Is a stereo amp, when bridged to mono, by definition differential?

Thank you Al,

I’ve always wondered how Clayton Audio gets 300 wpc class A into 8 ohms from a relatively small chassis/amplifier, albeit robustly built. I guess part of the answer is a fixed bridged design with 2 x 75 watt class A amps per channel. If power draw in high bias is indeed 800W, perhaps it truly delivers class A performance into 8 ohms but partly class A/AB into 4 ohms?  If one can build a class A amplifier of considerable power using bridged design (with the needed robust power supply and build parts), allowing for a much smaller amplifier, is this design any less desirable sonically than a non bridged class A amplifier such as Pass, Gryphon etc with considerably larger and heavier amplifiers? Manufacturers that have gone down the fixed bridged monoblocks design, not all in class A like Clayton, include Steve McCormack’s DNA 500, all Constellation amplifiers and Naim Reference Series, amongst others.
Thanks so much!

Some of the best amplifiers I have seen were unbalanced input but fully differential and complementary and direct coupled once past the input stage. One of the best I ever heard was a 'build it yourself' kit that was available many years ago thru "popular electronics" magazine. I had a couple of those amps for a while until a loose wire shorted the output and caused a chain reaction that took out every transistor in the chain. I fixed it at an expense greater than was reasonable but moved on pretty quickly to something less inflexible with regard to load impedance. :) Still, that was a fine sounding amp in its day. Today I don't know how well it would hold up against modern designs.