I used vintage, ex-Soviet Silver Mica capacitors (dipped type) to bypass the cathode in a RIAA circuit (EAR clone). Measured stated capacitance and shows up pretty accurate in my ESR meter. They are in parallel with an electrolytic and an axial polycarbonate film.
After adding them, I noticed some strange interference in both channels.
I investigated the effect by gently touching the cap with my finger. The interference increased.
Same thing happening when a mobile phone comes near it.
The interference is more severe in the right channel, so one cap must be more sensitive.
Before adding the Micas, I wasn't picking up interference.
At least not anything obvious.
Are Silver Mica more sensitive to picking up interference?
Do they go bad with time?
Also, do they have a construction requiring one side tied to ground, for better shielding?
After adding them, I noticed some strange interference in both channels.
I investigated the effect by gently touching the cap with my finger. The interference increased.
Same thing happening when a mobile phone comes near it.
The interference is more severe in the right channel, so one cap must be more sensitive.
Before adding the Micas, I wasn't picking up interference.
At least not anything obvious.
Are Silver Mica more sensitive to picking up interference?
Do they go bad with time?
Also, do they have a construction requiring one side tied to ground, for better shielding?
"Are Silver Mica more sensitive to picking up interference?"
Exactly the opposite.
Silver Mica have excellent RF properties and I suspect the problem you have is airborne interference amplified by your circuit because of too many capacitors of RF quality.
Silver Mica are for high frequency use, not audio!
Exactly the opposite.
Silver Mica have excellent RF properties and I suspect the problem you have is airborne interference amplified by your circuit because of too many capacitors of RF quality.
Silver Mica are for high frequency use, not audio!
Those silver micas are extending your Audio preamp gain into the RF regions.
Replace that finger, NOW!
It is obviously defective! 😛
Replace that finger, NOW!
It is obviously defective! 😛
Is there a way to evaluate if they are faulty?
They are a bit old in the tooth (K31-11 USSR NOS) and not the best specimens either..
They are a bit old in the tooth (K31-11 USSR NOS) and not the best specimens either..
If the capacitance is correct and the insulation open circuit on a DMM, there is nothing wrong with them
Silver mica capacitors sometimes go noisy, I do not know what the exact mechanism is, but my advice is to remove them, and throw out the lot they came with. (Maybe moisture infiltration??)
Silver mica capacitors were frequently used in precision RIAA networks in the past - that said I much prefer polystyrene (styrol, mallory, etc) - REL currently makes good ones (RTE) if you don't mind paying for them.
Silver mica capacitors were frequently used in precision RIAA networks in the past - that said I much prefer polystyrene (styrol, mallory, etc) - REL currently makes good ones (RTE) if you don't mind paying for them.
I’d probably see if you can live with it without the mica caps, replace the polycarbonate ones with something better like polystyrene, and keep those phones away from your gear, definitely don’t use your phone as an internet hot-spot anywhere nearby.
Thanks guys!
I'm a bit suspicious about this capacitor lot.
Humidity might have infiltrated their insulation.
Will replace them with a brand new CDE Mica pair, when possible.
These things are expensive. Ouch!
Btw, those polycarbonate types have won me over.
I've tried polysterene and polypropelene in their place but to my ears those polycarbonates are slightly better.
Also, noise issues aside, I've noticed that Silver Mica caps offer improvements when used in parallel to other caps.
And for RIAA duty they are unbeatable in my opinion.
Too bad they are so expensive (for an industrial part).
I'm a bit suspicious about this capacitor lot.
Humidity might have infiltrated their insulation.
Will replace them with a brand new CDE Mica pair, when possible.
These things are expensive. Ouch!
Btw, those polycarbonate types have won me over.
I've tried polysterene and polypropelene in their place but to my ears those polycarbonates are slightly better.
Also, noise issues aside, I've noticed that Silver Mica caps offer improvements when used in parallel to other caps.
And for RIAA duty they are unbeatable in my opinion.
Too bad they are so expensive (for an industrial part).
Cover the open side of the chassis with something opaque -- keep light off them. ANy difference? Also, does putting a metal cover over the open side make a difference?
Make a substitution test with something newer, of known quality, typically COG ceramic.
It has similar performance regarding HF, etc, and if your problems disappear, it means the SM's have problems.
They can become contaminated, get a silver plague and produce weird non-linear effects that regular testers cannot catch, because all the dominant parameters remain within limits.
When I stumble upon capacitors exhibiting such an unusual behaviour, I don't throw them away: I keep them as precious examples of degradation/abnormality to compare them with other suspect examples.
I have many such samples in my cabinet of curios, not only silver mica: mylar, paper, polycarbonate, E-caps, etc.
They can all fail in weird and wonderful ways