Technics SU 7700 (1976)

A high-fidelity integrated amplifier from Technics’ SU-V series, designed for precision and low distortion.

Overview

The Technics SU-7700 is an integrated amplifier produced by Technics, a brand of Matsushita Electric Industrial Co. (now Panasonic). Part of the SU-V series, it was released around 1976 with a focus on clean signal handling and robust internal construction. The amplifier features a unique side-terminal layout that enables a direct, wire-free connection between terminals and the circuit board, minimizing signal degradation. Designed for high fidelity, it includes precision components and protective circuitry to ensure stable operation.

Specifications

Power Amplifier Unit Effective output (both channels)	1kHz: 70W + 70W (4 Ω) 53W + 53W (8 Ω) 20 Hz to 20 kHz : 50W + 50W (8 Ω)
Total harmonic distortion factor	0.06%
Output Bandwidth (both channels, 8 Ω)	8 Hz to 55 kHz -3dB
Residual noise	0.6mV
Damping factor	60 (8 Ω)
Load impedance	Main or Remote : 4 Ω ~ 16 Ω Main + Remote : 8 Ω ~ 16 Ω
Preamplifier Section Input Sensitivity / Impedance	Phono : 2.5mV/47k Ω Tuner, Aux, Tape1, 2 : 150mV/47k Ω
Phono Maximum Input (1 kHz, RMS)	150mV
Signal-to-noise ratio (IHF-A)	Phono:78dB Tuner, Aux : 97 dB
Frequency characteristic	Phono : RIAA standard curve ± 0.2 dB Aux : 5 Hz to 80 kHz + 0 -3dB
Tone control	Bass : 50 Hz, ± 12 dB Treble : 20 kHz, ± 12 dB
Filter EQ	Subsonic : 30 Hz, -12dB/oct. High : 8 kHz, -6dB/oct.
Output voltage	Tape1 and 2 : 150 mV
Power	100 VAC, 50/60Hz
Power consumption	122W
External dimensions	Width 410x Height 140x Depth 315 mm
Weight	7.2kg

Design

The SU-7700 uses a pre-main amplifier design with a side-terminal structure that allows input signals to connect directly to the printed circuit board without wires, supporting a straight signal path. The equalizer circuit uses an IC configuration with differential amplification via a current mirror load and an emitter follower output stage with constant current load. Precision components include ±1% metal film resistors and ±2% polypropylene capacitors in the equalizer. The main amplifier’s first stage uses a differential amplifier with a paired transistor in one package and current mirror load. Power transistors are high-capacity complementary types for low distortion and noise. A protective and muting circuit uses relays to suppress power-on/off noise. The power supply features a high-density winding transformer and a 10,000 μF electrolytic capacitor, with a ±2 constant voltage supply using transistors or Zener diodes for the preamplifier. The subsonic filter uses an NF loop in the equalizer circuit. Separate tape monitor and recording selectors allow dubbing while playing other sources. Volume control is a 41-point step type, and the tone control uses a newly developed potentiometer that disconnects the signal at the midpoint. The tone control circuit employs the NF circuit of the main amplifier, and the power meter uses germanium diodes for improved linearity at low output.