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Author Topic: Ceramic vs Film Capacitors in Microphones  (Read 1515 times)

AusTex64

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Ceramic vs Film Capacitors in Microphones
« on: September 30, 2017, 03:33:35 pm »

I'm working on some small diaphragm condenser mics where space is VERY limited. I need to add a 160pf 100V cap and 250K ohm 250mW resistor in series, that will fit between two terminals about 8mm apart.

Has anyone tried multilayer ceramic capacitors in place of film caps in a mic application? This will be in a negative feedback circuit, so it's in the audio path. I am hearing good things about MLCC's for lower voltage applications in comparison to film caps. But I could also probably use silver mica, it looks as if they are small enough to fit.
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Jim Williams

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Re: MLCC vs film capacitors in microphones
« Reply #1 on: September 30, 2017, 04:04:27 pm »

A WIMA FKP-2 (5mm) with a Dale CMF50 resistor should fit.
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AusTex64

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Re: MLCC vs film capacitors in microphones
« Reply #2 on: September 30, 2017, 04:23:44 pm »

Thanks Jim!
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Kai

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Re: MLCC vs film capacitors in microphones
« Reply #3 on: October 01, 2017, 04:50:46 am »

Ceramic caps in general should be avoided in the audio path. Unlike other types of caps, where the the problems for audio are hardly measurable, ceramics clearly cause distortions due to their nonlinear behavior.
There might be differences between several types of ceramics, but it's hard to find out which ones behave better, so it's best to avoid them completely.
 
The ranking for audio is:
Film caps
High quality electrolytic caps
Tantal caps
Nothing
Nothing
Nothing
.
.
Ceramics

Ceramics are very usefull outside the audio path, for HF blocking e.g.
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AusTex64

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Re: MLCC vs film capacitors in microphones
« Reply #4 on: October 01, 2017, 09:32:01 am »

Thanks Kai. Would you include silver mica in the ceramic category?
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soapfoot

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Re: MLCC vs film capacitors in microphones
« Reply #5 on: October 01, 2017, 11:11:39 am »

Ceramic caps in general shoul be avoided in the audio path. Unlike other types of caps, where the the problems for audio are hardly measurable, ceramics clearly cause distortions due to their nonlinear behavior.
There might be differences between several types of ceramics, but it's hard to find out which ones behave better, so it's best to avoid them completely.
 
The ranking for audio is:
Film caps
High quality electrolytic caps
Tantal caps
Nothing
Nothing
Nothing
.
.
Ceramics

Ceramics are very usefull outside the audio path, for HF blocking e.g.

Do you feel this way even about NP0 and C0G ceramics?
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Jim Williams

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Re: MLCC vs film capacitors in microphones
« Reply #6 on: October 01, 2017, 12:34:15 pm »

Thanks Kai. Would you include silver mica in the ceramic category?

Mica caps are very stable, the dialectric is one of the best. They have some issues. First, they are very microphonic. They also sound different than a film and foil polystyrene or polyprop cap. They sound a bit "softer" or less forward sounding. They are a good choice for some hf usage, a good sub for a ceramic NPO cap in the high frequency range.

With silver at $17 per ounce, thay are also a bit expensive. I found one of their best audio uses is in electric guitar amps for treble EQ and a general ceramic cap substitution.

I have tried them to couple a capacitor capsule to a jfet gate, not a great result there. Polystyrene or teflon caps are a better choice for that position.
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Kai

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Re: MLCC vs film capacitors in microphones
« Reply #7 on: October 01, 2017, 05:03:49 pm »

Do you feel this way even about NP0 and C0G ceramics?
I have no idea, but why bother, they have no advantage.
You can test by yourself, build a 50% voltage divider with a resitor and such a cap and measure the distortion.
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soapfoot

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Re: MLCC vs film capacitors in microphones
« Reply #8 on: October 01, 2017, 05:13:35 pm »

I have no idea, but why bother, they have no advantage.
You can test by yourself, build a 50% voltage divider with a resitor and such a cap and measure the distortion.

Cyril Bateman did just that a few decades ago, and published the results. The NP0/C0G ceramics measured best of all types tested in terms of distortion-- better even than than teflon film, polypropylene film, and polystyrene film.

