The EAR 834P has an output impedance of ~525 ohms and sounds nice running through John's TVC. I also had George Wright's WPP100C and WPP200C running though the TVC. They both have an output impedance of 2k ohms, yet they sound spectacular. IMO, they were better than the 834P in terms of tonal accuracy and in creating a sense of spaciousness. I often wondered whether I was missing something due to their high impedance, but Jonathan Dunham's tech notes for the TX-102 says:
"At the highest source impedance point the bandwidth may be somewhat compromised and distortion will rise. For the unity gain connection the sensible upper limit of impedance is around 5kOhm, this causing a -1db point of 20Hz. If more attenuation at very low frequencies is allowable (or indeed desired) however, a source impedance of around 15kOhm will result in a -2.7db roll off at 20Hz."http://www.stevens-billington.co.uk/page102.htm
This confirmed what my ears already knew... that a 2k ohm source impedance wasn't a problem for the S&B trannies. My ICs were 1m Kimber Hero's.
John, I'm curious how your new autoformer-based preamp will handle source impedance. Will it be similar to the S&B's?