BJT power amp question (odd design)

[imJonWain]

I'm working on this amp for a friend but am a bit puzzled by the poweramp design.  What's going on here exactly?  I've been trying to wrap my head around it a few hours and am about to model it in spice.

[anotherjim]

I was puzzled by the "amp is driving ground" in a Peavey amp. But you'll also note the speaker is driven by the power rails. As they are "floating" about ground (its own transformer secondary) it pushes & pulls current via ground and the speaker just the same. I don't know why it's done that way, but it must work.

[Mick Bailey]

It's a 'Flying Rail' amp design. The main benefit is the output stage is driven directly off an opamp due to the topology providing voltage gain. Note that there's no differential pair or Vas in this circuit.

[imJonWain]

ahh neato! I realized late last night it was being driven through "0V" but couldn't figure out why one would do that.  The direct drive from an opamp/minimal parts makes a lot of sense now that you mention it. 

[Clint Eastwood]

The opamp that drives the output stage has two leds in its feedback loop, making the output stage clip sort of softly. Quite clever design.