A stereo amplifier.
Yes. Well, think of it as a bulked-up headphone amplifier. The design is one of those "ah, I should have thought of that" moments, but the details are quite tricky, as usual.
If the extend the basic "voltage stage + current buffer" topology of the 47 Labs 0147
headphone amplifier out to 40 wpc territory, you end up with the 0347.
The high power means than unlike the headphone amp design you have to run it out of class A, and that means closed loop operation.
While most people might be tempted to wrap the voltage feedback around the whole shebang, this basically ends you up with a big op amp. Op amps, with their massive negative feedback design, are not so happy driving high inductance/capacitance loads like speakers.
The trick 47 labs uses is to have two feedback pathways, with heavy "local" feedback around the op amp and a small secondary...