Sansui AU-719 recap and restoration

[pete_mac]

Skippy124 (Dad) and I picked up this Sansui AU-719 a while back with a fault in one channel. I've been keen to try one of the AU-719/819/919 series as this is the next generation of circuit design compared to my AU-517 (and the 717) and from all accounts it sounds very good. The 719 is 90WRMS/ch vs 65WRMS/ch for my AU-517, which is not a huge difference. The physical layout is very very similar to the AU-517, but with a simpler control amp section, a more complex/sophisticated power supply board, and the diamond differential circuitry in the driver boards.

We've kept this amp as a long-term project without any great rush to finish it, however I've recently been blessed by the birth of my second son on 22 October, so I'm currently on paternity leave for a few weeks. You know what the say about idle hands, so I figured I should keep myself busy... and what better way than to undertake recap of this beast.

As you can see from the internal shots, the 719 didn't have the same build quality standard as the 517/717 wich were all black inside with internal trim/cover panels etc. The transformers are also bare with no black cladding. I do wish this amp had the same black finish as the others, and I was tempted to strip the whole amp down and paint the chassis... but a painted chassis doesn't make an amp sound any better, so I decided to leave it as-is.

The caps used throughout are Panasonic FC series, Nichicon Muse bipolar, Elna Silmic II for signal path applications, and also some small Panasonic and Epcos stacked film capacitors for the 1uf capacitors. All of the MV12 diodes (same as the VD1212) were replaced with a series pair of 1N4848 diodes, and the notiorious 'black flag' ceramic caps were replaced with silver micas. I also added 1uf 100V bypass caps across the PSU filter caps as per the other Sansuis of this era.

I also replaced the original binding posts with proper 5 way units which allow the use of speaker cables with banana plugs. Thankfully the 719 already has binding posts as standard, so the rear panel has circular cut-outs. This made the retrofit much easier. I also 'cheated' a bit by using small ring crimps to connect the internal wiring to the binding posts. All connections are soldered, and it was a LOT easier and neater than soldering directly to the chunky binding posts.

Overall, the recap has turned out really nicely. The amp will now be taken back to Laboratoire Skip to track down a high gain issue in one channel that was there prior to the recap. Once we have this sorted... time to listen!

[pete_mac]

[little blue penguin]

In the 4th picture on the right hand PCB there is a blue resistor by 2 transistors.

Partially hidden by the blue resistor is a beige one which appears to be charred.

I'd start there in your search.

[pete_mac]

In the 4th picture on the right hand PCB there is a blue resistor by 2 transistors.

Partially hidden by the blue resistor is a beige one which appears to be charred.

I'd start there in your search.

Nice spotting! Thankfully, that's only a bit of the notorious Sansui glue on the body of the resistor. The original 470uf 63v caps are HUGE so the glue is used to hold them secure. I cleaned all of the glue (which becomes conductive and also causes corrosion!) off the PCB and off all metal parts of each component, but didn't bother cleaning the body of the resistor as it would have rubbed off the markings. This conductive/corrosive glue causes all sorts of issues in many Sansui amps - it's really nasty stuff.

We are pretty certain of the issue, but if this fix doesn't work, we will probe each of the driver boards and take down voltages at critical locations and do a comparison. We'll get it sorted one way or another!

Edited November 2, 2011 by pete_mac

[little blue penguin]

That's the beauty of stereo gear. As long as one channel's ok you have a good point of reference.

Happy hunting.

[Guest Muon]

Very nice clean amp Pete

I'll look forward to your listening impressions.

BTW, what type are the big black power supply ones you used?

[pete_mac]

Thanks mate.

The big black PSU filter caps are the original Elna 12000uf 63V jobbies. We will test them and see how they are holding up.

I have four Panasonic TSHA 15000uf 63V caps here ready to go into either the 719 or the 517, but they are only half the height of the originals @ 40mm x 50mm. As a result, they will look a little funny. They should do the job fine though! Otherwise, I could spend $100 for a quartet of Nichicon Gold Tunes which are 40mm x 100mm as per the original caps, but it's a fairly pricey upgrade. Panasonic also have some 15000uf 80V caps which are 40mm x 80mm so a nicer physical fit than the ones I currently have ready to go.

Also, here's a quick pic to compare the build quality of the 517 to the 719. Of course, it's largely cosmetic in nature, but still... the 517 is pure sex in comparison! Let's hope that the 719 can prevail in the sound quality stakes...

AU-719:

AU-517:

[LogicprObe]

Congrats on the new kid and good luck with the amp!

[lebowski]

Great job Pete and good to see another classic Sansui restored. Will be interesting to hear how the 719 sounds compared to the 517.

[Monkeyboi]

I just love looking at and reading about these vintage restoration jobs. Nice work. Keep 'em coming!

Cheers,

Alan R.

[Saxon Hall]

I just love looking at and reading about these vintage restoration jobs. Nice work. Keep 'em coming!

Cheers,

Alan R.

I concur. Those Sansui amps are mighty fine looking units. I have never heard one but if they sound as good as they look they would be sensational!

[Monkeyboi]

I concur. Those Sansui amps are mighty fine looking units. I have never heard one but if they sound as good as they look they would be sensational!

