I assume you have checked all your soldering. Can you post good quality pics of the board(s) front and back? The group here have an uncanny knack for finding problems with some good pics.
What voltages are you seeing across R49 and R31,, is the negative voltage side conducting? Have you checked voltage across R20 and R23 to see if those BD139/140 are conducting?
This is some of the reading -vdc side behave normally. I just observed that the vdc+ is actually conduct current it responds to Bias trim but the bias current rises slowly about 1/10 compare to the -vdc side. Picture of board will follow, but I check with the working board and they are indentical.
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By the way, what voltage supply rails are you using?
More data points can help, hopefully something simple.
Assume the resistor values are correct ?
Odd biass behaviour can be caused by parastic oscillations, especially when working on a bench in an experimental mode of working, from having wires in a mess, output wires near input, near power rails, long ground wires, etc. has a way to punish you like that.
I assume you don't have an old pcb board where the silk screen labels were messed up and the biass pot and dc offset pot labels were swapped? That was a careless thing by me but fixed some years ago for all the design files.
More data points can help, hopefully something simple.
Assume the resistor values are correct ?
Odd biass behaviour can be caused by parastic oscillations, especially when working on a bench in an experimental mode of working, from having wires in a mess, output wires near input, near power rails, long ground wires, etc. has a way to punish you like that.
I assume you don't have an old pcb board where the silk screen labels were messed up and the biass pot and dc offset pot labels were swapped? That was a careless thing by me but fixed some years ago for all the design files.
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It's 30vac around +/-42vdc. I have latest pcb and so far all resistors value are correct. Voltage readings quite stable, it responds to trim pot very well, no jumping around. Offset is adjustable and I can get it to be stable around <10mv. I will take all cpacitors out of the path way to ground and see what will happens.
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OK, so you see 100mA through R30 to the output node, and there’s no evidence of naughty oscillations so it is stable dc current which has to go somewhere to complete it’s circuit. It can’t be a bad C9 because you don’t see this much current in R15. It’s not R8 because the value is too high to flow 100mA with the voltages available. You don’t see it flowing through R31, so that leaves the following options to investigate:
R19 ( seems unlikely if the dc blocking cap C12 is good)
R10
D6 (not installed ?)
D7 (installed ? Correct polarity ? seems unlikely)
or, a rogue connection to the output that shouldn’t be there.
R19 ( seems unlikely if the dc blocking cap C12 is good)
R10
D6 (not installed ?)
D7 (installed ? Correct polarity ? seems unlikely)
or, a rogue connection to the output that shouldn’t be there.
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Congratulations !
Your perseverance paid off, a bit of detective work. And now to enjoy the sound
Your perseverance paid off, a bit of detective work. And now to enjoy the sound