I was really curious how this amp should perform and how it could have performed when it was new. As the circuit is simple, I have put it into MicroCap, trying to keep parts as close as they were.
This is the schematics
and it was designed by a competent circuit designer. R4+C2, R27+C9 and C6 make very interesting and perfectly working frequency compensation. Small signal frequency response looks like this
It is wide and flat. Remember I speak about the power amp section only, without bass/treble eq.
The idle current is quite low, due to simple bias circuit with 5 diodes in series. This is the point that might have been grossly improved. Because of the low idle current, distortion is rising at low power. However, the value of distortion above 100mW is fully acceptable.
In this distortion/power simulation, please take into account that ideal voltage sources are used to supply the amp.
I will investigate the PSRR as well, and I expect it will not be as good as these basic parameters.
I am pretty sure I would be able to re-create this power amp section of the Locanthi amplifier, with new PCB design and parameters close to the original.
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EDIT: PSR below. It is good at middle and high audio frequencies, but deteriorates at low frequencies.