[sdiy] Sallen Key caps

Richie Burnett rburnett at richieburnett.co.uk
Thu Apr 23 20:20:39 CEST 2015


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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