[sdiy] Pin 14 on the 3340

[Roman Sowa]

Maybe the capacitor at pin 9 (soft sync) to GND is broken...

Roman

W dniu 2018-07-18 o 14:13, Oakley Sound pisze:
> 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
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