When to use Polyester / Polypropylene or Mica / Monolithic Caps? - diyAudio
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Old 20th March 2010, 12:15 AM   #1
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Default When to use Polyester / Polypropylene or Mica / Monolithic Caps?

When using low values (0.1uF, 0.22uF, 0.47uf) which type should I use?
I know I should use Monolithic for bypassing (opamp rails, power stiffener bypass) but what about other applications? Can I safely replace poor ceramic disc caps with Polyester / Monolithic, and which one is better?

And what about output caps? I'm talking about 0.1uF, 0.47uF and 0.22uF that can be found here: http://www.e-ele.net/DataSheet/TA2020.pdf
P. 5 Right Side of Diagram (goes into the speakers).

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Old 20th March 2010, 02:34 AM   #2
jcx is offline jcx  United States
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stacked metallized film caps, surface mount preferred for low esl, "4-pin" through-hole pkg for switching ps style also OK

smt means PEN for larger values, PPS or NP0 ceramic for smaller caps
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Old 22nd March 2010, 12:46 PM   #3
marce is offline marce  United Kingdom
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SMT COG are OK for decoupling
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Old 22nd March 2010, 12:57 PM   #4
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I hardly understand what you both said now. A possible explanation please?
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Old 22nd March 2010, 01:11 PM   #5
AndrewT is offline AndrewT  Scotland
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ceramic change capacitance with changing voltage.
i.e. vary the signal voltage and the capacitance varies.
They are very good if the voltage is held steady. eg decoupling the supply pins of an opamp.
All ceramics suffer from this.
In addition tolerance and capacitance stability changes with with temperature. NP0/C0G are the tightest tolerance and the most stable, the Xs and the Ys are very dependant on temperature.

MKT/PES/Mylar generally have a higher ESR than MKP/PP and this makes the MKT slightly more resistant to oscillation when there are fast signals and inductance around.
regards Andrew T.
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Old 23rd March 2010, 06:02 PM   #6
jcx is offline jcx  United States
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for filtering Class D you want the caps to have both low parasitic R and L, cap construction details such as electrode termination and lead length are critical, dielectric type is less important

surface mount caps are the best on the low L, provided you've done the PCB correctly with gnd plane and kept filter components close together

surface mount film types need to be safe at soldering high temps because the whole body heats up so PEN and PPS are the most commonly used plastic film dielectric types

NP0/C0G ceramic caps are not V sensitive like the higher "k" types- in fact their performance in high impedance filtering situations is better than some plastic films and mica caps

Class D filtering is not a high impedance application and "audiophile" dielectric "quality" is largley irrelevant - just avoid high k ceramics which do have large Vcoefficients

Last edited by jcx; 23rd March 2010 at 06:21 PM.
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Old 23rd March 2010, 06:07 PM   #7
Salas is offline Salas  Greece
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I am about to commit the utter sin. Gonna try NP0/C0G in Riaa filtering. Has anybody sinned in Riaa before? How was it?
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Old 23rd March 2010, 06:32 PM   #8
marce is offline marce  United Kingdom
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In my daytime world we use X7R's for general de-coupling usualy 0402 to 0805 depending on value (0402) preffered due to inductance.
For critical/RF NPO/COG are used but cases tend to be larger due to the construction. Despite rumors NPO/COG is a stable dielectric, and even X7R's arn't going to cause you problems, they are used to de-couple circuits that are a lot more sensitive and critical than audio.
There has been another thread that has covered this topic with a link to a good paper on MLCC capacitors, the different dialectrics etc, I'll look through my stuff and get a link.
The problem is that some people class ALL MLCCs as the same, this is not true, and they do have there place especially in de-coupling digital circuits where the small packages available and low impedence makes them the right choice for high speed de-coupling. If you use multilayer boards capacitor position and via placement become more critical as circuit speed increases.
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