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View Full Version : So, I'm being told confusing stuffs about caps

elkym
10-31-2008, 06:52 PM
Is it true that ALL caps in an amp need to be polarized?

If not, which ones do?

And what kinds of capacitors (other than the standard electrolytic ones) are polarized?
Structo
10-31-2008, 07:10 PM
They may be referring to finding which end of the film type cap is connected to the foil inside. Supposedly if you connect the foil end towards a lower potential (ground) the amp will be less noisy. It's kind of one of those urban myths that some believe while others don't.

You can use an oscilloscope to find the foil side.
SatelliteAmps
11-01-2008, 05:41 AM
No. Not all caps are polarized. Those that are will be labeled as such.

Film types are not polarized. People used to say that there was a mark that would show polarization on some film caps, but there has never been any evidence that supported it. Try it if you want.

Some electrolytics are, some aren't. They will be labeled with either a positive, or a negative sign, or sometimes both.

Some amps use other styles of capacitors as well, and they aren't polarized either.
Norse
11-02-2008, 03:57 PM
Structo - would you please elaborate on the oscilloscope tesing of caps? Live circuit, or single unit in your hand?

Thanks!
Greg
hasserl
11-02-2008, 05:58 PM
Is it true that ALL caps in an amp need to be polarized?

If not, which ones do?

And what kinds of capacitors (other than the standard electrolytic ones) are polarized?

No, no caps NEED to be polarized. Often the electrolytic caps in an amp ARE polar, but they don't NEED to be. They are because polar caps are cheaper and smaller than non=polar electrolytics.

Coupling, blocking and tone caps in an amp do NEED to be polar. In fact, they usually are not.
RedMan
11-02-2008, 07:34 PM
The polar caps are melting.
plexi67
11-02-2008, 08:08 PM
you can build one of these..

http://www.youtube.com/watch?v=VP6ZIHXq6Yg
hasserl
11-02-2008, 08:24 PM
The polar caps are melting. :D

Actually, only the Arctic cap is shrinking. The Antarctic cap is actually growing in size/thickness. But that's funny anyway!
donnyjaguar
11-03-2008, 09:26 AM
Is it true that ALL caps in an amp need to be polarized?

If not, which ones do?

And what kinds of capacitors (other than the standard electrolytic ones) are polarized?

No, the only capacitors that are polarized are those that will never see a current reversal. Power supply caps will never go negative, nor with bypass capacitors attached to voltage-amplifier tube cathodes.

It *is* possible to use many more polarized capacitors in an amplifier. But given the values are much lower, there aren't that many polarized cap's to choose from. Tantalum capacitors are used extensively in digital equipment and they are polarized. They also have three issues that make them a poor choice for a tube amp. They don't like higher voltages; they have a finite lifespan and their failure mode is a short circuit.