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

Tom Wiltshire tom at electricdruid.net
Fri Jan 29 11:46:57 CET 2021


Ok, so the AS3320 has a slightly different frequency range and you might run out of frequency offset trimmer in some cases?

Once it is trimmed in, has anyone tried a “can you spot the Alfa chipping amongst the CEM voices?” test?

Thanks,
Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================



> On 29 Jan 2021, at 10:34, John Staapel <j.staapel at gmail.com> wrote:
> 
> 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 <mailto: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 <mailto: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 <mailto: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 <mailto: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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