In addition to being the best performers, these types also have the advantage of being very compact, and being more temperature- and time-stable than most capacitor types. The only disadvantage is a comparatively narrow range of widely-available values.

https://linearaudio.nl/cyril-batemans-capacitor-sound-articles

Of particular interest is "part 3"

One relevant quotation:

Quote
Class 1 ceramics do not contain Barium Titanate, so have a low ‘k’ value. The best known is C0G. With its controlled temperature coefficient of zero ± 30 ppm, it was originally called NP0 by the Erie Corporation. It is non-polar and has a small dielectric absorption coefficient. From my tests it has almost no measurable harmonic distortion. COG ceramic is more stable with time and temperature than mica capacitors and from my tests COG can produce less distortion. see Fig. 5

C0G ceramic provides the most stable capacitance value, over long time periods and temperature excursions, of all easily obtained capacitor dielectrics. It is frequently used as a capacitance transfer standard in calibration laboratories. Yet as a small disc capacitor it costs only pennies. Assembled as a multilayer, it can provide capacitances of 100 nF and above, rated for 100 volts working, and much higher voltages for smaller capacitances.

Other Class 1 ceramics, sometimes called ‘low k’, provide increased capacitance within a controlled temperature coefficient, e.g. P100, N750 etc. in ppm. These also are non-polar and exhibit little dielectric absorption. I have tested up to N750, sometimes called U2J, and found very low distortion.

Class 2 ceramics do include Barium Titanate. It produces a very high dielectric constant, with ‘k’ values ranging from a few hundred to several thousands depending on other additives used. Class 2 ceramic is strongly polar, its capacitance varies with applied voltage and temperature. It exhibits an easily measured dielectric absorption, which increases with ‘k’ value.

Popular Class 2 ceramics include the X7R, W5R, BX capacitor grades and the exceptionally high ‘k’ Z5U. These do produce extremely large measured distortions, so are not suited for use in the signal path of an audio system.
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AusTex64

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Re: MLCC vs film capacitors in microphones
« Reply #9 on: October 01, 2017, 10:11:20 pm »

Brad, fascinating and provocative info. I'm interested in MLCC due to their very small size, very handy in tiny SDC body tubes like the ones I'm working on. I'm also considering going SMD and the only good caps available are MLCC.
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Kai

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Re: MLCC vs film capacitors in microphones
« Reply #10 on: October 05, 2017, 05:07:56 pm »

Do you feel this way even about NP0 and C0G ceramics?
I have now carefully read all through the documents:
https://linearaudio.nl/cyril-batemans-capacitor-sound-articles
 (took some time) and it seems that these are best choice for most applications where a small cap is suitable.

You can use a capacitance meter to determine if you really have such a specimen in front of you.
If you heat it up the cap may not change its value, opposed to "standard" ceramics which are highly temperature dependent.

MLCCs are usually made to achieve high capacitance, not good linearity. They are not suited for audio.

BTW, I'm about to build a modern version of the distortion measurement jig by myself, based simply (more or less) on AD- [Device under Test]-[Double-T-Filter] -DA conversion.
Currently I'm in search of a very clean DA-converter for generation of the needed sine wave.
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soapfoot

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Re: MLCC vs film capacitors in microphones
« Reply #11 on: October 06, 2017, 09:20:21 am »

I have now carefully read all through the documents:
https://linearaudio.nl/cyril-batemans-capacitor-sound-articles
 (took some time) and it seems that these are best choice for most applications where a small cap is suitable.

You can use a capacitance meter to determine if you really have such a specimen in front of you.
If you heat it up the cap may not change its value, opposed to "standard" ceramics which are highly temperature dependent.

MLCCs are usually made to achieve high capacitance, not good linearity. They are not suited for audio.

BTW, I'm about to build a modern version of the distortion measurement jig by myself, based simply (more or less) on AD- [Device under Test]-[Double-T-Filter] -DA conversion.
Currently I'm in search of a very clean DA-converter for generation of the needed sine wave.

I certainly found it fascinating!

Interesting point about MLCCs.

I suppose, then, that we shouldn't assume C0G/NP0 ceramics, if configured as multi-layer caps, to exhibit the same "near-ideal" behavior as their small-value counterparts? If you're replicating Mr. Bateman's methodology, I'd be interested to see some tests on multi-layer class 1 ceramics!
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Jim Williams

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Re: MLCC vs film capacitors in microphones
« Reply #12 on: October 06, 2017, 11:13:37 am »

I have now carefully read all through the documents:
https://linearaudio.nl/cyril-batemans-capacitor-sound-articles
 (took some time) and it seems that these are best choice for most applications where a small cap is suitable.

