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-   -   Mundorf M-Cap Supreme as bypass cap? (http://www.diyaudio.com/forums/power-supplies/218862-mundorf-m-cap-supreme-bypass-cap.html)

MGH 1st September 2012 06:34 AM

Mundorf M-Cap Supreme as bypass cap?
 
Hi, I'm going to be bypassing the power supply caps using 0.1 microF Mundorf Supreme caps which are suppose to be noninductive metalized polypropylene caps. Not so much as to lower ripple, but to block really high freq noise outside of the audible range. The power supply caps to be bypassed are 430 and 760 microF (voltage 500 V). Are these Mundorfs a good choice? Anyone used these in this application? Better alternative? Thanks.

fas42 1st September 2012 11:19 AM

This does not sound like a good idea to me. Irrespective of what their website claims, the size of the caps means that the ESL, which that manufacturer never tells you for the plastic caps, is going to be too high to do much good here. Plus, they're manufactured to have very low ESR which means that there is a chance of resonance occurring. Ie, worse sound. Much better, I believe, to try something like multi layered ceramic caps precisely where they're needed, leads as short as possible, if you want to kill very high frequency noise ...

Frank

MGH 2nd September 2012 12:10 AM

Thanks Frank. You are the second person who suggested this.

MGH 2nd September 2012 01:00 AM

Frank, I thought ceramic caps, although very low in ESL, have virtually no ESR to speak of. So aren't ceramic caps prone to resonance as well?

fas42 2nd September 2012 01:53 AM

1 Attachment(s)
Quote:

Originally Posted by MGH (Post 3148746)
Frank, I thought ceramic caps, although very low in ESL, have virtually no ESR to speak of. So aren't ceramic caps prone to resonance as well?

Yes, indeed they are. But the quality factor, the Q, sharpness of any resonance peak should be significantly less for that ceramic compared to the high performance plastic. What you're looking for is a curve of impedance with frequency that looks something like this:

Attachment 299216

That Mundorf would show a very sharp, head of a needle shape, plummeting of impedance at some frequency. And that's not good for preventing resonance. The ideal shape for that impedance behaviour is for 2 straight lines to come together to form a perfect V: that mimimises impedance over the biggest range of frequencies without encouraging resonance. Note, this is referring to very high frequencies; at audio frequencies the curve typically looks like the bottom of a bath tub with the usual capacitors used to do the work there ...

Frank

MGH 2nd September 2012 02:38 AM

Thanks for the explanation. I guess I will have to return the Mundorfs, and get the ceramics to bypass each of the power supply caps. Do you have any recommendations? They have to be high voltage though, 1kV. Is 0.1 microF an appropriate value?

I was also told to bypass on the amplifier end, using a 0.1 microF cap with another larger value bypass cap (10-22 microF). Are ceramic caps available in this larger value or should I use film cap?

fas42 2nd September 2012 04:50 AM

Ahh, high voltages of that order? That limits your options, I note that ceramics are only easily available in sizes up to 0.01uF with those ratings. And they start getting expensive too! I haven't played around with equipment using these voltages so can't really make recommendations there ...

I would still steer clear of bypassing the supply, especially if bypassing the amplifier end; this, at the actual point where the high frequencies could cause problems is where the real value of bypassing occurs. A rule of thumb is to maintain a value ratio of 50 or more when paralleling ceramic and/or film, so could use 0.01uF ceramic, 0.47uf film and 22uF film all in parallel to squash everything from a few 100kHz up to 10's of MHz. Cheap, small film cap's that can handle the voltage are the way to go, no fancy stuff. And, make the leads as short as possible, the smaller the capacitance the shorter the length of the cap lead when in place!!

Frank

MGH 2nd September 2012 07:16 AM

Thanks Frank,

"I would still steer clear of bypassing the supply, especially if bypassing the amplifier end"
The reason to bypass the amplifier end is because the power supply is separate from the amplifier. I haven't decided on how long the umbilical cord would be but, it could be as long as 1 to 1.5 meter. I suppose I could get the power supply as close to the amplifier I can, so that effectively the umbilical cord will be around 10 to 15 cm. What is the reason for not bypassing the amplifier end?

"this, at the actual point where the high frequencies could cause problems is where the real value of bypassing occurs."
By actual point, you mean across each power supply cap? I have 14 power supply caps to bypass, so using those 3 bypass caps for each of the 14 power supply caps will be expensive too. Why can't I use those 3 bypass caps at the amplifier end, and skip the power supply caps? It won't be as effective, I'm guessing? If you really think bypassing each power supply cap is the way to go, I will give it serious consideration, despite the cost.

fas42 2nd September 2012 10:48 AM

Quote:

Originally Posted by MGH (Post 3148915)
Thanks Frank,

"I would still steer clear of bypassing the supply, especially if bypassing the amplifier end"
The reason to bypass the amplifier end is because the power supply is separate from the amplifier. I haven't decided on how long the umbilical cord would be but, it could be as long as 1 to 1.5 meter. I suppose I could get the power supply as close to the amplifier I can, so that effectively the umbilical cord will be around 10 to 15 cm. What is the reason for not bypassing the amplifier end?

"this, at the actual point where the high frequencies could cause problems is where the real value of bypassing occurs."
By actual point, you mean across each power supply cap? I have 14 power supply caps to bypass, so using those 3 bypass caps for each of the 14 power supply caps will be expensive too. Why can't I use those 3 bypass caps at the amplifier end, and skip the power supply caps? It won't be as effective, I'm guessing? If you really think bypassing each power supply cap is the way to go, I will give it serious consideration, despite the cost.

We have a real misunderstanding going on here now, MGH! Not quite sure how it happened, shows you how important one's choice of words is, but what I've bolded above is exactly what I would suggest strongly that you do do! In other words, bypass the amp end, don't bypass the supply end. Are we in sync now ...?? :)

Frank

MGH 2nd September 2012 07:10 PM

Got it! Thanks.


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