Marantz PM-15
(november 1994 - 1998)

Not to be mistaken with the current PM-15S1 - this is the ORIGINAL PM-15.

All elements that make the PM-15 are either copper-plated diecast aluminium or... copper-plated diecast aluminium. The chassis base is that at 3mm thickness (!) while the front, sides and knobs are extruded aluminium. The 600VA transformer is fully shielded with a copper foil and most of the other elements -power transistors, caps, chassis separations, etc-- are... copper-plated. The PM-15 makes for a massive amount of copper: 32kg :-)
At the center of Marantz technology, then, were HDAM modules: Hyper Dynamic Amplifier Module. HDAM modules are op'amps built with discrete components: 2 FETs, 5 bipolars, 4 diodes and 10 resistors all rolled into a copper enclosure.
The phono stage uses discrete componentry in its first srage and HDAMs in its second ; the XLR input's buffer uses HDAMs with ten FETs around it ; the preamp stage is configured as balanced DC servo. PCBs aren't double-sided but of the 70µ kind just the same.
The volume pot is a 3,3cm diameter 4-gang from Panasonic structured like Victor's JP-S7 (among others): acting on input gain and output level at the same time for better linearity at low levels and even less noise. Added to the power supply is a "CCNE" circuit: a cap and precision resistor are added between the power transformer and the rectifying diodes and shielded into resin... The two beer-size cans are 22,000µF/80V ELNA caps made for Marantz. Output stages are HDAM driven, of course, while the output devices consist of two pairs of Sanken bipolars per channel: 2SC2292 and 2SA1216 (Pc=200W / 180V / 17A). Like all the amplifiers from the eries (PM-99SE, , PM-90, SM-80 etc), the PM-15 works in Class A/B so the first 20 or 30W per channel are in full Class A.
Click the buttons below for the main schematic and more detail views !

Look-wise a little heavy on heaviness (far more elegant however than Marantz' current "designs"), sound-wise the PM-15 is... perfect. I for one don't see any reasons to go beyond this level of quality - State of the Art as they say.

Now, abouth that other, more recent, PM-15, if a glance at the guts of it tell more than many words, there is another way to look at this evolution: between 1993 and 2007, the price of copper has quadrupled and that of aluminium has tripled. Simply put: building a PM-15 the way it was built in 1994 just isn't possible anymore.

The original PM-15 was in the supreme league - and it still is.

The images for this post come from a very detailed but badly printed october 1994 japanese catalog. I probably have a less blunt and frontal view of the PM-15 somewhere...