LUXMAN   vintage audio

Sansui AU-666 integrated amplifier

 

General: 

This amplifier produced in the early 1970s by Sansui Company inc. Japan .

 

Photos:

front ^

Front detail ^

 

> Brochure of the Sansui AU-666 click here

 

detail back ^

 

 

Bottom view ^

Original interior view with main pcb ^

 

RIAA phono pcb updated ^

 

power on ^

 

The power supply pcb updated ^

 

pcb of the power amp and the heatsinked driver transistors ^
 

Tone amp pcb ^
 

Special futures:

This amp was well known by audio enthousiasts, it has the mid-range tone control, very typical for this AU amplifier range of Sansui.
All High quality amps of Sansui made in that time frame are equipped with mid-range tone control.

Old broken power transistors ^

New Toshiba power transistors ^

 

Schematic:

Click here to see the main AU-666 schematic diagram in PDF format

Click here for the user & service manual of the Sansui AU-666 in PDF format

 

The original power amp pcb not modified ^  and the RIAA phono pcb not upgraded >

 

The new speaker protection-circuit: sitting on the place of the old crowbar pcb, fully wired and operational, with green power led and wiring to the blue "OK" led. ^

 

Modifications:

Exchange the crowbar-circuit pcb for a better and more modern DC-offset protection-board as on the photo.
Sansui has a habit to wire amplifiers with too long wiring, in this AU-666 its advised to shorten many wires.
Most electrolytic capacitors can be replaced. The driver transistors can get quite noisy, they can be replaced by
modern drivers. The driver section of this amp should be changed to let the amp work correctly.
The power amp input transistors can be replaced by modern input transistors when the amp starts producing noise,
a 2SA1015 or a BC560C & complementary will do the job ok.
The diodes of the power supply should be replaced by modern >100V 10A diodes.
Coupling capacitors in the signal path should be replaced.
There are some electronic design flaws in this amplifier: you should be aware of this, but:
If you are familiar with electronics and amplifier design and amplifier building principles,
you will be able to make this to a very good HiFi amplifier with outstanding specs
and very good sound, even lift it to a higher level and outperforming many competitor amps.
(There are many tricks that the electronics expert knows to get the most out of an AU-666).
This amplifier is worth updating:

Heatsinking should be checked and set correctly when you upgrade this amp, the power transistors can get hot.
The Mitsubishi 2SC871 may suffer from silver creaping disease, you may replace these transistors.


2SC871 ^

 

The blue LED shining through the hole of the Treble knob, it shows that the protection-cuircuit is operational and DC offset is ok. ^

 

Sound:

The sound of this AU-666 is powerful. When you do the upgrade right, this amp will be capable of 2x 44 Watts RMS output power.
This amp has more power than the AU-555A and has cleaner sound at higher levels.
Its obvious when listening to this AU-666 that the electronic technology inside is more modern and better than in the AU-555A.

These Sansui series of audio components soon got legendary by their outstanding build quality and extra features and good sound.

 

 

Hans Hilberink - PE1MMK - 2003, Last update: 10-11-2019.