[sdiy] Fixed filter bank questions

chris chris at chrismusic.de
Mon May 13 11:21:58 CEST 2019


On Sat, 11 May 2019 12:27:34 +0200 ASSI <Stromeko at nexgo.de> wrote:

> On Friday, May 10, 2019 5:06:01 AM CEST rsdio at audiobanshee.com wrote:
> > Earlier this year, I got a copy of Douglas Self’s “Small Signal Audio
> > Design” book. In that, he seems fond of a technique of using multiple
> > capacitors in order to improve the tolerance. I didn’t pay close attention
> > to the math, but two 20% capacitors end up giving you a value that is
> > within 10% of the combined value.
> 
> It doesn't (the resulting tolerance wuld be slightly above 14%), you'd need to 
> parallel four capacitors to get to half the tolerance of the individual parts.  
> Actually that is only true if the deviation from nominal for all the 
> capacitors that you combine are independent (not correlated), which however 
> they will be (strongly so) if you pick four capacitors from the same batch.

My guess would be that from the same batch they will NOT be independent,
but that may be what you meant to say anyway. 

Chris




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