Rare (outside Japan) integrated amplifier launched alongwith the POA-S1 monster : same circuits, same output transistors, same no limit construction.
Except here it is all in one enclosure, therefore a bit cheaper, a lot cheaper... at 400,000¥ !
Inside is (was) some of the old and some of the new : old is the circuit structure and simplified power stage, new is (was) the UHC-MOS MOS-Fet power devices which were sourced from Hitachi, alongwith the related pre-driver circuit design and, apparently, an evolution of a Hitachi-patented circuit for the output section.
Copper rails, copper plated feet and bottom plate, quality 4-gang attenuator, sand-cast aluminium frame which includes the main heatsink (even Marantz didn't go that far in the contemporary PM-15 or sm-5 !) on which everything is directly bolted : power supply and output stages.
The preamp stages are isolated above on a single dual-mono PCB. Sand-casting, with the addition of a special powder in the process, allows to delay the transformation of vibrations into heat dissipation...
The phono stage, a soon to vanish feature in 1993, is powered by a 2-stage constant voltage supply and completely absent from the circuit when turned off.
Better yet : again, all about the POA-S1 can be read here - in french.
The UHC-MOS and circuits apply to the PMA-S1 as well.
Do use the Google translation tools for the ultimate meat on the circuits of these ultimate Denon monsters. This review is complete with measured specs, tests, all circuit descriptions and diagrams aplenty - read it !