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Old 16th October 2006, 03:41 PM   #11
dinu is offline dinu  United States
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I know the protection circuit operates both channels independently (2 separate relays). When I was building the amp it often happened that 1 or the other channel would be shut off. Anyway, it's all speculation til I see it.
Florida is not a good place for large class A amps.
P.S.
Didn't find a good link for DC servo yet.
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Old 16th October 2006, 03:52 PM   #12
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What is common to both channels? The front end PSU with high dissipation. If one of the pass devices fails shorted, you'll have ~80V on one rail, and 50 on the other. That would cause a lot of offset. That's where I'd look first.
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Old 16th October 2006, 04:12 PM   #13
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Is the LED any indication? I mean, if it works, does it mean the PSU works fine? I'm guessing NO.
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Old 16th October 2006, 04:24 PM   #14
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If one rail has failed high, the LED will be on, marginaly brighter than before.
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Old 16th October 2006, 04:26 PM   #15
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Will this kill the front end? Worse yet, will this kill the output stage?
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Old 16th October 2006, 04:39 PM   #16
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It won't instantaneously kill the front end, but leaving it on to try to let the offset settle out isn't a great idea if this is the problem. Dissipation in the front end goes way up since it's got more voltage across it.

The output stage should be OK, as long as the front end doesn't fail. Then it may or may not be damaged.
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Old 16th October 2006, 04:45 PM   #17
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I made alot of progress on the front end design over the weekend. I'll be ready to post tomorrow, headers and all. The only outstanding problem so far is the LM reference devices replacing the Zeners. I have not found a suitable unit with a TO-220 package. Well, you'll have a chance to look tomorrow.

It would be awfully nice to be able to incorporate a DC servo circuit into the design, were any to present itself.
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Old 16th October 2006, 04:47 PM   #18
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I meant TO92 NOT 220. .
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Old 24th October 2006, 05:46 PM   #19
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Here's the schematic everyone. I've added a DC servo in case anyone wants to use a feedback selector like I did in my last one. It should keep the offset in check.
Rail bypass caps are on board. The gate protection for Q9 and 10 also on board. TO 220's all around and mounted at board edge so they can all sit on a large heat sink.
I want to run mine on 77V rails.
The high current PSU will use (2) 1.5KVA transformers (8) 68000uF caps.
Please comment.

http://i125.photobucket.com/albums/p...25cboardhr.jpg
http://i125.photobucket.com/albums/p...cschematic.jpg
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Old 24th October 2006, 05:54 PM   #20
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better resolution schematic.

http://i125.photobucket.com/albums/p...cschematic.jpg
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