R3=1K; R4=4.32K Gain of ~5.
Biased to Class A at 1.5mA
DB Bias voltages set to 50mV
LT1028CN8 in left and right opamp sockets and opa627 in ground socket.
STEPS power supply at 24V.
The offset voltages are what concern me. With the LT1028 I get the following:
IG to OG 0mV
IG to OL 7.5mV
IG to OR 3.XmV
Same measures between pins 6 on the DB unit.
However, the DC offset varied dramatically when I turned the volume pot...at the highest volume it reached 12mV in the Left channel and 9mV in the right.
Is this OK?
These offset reading are pretty high compared to the OPA627/637s I've tried. With a pair of Grado SR60s I get a very loud pop when I turn the amp off and on...I didn't try it with my HD600s!
How can I adjust the offset of an opamp? Would raising the gain to 11 help (R4=10K)?
PS. I also tried the LT1028ACN8 but those gave me DC offset voltages of 25mV in each channel.