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Old 19th November 2012, 04:39 PM   #1
ridikas is offline ridikas  United States
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Solved.

Last edited by ridikas; 30th November 2012 at 06:46 AM.
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Old 19th November 2012, 04:44 PM   #2
lineup is offline lineup  Sweden
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Sounds as you have vert bad bias.
There should be one little potentiometer somewhere close to the MOSFETs or a bit from them in the middle.
You should adjust this potentiometer so that you get some current warming the MOSFETs up.
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Old 19th November 2012, 04:48 PM   #3
ridikas is offline ridikas  United States
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The bias is via a fixed resistor, 270 ohms. I've tried a 470 ohm resistor. It more than doubled the gate voltages, but the results were identical, distorted sound and not even warm to the touch, even if touching the body of the MOSFET directly.
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Old 19th November 2012, 04:50 PM   #4
lineup is offline lineup  Sweden
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Strange.
Because the 470 Ohm resistor should be enough.
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Old 19th November 2012, 04:52 PM   #5
lineup is offline lineup  Sweden
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I think you better check those mosfet.
Setup a little circuit, take them away from heatsink and do some testing.
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Old 19th November 2012, 04:54 PM   #6
ridikas is offline ridikas  United States
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Strange.
Because the 470 Ohm resistor should be enough.
That's what I thought too. I'm a little baffled. Is there any chance that either the power caps, or the MOSFETs are bad? That would mean that all 4 MOSFETs in each of the two channels are bad, because none of them are warming up.
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Old 19th November 2012, 08:28 PM   #7
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Show us the circuit and maybe we can find out whats wrong
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Old 20th November 2012, 12:29 AM   #8
cjkpkg is offline cjkpkg  United States
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You need like 3vdc on the gates to get the buz to bias up.
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