[sdiy] Littleman capacitors

[harry]

There are places where a parallel cap can help you... others where it connot.

In Crossover networks you often need a fairly large value cap... often an
electrolytic.  These have quite a bit of series resistance and series
inductance...

Putting a "good" small cap across this can improve the transient response... the
lower
self inductance of the film cap will allow the leading edge of a rapidly changing
wave to 'bypss' the main cap. The overall capacitor value is only slightly
changed.

This is similar to the technique of using several different bypass caps on a
power supply.

If you were... lets say... to use multiple parallel film caps to get the value
you needed... it would work slightly better still... at probably 10X the cost and
size....
The inductance would go down drastically.

NOW OTOH... I would NOT use this technique of parallel "good cap - cheap cap"
in a critical application like VCO timing cap, VCF frequency determinimg cap, or
especially, sample and hold cap.  These need temperature stability, and usually
low
dielectric absorption.  Parallel caps can't help you here....   Usually the best
choice
is Polystyrene (if you can get the value you need) or Polycarbonate (if you can't
get
the polystyrene).

Polyester (Mylar) is 20x worse in dielectric absorption... bad where you need
high
performance.   I use Polyester in non critical applications all the time.

If you don't see temperature extremes, use long S/H times... you might never
notice the better cap....  ;^P

H^) harry

Peter Grenader wrote:

> I just went through this.  Again, bare in mind I am a hack designer...BUT, I
> work for a speaker company and what better source of info on types of caps
> for best sonic performance than the guy who does our crossovers, right?
>
> I recently built a filter and asked his advise on this subject and his info
> was surprising to me, in regards to certain locations where you'd swear a
> polycarb or polystryrene would be required where they ain't.
>
> Why I am mentioning this is he taught me a trick that many of you probably
> know, but some might not (I didn't):  I was having a dickens of a time
> finding caps in my area (and I live in Los Angeles, go figure). If you need
> a polycarb in a critical location where one of the spec'd value is cap (disk
> or whatnot) and run a small value polycarp across it, something like a .01.
> By doing this, you will get most of the sonic benefit of the polycarb.
>
> I found this interesting. Anyway, I trust this guy.  Many many years at JBL
> where he got a bit of a name for himself.
>
> best,
>
> Peter
>
> on 3/8/02 12:56 PM, Jimmy Gogas at toothpick_77 at hotmail.com wrote:
>
> > What type (electrolytic, ceramic, ...) of capacitors do you guys suggest I
> > use for my Littleman synth project? The schematics have the capacitor
> > values, but not the type.
> >
> > the schematics can be seen at:
> > www.itn.liu.se/~nikro/littleman/littleman.pdf
> >
> >
> >
> > _________________________________________________________________
> > Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp.
> >

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