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danielwritesbac 23rd January 2008 11:41 PM

Survey fun!
 
Which capacitor can be parallel (shunt) on an amplifier's speaker terminals and not cause harmful effects?

A). A polypropylene 0.01uf with 100 volt rating
B). A polyester 0.01uf with 100 volt rating
C). Either
D). None

SY 24th January 2008 12:23 AM

Which amplifier? That is kinda important.

danielwritesbac 24th January 2008 01:05 AM

Either an approximate average or a specific scenerio can make an answer that I'd like to see.

If the answer is application specific, I'd like to see specifics about real amplifiers that are currently in service.

Photographs of actual conditions. . . ah, now that would be excellent!!!

danielwritesbac 24th January 2008 02:24 AM

Even a guess at the answer is fine. This is just a survey.

SY 24th January 2008 03:02 AM

OK, then I can't figure out what you're after. The question makes no sense to me without some context.

aniruddha 24th January 2008 03:06 AM

Just a guess :D

.01uf in parallel may act as a low pass for speaker, all high frequencies above some point will pass through capacitor.

i have done that in past but with 2200uf and the result was, capacitor absorbs high frequencies and bass was clear.

It may be a little dangerous because high frequencies are getting short for amplifier.

but i think frequency corresponding to .01uf will be very high and it should not damage a 10-25 watt amplifier.

Note : Just a Guess :D

BWRX 24th January 2008 03:35 AM

Quote:

Originally posted by danielwritesbac
If the answer is application specific, I'd like to see specifics about real amplifiers that are currently in service.
Generally speaking, linear amplifiers do not like having capacitance directly at their output. I believe you are asking this question because you saw or read that the T-amp (class d) has small value capacitors directly across the outputs. This is OK for most class d amps because they have a LC lowpass filter between the switching output stage and the speaker in order to recover the audio signal. That cap across the output is effectively in parallel with the C of the LC filter, and its only purpose is to provide some more RF filtering at the point where the speaker wires exit the chassis.

danielwritesbac 24th January 2008 04:33 AM

2 Attachment(s)
That was interesting!
Howabout this?

danielwritesbac 24th January 2008 08:33 AM

clues
 
2 Attachment(s)
Here's your Sonic T-amp's speaker-terminal capacitor.
Its better quality than we thought. Note the decimal place activated on the meter. 3.5

danielwritesbac 25th January 2008 07:08 AM

A quote from Texas Instruments Filter Pro
 
The TI Filter Pro design software has this to say about capacitors.
Quote:

Keep in mind that capacitors generally have a wider tolerance. For this reason, when precision is desired, buy precision capacitors, or enter measured values
Texas Instruments doesn't mean a capacitance-only measure if they direct you towards "precision capacitors."

Measures for capacitors:
Capacitance
ESR
Speed/Signal/Ripple

It takes those three measures (at least) to employ a capacitor reliably.
For example, if an audiophile marketed capacitor and an economy capacitor match on all three measurements, then they will sound the same (not including bypass divisionals, component interreactions, and operating temperature).

ESR, and capacitor types, from lowest to highest:
(per same voltage rating)

Ceramic (lowest ESR)
Polypropylene
Electrolytic
P.E.T
(blend)
Mylar
(blend)
Polyester (highest ESR)

Lowest ESR types will almost-exactly match design software, however they are costly. Manufacturing specs, unless otherwise mentioned, are calibrated to least-cost components. See the conflict?

The T-amp cap appears to have a P.E.T-Mylar blend, scoring 3.5. That looks like a weird choice.

On the post above that is a polyester 50v cap, scoring 22; however, if that were a 100v version, you may expect from ESR 10 to 15.

For a polypropylene cap, you should expect ESR1 or less (best quality goes less ESR--much less).
If it is a greater figure than 1, then its either defective or an economy version; however, smaller physical sizes have higher ESR as a consequence of their size (usually indicates a lower voltage rating than advertised).

ESR is resistance during an AC signal, such as audio.


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