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Old 15th August 2011, 07:56 PM   #1
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Arrow Capacitors for this amp ?????

hello everyone

I built this amp and now I want to build its power supply but I don't now how much capacitors should I use and in what voltage range

The maximum amp voltage is 90-0-90

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Old 16th August 2011, 06:11 AM   #2
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The schematic is pretty clearly labeled for +-75V rails. If you install that transformer you need 80V rated power supply capacitors. Four O.T.'s with suitable heat sinks indicates about 260 W/channel, so I would try 4700 uf PS capacitors. Parallel them with a 0.1 uf 80v ceramic capacitor for speed. The schematic says 350 W out, but I wonder for how long before it heats up.
If you install 90 V transformer, you need 100V rated capacitors. Adjustments need to be made then in the resistors and possibly transistor ratings.
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Old 16th August 2011, 06:23 AM   #3
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Thanks indianajo

Transformer with what voltage you think I should use ?(Suitable)
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Old 16th August 2011, 07:49 AM   #4
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With 75V rails, I would use no less than 100V capacitors.
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Old 16th August 2011, 08:09 AM   #5
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Transformers are rated RMS voltage so if you use 80V capacitors I would buy a 65V transformer. If you buy a 75 V Rms transformer you do need the 100V capacitors and same transistor Vceo rating as the voltage could creep up to 95 with no load if the O.T. bias current is low.
If you buy a switching power supply, the rated voltage is what you get out. Don't buy a computer switcher supply, they are not quiet enough.
My 650 W/ch @ 4 ohm PV1.3 K amp has two 10000 uf capacitors parallel for each rail, so a 250 W amp maybe could use two 4700 ohm capacitors per side. Two smaller capacitors gives better series resistance.
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Last edited by indianajo; 16th August 2011 at 08:28 AM.
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Old 16th August 2011, 08:29 AM   #6
MiiB is offline MiiB  Denmark
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Interesting network around the Q11-Q12.. feed forward..???
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Old 16th August 2011, 09:21 AM   #7
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"MiiB" you can read any information about this amp in this thread

http://www.diyaudio.com/forums/solid-state/162043-mosfet-amplifier-irfp240-irfp9240.html

is there capacitor with 100V ? or should I use 160V instead ?
How about using capacitor of 50V in series order?
I saw lots of pictures in DIYaudio that in their power supply they have many capacitor
anyone knows why?
Like this picture

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Old 16th August 2011, 10:54 AM   #8
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Stick with the +75V rails. All of the designer's work was based on that. You can usually go a little lower, but if you go higher you will get into trouble on a high-power job like this one.

A rough guideline for capacitors is 10,000uF for every 100W. For 350W into 4 ohm that is 35,000uF. Times two (for both rails) is 70,000uF. Might as well make it a round 100,000uF.

Putting caps in series does not help much Two 10,000uF caps in series gives you half the capacitance i.e. 5,000uF.

For cap voltage you need a bit of a safety margin. 80V caps on a 75V is a bit close for comfort. 100V is good and higher still is better but more expensive.

To get the peak voltage from RMS, multiply by 1.4. For 75V DC rails you therefore need about a 55-0-55V transformer. The 1.4 factor is not exact science because of transformer losses etc. You might only have 70V under full load, but you are still in the ballpark.

Have you done the sums for the heatsink yet? Even at 70% efficiency this monster will put out about 150W of heat. The heatsink in the picture above gives an indication of what is needed.

Last edited by ingenieus; 16th August 2011 at 11:20 AM.
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Old 16th August 2011, 11:09 AM   #9
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"ingenieus" thank you for your complete and helpful advices
I think buying this much capacitors(50,000 uf) for each rail will cost me more than I spent on amp (Just kidding)
Thank you
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Old 16th August 2011, 11:16 AM   #10
ilimzn is offline ilimzn  Croatia
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Quote:
Originally Posted by MiiB View Post
Interesting network around the Q11-Q12.. feed forward..???
Classic overcurrent protection... without SOA correction of any kind, too.
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