AU-999 restoration

Yep... ANOTHER AU-999 thread! hehe :thmbsp:

I'm embarking upon a full restoration of a clean AU-999 on behalf of a stereo.net.au member.

I'll be throwing some nice components into this amp, along with the various preamp and EQ mods and enhancements as outlined in various threads on audiokarma.




Top cover removed:




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




I'm loving that 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!

Nice thread Pete,did you check the big power caps value???Does it degrade too?I have told my tech to recapped but not asked him to change the big power cap yet. Thanks for the pictures

I don't have a sufficiently large capacitance tester for caps of this size.

Notwithstanding, 40 year old filter caps are well past their used by date. It's a false economy to restore an amp of this age whilst retaining the original filter caps IMHO.

pete_mac said:

Yep... ANOTHER AU-999 thread! hehe :thmbsp:

I'm embarking upon a full restoration of a clean AU-999 on behalf of a stereo.net.au member.

I'll be throwing some nice components into this amp, along with the various preamp and EQ mods and enhancements as outlined in various threads on audiokarma.


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!

Click to expand...

Nice one Pete.....:thmbsp:

I think I might be buying another AU999 to do up and sell, just because they are fun little amps to work on.....

There are no Germanium transistors in these amps, they are silicon, the CDC8002 and 9002 and the XA495 are all silicon.....
Lucky they are because if they weren't we would have to modify the circuit because germanium transistors require different biasing.....

When I bypassed the sub-sonic filters in mine, I actually removed those tag boards and went right back to the molex connector with the signal cable, it ended up being quite tidy after the unused parts were removed...

I'm keen to see your binding post mod, I am thinking I would like to put some nice binding posts on mine, I was just thinking about it yesterday....

Will be definitely watching your thread with interest Pete....:yes:

Very Nice Pete :thmbsp:

I have always thought these must be nice to work on - the AU-999 and the AU-888 have the same internal construction. Just looking down onto the amp (nice pics) you can see how balanced and symetrical the layout is.

Not seen a binding posts mod to one of these yet, as far as I can remember.... so

kevzep said:

There are no Germanium transistors in these amps, they are silicon, the CDC8002 and 9002 and the XA495 are all silicon.....
Lucky they are because if they weren't we would have to modify the circuit because germanium transistors require different biasing.....

When I bypassed the sub-sonic filters in mine, I actually removed those tag boards and went right back to the molex connector with the signal cable, it ended up being quite tidy after the unused parts were removed...

Click to expand...

An, I had read about them being germanium in a different thread. My bad!

Nice suggestion regarding the subsonic filter. I will most likely do the same thing.

A nice box full of transistors arrived today form skippy124. Hopefully I can make decent progress this coming week.

Very nice work Pete...

pete_mac said:

An, I had read about them being germanium in a different thread. My bad!

Nice suggestion regarding the subsonic filter. I will most likely do the same thing.

A nice box full of transistors arrived today form skippy124. Hopefully I can make decent progress this coming week.

Click to expand...

Yeah, I thought they might have been germanium too at first, so I looked them up to check......Thankfully they aren't....

I think I might be set to pull the trigger on a AU999 soon, so looks like we can flood this forum with AU999 restorations!!.......:thmbsp:

I'm thinking what else we might be able to do to these amps to etch a little more performance....:scratch2:

pete_mac said:

...

Notwithstanding, 40 year old filter caps are well past their used by date. It's a false economy to restore an amp of this age whilst retaining the original filter caps IMHO.

Click to expand...

That's why I never hestate in recapping totally any gear of 35+ old.

One question, Pete: You replaced the original 4700uF with 6800uF. A 44% increasing in capacitance?

Karl vd Berg said:

One question, Pete: You replaced the original 4700uF with 6800uF. A 70% increasing capacitance value?

Click to expand...

Yep, my understanding is that the original bridge rectifier can handle this. Happy to be corrected by those in the know, of course! :yes:

Those who have upgraded to 10,000uf fit a new bridge rectifier. :thmbsp:

Yes, I did a little upgrade in a small amp, two main power caps from 1000uF to 1360uF (2 combined 680uF in series per channel), but the very tiny rectifier diodes I felt I had to replace them as well, to my peace of mind. (Put stronger and faster ones)

Hi Pete,

Thanks for the update...,I have called and asked my tech to change all the power caps to a newer ones.This is a great amplifier,i feel its like 2 * AU 777 in term of sound quality,i realize this after connecting the AU 777 pre to 70 watt Rotel Power amplifier.The sound is very alike. I pass over the AU 999 to other sansui fan because the internal body has heavy rust coated and i am not a guy who can rebuild.

THATS IT !!! selling my 517 and 2245 for a 999 - cant pass up all this modding. If this is a 777 with more power and "bells" then it must be spectacular sounding.

Hoping we can end up with just one 999.mod thread, perhaps even a sticky vs all the scattered info.

1) Sub sonic disconnect
2) protection bypass ?
3) Main filters recommendation with or without bridge rectifier replacement
4) Kevins pre-amps mod
5) ------ Bass Eq mod
6) Jim's low end mod
7) pete's terminal mod
8) Recommendations for flying saucer and signal trannys
9) Cap recommendations pr. section (signal vs. power)

Thanks guys - for sharing all these mods and improvements. Cheers!

stereofun said:

THATS IT !!! selling my 517 and 2245 for a 999 - cant pass up all this modding.

Click to expand...

If time permits, I will compare the 999 to my restored 517 and 719 once the resto is completed. It should be an interesting comparison indeed.

pete_mac said:

If time permits, I will compare the 999 to my restored 517 and 719 once the resto is completed. It should be an interesting comparison indeed.

Click to expand...

This is a comparison I will be interested in hearing about for sure!!

Now, off to find another AU999......:thmbsp:

My guess is '517 blown away, , Marantz 2245 no contest, very difficult to topple '719

As for (my) AU-919 & (my) AU-D11 II - dream on (but then I haven't heard a modified AU-999 yet :scratch2

My guess is '517 blown away, , Marantz 2245 no contest

Click to expand...

Jim from qrxrestore did a great job on my 777a that he said sounded very similar to the 999. So for a little comparison I yanked out the 2245 and a/b'ed against the 999 little brother. The 2245 is nice and amiable - but compared to the 777a it is classes apart. The 777a being significantly more transparent, "full" and energized with the proverbial veil unveiled to the point where the difference is live concert feel vs just listening to a good stereo.

With the 517 - its a closer match - only differentiated by the additional sense of depth and space provided by the 777a.

Hi Kev,

I suggest you to look for a AU777/777A first since we dont have anyone to modify and get the best from this model amplifier yet. It should be interesting because there is only very few users who own this amplifier in AK,if i am not mistaken.,Have you saw one in your place??
Anyway Good Luck for your search for the 2nd AU 999.

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!!




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.

Awesome work! Such a dedication and craftsmanship skills! :tresbon:

Edit: curious to see the TRs replacement in this vintage unit... :scratch2: