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Author Topic: Ceramic vs Film Capacitors in Microphones  (Read 1205 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
German Masterworks
www.GermanMasterworks.com
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