[sdiy] Looking for OB-8/CEM3320 filter gurus

[jhaible]

> >Just to be sure: the oscillation was also there without the extra
> capacitive loading from the scope probe?
>
> I can't remember the exact details about it now, but I am fairly sure I
> wouldn't have fallen for that one.

I would not really expect you to fall for that either (;->).

> And by stopping the oscillation with
> the cludged input cap, the 'CV breakthrough' dropped to the usual 3320
> performance. Remember this was the OB-Sx and this may not be present on
> the later Oberheims. It may even be horrible board layout, but I tried
> extra decoupling but this had no effect on the oscillation.

I have once tried to build a 16-stage phaser from four 3320's, and I did not
get this stable with *any* decoupling. OTOH Dave Amels definitely has
cascaded several 3320s for long AP filters in the Voce Spin. So I guess
the layout is very critical. (I didn't try other layouts, or RC decoupling
to individulal 3320s, I just threw it away when the first shot, and some
additional bypass caps, wouldn't work ...)

JH.