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Old 1st December 2015, 01:31 PM   #1
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Default 470uf feedback capacitor

In most typical class AB amplifiers exist a feedback capacitor and a resistor to ground

values are from 100-470 uf depending on the circuit Some also use in this application (in a more or less similar circuit ) bipolar capacitors instead .

Got an amplifier that uses 470uf/6.3v bipolar which is hard to get
will the circuit work the same if i replace with a normal polarized electrolytic ?

Kind regards
Sakis
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Old 1st December 2015, 02:32 PM   #2
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That's what a lot of amplifiers do, actually. Distortion wise it should be essentially irrelevant if capacitance is oversized that much, but a bipolar is definitely better when it comes to longevity. A standard polar does not like being operated at near zero DC voltage for many years and eventually becomes leaky. Only a bipolar or low-leakage type can take this. You definitely don't want a low ESR type here.

What's the resistor in series? Like I said, capacitance usually is substantially oversized, and if you can get a bipolar of 220/10V instead, well, then just use that. If nothing else helps, there's always the option of the "DIY bipolar" (two polars back-to-back). If you must go polar, choose a series with low leakage current and the highest rated voltage that'll fit.
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Old 1st December 2015, 03:57 PM   #3
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sure !! i can go from 6.3 volt that was originally installed easily till 63 size is no problem

I actually got two issues the one is Curys II which has 470-6.3 of a horrible quality resistor after this is 750R

And a Hafler DH 500 also 470uf /6.3V followed by 3K3 resistor to ground ...

Thanks for your help
Sakis
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Old 1st December 2015, 07:42 PM   #4
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Default RE: feedback capacitor to ground

My experience is that capacitor should be non-polar. You probably will
not notice a difference in listening, but there will be a significant change
on the test bench. The distortion will be worse with the polarized cap
at higher frequencies at higher power. So, if you are concerned about distortion at max power near 20kHz, use the non-polar.
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Old 1st December 2015, 08:05 PM   #5
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I cannot remember ever seeing more than a few NP capacitor in that position since I started repairing commercial and domestic amplifiers. I have been in the trade for over 50 years and for the last main service agent for most major manufacturers.
Normally there is a few millivolts of potential, so never a problem.
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Old 1st December 2015, 08:07 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by JonSnell Electronic View Post
Normally there is a few millivolts of potential, so never a problem.
Unless the output goes to one or the other rail, then it's good to have a NP cap there.
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