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Old 09-04-2012, 08:23 PM
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Good Coupling Capacitors - Silver Mica?

A friend of mine loaned me a pair of NOS silver Mica caps for use in my 2A3 SET amp, coupling the driver stage to the output stage. I had Russian paper in oils.
The improvements were pretty significant, and might be summarized as giving a more "airy" sound (exactly why I have a SET in the first place).

The PIOs are .22 uf per the schematic, and the ones he loaned me were .1 uf

Any suggestions on some caps that might be similar?
I attached a pic of a cap that looks pretty close to what he loaned me.

TIA
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File Type: jpg SilverMicaCap.jpg (34.6 KB, 43 views)
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Old 09-04-2012, 08:44 PM
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Id like to know this as well, Im a sucker for rolling caps. Like you, I run PIOs (Jensens and Ruskies), and love the sound of both of them, but I still feel that I can squeeze out more. Not that I find my PIOs lacking, but I feel theres more to the story. For what its worth, there are lots of Ruskie silver micas on eBay.
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Old 09-05-2012, 10:04 AM
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Interesting, thanks for reporting. Unfortunately I only have experience with the silver mica capacitors that are a lot smaller than the one in the picture.
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Old 09-05-2012, 10:17 AM
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0.1 uF is simply huge for a silver-mica. Be careful in evaluating sound if the values of the caps are different. Changes in the LF response will fool the brain into thinking the treble is different. Only compare identical value caps unless you want to go in circles and fuel the snake oil debates! I'd go with polypropylene or polystyrene. You might also try C0G/NP0 if you can find any that large, possibly a multilayer type or a few in parallel. Avoid all other ceramics.
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Old 09-05-2012, 04:07 PM
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Quote:
Originally Posted by Mr. Lin View Post
Interesting, thanks for reporting. Unfortunately I only have experience with the silver mica capacitors that are a lot smaller than the one in the picture.
Well...care to share?
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Old 09-05-2012, 04:13 PM
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Quote:
Originally Posted by ConradH View Post
0.1 uF is simply huge for a silver-mica. Be careful in evaluating sound if the values of the caps are different. Changes in the LF response will fool the brain into thinking the treble is different. Only compare identical value caps unless you want to go in circles and fuel the snake oil debates! I'd go with polypropylene or polystyrene. You might also try C0G/NP0 if you can find any that large, possibly a multilayer type or a few in parallel. Avoid all other ceramics.
Thanks Conrad. Actually I'm not looking to compare, just looking to get the sound back that I heard when his silver micas @ .1uf were in there. So if it was because of the value then that's good to know. If it was because of the materials used then that's good to know also.
Your recommendations are based on using the different types as coupling caps in similar amps to mine or different applications? And you recommend polypropylene or polystyrene over silver mica?
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Old 09-05-2012, 05:35 PM
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I'd be foolish to recommend one over the other, as they're all much better than good and I've had excellent results from all, though not in an SET. Silver-mica has surprisingly high dielectric absorption, not to be confused with dissipation factor, and the audibility of that is debatable. Let your ears be your guide, not somebody else's!
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Old 09-10-2012, 03:16 AM
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Quote:
Originally Posted by sebrof View Post
Well...care to share?
To be honest I've only used those in DIY projects where their "audibility" would be highly questionable, and I certainly didn't do any A/B stuff with them. If you're looking for recommendations for .1uf caps in audio, the most popular inexpensive option is polypropylene, usually.

I actually built a pair of Bottlehead Paramour 2A3 mono blocks last year and unfortunately haven't finished the chassis, but I intend to eventually listen to them as-is for a while and then replace the .1uf coupling caps in them with a pair of NOS Russian Teflon capacitors, which are another popular choice these days. You might want to consider those, they're readily available on ebay as they're surplus military parts from the Soviet days. I've read again and again though that they require lengthy break in periods.

The other capacitors I've used for somewhat similar purposes might be more than you're looking to spend, like Audio Note's tin-foil-in-oil version, which is their entry-level cap, and more recently for my Bottlehead Foreplay III tube preamp I've installed Jantzen "Z-Superior" metallized polypropylene w/copper leads. The latter made a very noticeable difference for the better in the Foreplay preamp, namely more clarity and thus more detail in general.
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Old 09-10-2012, 04:44 AM
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Quote:
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...Be careful in evaluating sound if the values of the caps are different. Changes in the LF response will fool the brain into thinking the treble is different. Only compare identical value caps...
Ditto this.

Going from .22 to .1 is a significant change in value for a coupling cap, and that alone may affect the sound.
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