Still digging out from some personal issues, but I'll try to help as I successfully completed my unit, and it sounds really fine. I am by no means an expert, but I have some nice test gear, and was able to look at multiple waveforms and Voltages simultaneously.
First, I could NEVER get the unit to put out unity gain without doing some extreme things to values. My solution was a 1:2 output transformer, and that works.
Second, I modified the bypass board so that the "electronically balanced" option on the bypass switch used the chip input, but the output is going through a big honkin' Jensen 123 transformer. The switch works like this, up position, Zutt input transformer, Carnhill output. Mid position hardwire bypass ("bypass-I don't believe in it"). Down position chip balanced input, output through Jensen 123. Additionally, I used a by-color LED so that up showed red, and down showed blue (the blue is TOO bright. Gonna have to fix that). I need to add that the "Festoon" (?) lamps for the meters draw a LOT of current. That combined with switching 6 (?) relays required a MUCH larger power transformer than I thought. The result was regulator starvation hum until I changed it out.
One of the "tricks" I discovered the hard way is that the differential transistor pairs need to be matched along with the diodes. I went through more than 20 types, and measured over 1000 diodes. I set up an "automated" test procedure with my AP DCX-127 that would step the diodes, and then imported the measurements into a database program, then sorted to find matches. Out of 100 diodes (that's how many I usually bought of one type), I could get 8-10 pairs that were really close matches.
More later.
Best,
Bruno2000
