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
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
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
Hello!
Bought micas from this guy on eBay. He might have some left: nonotis5@hotmail.com
Very nice guy and cheap price...
Tom
jewilson said: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.
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.
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.
I have used ploystyrene for small values ( 75pF -300pF), but those may be almost as expensive as silver-mica unless you can find good source.
One alternative would be to decide which of the silver-micas are the most critical to sound of the amp and bear the cost for those while sustituting film or ceramic for the others. Although I have not built a Leach, I have faced this dilema with other amps. The rule i used, (which may be not entirely valid) was that very, very small values 1p-20p are passing signals so far above the audible range so they couold be replaced by ceramic (I'm not sure there are film caps with such low values) and anything not in the signal NFB return can be replaced (film being prefereable to cermic, if possible). This is strictly a cost strategy, if cost were not an issue I would just order SMs.
One alternative would be to decide which of the silver-micas are the most critical to sound of the amp and bear the cost for those while sustituting film or ceramic for the others. Although I have not built a Leach, I have faced this dilema with other amps. The rule i used, (which may be not entirely valid) was that very, very small values 1p-20p are passing signals so far above the audible range so they couold be replaced by ceramic (I'm not sure there are film caps with such low values) and anything not in the signal NFB return can be replaced (film being prefereable to cermic, if possible). This is strictly a cost strategy, if cost were not an issue I would just order SMs.
Exactly. The silver micas in the Leach amp are very small lag compensation caps. Probably won't have much, if any, impact on sound. In a correspondence I had with Dr. Leach, he said that microphonics of ceramic disks gave the amp problems. NP0s don't have as big a problem with microphonics, since they aren't made of the same piezoelectric ceramic. However, I have found difficulty finding any good data on NP0s and microphonics. But other than that possible problem, they should be an excellent cap in that application.
The Miller [C-B] compensation capacitors on the leach amp determine open loop frequency response of the circuit above 1Khz [first pole] but these suffer some degree of distortion correction due NFB
Capacitor nonlinearities on the split-feedback network may also start to show some contribution to overall THD at high frequencies but here there is no NFB to correct that
Capacitor nonlinearities on the split-feedback network may also start to show some contribution to overall THD at high frequencies but here there is no NFB to correct that
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.