[sdiy] VCF caps in modern synths

Ben Gebhardt benjamin_gebhardt at yahoo.com
Mon Jan 11 06:09:44 CET 2021


Eric,

Care to comment on the brand of x7r’s you observed this with?

> On Jan 10, 2021, at 10:51 PM, Eric Schlappi <eric.schlappi at gmail.com> wrote:
> 
> 
> my two cents on filter caps:
> 
> I have experienced piezoelectric effects with x7r caps recently, I now only use them for decoupling.
> 
> One of the bigger upgrades for my filters recently was upgrading from 5% C0G/NP0 to 1% C0G/NP0. I had previously considered 1% too expensive but they really aren't anymore and it can really make a difference as far as getting your filter to oscillate reliably in edge cases.
> 
>> On Fri, Jan 8, 2021 at 12:51 PM David G Dixon <dixon at mail.ubc.ca> wrote:
>> I have the same experience.  Poly film caps oscillate much easier than C0G caps of the same value.  I have replaced C0G with WIMA polyester to get stable oscillation in filters.
>> 
>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom Wiltshire
>> Sent: Friday, January 08, 2021 7:26 AM
>> To: ColinMuirDorward
>> Cc: synth-diy at synth-diy.org
>> Subject: Re: [sdiy] VCF caps in modern synths
>> 
>> [CAUTION: Non-UBC Email]
>> 
>>> On 8 Jan 2021, at 16:02, ColinMuirDorward <colindorward at gmail.com> wrote:
>>> 
>>> Yesterday I did some very non-scientific testing of 3320 4pole BPF built using C0G vs polypropylenes. The test may have been more about the tolerances of the caps rather than the dielectric, since my polys are 2.5% vs the C0Gs at 5%. I noticed that at lower frequencies, the polypropylene version would go into oscillation before the C0G version. Any thoughts on this?
>> 
>> Yes, I think you’re right. That seems more likely to be an effect of the tolerance to me.
>> 
>> Tom
>> 
>> ==================
>>        Electric Druid
>> Synth & Stompbox DIY
>> ==================
>> 
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