[sdiy] Pin 14 on the 3340

[Matthias Herrmann]

> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
> Oakley Sound
> Sent: Wednesday, July 18, 2018 10:57 AM
> To: Synth DIY <synth-diy at synth-diy.org>
> Subject: Re: [sdiy] Pin 14 on the 3340
> 
 <snip>
> 
> I had already changed the output loading on the pulse output to 52K as the
> AS3340 requires. Additional decoupling on the -5V lines to the 3340 did help.
> Clearly the AS3340 appears to be more prone to pitch instability than the
> CEM3340. It doesn't help that the OB-Sx voice cards are pretty badly laid out
> for 0V with the tracks going all over the place.

This is exactly what I experienced. 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!).
I did a direct comparison between the AS3340 and a NOS CEM3340, and the latter had the same issue but less. I did not do exact measurements, though.

One crucial thing is to have exact -5V at pin3.

Cheers,
Matthias