[sdiy] Pin 14 on the 3340

[Oakley Sound]

MH > The overall pitch is very sensitive to the pulse width setting. 
Alex from AS wrote me that best practice would be to generate a variable 
pulse from the other waveforms and leave the internal PWM alone (sic!).

Oh crikey. That doesn't bode well.

I'm not getting steady state pitch changes with PWM though. What I'm 
getting is that the pitch is becoming unstable like it's being modulated 
with white noise at certain pulse widths. It's not even at the extremes 
either, it's something like 60:40.

I tried adding some hysteresis to the PWM comparator but that didn't 
help. Because of the fact that the scope probe fixes the problem and 
that it doesn't happen with all chips it's got to be something some 
stray HF edge that's retriggering the oscillator core. Decoupling to a 
solid 0V seems to help but it's not so easy when I'm dealing with a 
'vintage' PCB layout.

-5V is pretty solid but it's shared with the whole synth. Minimal 
decoupling of 10uF on the voice card's power inlet. Time to beef up the 
0V on the voice card motherboard I think.

Tony

www.oakleysound.com