On 7/7/08, acousmatique put forth:
>
>There are quite a lot of NOS styrene caps out there, I am sure I can
>find them. What I am not sure of is which ones I need.
Why pay NOS prices when you can get new parts for less money??
Also, make sure whatever caps you buy fit in the PCB. Even if you
can find polystyrene caps in large values at a decent price, they
might be too big.
> > Have you considered PPS??
>
>I don't know what this is. Polyester? Polypropylene? I'll look it up.
It's polyphenylene sulfide, a newer dielectric used in film
capacitors. PPS is quite temperature stable and has very low leakage
current at low frequencies. It isn't as good as polystyrene or
polypropylene at high frequencies, but that's not what you are doing.
If I were building a S&H or LFO, it would be my first choice. I'm
also considering it for envelope followers, but I have to see if it
is practical in large enough values.
Polypropylene also has low dielectric absorption. So that would be
another good choice. Afaik, it is what MOTM uses for the 100/101
sample and hold. Although not applicable here, unlike PPS or
polystyrene, it is widely available in large values and high voltage
ratings. So it is good for most audio applications, including tubes
and passive crossovers.
Polyester has relatively high DA and poor temperature stability. So
it is a poor choice for accurate filters, timing, and S&H. The only
good things about polyester is that it is inexpensive and space
efficient.
While teflon is touted as having the best DA, it isn't that much
better, is outrageously expensive, and only works for small values.
At large values, while still very accurate and extremely temperature
stable, their ESL goes out the window due to their massive physical
size. So I don't get these hi-fi guys buying huge teflon caps from
Russia...
On 7/7/08, Scott Deyo put forth:
>Watch those MinnesOHta digs, there, Mark.
>Watch it, or... Uff da, dontcha know!
>: )
Oh, Digikey is in Minnesota. Maybe you could drive over there and
get me a catalog :)
>Scott Deyo (In the land of two seasons: winter and mosquito-time)
I'd only worry about football season ;)