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Old 21st February 2005, 04:41 PM   #1
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Default DoZ power supply

Hello all, I'm getting ready to build a DoZ amplifier but not sure how big of a transformer is needed for the power supply. I would like to have 40 volts available because dropping some with a variac is no big deal. Have plenty of those salvaged

So how many VA would be required for running two channels at the spec'd 1.7a? I guess the secondary would be 35 volts? Would schottky diodes be better than fast recovery? Thanks.


Adam
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Old 22nd February 2005, 02:59 AM   #2
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A 30V secondary with about a 330VA transformer will give you about 42V under load. A 35V transformer is too much voltage. Even with 40 - 42VDC, you will need a hellova good heatsink.

I just built a Doz using a 330VA transformer from Parts Express, a 20,000f filter cap for both channels, and a 8200f cap for each channel (three filter caps total). Using two TO-3 devices per channel (On-Semi MJ15003's) and what I thought were pretty large heatsinks, the heatsinks got so hot that I couldn't touch them. I'm using fans on it now.

Also, the transformer on mine bled EMI into the audio path so bad that I'm making the transformer remote to the amp...

If I had to do it again, I'd design for a stupidly big heatsink, four TO-3's per channel (with a 30V secondary transformer), and I'd start from the beginning with trying to come up with some sort of shielding enclosure for the damn transformer.
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Old 22nd February 2005, 03:12 AM   #3
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I used 800va for stereo 53vdc rail, 3A bias. hehe, that was a potent amp next try, more voltage, more bias!

-Matthew K. Olson
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Old 22nd February 2005, 03:48 AM   #4
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Ah thanks everyone. Thats exactly what I was looking for.

www.apexjr.com has some nice large heatsinks already drilled for 8 TO-3 devices. I am thinking about making a channel like the picture and having a fan running at a very reduced speed.
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Old 22nd February 2005, 10:45 AM   #5
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That works, if you want more bias then, you might want to add more output transistors. I used 2sc5200's from www.digikey.com and they worked great. I used 8 per channel, plus for the driver transistors i also used 2sc5200, and for the to-92 transistors i used the mpsa ones, i forget which one though, i think mpsa92 or 42 that way they could handle a little higher voltage than the ones rod has spec'd.

-Matthew K. Olson
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