On Sun, 17 Apr 2011 15:27:13 -0700, Dennis Monticelli wrote: >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. >
Here's the stuff I just sent Richard off-list: FWIW, here's the most relevant portion of the R-390 discussion: ------------------------------------------------------------------------------------------------------- Date: Thu, 31 Mar 2011 00:05:53 -0400 From: 2002tii Subject: Re: [R-390] Orange Drop vs ceramic disc There have been many tests, back to at least the '40s (long before small surfacemountceramics were a gleam in anyone's eye), documenting this behavior of ceramic caps. Bob Pease published a chart in EDN in the early '80s comparing the dielectric absorption-related distortion of various types of capacitors that showed measured distortion of 1% or more at low audio frequencies for ceramics (though NP0 caps were much better). (Note that this is a different mechanism than the voltage coefficient of capacitance, and that both mechanisms cause distortion independently.) We comprehensively tested all kinds of capacitors in audio coupling circuits in the '80s, and I assure you that the distortion from ceramic caps is clearly audible. Yes, we used a high-resolution audio system, not a communications radio -- but different types of distortion are heard more or less independently (that is, one type -- for example, even-order harmonic distortion, which dominates tube communications radio distortion -- does not mask another type -- for example, high-order intermodulation distortion or digital quantization errors, even when it is present at much higher levels), so the distortion due to ceramic coupling caps may very well be audible even in a circuit with 10% even-order harmonic distortion. We also used signal cancellation techniques to listen to the distortion products alone, and the distortion products of ceramic caps are extremely uglysounding (high-order, non harmonically-related -- easy to spot at very low levels). Since it is no effort whatsoever to avoid ceramic caps in coupling applications, there is simply no reason to use ceramics in those applications (indeed, it is simply good engineering practice to avoid possible ill effects when there is little or no cost to do so). -------------------------------------------------------------------------------- ----------------------- Date: Thu, 31 Mar 2011 10:29:55 -0400 From: "Shoppa, Tim" Subject: Re: [R-390] Orange Drop vs ceramic disc Please keep in mind that when it comes to ceramic caps, the dielectric materials available vary widely in their characteristics. C0G or NP0 ceramic caps could well be golden in audio applications but don't have enough uF per package to be used in most situations. X7R ceramic caps are probably good enough for not-hi-fi applications. Indeed lots of low-end consumer tube stuff from the 60's used ceramic audio coupling caps. Y5V caps literally sound like crap in audio coupling circuits. The latest SMD ceramic caps and their MLCC leaded cousins, almost certainly outperform any 50 year old NOS ceramics we have lying about, every which way from Sunday. I look at the high-end microwave SMT ceramic caps (actually the highest end ones are glass) and they beat the pants off of any leaded component. ------------------------------------------------------------------------------------------------------- Also, I found the Bob Pease article on the web: http://www.national.com/rap/Application/0,1570,28,00.html Then, there's this, which doesn't seem to be downloading very well at the moment: http://www.designers-guide.org/Modeling/da.pdf It all could very well be moot for communications radios, but OTOH, distortion does tend to add up. -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime." HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
