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Sansui AU-999 restoration and enhancement

16 posts in this topic

I'm about to embark on a thorough restoration and re-working of a very clean AU-999 on behalf of a fellow SNAer. :)


All of the parts have been acquired, including Nichicon Super Through top-of-the-range filter caps, Elna Silmic IIs for the preamps and signal path locations, Nichicon HEs for the power supply, Nichicon ES for the bipolar caps, some Panasonic ECQV film caps to replace the 1uf electrolytics and below, and some AXON polypropylenes for bypass duties. The troublesome 'flying saucer' transistors will also be replaced with new equivalents.


In addition, a bunch of new metal film resistors will find their way into a few critical locations. A few techs on Audiokarma have identified deficiencies in the original preamp circuitry, bass EQ circuit and subsonic filter circuit, and minor mods to these circuits make a tangible improvement in clarity and bass extension, whilst also ensuring that gain levels throughout the amp are better matched.


Apologies for the initial crappy photo, as my main camera was misplaced during our recent move.


I'll provide ongoing pics of the restoration process, including some pics highlighting the build quality of these older amps. There are several nice touches like prope resistor ladder stepped attenuator controls for the bass, mid and treble, as opposed to standard potentiometers.






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Those "Super Throughs" are a work of art - I bought 4X10,000uf for a project that never eventuated. I still take them out of the box and marvel at them though haha - nice choice of components :)

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Yeah, they are beasts and very nicely made indeed. I've used the normal 'Gold Tunes' extensively, but this is the first time I've used 'Super Throughs'.

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Ha, SuperThrough, gotta love Japanglish for some odd combos.

They look great.




According to the datasheet, the Super Through offers "the highest tone quality grade by the low drag the gold plating terminal adoption".



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Will be watching this with interest, particularly the tweaks to the bass response. We will have to have a shoot out with my partially tweaked 999.

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According to the datasheet, the Super Through offers "the highest tone quality grade by the low drag the gold plating terminal adoption".



Wow is the ultimate! Sweet adopting sound for the ear friends! Amplification wonderment for joy and leisure.

(just getting into the spirit of things)


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A quick update.

Top cover removed:


The resistor ladder networks for various controls are very cool indeed!


Many of the boards are mounted vertically and fit inside slots on the chassis, making this amp quite easy to work on.


Original grey Elna caps:


New Elna Silmic II caps:


The caps on several boards looked fine when viewed from above, but when removed from the PCB, there are clear signs of leakage. Three capacitors were found in this condition, and many had seals which had not yet leaked but were in poor condition. This is the reason why you simply cannot judge the condition of vintage gear based upon a cursory glance, as everything looked fine from above. Put simply, any 30+ year old capacitor is simply well past its used by date!



Nichicon HE caps fitted in power supply locations:



One of the original filter caps in-situ:


A comparison of the original Elna cap with the new Nichicon Super Through cap. These are one step up in both voltage and capacitance, and are a direct fit for the original 40mm diameter clamp:


Nichicon cap installed:


Next up are further capacitor replacements, wholesale transistor replacement on several boards to remove all germanium transistors, resistor changes to fix gain issues in the preamp stage, disabling the 'crowbar' protection circuit, modifying the subsonic filter circuit which affects bass response, and the installation of binding posts in place of the original spring-style speaker wire connectors.

In other words... plenty of stuff to be done, but we're getting there!

Watch this space! :)

Edited by pete_mac
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Nice work so far!!!


Watching with interest, I still have to do a bunch of stuff to my 999.

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Another update.


The subsonic filter and crowbar protection boards have been removed, with the signal-carrying wire which previously connected to the subsonic boards now neatly soldered up to the connecting sockets for the plug-in boards. This removed some surplus wiring. 


The removal of these two tagboards has opened up the underside of the amp a bit more. Not quite as much of a rat's nest! ;)









Also... we have binding posts!!  :banana:





How did I get to this point? Well, I had a bag of smallish binding posts which appeared as though they'd screw into the holes left once the original push terminals were unscrewed and removed. I just needed to try and see if my theory held true.


The following pic shows one set of binding posts screwed in, and the old set of push connectors to the right hand side. To remove these, we snip off the metal solder tab and remove the fastening screw. This allows the push connector to be slid out completely, leaving us with a hole as shown in the second pic below. The shaft of the binding posts are the same size as the remaining hole, but the thread is slightly larger. This means you need to slowly screw the binding post into the rear panel and apply some gentle force at the same time. The benefit is that the binding posts are rock-solid.







One set completed! You will note that I've had to use both of the poly bushes on the front of the binding post to space them out enough. Otherwise, the keyed section of the binding post fouls on the hole in the rear panel. I installed binding posts the same way on an AU-101 recently and they look decent enough too.





Old vs new:





I note that the hole which accepts the speaker wire on these new binding posts is quite small - in fact, nigh on identical to the original push connector. The posts are also very close to each other, all but ruling out the use of bulky spade connectors. Banana plugs are the connector of choice.





Fixing nuts and split washers installed, and wiring installed and soldered up. I had to install new wiring for the negative binding posts as the original wire was too short to reuse.





She's slowly getting there! More recapping to be done, along with transistor replacements and also the resistor swaps for the bass and preamp mods.




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Certainly a tight fit with those binding posts. Be great if there was such a thing as offset binding posts wouldn't it.

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Ok, she's done!


All transistors (apart from the outputs) have been replaced.


Kevzep's preamp mods have been undertaken, along with the bass EQ mod and the deletion of the crowbar protection circuit and the subsonic filter circuit. 


The bias was set quite low (8mA) and is now set as per the required 28-32mA in the service manual.


The result is a very clean and detailed sounding amp, with a really nice tone to it. It has seriously made me reassess my expectations of what the very early Sansui gear is capable of. I hope to have a longer listen during the week.


I'm impressed and I hope that the owner will be impressed too! This is now one of the most thoroughly restored and tweaked AU-999s in Australia (if not the world) and one of the best sounding too. 



















Edited by pete_mac
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Fantastic thread and pics.Kudo's to you Pete.

I'm a luddite when it comes to electronics, but your explainations with pictures make the process you go through relatively easy to follow.

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Thanks mate, I appreciate your comments!


Ok, the 999 has a few hours under its belt now, and I've put it through its paces in my main system.


She sounds very nice indeed! Compared to my AU-X701 the midrange is more forward, and I believe there's less detail and a less defined sound stage. The bass extension is very good (no doubt helped by the removal of the subsonic filter circuit which is more of of a hindrance than help) and the tweaks to the preamp circuit mean that you can crank the volume right up and avoid the early clipping that plagues the standard 999. The bass EQ mods also mean that you can really rock the house with a few clicks of the bass knob if you are that way inclined. FAR better than the mild original EQ slopes.


Overall, it's a very impressive sounding amp and I could very happily have it as my main amp. It's not necessarily better or worse than my AU-719, AU-X701 etc... just 'different'.


The 999 is in the foreground and the 701 is giving it the evil eye from behind:



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