, simple single transistor amplifier to see, if the schmitt trigger levels could be increased that way to the cmos-level, there was suddenly this repeating noise pattern, where noise was on for 1 second, and 2 seconds off.
After a while, I was ready to open the external box, where the circuitry is, and to dig it all out. But no, luckily it wasn't necessary. When I removed the lid of the box, shortly after that, the noise disappeared.
After some head scratching, I noticed, that the 7809-regulator chip was rather hot. I checked its datasheet, and there it was: 'Thermal overload protection' caused repeating noises.
The whole circuitry draws 100mA, or less, so it was kind of surprising(at least for me), how hot it gets.
Now the regulator board hangs outside of the box, and all works just fine.
What comes to the transistor amp circuit, after some tinkering, it seems to provide enough gain/amplification. Form of the output isn't perfect rectangle/square wave, but as long as it 'triggers' external cmos-devices, it should be good to go. Next thing is to test that in practice.
Hopefully it's the last amplifier circuit needed, as there are few of them already in the main circuitry.
BillTodd:
--- Quote ---The whole circuitry draws 100mA, or less, so it was kind of surprising(at least for me), how hot it gets.
--- End quote ---
The dissipation is the product of the the current (0.1A) and the voltage drop across the chip (~2V minimum for a 5v device so 7V input), so your device is trying to loose at least 0.2W of heat a TO-220 package will have a typical thermal resistance of 70'C/W so expect at least +14'C over ambient without a heat-sink .
If your driving the regulator with more volts 9-12v expect a lot more heat :-)
sorveltaja:
Bill, no wonder then, that it gets that hot, as I'm driving it with 24V/1500mA supply. As the regulator chip is 9V 7809, 12 volt supply should be enough.
In fact, I used variable psu on earlier testings, and it was feeding the circuitry at 10 or 12 volts, and the reg. chip stayed a lot cooler.
Thanks for pointing that out :thumbup:.
sorveltaja:
Now, that the transistor amp circuit is built, the output levels should be good to go, to feed other cmos-based devices, or effects.
It brings the schmitt trigger outputs(about 2-3 V p-p(peak-to-peak)) nicely to ~9 volt p-p output at 9 volt supply. Very quick and dirty, and the resistor values were chosen simply by tinkering first with potentiometers, to find suitable output. Capacitor values were chosen by looking on the scope(and what I had on my shelf), which made the output to remain closest to square/rectangular wave. Pretty scientific approach, eh?
But after all, the frequency range of the strings/outputs is below 1Khz(unless one insist on shredding on the thinnest string on the frets above 12th one).
Only one section is shown, but as the circuits before, it also has six of them:
One, or few other outputs could then be clipped down with something like 5V zener diodes, if needed. Don't know about that yet, as I'm going to take a bit of a break from the guitar/pickups -involved circuitry, and take a look, what kind of cmos-devices I have, that could then be driven with those pickups/outputs.
So far, I have fiddled with 4046 pll(phase locked loop) -ic, just by feeding it with function generator, and listening to the output.
I used to tinker with that chip years ago, so it isn't entirely new thing for me.
There are so many different component combinations/options to alter, of how it works/sounds. This is only one variation of them, that tracks the frequency of the signal fed to it:
That chip has a vco(voltage controlled oscillator) in it, that runs at tracked input frequency, which could be interrupted, making some kind of "sample and hold" -situation, where the played note could be freezed/sustained to play longer, than the guitar string vibrates. Almost like on keyboard, that plays the note as long as the key is pressed.
The idea for that came from: https://hackaday.com/2015/08/07/logic-noise-4046-voltage-controlled-oscillator-part-one/
There is a lot of theory based stuff, of what that chip does, how it does it, and so on, for those interested, but I just don't understand it.
But that chip(basic version CD4046, not sure about the exotic, high frequency variations) is a very good one for testing on breadboard, as it is practically impossible to fry it out, unless intended.
sorveltaja:
It seems like I'm getting more and more drawn into testing, how different cmos-based contraptions sound. So far using breadboard, and function generator, and a small amp for listening.
I feel tempted to test with guitar/pickups, but the concepts/results are somehow easier to follow with simpler test setup.
This is going to be rather long off-topic babbling, and I should perhaps start another thread, considerig the 'after-effects'.
I was looking info about sawtooth generators on the net, as I've read, that they have a lot more harmonic content, than plain square waves do. But seemingly, making decent sawtooth generator isn't necessarily that simple.
I have, as long as I can remember, liked Hammond organ sound, and Moog(analog synth) also. I'm not actually looking for replicating those sounds, but to see, what could be achieved using simple circuits.
What comes to that sawtooth generator, I thought that 'does it really have to be in traditional sawtooth form, that was used on so many analog keyboards?'.
Then came the idea of some kind of primitive "sampling" technique. After more searching, I found a name for it - staircase generator.
There are schematics, of how to make a proper one, but again, I started looking for other(simpler) ways to test the idea.
Back to the shelf, to check, what chips, or other stuff I have at the moment. There was 4040(12-stage binary ripple counter), which was then test subject.
I cheated a bit, and did some simulations, to see, if it's worth breadbording.
Circuit itself:
The output waveform is not, what I expected, but nevertheless, it sounds like a cheapo analog synth. Good enough, so I breadboaded it, and yes, it sounds very much the same, as in the simulation.
One big drawback is, that the frequency of the input signal is divided down a lot. To get the output frequency to match the input one, I did some testings with 4046(phase locked loop), that could be used to multiply the frequency by the factor, that it's divided by.
I'm not sure yet, if it works in practice. More testings ahead.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version