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Old 6th December 2003, 03:15 PM   #1
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Default Questions about PS capacitors.....

DISCLAIMER: After having some doubts about which would be the most suitable forum for these questions. I decided to leave it in the "Digital" forum. The reason I did this is that the sole motivation behind these questions is the PS upgrade of my CD67SE.

I've received some excellent suggestions from my fellow forum members on how to improve both the digital and analog power supplies of my CD67 but I'm finding that my general lack of knowledge about capacitors is preventing me from going ahead. Here is the suggestion I'm currently looking at:

"The next step, increase the size & quality of your main filter caps C803 & C804. I was using 3300uf Elna for audio caps. You will want to parallel a small good quality electrolytic of about 2-3uf plus a .1uf good quality film cap. This will give you more bass definition and should also extend and smooth out your top end."

Using Percy Audio as my source I've concluded that the Nichicon KZ series will do for the large electrolytic. But, choosing a small electrolytic and a film capacitor is puzzling me.

First, I'm guessing that a suitable choice for the small electrolytic would be one of the Blackgate 3.3uF PK series?

Secondly, I don't really have a clue what a 'film' cap is so choosing one is daunting. Perhaps the very first .10uF Solen listed (at $1.40) would do?

Any and all advice would be appreciated.

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Dan
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Old 6th December 2003, 04:25 PM   #2
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Default Re: Questions about PS capacitors.....

Quote:
Originally posted by dantwomey

"The next step, increase the size & quality of your main filter caps C803 & C804. I was using 3300uf Elna for audio caps. You will want to parallel a small good quality electrolytic of about 2-3uf plus a .1uf good quality film cap. This will give you more bass definition and should also extend and smooth out your top end."
[/B]
The quoted paragraph is meaningless crap. What are the existing output coupling capacitors? You might want to replace them with film caps, but you also might not. Using an electrolytic as an audio coupling capacitor is an especially poor idea.

Using parallel capacitors is probably not your best strategy, if you don't have a basic understanding of them. The general idea when paralleling capacitors is that you have a large electrolytic, but the response is wrong at high frequencies, so you add a smaller capacitor in parallel, which presumably has a better response at high frequencies. But this should not be an issue in the audio band, and parallel capacitors, especially little high-q parts, can resonate.

Finally, "film" refers to the materials and construction of the cap. A film cap is made of stacked or wound layers of polypropylene, polystyrene, PTFE (Teflon), or other film. These have good leakage, stability, and accuracy, but they aren't available in high capacitance, and they tend to be physically large. The "metallized film" are smaller packages for the same capacitance.
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Old 6th December 2003, 04:58 PM   #3
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Default Re: Re: Questions about PS capacitors.....

Quote:
Originally posted by jwb


The quoted paragraph is meaningless crap. What are the existing output coupling capacitors? You might want to replace them with film caps, but you also might not. Using an electrolytic as an audio coupling capacitor is an especially poor idea.

The "quoted paragraph" is e-mail from another forum member and more or less duplicates the recommended power supply upgrades for the Marantz CD67 on the TNT Audio website. Their recommendations were:

Improving the Power-Supply for the 57 / 67 / 67SE

"In my Unit all other the original Regulators stayed in place. I decided however to beef-up some of the Capacitors in the PSU. Now in the analogue PSU for the 67 Units, Marantz uses two more "silmic" Capacitors of only 470uF. This seems highly suspect, but Ken Ishiwata has got his head screwed on the right way around, so I left these alone as well.

added later:
I also had another "stab" at the PSU. Out came the two 470uF "Silmic" Capacitors in the Analog PSU (C803, C804) to be replaced with two 6,800uF 63Volt Units. I used what I had at hand (Panasonic TSU Series). I again placed a Bypass-cap across these, this time two red 0.22uF WIMA Cap's.

There are more Caps directly following the +/- 12 Volt Regulators (C805, C806). In these positions I can only recommend the largest possible Low-Z Capacitor you can lay Your hands on. Panasonic HFQ 6,800uF 25Volt will be dandy. I had to settle for Dubiler 2200uF 35Volt (low -Z 105degree). Another set of yellow 22nF Wima bypass Caps go in here as bypass."

