Repair question Audio Research D100B

[muizel]

I really hope someone can give me some advise with this amp , I bought it second-hand and not in working order. At this moment I have replaced all the transistors and matched them for hfe and the amp is working again but on one channel there is quite a big dc offset about 6 volts dc. The other channel has about 5 milivolts dc wich is quiet normal. The offset goes to normal when I short the rca input, and when I lower the value off resistor R16 from 68K to 33K the high offset is also gone. Ic U2 is also replaced for a new one, as all the transistors.

My guess is that it is not in the output transistors but I cannot find the reason for this high offset.

Regards desperated René.

[dray177]

Originally Posted by muizel

I really hope someone can give me some advise with this amp , I bought it second-hand and not in working order. At this moment I have replaced all the transistors and matched them for hfe and the amp is working again but on one channel there is quite a big dc offset about 6 volts dc. The other channel has about 5 milivolts dc wich is quiet normal. The offset goes to normal when I short the rca input, and when I lower the value off resistor R16 from 68K to 33K the high offset is also gone. Ic U2 is also replaced for a new one, as all the transistors.

My guess is that it is not in the output transistors but I cannot find the reason for this high offset.

Regards desperated René.

AM1 module is out I think
Be carefull, offset might be growing to 55volts
Raymond