I have a a Hafler DH110 pre amplifier. First, this unit works, but has the following issue. The left channel voltages to the transistors are reading about .3 to .4 volts lower than the right channel. Second, what I have done is verify the left channel voltage drops on all the resistors and against the right channel. These are shown in the attached PDF file. Third, I checked every voltage at each transistor to validate the right channel and left channel voltage discrepancies. Fourth, I have included all my voltage measurements in the PDF file with a schematic. Lastly, my question is this, why is the left channel lower when the power rails are both 23.1V? Each resistor is showing this voltage on the rail side of the resistor. So the rail voltage going to the left or right channel resistors are spot on the 23.1V. Again the unit works, but the amperage draw on the output Q13 and Q14 is 8.1ma on the left channel while the right channel is 13.5ma due to the votage drops on R34 and R35. I did notice that the right channel differential pairs bases run about 12 to 21 mv on the right channel and on the left these volates are 1 to 2 mv. The only thing I can think of is that there is a faulty transisor in the drive path, but I do not know if this thinking is correct. I do have the BC series of transistors to replace everything on the left channel, but do not know if they require matching or if changing them all out is a wise decision. So I am asking for some help from the DIY community to solve this low voltage problem. I am open to all the DIY experts becasue I am at a loss of ideas.
It maybe that a resistor has drifted out of tolerance . Measure each resistor in circuit and compare between channels , you should not measure a value above the stated resistance but you may see lower value readings due to semiconductor conduction ( also meter polarity conscious ) . If all is ok then measure the base , collector , emitter voltages of all the semis with reference to earth/ground and compare .
Thank you for responding. I checked every resistor in both channels paying attention to polarity and all are the same or as close as my meter can read the ohms. I have attached a spreadsheet with the voltages as you suggested. My experience is limited so this what I am going to say is not expert stuff. Q7 through Q9 Base voltages seem off to me since they the left channel is low and not the correct polarity. Likewise, Q11 through Q14 collector voltages have differing polarities. These base voltages are in millivolts and from what I know millivolts is a very small number so I don't know if this can be affecting anything. Again, this unit plays well and maybe is not worth all of this, but still the channels should be closer. Thanks again.