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Old 30th November 2004, 11:45 AM   #1
s2kov is online now s2kov  Canada
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Default Polyprops as cathode bypass

Would there any advantage using or adding polyprop caps on cathode bypass? What sonic difference will i get?
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Old 30th November 2004, 01:00 PM   #2
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It depends on who you ask! I've used polypropylenes and polyester metal films to bypass electrolytic cathode caps. Never used films exclusively. It SEEMED to improve (placebo effect maybe?) and other times not. Try it yourself and let your own ears be the judge. It's your amp! And your money, hehe!

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Old 30th November 2004, 02:47 PM   #3
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Default Re: Polyprops as cathode bypass

Quote:
Originally posted by s2kov
Would there any advantage using or adding polyprop caps on cathode bypass? What sonic difference will i get?
No...

Especially considering they'll be as big as the amp itself.

Oops, shouldn't have mentioned that

Tim

(Which reminds me, who here has added lead weights to improve the power to weight ratio? Anyone? Raise your hand...*loads shotgun*)
(And yes I'm in an evil mood today)
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Old 30th November 2004, 03:00 PM   #4
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Quote:
Would there any advantage using or adding polyprop caps on cathode bypass? What sonic difference will i get?

The answer to your question depends on the general quality of your perception and whether you like the sonic effect of bypassing caps or not. I would usually recommend using the best sounding cap you can afford on its own but many times bypassing is a good compromise.

What seems to make a bigger improvement, if your circuit allows it, is to replace the cathode bypass with an 'ultracap' connection.
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Old 30th November 2004, 03:05 PM   #5
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Hi,

Quote:
What sonic difference will i get?
Use a good quality cap but do not mix various technologies together hoping to make a decent sounding cap out of crap.

Bypassing electrolytic caps often causes more problems than it cures IMO.

Quote:
What seems to make a bigger improvement, if your circuit allows it, is to replace the cathode bypass with an 'ultracap' connection.
Whazzz that? Or do you mean "Ultrapath"?

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Old 30th November 2004, 04:33 PM   #6
s2kov is online now s2kov  Canada
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Hi frank, you mean using both electrolytic and polyprop caps connected in parallel to use as bypass cap will only cause problem? Can you point me a sample ultrapath circuit and what advantage will i get with it.


Guys, thanks for all your inputs.
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Old 30th November 2004, 06:42 PM   #7
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Quote:
Whazzz that? Or do you mean "Ultrapath"?
Frank,

I realise i'm using the term liberally. In this case it only means connecting the bypass cap to B+ rather than to ground and thus achieving shorter AC loop. Of course the inherent balance of real ultrapath is not present here.
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Old 30th November 2004, 07:48 PM   #8
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Hi,

Quote:
Hi frank, you mean using both electrolytic and polyprop caps connected in parallel to use as bypass cap will only cause problem?
Yes, that's what I mean.

Connecting a bunch of small value caps to make a big one is also tricky in that it leads to stray inductance which can turn into nasty resonances.

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Old 1st December 2004, 10:10 AM   #9
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Seriously I don't generally (directly) bypass my electrolytic caps. I try to use good quality electrolytic caps in the first place. Now say I have a 100uF cap in the pwr supply that's located a good distance away from the circuit it's associated with, I may use a 100nF - 1uF polypropylene bypass mounted close to the associated circuit. After reading stuff saying BYPASS all your nasty sounding electrolytic caps, I've tried it many times. In most cases the resulting sound was either worse (harsh sounding, probably due to unwanted resonances) or had no effect at all.
Bypassing cathode caps in my humble experience seemed to improve the sound (in a few cases) only when that location was where NFB was applied in pre-amplifiers such as in phono preamps. Even the lowly polyester film cap sounded better in some cases(???). Go figure! So in general there's really no sonic benefit in doing so! Best to use high quality electrolytics to begin with, using a good layout! I must agree with Frank on this one!

Wayne
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Old 2nd December 2004, 08:08 PM   #10
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I'm on the side of using single caps. I do think polypropylenes sound better, and I would use them especially on input valves where needed. I use motor run caps for my PSU, for the same reason, so I just factor the size into designs. Motor runs are a cheaper option, but usually bigger.
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