SebVanDijk
New Member
Hi everybody,
Since about a year I'm the proud and happy owner of 2 Denon POA-S10 monoblocks with matching PRA-S10 preamp. The only problem I have with the PRA is the quite challenging volume control. Changing the volume is a matter of delicately touching the remote to prevent the volume being way too loud or way too low. Especially with headphones, there is not really a choice between no sound or no more eardrums.
Because I had a strong feeling that this wonderful preamp was too well designed for such clumsiness, I took the service manual and opened up the amp to do some investigations, altough I have a rather limited knowledge of electronics.
I started with adjusting the output offset voltage because the manual told me so. But there I immediately found a/the problem, because there was no way the difference between Pin 1 and 3 on TP001 was going to be less than 100mV. Best I could do was about 1V. The adjustment on TP002 however was a piece of cake.
After some hours of checking, measuring and looking at the schematic diagram, I started thinking that the two opamps which you can see in the image just beneath TP001 and TP002 cause the problem.
They both reveice 16.6V on pin 4 & 8. Then on pin 2-3 (R-ch opamp) and pin 5-6 (L-ch opamp) they receive 0.0016V. The output on pin 1/7 (L-ch) is 10.5/9.6V and on pin 1/7 (R-ch) is 0.002/0.001V. That appears to me to be a too big difference.
The bottom of the circuit boards look very nice, all solderings look great. I do not know where else to look, but I see no reasons to assume there are other defective parts. So I have a few questions actually:
- Am I right that the L-ch opamp is faulty?
- If so, how is that possible?
- If not, than what might be the problem of the impossible volume control?
Since about a year I'm the proud and happy owner of 2 Denon POA-S10 monoblocks with matching PRA-S10 preamp. The only problem I have with the PRA is the quite challenging volume control. Changing the volume is a matter of delicately touching the remote to prevent the volume being way too loud or way too low. Especially with headphones, there is not really a choice between no sound or no more eardrums.
Because I had a strong feeling that this wonderful preamp was too well designed for such clumsiness, I took the service manual and opened up the amp to do some investigations, altough I have a rather limited knowledge of electronics.
I started with adjusting the output offset voltage because the manual told me so. But there I immediately found a/the problem, because there was no way the difference between Pin 1 and 3 on TP001 was going to be less than 100mV. Best I could do was about 1V. The adjustment on TP002 however was a piece of cake.
After some hours of checking, measuring and looking at the schematic diagram, I started thinking that the two opamps which you can see in the image just beneath TP001 and TP002 cause the problem.
They both reveice 16.6V on pin 4 & 8. Then on pin 2-3 (R-ch opamp) and pin 5-6 (L-ch opamp) they receive 0.0016V. The output on pin 1/7 (L-ch) is 10.5/9.6V and on pin 1/7 (R-ch) is 0.002/0.001V. That appears to me to be a too big difference.
The bottom of the circuit boards look very nice, all solderings look great. I do not know where else to look, but I see no reasons to assume there are other defective parts. So I have a few questions actually:
- Am I right that the L-ch opamp is faulty?
- If so, how is that possible?
- If not, than what might be the problem of the impossible volume control?
