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Old 20th July 2003, 11:33 AM   #1
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Default Replacing ceramic caps by MKP??

Hi,

I have a new Marchand XM44 XO kit (very nice btw) and I just wonder if it will get better if I replace the 0.1 uF "monolitic axial ceramic" capicitors by 0.1 uF/160V Wima MKP 4???

Next to each OPA2134 opamp there are 2 of these ceramic caps (probably for decoupling).

It just happen they have the seam lead distance (7.5 mm as the holes on the PCB). Will it improve the sound?
http://www.wima.de/navig/pr.htm

Also there are a number of 22 pF Ceramic NPO. Is there a better replacement for that. (I dont know what NPO stands for)
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Old 21st July 2003, 11:38 AM   #2
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Class 1 ceramic capacitors have codes that indicate the temperature coefficient. For example, N750 capacitors have a nominal temperature coefficient of -750 ppm/K, while NP0 capacitors (also known as C0G capacitors) have a nominal temperature coefficient of 0ppm/K (usually with a +/- 30ppm/K tolerance). Class 1 ceramic capacitors are actually very good in all respects (low loss, low tolerances, low dielectric absorption and extremely low distortion).

Large ceramic capacitors are usually class 2. These are about the worst capacitors available (high distortion, high losses, high dielectric absorption, enormous temperature dependence), but they are very suitable for power supply decoupling because of their low parasitic inductance and their high losses, which help to dampen resonances of wiring inductances and the decoupling capacitors.

All in all, I would immediately replace the 0.1uF ceramic capacitors (which are almost certainly class 2) if these were in the signal path. If they are only used for decoupling, I would leave it as it is.
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Old 21st July 2003, 12:06 PM   #3
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I agree, ceramic caps are fine for supply decoupling, probably even better than stacked plastic film.

I am not sure that even COG is superior to polypropylene or polystyrene for audio signals.

Regards,

Eric
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Old 21st July 2003, 12:47 PM   #4
sajti is offline sajti  Hungary
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Quote:
Originally posted by capslock
I agree, ceramic caps are fine for supply decoupling, probably even better than stacked plastic film.

I am not sure that even COG is superior to polypropylene or polystyrene for audio signals.

Regards,

Eric

Agree. Due the higher inductivity of the polypropylene, or polystyrene they are not the godd solution for supply decoupling. Ceramic caps has lower impedance over 1MHz, and they succesfully avoid the HF oscillation.

Sajti
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Old 21st July 2003, 01:03 PM   #5
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Quote:
Originally posted by sajti
Due the higher inductivity of the polypropylene, or polystyrene they are not the godd solution for supply decoupling.

one of the TI application note (either for their power opam amp or opamps in general) actually calls for polypropylene caps for by-passing / decoupling. I am following that advice and have seen no ill.

But I do agree that ceramics get the job done fine.
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Old 21st July 2003, 10:07 PM   #6
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Thanks 4 the advice. I stick with the ceramics.
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Old 21st July 2003, 11:22 PM   #7
sam9 is offline sam9  United States
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The purpose of the caps is to protect the opamp from HF noise riding the PS traces. Ceramics have a significantly higher bandwidth than metalifilm types. I think we are taliking about frequencies of 250Mhz+ (mabe its's 500Mhz). Although it is not a likely you would have a problem with these, if you did, the metal-film caps may not protect the opamp. Remember, the only signals passing the caps metal or ceramic are signals you want to get rid of - so who cares if they are trashed. To audio signals a .1u cap just looks like an open circuit. To RF it looks like a short.
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