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Old 10th April 2012, 11:39 PM   #11
Flemming J P is offline Flemming J P
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I was one of the mosfet that had died
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Old 12th April 2012, 03:36 AM   #12
Daniel(Del) is offline Daniel(Del)  Brazil
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Do you have an idea why?
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Old 12th April 2012, 03:56 PM   #13
Flemming J P is offline Flemming J P
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No clue. When I turned the amp off, I head a pop in one speaker. The next time I tried to turn on the amp, it smoked (very hot resistors).

I ran the mosfets at 750 ma each at 32 v rails (350mv drop over 0.5 ohm source resistors).

I have chosen to run with lower bias (600 ma) after measuring how much or rather little power I actually use even when I play loud.
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Old 12th April 2012, 04:09 PM   #14
KatieandDad is offline KatieandDad  United Kingdom
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This thread started with you suspecting the input JFets. Have you now discovered that one of the power MOS-FETs has failed ?

The MOS-FETs can fail for a number of reasons.

However, the most likely is a short in the speaker leads, OR, overheating, OR, a foreign object shoprting MOS-FET to heatsink.
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Old 12th April 2012, 07:52 PM   #15
Flemming J P is offline Flemming J P
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I thought it was the input fets, due to the fact that it was the feedback resistors that got hot/smoked (that was after I had turned the bias down to 0).

After some measurements I found that one of the mosfets was conduction at full power all the time no mater what.
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Old 14th April 2012, 02:37 AM   #16
Nelson Pass is offline Nelson Pass  United States
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F5 problems
It happens occasionally.

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