[sdiy] VCF caps in modern synths

Mike Bryant mbryant at futurehorizons.com
Mon Jan 18 01:19:38 CET 2021


Agreed lead inductance would be tiny.  I was thinking more of inductive coupling between the lead inductances if the capacitors are mounted close together, or close to a high level signal.  This can easily happen in the MHz range and adversely affect the audio performance.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Gordonjcp
Sent: 18 January 2021 00:07
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] VCF caps in modern synths

On Fri, Jan 08, 2021 at 03:29:44PM +0000, Mike Bryant 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?
> 
> Was this SMD or through hole ?   It’s possibly down to lead inductance or series resistance being higher in the C0G.
> 

Lead inductance would be tiny, negligible at audio.  If your VCF is oscillating in the low GHz range you might have issues.

-- 
Gordonjcp

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