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The AU-317 amp schematics - thoughts and any room for improvements
The AU-317 amp schematics - thoughts and any room for improvements
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Old 18th October 2015, 08:25 PM   #1
Karl vd Berg is offline Karl vd Berg
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Default The AU-317 amp schematics - thoughts and any room for improvements

The Sansui AU-317 power amp design/schematics (50W/8Ω)

It's been a favorite amongst (vintage) commercial amps and the original design is from 1976.

I'd like to ask your thoughts on this design and how this amp could sound if rebuild with more modern parts (now every original semiconductor is obsolete), if it has room for further "improvements" (mods/tweaks) and a comparison with a DIY project in the similar range (50-75W) class AB amplifiers.

Here, we have the power amplifier section:

Click the image to open in full size.

And below, the power supply:

Click the image to open in full size.

Full schematics in GREAT resolution > here <

Power output: 50W into 8Ω / 72W into 4Ω
THD: 0.03%
Slew rate: 40V/μS
Freq. resp.: DC to 200,000Hz
Input Sens./Impedance: 150mV, 47kΩ

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Old 18th October 2015, 08:34 PM   #2
Karl vd Berg is offline Karl vd Berg
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Another picture with a few waveforms:

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Old 18th October 2015, 09:02 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Recap all electrolytics, and leave the rest alone.
But if it seems to work fine, don't do anything.

rgds, sreten.
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Old 18th October 2015, 09:06 PM   #4
stoN_Cold is offline stoN_Cold  Serbia
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Old 18th October 2015, 09:06 PM   #5
Karl vd Berg is offline Karl vd Berg
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Thanks, sreten.

This means that it is an awesome amp.
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Old 18th October 2015, 10:10 PM   #6
Lazy Cat is offline Lazy Cat  Slovenia
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Just recently upgraded Technics SE-A5, could not stand its original performance. Now playing very well but still miles away from my latest FO iteration. At least five major things to Sansui's VFA topology you've presented can be performed to improve sound substantially.
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Old 18th October 2015, 10:34 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

Suggest any of the at least 5 "improvements" that
is practical and cost effective or simply shut up.
Start with the most practical and cost effective.

rgds, sreten.

For substantial amplifier gains the original must be poor.

Last edited by sreten; 18th October 2015 at 10:36 PM.
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Old 18th October 2015, 10:35 PM   #8
Karl vd Berg is offline Karl vd Berg
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Quote:
Originally Posted by Lazy Cat View Post
... At least five major things to Sansui's VFA topology you've presented can be performed to improve sound substantially.

1. Power Supply mods?

What else?
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Old 18th October 2015, 10:43 PM   #9
Lazy Cat is offline Lazy Cat  Slovenia
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All five changes to front-end topology, still remaining VFA but improved substantionally soundwise. Power supply, recaping and similar mods are meaningless. Below SE-A5 and FO.
Attached Images
File Type: jpeg image.jpeg (548.7 KB, 209 views)

Last edited by Lazy Cat; 18th October 2015 at 11:00 PM.
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Old 18th October 2015, 11:48 PM   #10
ostripper is offline ostripper  United States
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No specifics , Cat ?

I know some (my Z3900 sansui) ---> GLA and kypton V.
Same basic 70's Japanese IPS.

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