[sdiy] Where to buy ceramic caps

David G Dixon dixon at mail.ubc.ca
Sat Dec 30 08:59:17 CET 2017

This is the very first design (after almost 10 years of semi-professional
design activities) where I actually care about the accuracy of caps.  I
don't believe that cap tolerances are very important unless one is trying to
achieve a certain value of RC (or, in my current case, 12 values).  This is
probably pretty rare.  In critical circuits, the RC is going to be tuned
with a trimmer anyway, so the cap value doesn't matter too much (as long as
it isn't too far off).  I'm just trying to eliminate trimmers and
calibration, because tuning 12 allpass stages is a lot of labor, and takes a
lot of time, and trimmer settings can be screwed up by customers which is a
big pain in the ass for all involved.

This stupid thing is going to be a eurorack module in the not-too-distant
future, and all the parts will be SMD.  I presume that SMD multilayer caps
can be easily and cheaply acquired in any tolerance you like, but I don't
use SMD components in my own personal builds, because I cant see them, and I
drop them, and I wanna kill myself whenever I have to solder an SMD part by
hand.  I'd rather just not do electronics than work with SMD parts by hand.

What I need to do is find a big ol' stash of those lovely blue Epcos caps
with the very legible white markings that I used when I first started out in
DIY (because that's what I found in the storeroom at UBC's Electrical
Engineering department).  There must be millions of them sitting in
storerooms around the world, unused and unloved.

> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On 
> Behalf Of mskala at ansuz.sooke.bc.ca
> Sent: Friday, December 29, 2017 11:10 PM
> To: rsdio at audiobanshee.com
> Cc: SDIY
> Subject: Re: [sdiy] Where to buy ceramic caps
> On Fri, 29 Dec 2017, rsdio at audiobanshee.com wrote:
> > Except that after you've gone to all of this trouble to sort 
> > capacitors into "within 1%" and "not within 1%" piles, you'll find 
> > that the manufacturer has already sorted them the same way and sold 
> > all of the "within 1%" caps to someone willing to pay more. 
> There will 
> > be a gap in your measured values, such that the 5% caps will all be 
> > >+1% or <-1% but none between -1% and +1%. If the capacitor 
> technology 
> > includes 1%, 5%,
> That depends how many people are willing to pay the premium 
> for the more-precise caps.  If there aren't so many such 
> people, then it may make sense for the manufacturer to sell 
> some caps that could qualify as 1% under the 5% label just 
> because there are a lot of those and many of them otherwise 
> couldn't be sold at all.  Bell curves mean that if almost all 
> caps are within 5% then a pretty large fraction of the caps 
> manufactured will also be within 1%; but it's not necessarily 
> true (and in fact, is probably false) that the demand for 
> caps sold as 1% and caps sold as 5% is in the same proportion.
> --
> Matthew Skala
> mskala at ansuz.sooke.bc.ca                 People before principles.
> http://ansuz.sooke.bc.ca/
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