Audio Database

AU-555A
Commentary

The PB series pre-main amplifier has been upgraded from the AU 555, and the contents and design have been renewed.
All stages are composed of silicon transistors.

Uses the SEPP, ITL and OTL systems of pure complimentary service and Darlington circuits that use silicon transistors as power transistors.

In order to avoid adverse effects of electrolytic capacitors on music signals, we use as many direct coupled circuits as possible, reduce the number of capacitors, increase the circuit impedance where necessary, and use Mylar capacitors.
Where electrolysis is absolutely necessary, a Mylar capacitor is connected in parallel to improve high-frequency characteristics.

Bass, Midrange, and Treble Triple Tone Control.
In addition, since it is a click step type control, more accurate compensation of program and room acoustic can be performed.

The preamp section uses specially selected low-noise silicon transistors to reduce the noise.

The entire amplifier circuit from the first stage to the final output stage is composed of NF amplifier, and frequency characteristics, distortion and S/N are improved.

The preamp section and main amplifier section can be separated.

The main amplifier and preamp power supplies are equipped with independent ripple filter circuits.
This completely shuts off the hum components and stabilizes the power supply.

Equipped with two speaker outputs.

It is equipped with functions such as NF type low filter, high filter, loudness control, tape monitor circuit for simultaneous monitoring during recording, headphone terminal, etc.

Model Rating
Type Stereo / pre-main amplifier
Main Amplifier Section
Rated output
Music Power (IHF) : 85W (4 Ω)
60W (8 Ω)
Effective power : 33/33W (4 Ω)
25/25W (8 Ω)
Total harmonic distortion factor 0.5% or Less (Rated Output)
Intermodulation Distortion Factor (SMPTE, 60 Hz : 7000 Hz = 4 : 1) 0.5% or Less (Rated Output)
Power Band With (IHF) 20 Hz ~ 40000 Hz (8 Ω)
Frequency characteristic 20 Hz to 40000 Hz, ± 1 db
Channel separation 60 dB or More (1 kHz, Rated Output)
Hum and noise (IHF) 100 dB or more
Input Sensitivity / Impedance 1 V (Rated Output) / 100k Ω or More
Load impedance 4 Ω ~ 16 Ω
Damping factor 50 (8 Ω Load)
Preamplifier Section
Output voltage Maximum power : 5 v
Rated output : 1 V
Total harmonic distortion factor 0.1 or Less (Rated Output Voltage)
Frequency characteristic 20 Hz to 30000 Hz, ± 1 db
Channel separation (1 kHz, rated output) Phono1 and 2 : 45 dB or more
Tuner, AUX : 50 dB or higher
Hum and noise (IHF) Phono1, 2 : 70 dB or more
Tuner, AUX : 80 dB or higher
Input Sensitivity / Impedance (1 kHz, Rated Output Voltage) Phono1, 2 : 2mV/50k Ω
Tuner : 180mV/50k Ω
AUX : 180mV/50k Ω
Tape Play (Pin) : 180mV/50k Ω
Tape Recorder (Din) : 180mV/50k Ω
Recording Output (1 kHz, Input Voltage) Tape Rec(Pin):180mV
Tape Recorder(Din):30mV
Equalizer Phono : RIAA NF Type
Controls Bass : 30 Hz, ± 12 dB
Midrange : 1.5 kHz, ± 5 dB
Treble : 15 kHz, ± 10 dB
Loudness : + 3 db (10 khz), + 8 db (50 hz)
SWITCH Low filter : 50 hz, -8dB
High filter : 10 kHz, -7dB
<General>
Pwer 100 V, 50Hz/60Hz
Power consumption 130W
External dimensions Width 395x Height 127x Depth 278 mm
Weight 8kg