just replaced bridge in Aleph 30 now problem

KevinLee · 27th December 2008, 01:41 AM

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

KevinLee · 27th December 2008, 02:40 AM

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

Bill Fuss · 27th December 2008, 10:09 PM

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

KevinLee · 28th December 2008, 12:25 AM

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

Bill Fuss · 28th December 2008, 11:57 AM

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

27th December 2008, 01:41 AM	#1
KevinLee diyAudio Member Join Date: Oct 2002 Location: Winnipeg MB Canada	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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27th December 2008, 02:40 AM	#2
KevinLee diyAudio Member 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

27th December 2008, 10:09 PM	#3
Bill Fuss RIP Join Date: Oct 2005 Location: Central Florida	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

28th December 2008, 11:57 AM	#5
Bill Fuss RIP Join Date: Oct 2005 Location: Central Florida	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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