Accuphase P-300X (P300X, not P-300/P-300S) schematic wanted

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Last edited:
images level meter control PCB
 

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images power amp PCB and power supply PCB for the front end unit
 

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Sorry for warming up an old thread. The PCB shown in post #5 is one of four types i've encountered. Maybe there are more, guess this amp was hugely successful and hence went alterations during active production period.

The first two iterations have the black/clear relay, the one in patrick101's post has the connector block near Q16/Q22, the other one has not. A third one has a connector block near C12/C13, the 2nd one just a hole that lets the cable pass through for handwired joints on the solder side of the PCB.

A later PCB has the second pot (offset) eleminated. An even later one carries the red NEC relay which seems to be more reliable (also used in quantity inside P-300L/P-300V). Oops, maybe these were five types already.

My guess is that the threadstarter's P-300X had a complete module exchange at some point for the 2nd last version PCB with just the one bias pot, but still the earlier black/clear relay fitted.

The circuit diagram in post #7 lacks R31 at Q12 collector (10R, same as R30), and shows 150R for R34, where i have always seen 56 Ohm.

I also note that earlier P-300X don't have those 3 parallel resistors R9/10/11 on the driver psu pcb carry quite so much current (no board discoloration). Some later P-300X even have an extra large hole in the beauty-cover to allow that heat getting away. Not a great success in most i've seen, the top lid is just a few mm away

Nice amp otherwise, very full-bodied, maybe even a bit on the warm side of neutral. Great for otherwise lean-sounding setups !
All the best,
Ralph