[sdiy] Hand-matching capacitors for filter stages

[thx1138]

On 2/9/10 6:59 AM, "Tom Wiltshire" <tom at electricdruid.net> wrote:

> It seems to me that some people spend quite a lot of time matching
> transistors for a fairly marginal benefit, given the quality of
> modern transistors. You may be a dedicated transistor-matcher and
> disagree with me. Fair enough - I admire your dedication.
> 
> However, capacitors are a different story. I often use polystyrene
> capacitors for filters, since these are widely regarded as the best,
> and breadboard experiments I've done do tend to support this. What
> I'm wondering is how much of this improvement is due to the material
> (e.g. polystyrene) and how much of it is down to the fact that the
> expensive capacitors are 1% tolerance rather than 5%, 10%, or worse.
> Improving the matching between filter stages is important for the
> filter response and sound of the filter, and given that l use 1%
> metal film resistors in these circuits, the capacitor component
> tolerance has to be one of the largest variations between stages.
> 
> So the question is - does anyone match capacitors for filters? Could
> I get some cheaper-but-still-quite-decent capacitors (like a 5%
> polypropylene film cap, WIMA FKP2 for example) and then hand match
> them to get 1% tolerance (or even better)? Does anyone have any
> experience to share?
> 
> Thanks,
> Tom
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Hi Tom,

Polystyrene, polypropaline,Teflon are usually the best for several reasons.

Dielectric properties and resistance to solvents in some cases.

Most boards are washed these days and the use of solvents or Freon type of
washers are eliminated by EPA.

One problem with these type of caps is that they can be easily damaged by
heat from soldering irons and wave soldering equipment.

I mask these areas off with latex and hand assemble on certain designs where
I am concerned about heat pileup or damage.

Matching capacitors is really a bit difficult as 10% caps start to get more
expensive. Notsure if 5% caps are even available as I still have a good deal
of inventory from the 1970's when I built Filter modules and such by hand.

I prefer the Epoxy covered Polystyrene that I bought as this is what we
built the SSM2044 , 2040 and such designs with.

Regards,

Terry Shultz