Audio Database

SU-7700
Commentary

A pre-main amplifier with a side terminal structure to realize a straight circuit structure.

The terminals are directly connected to the printed circuit board without wires, and input signals are directly input to the circuit.
In addition, the side terminal layout enables straight transmission.

An IC configuration is used for the equalizer circuit. The first stage consists of differential amplification of a current mirror load, which can select an operating current with very little noise, and the output stage consists of an emitter follower with a constant current load.
The noise level is reduced because the gain of the first stage is large.
In order to obtain accurate frequency characteristics, a metal film resistance of ± 1% deviation and a polypropylene capacitor of ± 2% deviation are used for the equalizer element.

In the first stage of the main amplifier section, a differential amplifier is composed of a pair transistor of one package, and it is operated by the current mirror load. In the first stage, a high gain is obtained with low distortion, and the negative feedback by NF technology is being promoted.
A large-capacity transistor is used for the power transistor at a complimentary service to achieve low distortion and low noise.

Equipped with a protective circuit and muting circuit using a relay to suppress noise when power is turned on/off.

The power supply section employs a newly developed high-density winding transformer in which a coil is wound densely in a small space by applying technology to the winding. As a result, it has a large volume-to-weight ratio and high output efficiency. It also has excellent regulation and low leakage flux. It uses an electrolytic capacitor of 10,000 μ F.
A constant voltage power supply of ± 2 power supply using a transistor or Zener diode is used for the preamplifier section. In addition, the common emitter power supply of the first stage differential amplifier of the main amplifier is supplied with a constant voltage using a Zener diode to enable stable amplification.

Equipped with a subsonic filter using NF loop of equalizer circuit.

The separate selectors for the tape monitor and recording mode allow other sources to be played during dubbing.

Volume uses a 41-point step type.

A newly developed volume is used for the tone control, and the signal circuit is disconnected at the middle point of the knob. In this position, the signal circuit is only an equalizer amplifier and a power amplifier, and the circuit structure is very simple.
The tone control circuit uses the NF circuit of the main amplifier.

Equipped with a high filter.

It is equipped with an output direct-reading power meter that adopts germanium diode for rectification and improves linearity at small output.

Model Rating
Type Stereo pre-main amplifier
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
<General>
Pwer 100 VAC, 50/60Hz
Power consumption 122W
External dimensions Width 410x Height 140x Depth 315 mm
Weight 7.2kg