[gta02-core] Caps for bass fix (ECN0022)

Al Johnson openmoko at mazikeen.demon.co.uk
Wed Aug 19 13:28:06 CEST 2009

On Saturday 15 August 2009, Werner Almesberger wrote:
> Joerg and I discussed the choice of capacitors for the bass fix on
> #gta02-core. Some conclusions:
> - as explained in ECN0022, the capacitor should have about 100 uF

> - ceramic is unsuitable because of harmonic distortions

I'll qualify this in case anyone gets the wrong impression. High-k dielectrics 
like X7R have extremely high distortion levels. Low-k dielectrics like C0G 
have exceptionally low distortion, but aren't available in values bigger than 
about 220nF.

> - Tantalum seems to be the best choice

Distortion from tantalums is typically >10x that of a low cost polar aluminium 
electrolytic. What makes them the best choice?

Cyril Bateman's articles on capacitor distortion are well worth a read. 
Article 6 covers capacitors in the range we're looking at here. 

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