[sdiy] Using AS3320 as a CEM3320 replacement in vintage polysynths

[John Staapel]

The AS3340 has the problems with PWM. I use an external opamp to solve that.
The CEM 3320 can be replaced by the V3320 and AS3320 .  The AS3320 has
a slightly different frequency setting.
The 3280 used in a filter has the same effect , a slightly different
frequency setting

JS

Op vr 29 jan. 2021 om 04:31 schreef Markus via Synth-diy <
synth-diy at synth-diy.org>:

> Hi all,
>
> I built a module based on the AS3320 from scratch and the schematics looks
> exactly the same in the CEM3320 specification. so I would say you can
> replace these including the weird max. 2V resonance CV.
>
> side note:
> as was said below between the AS3340 and CEM3340 the only difference seems
> to be the resistor on the PWM output pin 4 (AS 51k vs CEM 10k). you might
> also want to add some op amps and zener diode to get all waveform outputs
> up and down to the same level e.g. 0 - 10V...
>
>
> gruss,
> Markus
>
> On Thursday, January 28, 2021, 07:07:46 PM PST, Jay Schwichtenberg <
> jschwich53 at comcast.net> wrote:
>
>
> Yep, me bad, sorry.
>
> Jay
> On 1/28/2021 3:18 PM, ColinMuirDorward wrote:
>
> Jay is correct, but got his chips mixed up. The PWM issue is definitely on
> the VCO (3340) chip! Tom is asking about the vcf chip (3320) :)
>
> On Thu, Jan 28, 2021, 4:12 PM Michael E Caloroso, <
> mec.forumreader at gmail.com> wrote:
>
> Are you sure the PWM issue is the AS3320 and not the AS3340?
>
> MC
>
> On 1/28/21, Jay Schwichtenberg <jschwich53 at comcast.net> wrote:
> > I would go and read what's on Muffs about it.
> >
> > With the original AS3320 there are issues with the PWM affecting the
> > frequency. To resolve the problem it seems people had to add negative
> > voltage regulator (think it's -5V if I remember correctly).
> >
> > Then CEM and new AS chips seem to be better.
> >
> > Jay S.
> >
> > On 1/28/2021 10:46 AM, Tom Wiltshire wrote:
> >>
> >> Does anyone have any experience to offer having tried this? Are the
> >> old and new chips close enough to be direct replacements? Or maybe
> >> with a bit of trimming?
> >>
> >> There seems to have been a lot of focus on the AS3340 as a replacement
> >> chip (and there are a few little differences) but I haven’t seen or
> >> read much about the AS3320 as a drop-in replacement.
> >>
> >> Of course, changing all the filters to maintain consistency is a
> >> possibility, and then you have a few genuine CEMs for the next repair!
> >>
> >> Thanks,
> >> Tom
> >>
> >> ==================
> >>       Electric Druid
> >> Synth & Stompbox DIY
> >> ==================
> >>
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