[Trevor Wilson[_2_]]

"ScottW" wrote in message
oups.com...
On Oct 17, 1:40 pm, "Trevor Wilson"
wrote:
"ScottW" wrote in message
In fact, there are few suitable alternatives.

Low cost/form factor equivalent alternatives...but there
are alternatives.

**OK, I'll bite. List them.

Poly metal film is the most common.

**Completely impractical for decoupling. The smallest decoupling caps are
around 1uF. More usually, they range well up to 470uF.

In power supplies.....which is a fine place for electrolytics.
I should probably start looking into replacing the electrolytics
in my Krell....that beast gets hot.

**Unless it has fans, yes. You should consider replacing all the small
electros, at least. IME, these guys suffer long before the big guys. Of
course, it depends on the age of your amp and how much it gets used.


Anyway in the case of signal decoupling...which is probably
a rare app in audio now that I think about it...
electrolytics aren't always the best choice but due to size
and cost are still used.


Pack a few dozen film
caps into a case and there won't be much room for anything else. Then
there's the cost. 1uF film caps are MUCH more expensive than electros.

Big, expensive but better for bipolar applications.

**Of course, but we're discussing decoupling caps.

So where would that occurr in audio outside of a power supply?

**It doesn't. At least not strictly speaking. Most manufacturers decouple
power supply rails at each OP amp, or amplifier stage within a product. For
instance: A typical (not hugely expensive) CD player will contain between 4
and 8 OP amps. Each OP amp will have two power supply rails. Each rail at
each OP amp will have a capacitor to decouple that rail. Good designers
place the caps VERY close to the OP amps. Caps would typically range from
22uF to 220uF in this application. High end CD players (often fitted with
balanced outputs) may have between 8 and 16 OP amps.Or more, if headphone
amps and volume controlled output are used. A DVD or SACD player may have
even more, since 5.1 channels may need to be accommodated for.

Trevor Wilson