[sdiy] Sallen Key caps

[David G Dixon]

I have found that poly caps in filters lead to more stable self-oscillation
at low frequencies than C0G/NP0 ceramics.  That's why we put WIMA poly caps
in the Doc Oc.



> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Justin Owen
> Sent: Friday, April 24, 2015 7:45 AM
> To: SDIY List
> Subject: Re: [sdiy] Sallen Key caps
> 
> Thanks all....
> 
> So something like this COG/NPO Ceramic in 1206 at 10nF:
> 
> http://uk.farnell.com/murata/grm3195c1h103ja01d/cap-mlcc-c0g-n
p0-10nf-50v-1206/dp/8820155
> 
> ...would be a suitable replacement for this guy (with the 
> corresponding R value adjustments):
> 
> http://uk.farnell.com/kemet/r82dc3100dq50k/cap-film-pet-0-1uf-
63v-rad/dp/2429344?ost=242-9344
> 
> Cheers,
> 
> - Justin
> 
> 
> 
> -----Original Message-----
> From: Richie Burnett [rburnett at richieburnett.co.uk]
> Received: 23.04.2015 19:20:45
> To: SDIY List; Justin Owen
> Subject: Re: [sdiy] Sallen Key caps
> 
> Since they're plastic film capacitors you have to be careful 
> not to overheat them and damage the plastic during soldering. 
>  Ceramic surface mount chip capacitors are more forgiving.
> 
> 100nF is quite a large value.  I'm guessing your resistors 
> are around the 3k region for a 500Hz cutoff.  Perhaps you 
> could afford to make the resistances in your SKF a few times 
> larger, and use correspondingly smaller capacitors?
> 
> -Richie,
> 
> 
> -----Original Message-----
> From: Justin Owen
> Sent: Thursday, April 23, 2015 4:59 PM
> To: SDIY List
> Subject: [sdiy] Sallen Key caps
> 
> Hello,
> 
> I'm using a Sallen Key LPF as a DAC output reconstruction 
> filter with cutoff set at approx. 500Hz.
> 
> I've been using these PET through-hole caps:
> 
> http://uk.farnell.com/kemet/r82dc3100dq50k/cap-film-pet-0-1uf-
63v-rad/dp/2429344?ost=242-9344
> 
> Filter works as expected - but I was wondering if these PEN 
> 1210 SMD might be a viable space-saving alternative?
> 
> http://uk.farnell.com/avx/cb027c0104jba/cap-film-pen-100nf-25v
-smd/dp/1100602
> 
> Haven't used a cap like this in surface mount before - so any 
> info would be appreciated.
> 
> Thanks,
> 
> - J
> 
> 
> 
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