Q4 and Q9 together with R10, R13, R35 and R39 are of no importance at the moment.
Their sole purpose is protection.
What about the voltage over R7 and R36, and every other mosfet in the circuit?
Note that Q3 and Q8 are not mosfets, no need to measure these.
As stated before, I believe the one side (Q2 side) of your amp is working fine.
Try to take these components and their voltages as a reference to find out what is wrong with the other side. With power supply caps fully discharged or disconnected, compare every resistor value on the good side with the bad side.
I’m sure you’ll succeed.
/Hugo
Their sole purpose is protection.
What about the voltage over R7 and R36, and every other mosfet in the circuit?
Note that Q3 and Q8 are not mosfets, no need to measure these.
As stated before, I believe the one side (Q2 side) of your amp is working fine.
Try to take these components and their voltages as a reference to find out what is wrong with the other side. With power supply caps fully discharged or disconnected, compare every resistor value on the good side with the bad side.
I’m sure you’ll succeed.
/Hugo
Netlist thanks.
The problem was a bad resistor. I don't remember which. Sorry.
My next problem is setting absolute DC. Relative DC is fine never higher than 0.05V and I can easy set it for 0.00V.
But when firing it up initially the absolute DC starts about 7.5V and 6.5V for each channel. My 200 ohm trimpot is set for 0V. Turning it up to 200 ohm gives me 3.5V (for the 7,5V) and the other 2,5V. After an hour or so both channels goes down about 1V but never lower. So the 3.5V goes down to 2.5V and the 2.5V getting 1.5. I know I shouldn’t worry about 1-2 V but as the voltage only changes about 1 V when the heat sinks is getting hot there shouldn’t be a problem getting a DC offset around 0V.
So the question is where do I start?
Do I get a bigger trimpot?
Or do I change R1, R4, R44, R45. Bigger or smaller?
What would be the easiest solution?
The problem was a bad resistor. I don't remember which. Sorry.
My next problem is setting absolute DC. Relative DC is fine never higher than 0.05V and I can easy set it for 0.00V.
But when firing it up initially the absolute DC starts about 7.5V and 6.5V for each channel. My 200 ohm trimpot is set for 0V. Turning it up to 200 ohm gives me 3.5V (for the 7,5V) and the other 2,5V. After an hour or so both channels goes down about 1V but never lower. So the 3.5V goes down to 2.5V and the 2.5V getting 1.5. I know I shouldn’t worry about 1-2 V but as the voltage only changes about 1 V when the heat sinks is getting hot there shouldn’t be a problem getting a DC offset around 0V.
So the question is where do I start?
Do I get a bigger trimpot?
Or do I change R1, R4, R44, R45. Bigger or smaller?
What would be the easiest solution?
Glad you made it.
You will want to try fiddling with R24. A bit higher or lower in value, depending if the offset is positive or negative. 390 or 560 ohm will do the job.
The output to ground R's are fine if you used the given values, 30 to 100ohm.
Did you add the Macmillan resistors from diff-pair sources to outputs? Something like 3 to 5k seems to be in the ballpark for most people.
/Hugo
You will want to try fiddling with R24. A bit higher or lower in value, depending if the offset is positive or negative. 390 or 560 ohm will do the job.
The output to ground R's are fine if you used the given values, 30 to 100ohm.
Did you add the Macmillan resistors from diff-pair sources to outputs? Something like 3 to 5k seems to be in the ballpark for most people.
/Hugo
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