I believe the power supply is correct to both channels.
I corrected my probes and now get a + value for the Right resistors.
Right Offset is sitting stable at 0.005 V DC +
Right resistors are stable at 3.496 V DC +
I can change values with the Right trimpot either way +/-.
Does that suggest the right side is operating as expected?
I still can only increase values with the left trimpot.
Offset is stuck at 0.879 DC V +
Resistors are at 16.14 DC V +
Perhaps the left trimpot is not seated properly?
I think before concentrating on DC-offset we should first check bias current to get a feeling for if amp is working correct. The DC-offset is just a final "minor" adjustment if it is not very far away from 0V.
To check bias current measure voltage over the 0.47 ohm source resistors. Voltage should be about 0.6 - 0.7 VDC.
If you can get DC-offset on right channel to also be negative.....so you can adjust it to..... like say "minus" 50 mV to "plus" 50 mV.....this it s good indication that something is working.....but not a guarantee.....
The "stuck" offset at left channel is not a good sign.....but let us hear what bias current is....?
To check bias current measure voltage over the 0.47 ohm source resistors. Voltage should be about 0.6 - 0.7 VDC.
If you can get DC-offset on right channel to also be negative.....so you can adjust it to..... like say "minus" 50 mV to "plus" 50 mV.....this it s good indication that something is working.....but not a guarantee.....
The "stuck" offset at left channel is not a good sign.....but let us hear what bias current is....?
First, thanks for the assistance
Right R13 0.608 DC V
Right R14 0.608 DC V
Left R13 0.591 DC V
Left R14 0.641 DC V
Still no joy from left trimpot.
Right R13 0.608 DC V
Right R14 0.608 DC V
Left R13 0.591 DC V
Left R14 0.641 DC V
Still no joy from left trimpot.
You're getting reasonable bias current, so that's good.
Is the left channel DC offset really 'stuck'? You wrote earlier you can increase values
with the left trim pot. If that meant that you can increase but not further decrease
the dc offset then you probably need some adjustments of resistor/trimmer values.
Is the left channel DC offset really 'stuck'? You wrote earlier you can increase values
with the left trim pot. If that meant that you can increase but not further decrease
the dc offset then you probably need some adjustments of resistor/trimmer values.
I would expect about same voltage drop over both R13, R14 as same current goes through both resistors so if they have same value.....the voltage drop over them will be the same. So the question is if your R13, R14 in left channel both are 0.47 ohm?
If they are both 0.47 ohm.....then we have larger current in R14 than in R13....and how could that happen?
If they are both 0.47 ohm.....then we have larger current in R14 than in R13....and how could that happen?
......if your R13, R14 are 10% resistors and one is -10% and the other is +10%....then your bias current measurement may be correct.....but my mind say it should be closer to each other.....
So to verify, the offset trimpot IS actually working, you just can’t dial it down enough, is that correct?
...are you using the “Blasphemous Heresy” values or stock?
...are you using the “Blasphemous Heresy” values or stock?
I finally got around to swapping out my M2 clone boards for the M2x boards. Thing did not go as smoothly as I would have liked and I still need to troubleshoot what the problem is with the left board. As part of the swap out I decided to add led’s to the front panel so I could tell when the amp was on. The amp is setup dual mono with CAPMx power supplies for each channel. To keep everything clean I swapped out the wiring between the rectifiers and CAPMx boards in order to wire the led’s. I checked the voltages of each power supply before connecting the amps and the voltages were good and led’s lit up. I connected the amps and fired everything up. The right boards heat sinks got worm and I was able to adjust the offset to 0. The left board was a different story the heat sinks did not get worm and the reading for the offset was all over the place and not stable. Changes to RV1 made no difference.
The good news is there was no smoke, popping sounds, or burning smell. Next step is to check the wiring between the CAPMx and amp. I think that one of the wires from the CAPMx to the amp is not connected. It was late so I did not take any measurements. Hopefully I will have time tonight.
The good news is there was no smoke, popping sounds, or burning smell. Next step is to check the wiring between the CAPMx and amp. I think that one of the wires from the CAPMx to the amp is not connected. It was late so I did not take any measurements. Hopefully I will have time tonight.