I can see a problem with fully balanced audio amp design that has no
reference to ground. Both outputs can be floating together since
without output current or voltage difference feedback won't react to
that. It needs ground reference somewhere or some kind of servo on
common mode.
Ignoring ground and having a floating circuit are two very different things! Our circuits are referenced to ground but are designed to otherwise ignore it.
BTW if a transformer is used at an input or output (for example to allow a balanced input or output for otherwise single-ended operation) the best way to do it is to not have a center tap, with the winding of the transformer simply tied to pins 2 and 3 of the XLR (the signal pins). Pin 1 is then usually tied to chassis ground. This gets the best Common Mode Rejection Ratio (CMRR). The use of a center tap for ground will degrade the CMRR.
dear Ralph,
is your preamps transformer coupled? (or is it in the signal path or stages?)
btw, may i ask if your preamps are designed with absolute no local, no global feedback in power supply & audio circuit
Our preamps are not transformer coupled- instead they have a direct-coupled output that is balanced and differential. Any DC Offsets are controlled by a simple servo circuit (we went through quite a bit of effort to prevent the servo from being a feedback mechanism in its own right). We obtained a patent regarding this operation. We do not use feedback in our audio circuits (loop feedback or degenerative feedback) although the power supply regulation does.