That won't have any effect.
The 5mV is the probable cause of the excessive offset you are observing. It has to be flowing through C15 or some leakage path associated with flux contamination or similar. You can try replacing C15 with a 0.1uF ceramic or film cap. That's totally too small for actual use, but it's a useful diagnostic experiment as it will have low leakage and will keep the amp from oscillating. With luck, you'll see improvement in the offset problem; if not, you'll know to suspect a different leakage path, perhaps along the C35 path. Try cleaning board with denatured alcohol.
If you doubt this explanation, check the drop across R10 in the other channel. I predict you'll find less drop.
The 5mV is the probable cause of the excessive offset you are observing. It has to be flowing through C15 or some leakage path associated with flux contamination or similar. You can try replacing C15 with a 0.1uF ceramic or film cap. That's totally too small for actual use, but it's a useful diagnostic experiment as it will have low leakage and will keep the amp from oscillating. With luck, you'll see improvement in the offset problem; if not, you'll know to suspect a different leakage path, perhaps along the C35 path. Try cleaning board with denatured alcohol.
If you doubt this explanation, check the drop across R10 in the other channel. I predict you'll find less drop.
I changed C15 to a 16v 47uf which does not leak.
now i got 590mV dc on spekar output off channel 2
i will try to change C35 to and se if it dose any different
C35 is probably not the culprit, especially if in Stereo mode, rather than Bridge. I mention it only as a path of possible leakage. You can simply remove C35 entirely during troubleshooting, restore later when problem has been resolved.
So offset voltage got even worse? Did you recheck voltage drop acrosss R30? There should be 0mV drop across R30 if C15 is truly leakage free. Double check installation polarity--- negative terminal of C15 should connect to ground, positive to R30. How do you know the new C15 does not leak?
I assume you tried to adjust offset with VR3 and you can make offset even worse, but 590mV is lowest you can attain?
The easiest way to check Z8/Z9 is to leave them in-circuit. They appear to be 2.7V Zener diodes. Monitor the wiper terminal of VR3. Its voltage should move smoothly from +2.7V to -2.7V as you adjust the pot.
If voltage across R30 is near 0mV, set VR3 for lowest reading and report its voltage. Remeasure as in post 5: please measure voltages at bases of Q6 and Q7 and reconfirm output (at +590mV?).
If you find voltage across R30 is still non-zero, I'll suggest a way to test leakage out of circuit.
So offset voltage got even worse? Did you recheck voltage drop acrosss R30? There should be 0mV drop across R30 if C15 is truly leakage free. Double check installation polarity--- negative terminal of C15 should connect to ground, positive to R30. How do you know the new C15 does not leak?
I assume you tried to adjust offset with VR3 and you can make offset even worse, but 590mV is lowest you can attain?
The easiest way to check Z8/Z9 is to leave them in-circuit. They appear to be 2.7V Zener diodes. Monitor the wiper terminal of VR3. Its voltage should move smoothly from +2.7V to -2.7V as you adjust the pot.
If voltage across R30 is near 0mV, set VR3 for lowest reading and report its voltage. Remeasure as in post 5: please measure voltages at bases of Q6 and Q7 and reconfirm output (at +590mV?).
If you find voltage across R30 is still non-zero, I'll suggest a way to test leakage out of circuit.
Oscillation can sometimes produce strange behavior, including odd offset behavior.
I don't think believe you replied to this question. If this is the case, do you recall where the bias pot was positioned and can you return it to the same spot? Be careful--- too much bias current can cause damage.
You would probe amp output and look for signals that shouldn't be there. It might be insightful to monitor output with scope while you adjust bias current.
I don't think believe you replied to this question. If this is the case, do you recall where the bias pot was positioned and can you return it to the same spot? Be careful--- too much bias current can cause damage.
You would probe amp output and look for signals that shouldn't be there. It might be insightful to monitor output with scope while you adjust bias current.