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Old 20th October 2004, 05:33 PM   #1
Stabist is offline Stabist  Slovenia
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Default 10000uF in Zen's output

Hi!

One Question regarding output cap - is 10.000uF capacitance chosen because of current ripple or something else?
I mean - 10.000uF/50V Panasonic TS-HA which is pretty goog capacitor has around 4A ripple current - but 2200/50V Pan FC has 3A - so if I put 2 in parallel - I get 6A ripple - and 4400uF capacitance ... And 4pcs of 2200 Pan FC are still cheaper than 2pcs 10.000 TS-HA ... Or do I also need bigger capacitance??
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Old 20th October 2004, 06:42 PM   #2
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You can use anything you want. I usually just use whatever
cap I'm also using in the supply and parallel it with as much
film cap as I want to pay for. My Favorite: Zen capacitors from
Northcreek Music. (no pun intended). Buy them while you still
can.
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Old 20th October 2004, 06:50 PM   #3
Stabist is offline Stabist  Slovenia
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Thanks!

So if I understand correctly - my prediction about that the ripple factor is more important than capacitance is in this case correct ? Or is there still some minimal limit (Ok I'm talking about few 1000uF here as a min) regarding output capacitance??
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Old 21st October 2004, 05:21 PM   #4
Stabist is offline Stabist  Slovenia
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Default Snubers

One thing that has been changed in my redesigning of my Zen - is changing standard diode bridge with 4 MUR1560 ... And I've been reading some stuff about snubers ...
If I got it right - cap between 10 and 100nF will do OK and it doesn't mater much which type is - I have some MKS and some ceramic 100nF at hand - any particular reason which should I prefer or not?
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Old 21st October 2004, 09:22 PM   #5
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Ripple factor shouldn't be ignored, but is not usually an issue
with DIY projects as they tend toward over kill.

Almost any value snubber up to about .047 will be an
improvement over none. Nowadays we are using high speed /
soft recovery types without snubbers and they are working out
very well.
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Old 21st October 2004, 09:38 PM   #6
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Actually, this is one instance where you can make a case for using a ceramic capacitor. Considering that the little blips from the diodes go out into RF territory, the extended HF capability of a ceramic cap is of use. Note that this logic does not extend to use in the signal path.
I've used both film and ceramic caps--even on soft recovery diodes--on the theory that it's inexpensive insurance. When I say film caps, I mean something along the lines of Sprague Orange Drops, not MIT, Wonder Caps, or anything on that price level.
Nelson has to watch the parts cost going into his product. You don't. Overkill is good. To date, I've never heard anyone argue that caps across the bridge cause any harm. Given that it's only a dollar or two at most (mere cents in the case of ceramic caps), why not?

Grey
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Old 21st October 2004, 10:30 PM   #7
Stabist is offline Stabist  Slovenia
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OK I'll let it try with what I have at hand right now - 100nF ... But will get 47nF ones too as soon I'll go to city ...

Still a little in doubts about output capacitance - is maybe allready 2200uF enough? (I have those Panasonic FC in mind)
Or what is the rule for choosing the right MIN value? (OK apart that that you use what you have at hand at the moment)
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Old 21st October 2004, 11:21 PM   #8
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Output caps...the more the better. Your minimum value is determined by the impedance of your drivers. The formula is:

C= 1/(2*PI*R*F)

where:
R= impedance of the speaker
F= low frequency cutoff
C= capacitance in Farads

Nothing bad will happen if you use too little capacitance. You'll just lose a little bottom end.

Grey
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Old 22nd October 2004, 01:08 AM   #9
Stabist is offline Stabist  Slovenia
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If I get this correctly:
- my speakers are nominal 5R
- I guess low frequency cuttoff is 45Hz (the range is declared from 45Hz-23kHz)

So:
1/2*pi*5*45=7,1*10^-4F --> min C is: 710uF ...
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Old 22nd October 2004, 01:34 AM   #10
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Close enough, but remember that the formula gives you the -3dB point. If you set things that close to the lower end of your speakers you are, in effect, reducing the 45Hz response of your speakers by 3dB. Good idea to give it an octave or more of elbow room in order to keep from limiting your low-end unnecessarily. That would put you in the region of 1400uF (somewhere in the region of 23Hz). Another octave wouldn't hurt, and would put you back in the 2200uF range (about 11-12Hz).

Grey
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