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AU-X11 Repair attempt.

Thanks to you Rumnarv for your thread and parts listing, and to Hyperion and JOMARK911 for continuing my education. I believe the AU-X11 to have been a key amplifier in Sansui development.

So, if I may generalize and restate the history behind the evolution of Sansui amplifiers. In the not quite beginning there was AU-111 (1965) which was to become the Sansui sound standard followed by the early solid state amplifiers of the XXX series (1967 to 1970), noted for their "tube like" sounds. The goal was to create a solid state amplifier to match the AU-111. Important developments along the way were the diamond differential circuit first seen in the X19 series (1978) and X balanced circuits (1984) such as in the AU-G99X to reduce solid state amplifier distortion. Somewhere along the way Sansui engineers became convinced that the best way to reproduce the AU-111 sound was with fast transistors. While the AU-919 (1978) with its fast transistors and diamond differential circuit was a turning point, the real experimentation occurred in the X series with the initially unstable AU-X1 (1979) and its LAPT transistors, further refined in the AU-X11 (1981), and in the MOS FET models initially introduced in the AU-X111 (1984). I am not sure how the AU-X1111 MOS fits into this, if at all, if the X series is to represent a ground breaking experimental model. At the end, there was the LAPT / MOS FET dichotomy and the reintroduction of the tube amplifiers with the AU-111 Vintage (1999) and the AU-111G vintage (2001).

As far as solid state integrated amplifiers go the AU Alpha 907 Limited (MOS FET, 1994)

http://www.tube-amps.net/Hashimoto_Sound.htm

and the Alpha 907 MR and NRA (NM-LAPT models, 1995 and 1997)

http://www.sansui.us/issues_AU111vsAL907MR.htm

completed this evolution. Actual topological differences between late models may have been limited since, according to czubsi the 907 Limited (MOS FET, 1994) and the 907 XR (LAPT,1993) shared manuals. I'm not quite sure how the 07 Anniversary fits in but suspect, as czubsi states, it was the same as the 907 MR built with more expensive parts but with less power.
In general the LAPT amplifiers had more power than their MOS FET equivalents.

So, I'm 67 years old and hope to retire when I'm 70 and fulfill my dream of learning electronics and general relativity. Someday I will learn to solder and will always wear pants when doing so. Until then please realize that I have no idea of what I am talking about. Best wishes to all.

Marc
 
Yes. Mr Amp8 is really an education. A truly great tech.

I mean...he knows how to find contemporary replacements to FETs that everyone says are impossible to replace. (Well, at least everyone I've asked.)

2sk97 and the 2sk131 for example in his AU-X1 refurbs.
Sadly in his pics it is impossible to see the replacements he uses due to the angle of the photo relative to the new component's position. (Perhaps this is on purpose?)

Also the 2sk97 and the 2sk131 replacements seem to be in a single chip package and not the commonly suggested solution of putting two newer matched components together.

On his most recent X11 work, he does however heat shrink together a pair of mystery components to replace the 2sk129A FETs on the driver boards. On the equalizer boards he replaces the IC chip TL082CP with new chips that ends in a CP, but the rest of the marking seem to have been erased.

Yet it seems Mouser has 5,278 of those TL082s on hand ready to ship.
So no worries there I suppose.
 
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No updates, I've been really busy with work. I go through times where I'm slammed and then get a couple of free weeks back to back. Hopefully I'll get some time to get back on this thing soon.

I'm still irritated about the face, more so than the bent chassis. The chassis can be fixed, no idea what to do about the face at this point. Thats a good example of crappy packaging right there.
 
You could buy another one in japan and use it as a parts unit but its gonna cost a lot

Good luck with the repair:thmbsp:
 
Packing correctly

Rumnarv said:
No updates, I've been really busy with work. I go through times where I'm slammed and then get a couple of free weeks back to back. Hopefully I'll get some time to get back on this thing soon.

I'm still irritated about the face, more so than the bent chassis. The chassis can be fixed, no idea what to do about the face at this point. Thats a good example of crappy packaging right there.
Click to expand...

People who sell stuff like that but fail to pack correctly should be herded into a pit and (...insert your idea of some dark justice here...) !!
 
After a couple of months looking at this unfinished project I decided it was time to get this thing working.

On the back of the heat sinks, I removed the TO3 connectors and reconstructed the circuit with the same bus bars that I used to mount the TO3-p to the front. I used new resistors so that I could keep the connector assemblies in one piece just in case I found some original parts. Here are some pictures.

Just bus boards modified and installed.


Populated with electronics and wired.


Both completed


Both driver boards with replaced components ready for installation.


Finished!! Time to reinstall into the amp.


Got it back together and it passed the dim bulb test. When checking with the DBT, Igot nervous when none of the lights on the control panel came on. I double checked everything and tried different bulbs with the same result. After messing with it for about an hour I said screw it and just plugged it into my 100v converter and fired it up. All the lights came on and it came right out of protection. Whew....

When setting the DC offset and bias current adjustment, I started off using the specs for an AUX-1 because there isn't an AUX-11 manual anywhere and things seem to work well. Pictures are pre-adjustment. The bias spec is 25mv +or-1. These settings seem to be working fine.




Here it is and it sounds GREAT! It sounds more modern and has a clarity that competes with my powered studio monitors. This thing is a beast compared to my 717. Turning the volume knob between 1/4 and 1/2, brings the listening content to level that's not wife approved. One thing I don't like about it is the preamp outputs don't send signal with the integrated setting, so to connect my powered sub I had to use speaker level inputs wired to speaker B on the amp.



I did notice something that kinda pisses me off. When I measured for clearance between the bottom of the heat sink to the bottom cover with the amp apart somehow I screwed my measurements up. I thought I could run my output wiring across the bottom of the heat sink without clearance issue, but I was wrong. The wiring like it sits will not allow me to install the bottom cover. I have to make a decision to change my wiring or modify the heat sink. I guess because this unit is D rated on cosmetics as well as modified I'll just cut notches out of the bottom of the heat sinks to pass the wires through allowing me to install the cover to get it off the cardboard boxes.

To see what I'm talking about, look at the braided yellow, black, and red wires running under the heat sink. Any ideas?


All in all, the repairs were a success! It comes out of protection and sounds really good. Now I can work on restoring the rest of the unit electronically and cosmetically. The board behind the control panel has a lot of the Sansui glue and its starting to corrode the legs of some of the components. Another thing I noticed is the area around that board gets warm, is that normal? At first I though it was the front driver board causing it but its not.
 
This is great progress - well done indeed !

I am afraid I don't have any suggestions regarding the wiring, would it be too much to put longer lengths in? - otherwise your thought about notches seems ok providing it is done neatly (sorry I am a stickler for that).

As I said before this isn't 'an attempt' - this is the real thing! - really liking this thread.
 
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I'm with you on that. I don't like hacked up stuff either. I'll have to look at the bottom again to see if there is enough room to rewire it around the side of the heat sinks. I really don't want to notch them if I don't have to.
 
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