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Old 20th August 2002, 08:18 PM   #1
2Bak is offline 2Bak  Denmark
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Default BosoZ - damaged FETS ?

Today I finally could test my BoSoZ and get to listen to it. Unfortunately I've made something wrong, 'cause I measure 118 volt on drain of Q1 and Q2, where it should have been +30 volts. When turned on the amp plays (very quietly) for 10 sec and then fades out.
PSU works fine and I get 60 volt.
My amp is unbalanced only and I use 10K pots at P1 and zeners at input.
Any hints? Maybe I was not handling my FETS with care when I soldered them in on the board....
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Old 20th August 2002, 08:25 PM   #2
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Maybe it has something to do with that 118 volts......
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Old 20th August 2002, 08:39 PM   #3
2Bak is offline 2Bak  Denmark
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Thanks mr. Pass. What would one look for concerning the 118 volts...?
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Old 20th August 2002, 08:43 PM   #4
UrSv is offline UrSv  Sweden
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Maybe completely out of bounds but how about missing ground connection?

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Old 20th August 2002, 10:40 PM   #5
jwb is offline jwb  United States
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Yeah I'm guessing you lack a connection from somewhere to ground. You have +/- 60V rails which easily explains the 118V potential on the drain, although you didn't specify where the 118V was referenced.
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Old 20th August 2002, 10:41 PM   #6
jwb is offline jwb  United States
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One more thing: I wouldn't worry too much about having blown a FET. The IRF610 is rated for 200V from drain to source. If you used the protection diodes at the gate, the FET should still be fine.

Or you could just replace it with another one
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Old 20th August 2002, 11:21 PM   #7
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Aaaarrghhh! There goes another 75 cents!
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Old 21st August 2002, 07:00 AM   #8
2Bak is offline 2Bak  Denmark
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This is my setup:

Click the image to open in full size.
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Old 21st August 2002, 12:18 PM   #9
2Bak is offline 2Bak  Denmark
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Everything's OK now, yet right channel Q2 gets 35 v, while the other three FETS get about 30 v drain, but I guess this is within margin.
Forgot to connect ground from PSU to line. UPS x 1000.
Still have a lot to learn about electronics.

Thanks. Looking forward to listening to it.
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