Quote:
Using parallel capacitors is probably not your best strategy, if you don't have a basic understanding of them. The general idea when paralleling capacitors is that you have a large electrolytic, but the response is wrong at high frequencies, so you add a smaller capacitor in parallel, which presumably has a better response at high frequencies. But this should not be an issue in the audio band, and parallel capacitors, especially little high-q parts, can resonate.

As I understand it to date. A small value film cap is used in parallel with large value electrolytics to smooth the dc output of the power supply. Am I on the right track here?


Quote:
Finally, "film" refers to the materials and construction of the cap. A film cap is made of stacked or wound layers of polypropylene, polystyrene, PTFE (Teflon), or other film. These have good leakage, stability, and accuracy, but they aren't available in high capacitance, and they tend to be physically large. The "metallized film" are smaller packages for the same capacitance.
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Dan
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Old 8th June 2004, 08:21 AM   #4
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Default Size matters???

For analogue supplies, it seems like bigger is better - but what about digital power supplies and the supplies for the servo section?
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Old 8th June 2004, 06:32 PM   #5
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Bigger does not need to be better. Very big caps may worsen results, be it in digital or analog supplies.

Please realize that when big caps are used the diodes have to cope with larger or too large inrush currents.
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Old 8th June 2004, 06:44 PM   #6
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Quote:
As I understand it to date. A small value film cap is used in parallel with large value electrolytics to smooth the dc output of the power supply. Am I on the right track here?
A capacitor when placed across power supply lines appears as a "short" for AC signals and as a "block" for DC. The frequency where a cap stops being a short for AC is dictated by its capacitance. So your big electrolytic will short the AC and leave only the DC on the power supply lines. This is true only for the band where this cap is effectively a short for the AC. To push this band higher, a smaller film or ceramic cap is used. Since its capacitance is way smaller, it will short out the AC signal from the supply lines way higher in the megahertz range if chosen properly. Of course the electrolytic will also serve as a big smoothing device limiting the fluctuation of the supply lines. So yes, you are on the right track, unless, I also am in the obscurity...

Hope this helps!
Sébastien
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Old 8th June 2004, 06:44 PM   #7
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Exactly! Caps should be sized to produce the desired ripple voltage, not blindly made gigantic. If you don't know what ripple voltage you can tolerate, you have some more design analysis to do. If your desired ripple results in a too-large capacitor, consider something more intelligent, like a CRC or CLC fliter.

And of course, always pay attention to the conduction angle of the rectifier. The instantaneous current must not exceed the manufacturer's peak current rating, and the transient thermal response must also be considered.

The power supply is a system and the design should be approached from a whole-system perspective.
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Old 8th June 2004, 11:51 PM   #8
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Quote:
Originally posted by jean-paul
Bigger does not need to be better. Very big caps may worsen results, be it in digital or analog supplies.

Please realize that when big caps are used the diodes have to cope with larger or too large inrush currents.

Quote:
Originally posted by jwb
Exactly! Caps should be sized to produce the desired ripple voltage, not blindly made gigantic. If you don't know what ripple voltage you can tolerate, you have some more design analysis to do. If your desired ripple results in a too-large capacitor, consider something more intelligent, like a CRC or CLC fliter.

And of course, always pay attention to the conduction angle of the rectifier. The instantaneous current must not exceed the manufacturer's peak current rating, and the transient thermal response must also be considered.

The power supply is a system and the design should be approached from a whole-system perspective.

Thanks for the replies.

At present, there is a 6800uf and a 1000uf cap after the rectifier for the +/-10V and +/-5V supplies. If these supplies are separated - with a rectifier, capacitors and regulators for each supply - should the values for the main smoothing caps (6800uf and 1000uf) be changed or just duplicated for each supply?
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Old 9th June 2004, 12:02 AM   #9
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You'd have to know how much current you were drawing, and how much ripple is tolerable, before anyone can answer that question.
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Old 25th June 2004, 05:09 AM   #10
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Default Re: Questions about PS capacitors.....

Quote:
Originally posted by dantwomey
Using Percy Audio as my source I've concluded that the Nichicon KZ series will do for the large electrolytic.
Is Nichicon Muse KZ (or any other Muse) a good choice for PS capacitors for the analogue stage of a CDP?

Would they be suitable as PS Capacitors for the DAC?

Any idea how they compare to Panasonic FC (which everyone seems to like)?
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