If you have a differential input with any kind of decent Common Mode Rejection Ratio, the input transformer is really just a formality, serving nicely to limit RF input, which can wreck havoc on class D systems.
In most solid state and vacuum-tube balanced differential setups, as much care should be taken as possible to limit RF out-of-band intrusion as possible (of course, this is true of single ended circuits as well- RF isn't good for **anybody**).
What happens is out-of-band for balanced also means that it may not be balanced anymore either. Rectified RF can thus be amplified, just like in SE circuits. This is avoided by chassis work that shields RF (aluminum rather than steel), proper grid/base/gate stop resistors, proper grounding and proper B+/Vcc/Vdd bypass, just like in SE.
RF frequencies within-band will be rejected, just like high frequency AF noises (like from a power line or motor).
There are fully-differential true balanced line high end audio products. Since 1985 all Atma-Sphere products have been fully-differential and balanced in every aspect from input to output. Our MP-1 was introduced in 1989 and appears to be the first balanced line preamp made for home audio use.
Davemitchell,s post above on 04-04-08 is spot on.
In most solid state and vacuum-tube balanced differential setups, as much care should be taken as possible to limit RF out-of-band intrusion as possible (of course, this is true of single ended circuits as well- RF isn't good for **anybody**).
What happens is out-of-band for balanced also means that it may not be balanced anymore either. Rectified RF can thus be amplified, just like in SE circuits. This is avoided by chassis work that shields RF (aluminum rather than steel), proper grid/base/gate stop resistors, proper grounding and proper B+/Vcc/Vdd bypass, just like in SE.
RF frequencies within-band will be rejected, just like high frequency AF noises (like from a power line or motor).
There are fully-differential true balanced line high end audio products. Since 1985 all Atma-Sphere products have been fully-differential and balanced in every aspect from input to output. Our MP-1 was introduced in 1989 and appears to be the first balanced line preamp made for home audio use.
Davemitchell,s post above on 04-04-08 is spot on.