You can use a capacitance meter to determine if you really have such a specimen in front of you.
If you heat it up the cap may not change its value, opposed to "standard" ceramics which are highly temperature dependent.

MLCCs are usually made to achieve high capacitance, not good linearity. They are not suited for audio.

BTW, I'm about to build a modern version of the distortion measurement jig by myself, based simply (more or less) on AD- [Device under Test]-[Double-T-Filter] -DA conversion.
Currently I'm in search of a very clean DA-converter for generation of the needed sine wave.

If you build that, rent an AP 2600 and test the tester. Calibrating any test gear is very important to avoid false paths.
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Kai

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Re: MLCC vs film capacitors in microphones
« Reply #13 on: October 06, 2017, 12:53:35 pm »

If you build that, rent an AP 2600 and test the tester. Calibrating any test gear is very important to avoid false paths.
Of course, in this case the tester will easily be tested with itself.
My search for a "perfect" DA converter did not yield any results yet, might be I need to go the route with an analog ultra low distortion sinewave generator coupled with a passive filter.
Even RME Audio, known for their excellent converters, can't fulfill the requirement of -140dB distortion.
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klaus

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #14 on: October 06, 2017, 01:37:04 pm »

This is not a DYI forum. Could we please steer this thread back towards a language that can be understood my more than a few?
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Klaus Heyne
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AusTex64

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #15 on: October 07, 2017, 12:57:07 am »

I am under the impression that NP0/C0G ceramics are Class 1 MLCC's. Is that not correct?
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klaus

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #16 on: October 07, 2017, 02:01:06 am »

Please rephrase the post so that it can be understood my the majority of forum users (see my post prior to yours).
Thanks, KH
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Klaus Heyne
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Kai

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #17 on: October 07, 2017, 07:01:09 am »

I am under the impression that NP0/C0G ceramics are Class 1 MLCC's. Is that not correct?
NP0/C0G is a certain material, well suitet for audio because it's not causing much more distortions then the best film caps.
MLCC is a way to build a capacitor with higher capacitance by using several layers of any ceramic material.
So if you can find an MLCC made of NP0/C0G you're fine. I mentioned earlier how to verify that it's NP0/C0G.

@Klaus: you know I mostly try to use simple language, but in this topic from the headline on it's more of a technical, "DIY" thing.
Demystification of very common capacitor myths might be interesting for less technically oriented people too.
At least you get one explanation why different caps sound different.
I have learned enough going through Cyril Bateman's findings to make me curious to dig deeper.
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soapfoot

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #18 on: October 07, 2017, 10:38:28 am »

Yes-- sadly, there's not a much less technical way to differentiate between the "good" ceramics (NP0/C0G/"Class 1") and the "bad" ceramics (the kind containing barium titanate, or "class 2."

MLCC stands for "multi-layer ceramic capacitor." Since ceramic caps of both types are limited to relatively small values, if you want larger values you must combine several of them into a "multi-layer" type.

I haven't personally empirically verified that MLCCs behave the same as their single, discrete ceramic counterparts.
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klaus

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #19 on: October 07, 2017, 05:39:08 pm »

The last two posts prove my point that you can explain something complicated in a simple way.
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Klaus Heyne
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Jim Williams

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #20 on: October 08, 2017, 12:38:27 pm »

Dielectric absorption and dissipation factors must also be included in comparisons. That's where quality film caps are superior to ceramics.

Qualitative comparisons always pick the film caps over ceramics.
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soapfoot

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #21 on: October 08, 2017, 11:24:41 pm »

Bateman observed very low dielectric absorption in C0G/NP0 ceramics.

Has your experience been different, Jim?
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Jim Williams

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #22 on: October 09, 2017, 10:58:46 am »

COG/NPO are very good but limited to very small values. I use them for ultrasonic feedback purposes as they are stable and operate above the audible hearing range.

Dissapation factors are better with quality film caps. Ceramic caps are also microphonic, tap on one to hear that.

Anyone can do the sonic evaluations easily, just wire in a COG/NPO ceramic between the capsule and jfet gate. Then replace it with a good polystyrene film cap.

Alternatively, wire one into a treble boost EQ circuit to hear what that does. Then swap it with a polystyrene or polypropylene film cap.
You will learn a lot that way.
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soapfoot

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Re: Ceramic vs Film Capacitors in Microphones
« Reply #23 on: October 11, 2017, 08:37:19 am »

Interesting, Jim!

Is there a way to describe the differences one might hear?
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