[sdiy] Hand-matching capacitors for filter stages

[thx1138]

On 2/9/10 10:30 AM, "Tom Wiltshire" <tom at electricdruid.net> wrote:

> Harry,
> 
> Ok, I understand that there's a difference in the dielectric.
> Polystyrene is still 'top cap'.
> My thought was just that mostly we're not comparing like with like. A
> typical Polystyrene cap is 1% tolerance, and a typical polypropylene
> is 5% or 10%. So it's no surprise if your filter sounds better when
> you replace one with the other, even if the dielectric was identical.
> 
> If I had 1% caps of both types, I suspect I'd be more than happy with
> polypropylene (or one of the other plastic film caps probably), even
> if polystyrene is still marginally superior in all but soldering temp.
> 
> You pays your money and you takes your choice...
> 
> T.
> 
> 
> 
> 
> 
> On 9 Feb 2010, at 18:04, Harry Bissell wrote:
> 
>> Yes, the difference is in the dielectric. Polystyrene needs to be
>> thicker,
>> forcing the plates apart and the capacitance down, so you need more
>> area.
>> 
>> Polystyrene also has a lousy soldering temperature range, use is
>> only 85C.
>> Polypropolene is MUCH better temperature-wise
>> 
>> H^) harry
>> 
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Hi All,

I define good engineering as the ability to not have to use matched
components is projects whenever possible.

I am not saying you are not a good engineer, but it helps to reduce cost in
designs using cheaper devices and spend a bit more time eliminating matched
caps, resistors as much as possible.

In some cases I find that it is easier to use 1% resistors to tighten up a
circuit.

Transistors are a different case as I like to use transistor arrays like the
CA3046/CA3086 but these are getting harder to find in stock around town.

I think we are in for a bit of grief 10 to 20 years from now when people
quit building analog goodies for us to build with.

Having built some of the Modular projects at E-Mu and Oberheim, I found that
cost was key in a low income business.

I would love to analyze your filters a bit more and lend an eye on possible
cures or alternate approaches. This email chain does not allow us to put
jpeg or pdf's in attachment I believe.

Perhaps we should have a companion site that is used for circuit archival
for all to use for projects etc.

Regards,

Terry Shultz