"Oscillators" for circuit bent machines?

[Rolbista]

Ok, so here's a concept: take the most sinusoidal waveform of your bent keyboard and filter it a little to remove harmonics. Step 2: convert it to a square wave with a Schmitt trigger - here's your first waveform. Step 3: use a 4040 to get one and two octaves below. Step 3: either route the received square wave of chosen octave straight to the output or feed it into this: http://electro-music.com/forum/post-244968.html to get a sawtooth. Build 3 of such units and voila! you have 3 "VCO" on your cheap Casio keyboard! Ok, does that even make sense, I've never seen anyone do it, maybe there's a reason? And what would be the right Schmitt setup to get it to work? I used a TL072 set up as a non-inverting trigger from wikipedia with two 25k trimpots, but no matter how i set the trimpots, it doesn't output any square. Power: +/-5V, I'm viewing the signal on a scope. The signal from the Casio is around 1Vpp.

[Gordonjcp]

It's an interesting idea - by messing about with the loop filter for the PLL you would get some portamento effects (which the designer of that circuit mentions trying to avoid) - and of course, by setting up two tracking PLLs you could have different loop filter times so the notes would drift apart and "catch up" with the portamento at different rates.

[Rolbista]

Yeah, but so far I wasn't able to filter the signal in any other way than a 4 pole VCF, datasheet schematics for op amps don't seem to do anything. Too low input perhaps? So I'm still far from getting even a square...

[Gordonjcp]

Yeah, but so far I wasn't able to filter the signal in any other way than a 4 pole VCF, datasheet schematics for op amps don't seem to do anything. Too low input perhaps? So I'm still far from getting even a square...

I'm not sure what you expect the datasheets to do - they tell you how to wire the chips up, what do you expect?

[Rolbista]

perhaps I was unclear - by datasheet applications i meant sample schematics for schmitt troggers and low pass filters which I tried, but the signal viewed on the scope didn't change at all when i adjusted values (I used trimpots instead od fixed resistors)

[Gordonjcp]

That's not really the sort of thing you'd get from a datasheet, but possibly from an applications guide.  If you just want a "cookbook" approach to building filters, look for service manuals for old analogue synths.

[Rolbista]

http://www.aronnelson.com/gallery/main.php/v/DougH/fuzz/Moreoptimalfuzz/OptimalFuzzAdapter.GIF.html found this. This circuit is supposed to output a guitar signal converted to a square, do you think it would work for my purpose?