I would like to add from the excellent post of Kgturner above with regards to repairing the Supratek preamps. I read that the unit can be send to Kevin Covi in Upstate NY for repair as well. I hope that someone can confirm this.
Also, when I was having a paranoia regarding the channel imbalance of my preamp about 14 months ago, Mick sent me a schematic (plus phono)with info on the test points and levels to be measured. I measured all the voltages spot on. I found out that it was not the preamp responsible for the problem that I noticed after all and was able to isolate it to the source being use at the time.
rgds
Also, when I was having a paranoia regarding the channel imbalance of my preamp about 14 months ago, Mick sent me a schematic (plus phono)with info on the test points and levels to be measured. I measured all the voltages spot on. I found out that it was not the preamp responsible for the problem that I noticed after all and was able to isolate it to the source being use at the time.
rgds