Thank you Steve for helping me to understand this better. I now wonder how TVC designers must handle this trade-off between galvanic isolation and EMI/RFI. For it seems that if the input/output grounds were not tied together, then EMI/RFI would dump into the transformers, and contaminate the signal. But if the input/output grounds are tied together, then no galvanic isolation, and thus ground loop opportunities that can also contaminate the signal. Does this reasoning/question seem valid?
Well, usually high impedance transformers will use a Faraday shield between the primary and secondary windings to help keep RF from coupling across it via the interwinding capacitance. Not sure if the various makers of TVCs are doing this or not...
Thanks Steve for the info and the Jensen link, I put some reading time there. Let's see if I have this correct: If the input/output grounds of a TVC were
not tied together, then its input jacks and cables (which act like antenna) will pick up RF, direct it right through the transformers, and onward to the amplifier as noise. But if Faraday shields were used between the windings, this problem would be eliminated. Is this correct?
...Don't know what the TVC in the Prometheus is rated at, but S&B recommends no more than +20dBu (7.75V) above 40Hz and no more than +14dBu (3.875V) at 20Hz for their TX-102... With magnetic devices, whether TVC or AVC, core saturation at low frequencies becomes a limiting factor...
From the FAQ section of the Promitheus Audio website:
Maximum input Voltage of our TVC
All our TVC are tested in house at the voltage of 7.5vrms. They are design to take up to 20Vrms. Why do we need such a big factor when it used for a line level of only 2Vrms. Music is not just made out of continuous sine waves instead they are made up of complex sine wave and rather sudden transients like the triangle. This transients can output very high output for a short period of time. We design our TVC in a way that they do not limit any transients. Another reason for over sizing our TVC is allow full body bass just like an active preamp would have with no apparent bass thinning out. This info is not frequency-referenced, and I don't know if this info pertains to the new balanced version of the Promitheus transformers, or only to the previous unbalanced version.
choariwap: If this info does apply to the balanced transformers, then it seems you could simply set your Benchmark into non-variable mode (disabling the front volume dial), dial-back the fixed trim-pots (on the back of your Benchmark) just a tiny amount, and this should work very well with the balanced Promitheus TVC...
