[sdiy] Hand-matching capacitors for filter stages

[thx1138]

On 2/9/10 7:14 AM, "cheater cheater" <cheater00 at gmail.com> wrote:

> Tom,
> good question regarding the tolerance vs material. I'll be thrilled to
> find out what is going on there.
> 
> 
> Regarding hand matching capacitors: Is your time worth the price difference?
> 
> D.
> 
> On Tue, Feb 9, 2010 at 15:59, 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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My time is worth a lot as I find that matching transistors much easier than
Caps. 

If I want to really take the fun out of Filter design, then I revert back to
24-bit DSP's we build and just build coef. To match Pole and Zero and
response I need.

I have really decent tools for this in DSP world, but I prefer the old
school analog just because I have done it so many times.


Active Filter Cookbook by Don Lancaster from the Howards Sams Books  #21168
is a good old book for many ideas. I have tried many of these and with most
situations they seem to work well.

Dave Rossum and I both have 1st editions I think as this is when I go mine
back in the early 1970's.

Regards,

Terry