There was recently a lengthy argument on this subject where one continually insisted they cause all sorts of perceived problems.

I just started an overhaul of an untouched Hammarlund HQ-150 that puts a lie to their problems, at least at the signal levels encountered in a standard radio. A pair of Z5U .02uF are used in the first audio and output stages, 12AX7, 6V6, and at any audio level there is no signs of the claimed mythical microphonics or voltage induced shifting of the audio passband. Distortion is within published 6V6 specs using my restored HP-205AG oscillator and HP-334a distortion analyzer at comfortable speaker levels and increases as expected when the 6V6 is pushed hard. Temporarily changing to a pair of film caps changed absolutely nothing. This is a 1956-58 produced 13 tube radio of well above average performance for its day and sought after today.

This particular model did not have the Couplate shown on the schematic and was factory built with discreet components using different values and circuit in some places.

Carl

It's amazing what you can hear if you put your mind to it.

In the late 1970s I subscribed to Audio Amateur magazine. It had lots of construction projects, and modifications of commercial gear (substituting "better" components). Authors frequently claimed that components with steel leads rather than copper sounded worse. It was usually described as a "gritty" sound.

I sent a letter to the Editor, pointing out that all power transistors and vacuum tubes used magnetic parts, as did most integrated circuits. You know, I never saw another claim about steel-lead components from that time on.

Plus 2. A lot of stuff is accepted as gospel because someone posts it as fact,
and the rumors never die off.

I own a HQ-150 and HQ-145 and I've never found an issue with the ceramic
disc caps used in the audio or RF stages. One former moderator refused to
believe that C0G or NP0 caps were ever used in RF tuned circuits. I set up a
couple of test jigs to try and prove some of the rumors concerning these caps,
and I could never duplicate the alleged microphonic traits.

Carl, do you ever feel like Don Quixote?

Pete

Just about any capacitor or tube can be microphonic. Repl,ace the caps whatever. Soggy old wax types not likely, early stage auseo types possibly, resistors most likely not ever.

We'll never get rid of the rumors, legends, misinformation and downright disinformation. Not now, anyway. They've gone too far now, and the voices of reason are too few, maybe because reason is usually hard work, and it has no appeal to the "bumper sticker" sort of "thinker" who is always looking for a short cut to "knowledge."

Meanwhile, I've said it before and I'll say it again: I personally have encountered none of the alleged horrors of using ceramic caps in audio signal paths, and I have witnessed and have been using them in audio paths for decades now.

Larry

The fact that you, or others on this forum, have never seen it, is not proof that it never happens. I have seen an extreme case, but only once in almost 60 years of working on electronic equipment. About 11 or 12 years ago, when I was working in Durham, NC, I had an old Harman-Kardon preamp on the bench. It appeared to be kit-built. In the phono stage there were some grey-green, .1mfd ceramic coupling capacitors of no obvious brand. When picked at with a non-conductive probe, there was a sound in the speaker that was similar to a plucked guitar string. Connecting the output of the preamp to my 'scope, and speaking close to the capacitor, I could see the waveform of my voice on the screen. If that doesn't fit the definition of microphonic, I don't know what does. It was a definite piezo-electric effect. Whether it was just that particular brand, type or batch of capacitors (both channels exhibited the effect, but to a different extent) I do not know, but I do know it was not imagination. Other capacitors of the same type, in a lower gain circuit, seemed fine.
At a subsequent hamfest in Raleigh, i came across a bag of what appeared to be the same type of .1 caps. I bought them, intending to do some experimentation. Unfortunately, they strayed during my move back to Florida, in 2002.

At the mV levels in a phono or mike preamp, a microphonic part could be a problem. But I think designers leaned to avoid them there pretty quickly... and as far as distortion, a cap would have to have considerable AC voltage across it before any non-linearity became serious. And coupling caps DON'T have much AC across them.

There was a popular page on the net years ago from a reputable guy who actually did some good tests and displayed things like the microphonics from disc caps. I was convinced that the phenomenon was real but it was at such a low level that it shouldn't be a bother to anybody other than the golden eared crowd who could hear such things (when prompted).

Signal level and gain is the ticket. Even Tektronix shock-mounted some circuitry.

Those no name discs were apparently either rejects or poorly constructed so now we have the world believing that ALL high value discs are bad. Thats how these myths start and that example will be picked up by the audiophools and become more by the gospel "proof"

Paper and film caps can also be microphonic when shocked into that condidition according to other sources but my SS-396 can also get a knocking if I wind it beyond reason



Pete, it seems that a few here have that role under several hats as we try to do our best to debunk some of the complete misinformation that is tossed around one here by, thankfully, a very small minority. I seem to remember you wading in several times . Thankfully again, it appears that the problem generators have been thinning out as they move to other pastures to fertilize

I do think that even Curt finally understood what COG/NPO meant; he could be very dense at times

Carl

Perhaps the derogatory remarks toward the dead could be left out.

Agreed. Very poor taste.

L

Man, some of you guys are either dense of just don't understand, Ceramics should never be used in audio. Pure logic proves it too. Ceramics come from sand which come from the ground, right? Now at dinner tonight sprinkle a teeny bit of sand on your food. Next take a bite and notice how gritty it makes good food. Well it does the same to audio - makes it gritty. But that relationship to ground makes them an excellent bypass cap. Pure logic. You guys just don't know audio.

Well, when you finish digging your tongue out of your cheek, we can talk about it.

Larry

I hate to spoil a perfectly sensible audiophool argument, butActually no, Z5U is barium titanate, and is piezoelectric. C0G ceramics are different titanium compounds and are not (or at least my reference doesn't say they are) piezoelectric.

Yeah I know Alan. I caugh myself after posting but was still hoping for an uprising. Dang!

Guess I sold into that certain group for too long a time.

Dead or alive I dont see any difference plus it wasnt meant to be derogatory as we were friends. Besides I told Curt that several times on here, in PM's and on the telephone. In some things he was stuck in the 50's and earlier, nobody on here is perfect.

BTW, when I reach room temperature I dont give a damn what is said.

Carl

Bruce, that was the best caricature I've read in a while. Made me LOL several times. They are just like that!

Dave

I don't think it makes one bit of difference in low-fi table radios. Every once in a while a bag of .01 or .05, etc... 1KV ceramics comes up for sale for a couple of cents apiece. For restortion of non museum quality sets, they're fine.

Maybe you are thinking of Walt Jung and Dick Marsh articles from Audio magazine?
http://waltjung.org/PDFs/Picking_Capacitors_1.pdf
http://waltjung.org/PDFs/Picking_Capacitors_2.pdf

Walt measured as much as 0.6% THD from ceramic caps, but his test circuit uses a fairly high signal voltage across the cap (and a low-impedance circuit, though it's not clear to me that matters).