[sdiy] Sawtooth frequency doubler and phase shifter schematic errors

[Magnus Danielson]

Hi!

I have had a schematic page which gives some circuit ideas. It seems 
people have liked them and I've seen comments on cloning them even.
Unfortunately the schematics contains stupid errors, and I have decided 
to correct a few of them. So, you should attempt the Sawtooth doubler V3 
and phase shifter V2:

http://rubidium.dyndns.org/~magnus/synths/schematics/

I have decided to keep the old versions for historic reasons. It's over 
12 years ago now since I put them up, and there is even a YouTube video 
showing the phase shifter at work, complete with it's errors.

Essentially, the R1 and R2 resistor values got swapped, and the gain 
needed some work. I suspect that the given variants is closer to 
functional compared to before. Still have not test-built them, but I 
suspect a friend will do that as he has been asking questions about them 
so now he has some fresh schematics (and formula) to work from.

For those who don't see it, the operating voltage of the op-amps is 
assumed to be +/- 15V and the op-amp comparator is assumed to provide 
rail-to-rail voltages (almost).

The phase-shifter has a few neat tricks in it, as it tries to retain the 
DC balance after shifting. I suspect it isn't perfect, but it should be 
better than doing nothing.

Cheers,
Magnus