Agreed. I have an AU-417 that's faulty in one channel. When I get around tuit (very rare these tuits are - especially the round ones) I'll lift the lid on it, find out what's wrong with it and get it going again. Got it for $50 with a TU-417 tuner and a Sansui cassette deck. All cosmetically A1 so probably worth resurrecting. The tuner works just fine.

Cheers,

Alan R.

[madamesimplifi]

Excellent sharp photos. Soon I will join the Sansui family as awaiting delivery of a baby 317.

[Guest Muon]

That's a great buy @ $50 Alan, even with the faulty channel

I bet they look real nice in a stack too...

[skippy124]

Excellent sharp photos. Soon I will join the Sansui family as awaiting delivery of a baby 317.

Nice, the 317 is a nice Amp!! There is a maintenance issue with these, I can advise how to check for the problem if you have a multimeter.

That's a great buy @ $50 Alan, even with the faulty channel

I bet they look real nice in a stack too...

Absolutely!! The Tuner alone is worth more than $50. If you need any bulbs for the tuner let me know, the originals are NLA, but I have an alternative that keeps it looking original.

Cheers

John

[madamesimplifi]

Nice, the 317 is a nice Amp!! There is a maintenance issue with these, I can advise how to check for the problem if you have a multimeter.

Thank you for the kind offer.

[Prana69]

Cracking amp Pete. I know the 719 has been a real labour of love, but you guys love a challenge. Most tenacious hi-fi f*ckers I've met!

Great work. Let us know how it sounds.

I take it you weren't able to do a 717/719 comparison as hoped?

Dave

[pete_mac]

Howdy Dave!

Thanks to you for collecting and shipping the amp too. Muchly appreciated

We had a dabble last night, but there is certainly something funny going on with one of the driver boards. We purchased a NOS board from sansui-parts-shop but it's a slightly revised board and it also features a bunch of changes to various resistor values on the board. This could well be the cause of the low gain that we're seeing in this channel. We've thankfully got a plan of attack and will be putting some time aside over the next week or so do tackle this damn board!!

We haven't commenced the 717 rebuild as yet, so the planets may yet align for us! If not, my recapped 517 will be used for the comparison (as it is substantially the same 'amp' as the 717 but with 20W less and a less complex tone control section).

[Prana69]

Hey mate

No worries. Those big Sansuis look drop dead gorgeous with the top popped.

I can't believe you actually have time to work on this stuff at the moment. Shouldn't you be inside changing nappies?

Can't wait for your next report.

D

[pete_mac]

Hey mate

No worries. Those big Sansuis look drop dead gorgeous with the top popped.

I can't believe you actually have time to work on this stuff at the moment. Shouldn't you be inside changing nappies?

Can't wait for your next report.

D

Yep... changing nappies... washing up... recapping amps... fitting bigger swaybars to cars... resurrecting the audio setup for the back deck... all sorts of baby-related shenanigans

[Prana69]

Good to see you have your priorities right.

D

[Ahh- Schnoo Schnoo]

Thanks for the write up and pics. The build quality of the AU-517 sure is impressive under the hood.

Looking forward to your listening comparos.

[Monkeyboi]

Absolutely!! The Tuner alone is worth more than $50. If you need any bulbs for the tuner let me know, the originals are NLA, but I have an alternative that keeps it looking original.

Cheers

John

Thanks for the heads up John. Appreciated. Fortunately they are all still working.

Cheers,

Alan R.

[Monkeyboi]

That's a great buy @ $50 Alan, even with the faulty channel

I bet they look real nice in a stack too...

They do! Something simply elegant about the Sansui panel layouts and the black finish that appeals to me of vintage gear from that era.

I really must pull my finger out and repair the amp. It will be a good excuse to post some pics.

Cheers,

Alan R.

[skippy124]

Touchdown!!!!!

As Pete had noted, this amp has caused a little pain in getting it back to spec, it had a right channel driver problem, and a while ago I chickened out and bought a NOS right channel driver board. Installed it and it worked fine, but was 5-6 db lower in gain than the original left channel. I had replaced the left channel FET differential input pair with a later version of the dual fet, and was not sure if there was a gain difference in the fets, so the amp was put aside whislt I sourced an original FET pair. Finally received these a couple of weeks ago, and Pete grabbed the amp for the recap prior to me getting back into it to try and resolve the gain problem. The NOS driver board is a later version of the board (the original boards have a couple fo tracks cut, and the later version board has these changes properly inplemented).

With Pete assisting we did some gain measurement comparisons between the good left channel and the suspect right chanel. Whilst doing this we noted some component differences between the two boards that I didn't pick up earlier, notably in the section highlighted in the red circle.

The original right Channel Driver

The NOS "-A" later version

The Driver schematic

Note that the new board has four 150 ohm resistors where the 22 ohm resistors should be, and one 22 ohm where the 150 ohm should be.... and the board showed no signs of tampering with these resistors. I'm thinking that this was a manufacturing mistake.....

Replaced with the correct values in the correct places, and bingo.... gain problem fixed, right and left channels now pretty close.

Just needs a general service (pots and switches cleaned and lubed) and bias and offset settings rechecked and after Pete's recapping she will be good for another thirty years.

Enjoying listening to some nice tunes from her whislt I am typing this.......

Cheers

John