Marantz PM-6A (circa 1981)

Name: Marantz PM-6a
Brand: Marantz

The Marantz PM-6A is a stereo pre-main (integrated) amplifier from the early 1980s, part of the Esotec series. It was listed at ¥160,000 in Japan around 1981. The big feature is the "QuarterA" system. The amp runs in pure Class A up to 30 watts per channel, then electronically switches to Class AB for everything from 30W up to its rated 120W + 120W into 8 ohms. Marantz developed a high-speed switching circuit specifically for this.

The power amplifier section is fully push-pull DC with a DC-servo circuit. It is a Low-TIM design that uses less negative feedback. The power supply has a resin-filled transformer and dual 22,000 µF capacitors. Cooling is done with a heat pipe system, which makes sense given the current draw of pure Class A operation. Rated power consumption is 350W.

Marantz put extra effort into the phono stage. It has a dedicated MC head amplifier with 13 transistors per channel, running from a 4-parallel push-pull input stage to a SEPP output stage. The MM section has switchable loading of 27kΩ, 47kΩ, or 100kΩ on Phono 1. The equalizer uses 1% metal-coated resistors and 2% polypropylene capacitors. RIAA deviation is ±0.2 dB from 20 Hz to 20 kHz. Signal-to-noise is rated at 86 dB (MM), 68 dB (MC), and 110 dB for line inputs.

A TONE switch bypasses the entire tone amplifier circuit for a cleaner signal path. There is also a two-deck tape copy switch, two loudness levels, and independent tone controls per channel. A wood cabinet (WC-77N) was sold separately for ¥12,500. The amplifier measures 416 x 146 x 332 mm. Weight is cited as 16.0 kg by audio-database.com, though another listing says 9800g (possibly shipping weight).

Documentation on this model is thin. The approximate date comes from the price listing year, and one repair technician notes a unit built in 1982. Enthusiast commentary on forums describes the sound as warm and detailed. Bias adjustment is a known service topic, and one diyAudio thread is devoted entirely to a "PM-6A Bias problem." No original US market price, production totals, or period magazine reviews have turned up in the archive's sources.