Hi, I know this thread is a couple of years old, but I found it by searching for hum/noisy C85 preamp, so others may do the same.
I too encountered the same problems with hum and basically went through same procedures as Sonavor. In addition, I disconnected first one and then the other PSUs, the C85 has two independent PSUs, one for phono and a couple of other stages and one for flat amp and output stage. After disconnecting them one at a time, to my surprise, hum still there with not a lot of change. I then disconnected the DC feeds to each section and hooked in a couple of standalone high quality PSUs, you've guessed it hum still there. One of the PSUs I used had it's own transformer, for the other one I used the windings of the Yamaha transformer after disconnecting it from bridge rec. At this stage I thought there could only be one explanation why hum still persisting, the transformer. I removed it from the enclosure, fortunately the leads were long enough to facilitate this and hey presto, hum gone. I'm not sure if this was a bad example of tx or if this is typical of the C85s. I had been blaming my Power Amplifiers for the hum, but after swapping a couple over and then using a pair of quite sensitive active speakers, to my surprise I found it to have been the preamp all along. I then decided to take things a little further and built an outboard PSU using 2 high qualty transformers, 2 high quality power supply/regulator boards ( upgraded some signal caps as well)and it now sounds fantastic. No hum whatsoever. Hope my long ramble will be of assistance to someone out there.
I too encountered the same problems with hum and basically went through same procedures as Sonavor. In addition, I disconnected first one and then the other PSUs, the C85 has two independent PSUs, one for phono and a couple of other stages and one for flat amp and output stage. After disconnecting them one at a time, to my surprise, hum still there with not a lot of change. I then disconnected the DC feeds to each section and hooked in a couple of standalone high quality PSUs, you've guessed it hum still there. One of the PSUs I used had it's own transformer, for the other one I used the windings of the Yamaha transformer after disconnecting it from bridge rec. At this stage I thought there could only be one explanation why hum still persisting, the transformer. I removed it from the enclosure, fortunately the leads were long enough to facilitate this and hey presto, hum gone. I'm not sure if this was a bad example of tx or if this is typical of the C85s. I had been blaming my Power Amplifiers for the hum, but after swapping a couple over and then using a pair of quite sensitive active speakers, to my surprise I found it to have been the preamp all along. I then decided to take things a little further and built an outboard PSU using 2 high qualty transformers, 2 high quality power supply/regulator boards ( upgraded some signal caps as well)and it now sounds fantastic. No hum whatsoever. Hope my long ramble will be of assistance to someone out there.
