Korneff 45 Stereo SET Amp Rebuild/headphone modification Project

1x 45 and 1x 6SN7 per channel, 5U4 rectifier

Built for Shaharyar Khan

Completed on 12/10/10

Sharharyar approached me a couple of months ago about getting some work done on his beloved Korneff 45. He initially just wanted to put in a headphone hook-up but we decided to give the amp a fresh start. The amp was severely damaged in shipping as shown in the pictures below. The Korneff 45 has a cult-like following among SET enthusiasts and I can only imagine how many owners this amp has gone through that resulted in such a damage. It's sad, as a builder like myself, to see such a beautiful piece of work get destroyed by commercialism. 

I would choose not to disclose any specifics about the amp (sorry, please don't ask me for the schematic), but if there is one thing I could say about the amp is that the 6SN7 is a great match for the 45. It's a very musical and transparent combo!

The rebuilding process involved tearing everything down and building on new chassis using a reverse-engineered schematic. I took the liberty of upgrading some vital components in the amp, one of which was the coupling caps. Jeff had a pair of Solens for the bypass duties, I personally really don't care for those cheap plastic stuff that only belong in speaker crossovers or guitar amps. Instead, I wired up a pair of NOS Russian PIO caps for more natural and smooth sound. I also optimized wiring paths for even quieter operation. 

For the headphone mod, Sharharyar and I had to do some thinking. I also had to consult with some of my tube buddies for their suggestions and we came to a consensus that the easiest and most-sonically beneficial way to do this was to wire a 100-ohm resistors in series on the hot side of the OPT secondary then strap a 8-ohm dummy load to the ground every time the headphone is plugged in. I did with this with a flick of a toggle switch. The result was stunning. The amp sounds fantastic with Grado RS1 32-ohm headphones. I also added a 100K stepped attenuator as a part of the mod.

Overall, this has been a great project for numerouse reasons. First, I got find out more about Jeff's amp. Second, I found another amp to build for my own, Third, fell in love listening to tubes with headphones. What a way to listen!