As I understand it, the only true concern one should have about the ceramics is the piezo effect of the high K material. This makes the circuit microphonic so unwanted acoustic feedback from the PA can take place. I agree that voltage coeficient is not a significant effect unless you're trying to build high accuracy stuff. In the world of integrated circuits of which I'm familiar, the votlage coefficient only rears its ugly head beyond the 12b level. At 16b it's a real concern, but we're talking very high linearity here.
Dennis AE6C On Sun, Apr 17, 2011 at 2:23 PM, Richard Knoppow <1oldle...@ix.netcom.com>wrote: > > ----- Original Message ----- From: "Jim Shorney" <jshor...@inebraska.com> > To: <drakelist@zerobeat.net> > Sent: Sunday, April 17, 2011 12:59 PM > Subject: Re: [Drakelist] R-4B audio problem traced to low beta Q7 (2N3394) > > > > On Sun, 17 Apr 2011 15:13:23 -0400 (EDT), kc9...@aol.com wrote: >> >> Very good explanation...I understoof about 30% of it...but then I am a >>> tech., not an engineer. Hi, Hi. >>> >> >> What made this tough is that Q7 was kind of working...so I was >>> checking, replacing everything BUT Q7. >>> >> >> My experience as a tech in situations like this has taught me to suspect >> capacitors first, transistors next. I've seen transistors fail in some >> strange >> ways over the years. :) >> >> I've recently learned that disc ceramic caps are not ideal for audio >> coupling. >> You guys have got me thinking about distortion and such. I'm thinking >> about >> putting the TR-7 on the bench and trying out that nifty surplus distortion >> analyzer that's languising out in the garage. >> >> 73 >> >> -Jim >> > The use of ceramic caps in audio circuits is somewhat controversial. > Ceramics of some types, mainly high-K types, do tend to have a variation of > capacitance with voltage and some audio folks think this contributes some > distortion. However, in most coupling circuits there is a steady DC voltage > on the cap that exceeds the AC voltage. Also, I have never seen any rigorous > research on this showing that a real difference exists. High-K ceramics do > have high temperature coeficient of capacitance but low-K ones can have zero > temperature variation (NPO types). There can also be a small variation in > effective capacitance due to interfacial polarization (don't ask) but mica > caps have the same problem. This is of concern only were a cap is used for > precision measurement at low frequencies. Paper and plastic film caps have > virtually none of this effect. I doubt if it has any significance for normal > audio use. > Ceramic caps have the virtues of small sizes, availability in high > voltages, and great reliability and long life. > > > -- > Richard Knoppow > Los Angeles > WB6KBL > dickb...@ix.netcom.com > > > > _______________________________________________ > Drakelist mailing list > Drakelist@zerobeat.net > http://mailman.zerobeat.net/mailman/listinfo/drakelist >
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