COG capacitor microphonics

pooge · 19th February 2004, 12:20 AM

Been looking for information about microphonic tendencies of COG ceramic caps, but haven't been able to find much. Bateman's "Capacitor Sound" series didn't even mention microphonics. Although I have found a little bit of info stating that COG is better than other ceramics in this regard, I haven't been able to find out just how microphonic they are, especially compared with silver mica or other caps. Since they seem to be the perfect capacitor, otherwise, especially for such applications as lag compensation, etc., the degree of microphonics appears to be the only potentially bad trait that would keep me from using them. Anyone know of good info regarding COGs and microphonics?

Steve Eddy · 19th February 2004, 01:44 AM

Quote:

Originally posted by pooge
Since they seem to be the perfect capacitor, otherwise, especially for such applications as lag compensation, etc., the degree of microphonics appears to be the only potentially bad trait that would keep me from using them.

Why don't you just try 'em and see how you like 'em instead of worrying about objective specs?

se

pooge · 19th February 2004, 02:36 AM

I doubt that subjectively liking them or not really applies to a lag compensation cap. That is more of a stability issue. I think that's a area better left for objective interpretation.

thoriated · 19th February 2004, 08:06 PM

I understand that even COG ceramics have a fairly high dielectric constant of around 7 or so - higher than micas. That puts me off right there.

tiroth · 19th February 2004, 08:51 PM

Linear tech has an example of >1mV of noise from a ceramic cap in response to tapping it with a pencil. A storage scope with a high-sensitivity input or a quiet preamp should be able to identify such behavior easily.

I was under the impression, though, that C0G was not microphonic. I also have some Taiyo Yuden ceramics that are supposed to be "low distortion/low shock noise." If anyone ever decides to do any serious investigation I'd be happy to send some over.

pooge · 19th February 2004, 10:42 PM

I think I read somewhere that k is around 4 for COGs, and that silver micas were microphonic, also. Actually, I guess all are, it's just a matter of degree. Still looking for how many "degrees".

johnferrier · 19th February 2004, 11:35 PM

The best I could find Googling...

http://www.atceramics.com/pdf/techno...ric_effect.pdf

https://reu.magnet.fsu.edu/program/2...per/amwake.doc "Polytetrafluoroethylene, PTFE for short, but better known as Teflon, was chosen as the substrate because it contains no piezoelectric properties."

http://www.murata-europe.com/autumn01.pdf (page 8)

Nothing substantial. Maybe this will lead to something better??? Interesting issue.

JF

thoriated · 20th February 2004, 02:22 AM

Your first cite states that capacitors such as ceramics exhibiting the piezoelectric effect should not be used in any circuit requiring phase stability, including phase shifters and filter circuits. Works for me.

pooge · 21st February 2004, 12:46 PM

Thanks JF, your Googleing came up with some stuff I didn't find. I also tried to look specifically for a relative comparison with silver micas, but didn't come up with anything more revealing. I think, though, that substitutinng a COG in place of a siver mica application would not be a bad thing.

pooge · 21st February 2004, 03:46 PM

Here's another article:

http://www.tscgroup.com/acrobat/sm01001b.pdf

19th February 2004, 12:20 AM	#1
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	COG capacitor microphonics Been looking for information about microphonic tendencies of COG ceramic caps, but haven't been able to find much. Bateman's "Capacitor Sound" series didn't even mention microphonics. Although I have found a little bit of info stating that COG is better than other ceramics in this regard, I haven't been able to find out just how microphonic they are, especially compared with silver mica or other caps. Since they seem to be the perfect capacitor, otherwise, especially for such applications as lag compensation, etc., the degree of microphonics appears to be the only potentially bad trait that would keep me from using them. Anyone know of good info regarding COGs and microphonics?

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19th February 2004, 02:36 AM	#3
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	I doubt that subjectively liking them or not really applies to a lag compensation cap. That is more of a stability issue. I think that's a area better left for objective interpretation.

19th February 2004, 08:06 PM	#4
thoriated diyAudio Member Join Date: Nov 2003 Location: flyover country	I understand that even COG ceramics have a fairly high dielectric constant of around 7 or so - higher than micas. That puts me off right there.

19th February 2004, 08:51 PM	#5
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Linear tech has an example of >1mV of noise from a ceramic cap in response to tapping it with a pencil. A storage scope with a high-sensitivity input or a quiet preamp should be able to identify such behavior easily. I was under the impression, though, that C0G was not microphonic. I also have some Taiyo Yuden ceramics that are supposed to be "low distortion/low shock noise." If anyone ever decides to do any serious investigation I'd be happy to send some over.

19th February 2004, 10:42 PM	#6
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	I think I read somewhere that k is around 4 for COGs, and that silver micas were microphonic, also. Actually, I guess all are, it's just a matter of degree. Still looking for how many "degrees".

20th February 2004, 02:22 AM	#8
thoriated diyAudio Member Join Date: Nov 2003 Location: flyover country	Your first cite states that capacitors such as ceramics exhibiting the piezoelectric effect should not be used in any circuit requiring phase stability, including phase shifters and filter circuits. Works for me.

21st February 2004, 12:46 PM	#9
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	Thanks JF, your Googleing came up with some stuff I didn't find. I also tried to look specifically for a relative comparison with silver micas, but didn't come up with anything more revealing. I think, though, that substitutinng a COG in place of a siver mica application would not be a bad thing.

21st February 2004, 03:46 PM	#10
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	Here's another article: http://www.tscgroup.com/acrobat/sm01001b.pdf

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