New Yamaha preamp

Hello

My "new" toy. A Yamaha C-70. I had to re-solder the power supply, It runs quite hot and there was a lot of cold joints. I removed the glue of the main PS capacitors also. Seems to work fine...

P.D: Is there any adjustment that needs to be checked?

It appears there are adjustments. You will need to find a service manual.

Of that era of Yamaha preamps the C-70 is probably the heaviest. Those big mechanical relays! However, I don't think they sound as fine as the lighter weight C-80/85. I think the SM is pretty clear on how to dial these in.

Thank you. I have the schematics but I can not find the service manual. I will keep on searching...

I have found a slight difference between channels. The voltage at the input is the same on both channels (measured just before the volume pot), but at low levels, one channel has a few millivolts more than the other. At maximum level, both signals are ok. I can adjust the gain of each channel independently, but if I match the levels at low voltages, then they are mismatched at maximum level (I think that due to the feedback of the “varigain” topology).

I've found the problem: The potentiometer tracking error in this kind of topology.