Sansui AU-317 amplifier
Modification by Frank Speet

 

General:

At the end of 1978 Sansui company came with its AU-317 amplifier.

 

 

 

Specifications:

• Power output: 50 watts RMS per channel into 8Ω (stereo)

  Frequency response: 5Hz to 70kHz

  Total harmonic distortion: 0.03%

  Damping factor: 70

  Input sensitivity: 20mV (mic), 2.5mV (MM), 150mV (line)

  Signal to noise ratio: 77dB (MM), 100dB (line)

  Channel separation: 65dB (MM), 73dB (line)

  Output: 150mV (line), 1V (Pre out)

  Speaker load impedance: 8Ω (minimum)

  Semiconductors: 51 x transistors, 25 x diodes, 2 x FET

  Dimensions: 430 x 110 x 340mm

  Weight: 9.5kg

  Year: 1978-1982

Back panel, pre-amp and power-amp can be used separate, 2x speaker connection: A-system and B-system ^

 

This old broken AU317 will be subject to restoration ^

 

Owners manual:

not yet available.

 

2x AU-317 main pcb boards, the left is updated: all leads are as short as possible and bound together: no spagetti anymore as on the original right board ^

 

 

Special futures:

The AU-317 amplifier is a well built and very good medium power performance amplifier.

 

 

One amp (left) got very hot, the 2nd only moderate heat dissipation ^ Also the broken power transistors ^

 

Schematic:

Click here to download the service manual of the Sansui AU-317 in PDF.

 

Cleaned power transistors, now we can see the type # ^

 

New capacitors and wiring modified ^

 

Detail of the restoration ^

 

Cleaning the pcb from glue and preparing for the new power supply main capacitors ^

 

Since the original capacitors are not available anymore and we want the new ones to sit tightly on the pcb, we have to invent a new fixation ^

 

This is how Frank gets the new 17,000 µF caps fitting in the pcb ^

 

Modifications:

Sansui applied some type of glue to secure the main ps. capacitors and that glue makes the pcb and parts corroding,
this glue should be taken off the pcb, the copper side can be protected by flux spray.
Frank used in this amp the same plastic power transistors as in the AU-417, that works great: Sanken 2SA1491 & 2SC2837.

After the restore and alignment this is what we get out of the amp at 10 KHz,
on the screen: above the output signal of the pre-amp, below the output signal of the power-amp section. ^

 

Sound:

The sound is excellent.

Final result of the restoration, looks good not? ^

© Hans Hilberink, ON9MMK & Frank Speet, ©® 2019 - Last update: 25-08-2020.