Denon PMA-770 (1979–1981)
A compact integrated amplifier with genuine Class A circuitry inside an unassuming chassis.
Overview
The Denon PMA-770 weighs 8.6 kg and measures 434 x 150 x 337 mm. It looks like a modest mid-fi component from the late 1970s, which is what it was. But Denon put something unusual inside: a Non-Switching Type amplifier stage that runs in pure Class A for both channels up to 30W into 8 ohms. That's a real circuit choice, not marketing gloss, and it sets the amplifier apart from the typical Class AB designs crowding the shelves at the time.
Produced from 1979 to 1981, the PMA-770 sat at the affordable end of Denon's integrated amplifier lineup. The engineers still gave it dual independent power supplies for the left and right channels, a direct-coupled power amplifier, and a discrete component phono equalizer circuit. That was a lot of technical sophistication per dollar for a budget-conscious buyer in the late 1970s.
Power output is listed as 2 x 30W at 8 Ohm (hifi-wiki.com, audio-database.eu) or 2 x 38 watts into 8 ohms (Audio Database). It looks modest on paper, but the high-current capability design underneath makes it adequate. The ratings are honest. It drives 4-16 ohm loudspeakers, though it does best with efficient speakers.
Key Features
Non-Switching Type Amplifier
The headline feature of the PMA-770 is Denon's Non-Switching amplifier technology. In conventional Class AB designs, output transistors switch between states as the signal crosses zero, and that switching introduces distortion. Denon kept the power amp section in pure Class A for both channels up to 30W/8 ohms, which eliminates switching distortion within that range. Past 30W the amplifier moves to another mode of operation.
Dual Independent Power Supplies
Rather than sharing a single supply between channels, the PMA-770 uses dual independent power supplies for left and right. That's an architecture you'd expect in separates, not in an affordable integrated. The benefit is reduced crosstalk, rated at 50 dB, and cleaner stereo imaging, since each channel's power draw doesn't modulate the other's supply rails.
Direct-Coupled DC Design
Denon specified a direct-coupled DC amplifier design throughout the signal path. That means no coupling capacitors in the audio chain, so no phase shift or bass roll-off from capacitor coupling. The power amplifier section is direct-coupled too, which keeps the signal path clean from input to speaker terminals. Combined with the high-current capability design, this gives the PMA-770 tight, controlled bass for its modest power rating.
Discrete Component Phono Stage
The PMA-770 uses a discrete component phono equalizer circuit rather than an op-amp-based stage, which contributes to the clarity and low-noise performance the amplifier is known for. Phono input sensitivity is 2.5 mV (MM), with a phono overload margin of 100 mV, so it handles hot cartridges without strain. The signal-to-noise ratio on the MM input is 80 dB (hifi-wiki.com, audio-database.eu) or 75 dB (Audio Database).
Flexible Inputs and Outputs
The rear panel has Phono MM, tuner, aux, and two tape inputs - tape 1 and tape 2 - with tape record outputs. A pre-out lets you bypass the internal power amp if you want to add an external amplifier later, which is unusual in this price class. Input sensitivity is rated at 150 mV for line-level sources, which suits any tuner, CD player, or tape deck of the era.
Historical Context
The PMA-770 arrived while Denon was building its reputation for turntables and professional broadcast gear and refining its consumer amplifier lineup at the same time. The late 1970s and early 1980s saw Japanese manufacturers competing hard on measured performance. Denon's answer was the Non-Switching amplifier topology, a different approach to the distortion problem than most competitors took with ever-higher feedback and more elaborate output stages.
HiFI-Stereo (1982, p.61) presented a new integrated amplifier, the $800 A-1060, which is clearly not class-A but puts forth 140 W/ch over the full audio bandwidth.
Denon positioned the PMA-770 as a compact but technically advanced integrated amplifier. The direct-coupled DC design throughout the signal path, the discrete phono stage, and the Class A operation to 30W all put measured performance and sonic accuracy ahead of feature count. Power consumption is rated at 200W, which reflects the inefficiency of Class A operation at moderate levels.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.
Related Models
- Denon DL-160 (1979)
- Denon PMA-717 (1984–86)
- Denon AU-310 (1975)
- Denon AU-340 (1978)
- Denon DA-401 (1975)
- Eico 3150 (1967)
- Fisher CUSTOM-ELECTRA-I (K-14/K-15) (1957)
- Fisher CUSTOM-ELECTRA IV (E33/E44) (1960)
- Akai AM-2400 (1978)
- Akai AM-2600 (1977)