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Old 23rd June 2004, 09:47 PM   #1
Franz G is offline Franz G  Switzerland
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Default What chip for 2 x 60 V?

I have a big main transformer, out of an Fostex PA-amp.

Without load, I measured 2x60V and on a second secondary 2x16V.

Any idea to build a great amp around this stuff?

Franz

http://mypage.bluewin.ch/gysiaudiophil/fostextrafo.JPG
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Old 23rd June 2004, 09:57 PM   #2
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That main seconday is way to large for anything in here. 30Vac secondaries are about the tops for National chip amps at least.
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Old 24th June 2004, 01:16 AM   #3
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you have to go discrete and build a real amp.

http://www.passdiy.com/amps.htm
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Old 24th June 2004, 01:52 AM   #4
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Default High Voltage chips.

Have you checked LM4780 ?

Supply Range 20 - 84 V

It's on National's web site. I didn't look at it closely but if it does go that high it might not have enough current handling capability for your application. Add some external power devices.

Cheers,
Ashok.
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Old 24th June 2004, 02:06 AM   #5
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Another solid state discrete possibility. Can take up to a 70v supply.

ESP P101
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Old 24th June 2004, 11:46 AM   #6
djk is offline djk
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"Have you checked LM4780 ?

Supply Range 20 - 84 V

It's on National's web site."

That is an error, it should read 84V total swing, or 42V.

A 2X 60V transformer will give 85V rectified and filtered. This is consistent with the pair of 18,000F 100V filter caps in the photo. The filter caps are big enough for a two channel amp running on 50hz (or higher) driving a 4 ohm load (or higher) per channel.

My guess is that with typical construction what you have would give 250W X 2 at 8 ohms and about 400W X 2 at 4 ohms, with about 3dB of dynamic headroom.

The dual 16V windings are intended to drive opamps, relay circuits, etc. They would normally be rectified, filtered and then regulated to 15V.

I could recommend a circuit if I knew the intended use.
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Old 24th June 2004, 12:10 PM   #7
Franz G is offline Franz G  Switzerland
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Default no project yet

Your guess is perfect: this is an transformer, out of an Fostex 2x350W amp!

Actually, I have no big intention or special application for such high power, specially not with my Coral Beta 8 Speakers, normally driven by my 300B SET.

So I think, I will put this transformer in my box, for a later project.

Many thanks!
Franz

P.S.
The power from the chipclones is already to high to try them with the Corals. To much risk for this gems.
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Old 24th June 2004, 12:24 PM   #8
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Thumbs up Choke-input filter.

If you use a choke-input filter, once you have more than a certain minimum load, the dc voltage will sit at 0.9x the transformer voltage, i.e. +/- 54vdc. At zero load it will go up to the peak voltage though, so some kind of preloading is necessary for anything other than a class A amp.
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