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Old 14th January 2009, 07:16 PM   #1
Klimon is offline Klimon  Belgium
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Default Passive RIAA and cap variation

Hi,

Regarding component choice for a passive RIAA compensation circuit consisting of three resistors and two caps (amp in question is Thorsten's simple phono pre http://www.diyaudio.com/forums/attac...amp=1077837811); how should I visualise what is happening in the capacitors? Does each 'handle' a certain frequency range (1n and 10n in the given schematic)? Reason why I'm asking is that for both caps I'll be using silver mica's of a different breed and it wouldn't seem desirable to me if each would give their (differing) sonic signature to a part of the frequency response.

Thanks!

Simon
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Old 15th January 2009, 06:10 AM   #2
robmil is offline robmil  United Kingdom
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Hi Klimon

I would not use Silvered Mica caps in this application. The preferred type is a 1% or better film type. Polypropylene is an excellent choice here. RIAA filters, or any other really need low noise close tolerance film.

I hope that helps.

regards

Rob
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Old 15th January 2009, 06:55 AM   #3
Klimon is offline Klimon  Belgium
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Hi Rob,

I've read quite the contrary, silver mica's being the preferred choice even when used as coupling caps if thou can find high enough value. As in many cases personal preference might be a factor though. Regarding tolerance the silver mica's I have are 5% for the 1n (but hand matched by the vendor, I'll recheck) and 0,3% for the 10n!!

Simon
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Old 15th January 2009, 07:04 AM   #4
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Quote:
Originally posted by Klimon
Hi Rob,

I've read quite the contrary


You will have to try for yourself. People have strong reactions to silver mica caps: it's either love them or hate them. Maybe some types are absolutely great but i've never had a chance to try those.

Don't assume that the different caps deal with different frequency bands as they significantly overlap.
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Old 15th January 2009, 08:33 AM   #5
Klimon is offline Klimon  Belgium
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Quote:
Don't assume that the different caps deal with different frequency bands as they significantly overlap.
Good thing

I think I know what type of sound to expect from the silver mica's; if I don't like it I can always go polypropylene. All power supply caps and the output caps are paper and PP in oil so a little silver mica might blend in nicely for some more bite.

Cheers, Simon
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Old 15th January 2009, 09:44 AM   #6
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Quote:
Originally posted by analog_sa
You will have to try for yourself. People have strong reactions to silver mica caps: it's either love them or hate them.
Agreed.

When playing with passive phono stages, I tried several types of caps and all were different sounding, though the RIAA curve measured the same.

I wouldn't say any was better, just different sounding.

Cheers!
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Old 15th January 2009, 07:48 PM   #7
robmil is offline robmil  United Kingdom
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Hi Klimon

only one of the 10n caps is used for coupling, the other 2 for part of the RIAA filter network. I must try sm caps to see what they sound like.
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Old 15th January 2009, 08:03 PM   #8
Klimon is offline Klimon  Belgium
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Quote:
only one of the 10n caps is used for coupling, the other 2 for part of the RIAA filter network. I must try sm caps to see what they sound like.
Yes.

Thanks for the input all.

Simon
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