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Old 2nd May 2004, 02:36 PM   #1
Wagener is offline Wagener  South Africa
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Default mica capacitors in amplifier

Dr. Leach specified mica capacitors in his leach amp. They are extremely expensive here in south africa. What substitutes can I use?

I read about normal caps being resonant which causes noise in the amp.
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Old 2nd May 2004, 02:42 PM   #2
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Mica caps are good, however you will be able to use any good film caps in the Leach amp without problems !
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Old 2nd May 2004, 02:45 PM   #3
Eva is offline Eva  Spain
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For very small capacitance values, where film capacitors are not allways available, you may use ceramic capacitors, but take into account that these are so non-linear that you can actually see waveform distortion on the oscilloscope and different capacitance values may be easily measured at different bias levels

In contrast, mica capacitors are also available in small capacitance values and show decent linearity, so they are a much better choice for frequency compensation applications since amplifier linearity at high frequencies depends on these small capacitors
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Old 2nd May 2004, 03:18 PM   #4
pooge is offline pooge  United States
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NP0 Class 1 type ceramic would be a good alternative. Very linear and stable. Might have a bit of microphonic behavior, but much less than other types of ceramic capacitors, which you should not use.
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Old 2nd May 2004, 03:24 PM   #5
Zombie is offline Zombie  Sweden
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Default Micas in Greece

Hello!
Bought micas from this guy on eBay. He might have some left: nonotis5@hotmail.com
Very nice guy and cheap price...
Tom
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Old 3rd May 2004, 04:38 AM   #6
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NPO-COG capacitors or no better than other ceramics for audio, however if your equipment is going to running at 150F that would be a great cap to use.

The Mica's are the best caps to use for small values.
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Old 3rd May 2004, 08:31 PM   #7
pooge is offline pooge  United States
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Quote:
Originally posted by jewilson
NPO-COG capacitors or no better than other ceramics for audio, however if your equipment is going to running at 150F that would be a great cap to use.

The Mica's are the best caps to use for small values.

In what way? That's a broad statement with no facts. NP0s are a LOT more voltage and termperature stable than other cheap ceramics, and offer distortion as well or better than micas. They have a very low DA. The only issue that is not clear is in microphonics, but they are better than other ceramics in this regard. Also, the thread starter asked for a mica alternative.
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Old 3rd May 2004, 09:51 PM   #8
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It would seem to be cheaper just to use mica. They can't cost that much extra.
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Old 4th May 2004, 12:51 AM   #9
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I was shocked just recently when I priced out good CDE silver mica caps for a project I'm working on now; they cost about as much as output transistors!

Maybe I was too used to picking them up cheap at surplus electronics houses in the 80's...

~Jon
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Old 4th May 2004, 04:25 AM   #10
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Thumbs down NOP BAD SOUND

One of the phono amp designed away back used polystyrene caps. At the time, I had access to any vendor’s capacitor cause we were purchasing million of dollars in caps/
The job was design high-speed digital controlled sampling amps for oil exploration. We used a lot for ceramic for power supply decoupling and some timing circuits. A company called KD Components were making a lot of claim about the super duper NPO’s so I got a bunch of samples. They claimed to highest quality NPO and with DA equal to the better film caps, so I got a bunch of samples.

So I decided to try these super NOP so I remove the polystyrene caps in the RIAA network and replace them with the NPO, well this was the driest sound I had ever heard from my systems. They lasted in equalization network for 2 days, they sounded bad. On several other occasion I have tried other NPO-COG from different vendors, with the same results.

My favorite capacitor for the phono amps and filters are CDC Teflon’s, polystyrene, and finally polypropylenes. Having said that, if I need a small value the Mica is good, if I need a high voltage small value the Mica is the best.
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