While COG capacitors don't have the very high K's of barium titanate types that are in the several thousands, they still range from 20 to at least 95. Furthermore, since COG's are spec'd for stability over temperature and aging, they might be constructed with a variety of dielectric formulations including mixed dielectrics that compensate for each others' temperature and aging characteristics, so it may not be possible to achieve any predictable sonic characteristic when using them in an audio circuit.
Excellent dielectric properties, high bandwidth, low inductance, low microphonics.
I wouldn't call anything with a K over 10 'excellent' for audio. Heck, I have problems with polycarbonate dielectrics with a K of 2.75 or mylar with a K ~ 3, and that with the older solo foil wound inductors as well as with capacitors. I couldn't wait to rip all the
'hot' & grainy sounding mylar dielectric Solo inductors out of my speaker's xover at the time, and put in Goertz polypropylene dielectric inductors after a few good listening sessions.
'hot' & grainy sounding mylar dielectric Solo inductors out of my speaker's xover at the time, and put in Goertz polypropylene dielectric inductors after a few good listening sessions.
Except K isn't a quality measure any moreso that other internal parameters (like zinc thickness). DF, L, ESR, stability, tempco, leakage, and microphonics are externally measurable figures of merit and C0G excels in all of those areas. It's a great cap for audio when the capacitance values are appropriate. AFAIK, there is absolutely no controlled listening tests that show anything to the contrary.
C0G generally have zero barium titanate, so that's something of a red herring.
I was testing a ceramic I thought wasn't an NP0/C0G, but it performs so well that now I'm not sure. As said above, I too think you have to test because there are so many ceramic formulations. Everybody wants a rule of thumb, but it's risky to generalize. Over the weekend I "hot-rodded" my capacitance bridge and did some careful calibrations and will be expanding on what I wrote a couple weeks ago-
Measured Differences Between Capacitors for Audio Applications
I've also tried square wave inputs per the Curl/Jung paper. The reveal some interesting things, but also complicate the interpretation. I continue to hold that there are problems trying to compensate esr at the multiple frequencies of a square wave, but what's more interesting is I think I see polarity effects in supposedly completely non-polar film capacitors. More to follow when I confirm or dump this idea.
Measured Differences Between Capacitors for Audio Applications
I've also tried square wave inputs per the Curl/Jung paper. The reveal some interesting things, but also complicate the interpretation. I continue to hold that there are problems trying to compensate esr at the multiple frequencies of a square wave, but what's more interesting is I think I see polarity effects in supposedly completely non-polar film capacitors. More to follow when I confirm or dump this idea.
Hi -
Wonder how 'back to back' mylars would fare in your bridge test🙂
I had gotten the impression that high K was well correlated with poor DA which may not show up so much as 'unpleasant sound' per se as in reduced detail & apparent dynamic range due to the delayed release of stored audio energy.
Wonder how 'back to back' mylars would fare in your bridge test🙂
I had gotten the impression that high K was well correlated with poor DA which may not show up so much as 'unpleasant sound' per se as in reduced detail & apparent dynamic range due to the delayed release of stored audio energy.
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Not sure about ceramics, but I can concur that high DA does indeed correlate with bad sound. The depletion layer of a VAS is a rapidly changing beast, and leaky as hell since the entire collector current passes through it. If you can improve the quality of this cap by using a Cdom with very low DA, all the better.
Hugh
Hugh
Not like Teflon in my non scientifically controlled subjective test, still preferable to some stacked radial MKP, and they solved the economic problem* of sourcing many decent capacitors to match exactly for RIAA passive filtering, also kept the layout size acceptable. In the big picture of the final build they blended as any good quality capacitor, short of extraordinary.
*It took 30pcs 10% tolerance to get 7pcs and match 2 channels, plus adhere to the theoretical. 3+3 mixed to make identical triplets, and 2 singles. If it was for boutique MKP or Teflon, such a matching luxury it would cost crazy.
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NPO is tolerable for audio, but impractical in many applications, and has Dielectric Absorption of a measurable quantity. Polystyrene, polypropylene or Teflon is better, and even Mica is at least as good, except for SMT applications.
Generally, many people confuse NPO or COG with other, inferior forms of ceramic and they are REALLY bad.
Some here use the really bad ceramic with impunity. Go figure.
Generally, many people confuse NPO or COG with other, inferior forms of ceramic and they are REALLY bad.
Some here use the really bad ceramic with impunity. Go figure.
I've always had a sneaking suspicion that the microphonic properties of many "audiophile" Teflon caps was the reason for their popularity. Not that I'm cynical or anything...
Conrad, we used asymmetrical pulses rather than square waves in the cap test. This is important. There are some difficult problems with total minimization of difference error. This includes ESR, inductance, AND a slight loss in the 'lossier' cap of overall total output.
ESR can be approximated by a small series resistance; inductance, by bandwidth limiting the pulse; and a slight difference in drive level for the two caps being compared.
ESR can be approximated by a small series resistance; inductance, by bandwidth limiting the pulse; and a slight difference in drive level for the two caps being compared.
Just to test, I took a 1 uf Mylar and 1 uf Teflon cap and put them across my oscilloscope terminals and set the sensitivity to 5mV/ div. I got measurable output from the Mylar, and virtually nothing from the Teflon. Maybe there is something more to this than just size.
Mine comparing were not audiophile, just Russian military FT-1-2-3. Those were the most resolute and steady among many MKP & PIO with neutral tone too, where the C0G had a little second harmonic style added ''niceness'' coloration to my perception, still open and big, when MKP10, FKP1, SCR fast cap, came across as ''pinched''. I was cross checking between DC coupling each time I exchanged. All in all C0G had the best value for money and size, ranked amongst best in my not serious subjective test, and yes, that makes them ''terrific for audio'' to me too, where their small values and voltages apply.
Best of polypropylene can be better but there are so many tonally weird MKP, someone has to do an own survey. Teflon is in my opinion head and shoulders better above all, C0G cleaner than Mica in my humble experience. Some of the best combinations for enough value and voltage, for valve audio too, are Mylar in oil and some PIO bypassed by Teflon IMHO. And nothing is best value and fidelity than DC coupling, goes without saying. May your servos track well.
Sorry to say Salas, but the concept of delay in this context is totally without any technical merit. The whole DA delay/memory thing is a figment of peoples imagination.
Why it takes less value for a Mica than a ceramic to do the same job in this Cdom concept...hmm inductance maybe? Isn't there DA giving time error in analogue processing as per Bob Pease? Must be doing something somewhere. Second harmonic?
Understand Capacitor Soakage to Optimize Analog Systems
Understand Capacitor Soakage to Optimize Analog Systems
I think the model for DA in Bob Pease's article referenced above says it all:- the DA bit is a much smaller cap with a series resistance of many meg Ohms in series placed in parallel with the main capacitor. This may explain why silver mica fares well in subjective listenning tests (Conrad's caveat's notwithstanding!) and yet its DA is relatively high compared to other dielectrics. I'll carry on with the silver mica's!
🙂
SY, reversing the caps does not significantly change the vibration pulse, except to invert it. The 1uF Mylar is at least 10 times worse. An 8 uF Wonder polypropylene was better than the Mylar as well, but not as good as the 1 uF Teflon.
I beg to differ - if there's hysteresis, there's memory. Almost every electrolytic, as well as most ceramic and film dielectrics will exhibit hysteresis.
Permittivity - Wikipedia, the free encyclopedia
(A bit heavy on the physics, but the commentary is fairly succinct.)
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