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Old 27th December 2008, 01:41 AM   #1
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Join Date: Oct 2002
Location: Winnipeg MB Canada
Default just replaced bridge in Aleph 30 now problem

Hello,

I just replaced the stock bridge rectifier in my Volksamp Aleph 30 with discrete Fairchild Stealth diodes.

The bridge I built is using (4) 50 amp 600V TO-247 diodes, They are not mounted to any type of heat sink.

I get equal voltage out of the power supply pcb, plus and minus 25.2V on both channels.

One channel has 10mv of DC offset, the other channel has minus 200mv DC offset.

I am measuring about 8.9 volts across Z5 on both channels and also about 5.5volts across R11 in both channels.

What could be causing this dc offset difference? I did not measure DC offset before I replaced the bridge. The amplifier was working fine before replacing the bridge.

I am not sure what else to measure?

Any ideas or suggestions would be appreciated.

Best Regards
Kevin
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Old 27th December 2008, 02:40 AM   #2
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Join Date: Oct 2002
Location: Winnipeg MB Canada
so, I traced some voltages at Q4 in both channels and things were equal.

now at R14, in one channel I get -20.5 volts on one side of resistor and -25.2

and in the other channel I get -20.7 volts on one side of the resistor and -25.2 on other

would the -.2v difference be the -200mv I am seeing?

Kevin
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Old 27th December 2008, 10:09 PM   #3
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Join Date: Oct 2005
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If it's a factory unit I would email Pass Labs. If it's home built it's just a mismatch of the front end, probably always there if you never checked offset. I think the Wiki has some info on balancing the front end.

Best, Bill
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Old 28th December 2008, 12:25 AM   #4
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Location: Winnipeg MB Canada
Quote:
Originally posted by Bill Fuss
If it's a factory unit I would email Pass Labs. If it's home built it's just a mismatch of the front end, probably always there if you never checked offset. I think the Wiki has some info on balancing the front end.

Best, Bill

Yes, it is a Volksamp Aleph 30.

I suppose it always had the dc offset discrepency but I am not sure. The side that has -200mv offset runs hot compared to the side that has only 10mv of offset.

The -200mv side runs 4 to 5 degrees farenheit hotter. Is the 200mv dc offset responsible?

Thanks

Kevin
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Old 28th December 2008, 11:57 AM   #5
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That in itself wouldn't make one side run hotter. I doubt that the unit left the factory with 200mv of offset, you should contact Pass Labs.

Bill
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