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New to me Au 777A and restoration questions

toneriderMUC

toneriderMUC

Active Member
I finally got hold of the rare bird that is the Sansui Au 777A. In the past years I have seen the amazing rebuilds (Smurfer! Leestereo!) and also followed Smurfers journey in comparing the humble 777A to a lot of other contenders.

I was able to score a unit in pristine condition. Its almost mint, very clean outside and inside and works flawless. I got it from the first owner whos brother bought it in Tokyo in 1970! It has the original owners manual and schematic.

VAxQw13.jpg


What a beauty!! Nude pics following when I start working on it. I have hooked it up to my restored Yamaha NS 690 IIs and boy, what a beautiful sound. Very clear, detailed and yet full bodied and alive. Sweet, lush, gorgeous midrange. And just the right amount of punch. Hard to believe its already this good sounding, running on its 50 year old components.

~

I want to do a full restoration, mostly following Smurfers and Leestereos threads. I do have two questions though that I'd like to solve before starting:

1. I do not have a scope and do see in the SM that I'd need one to do one part of the necessary adjustments. I have read hints that there is a rough way of doing it without a scope - how would that work? I do have a multimeter.

2. C458 replacements. Leestereo uses KSC945C while Smurfer sticks to KSC1815. Both discard the widely suggested KSC1845. There is a discussion on there the thread, but no real consensus.
I am tempted to also go the KSC1815 route - but what do you say?

~

Serial for the AK database: 119090253
 
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Fantastic specimen - I am lucky to have one with the dark wood sleeve too - I have it on permanet display in the house like showing off a beautful art piece, even my wife have approved. Beautiful industrial design.



1) It is best with a scope - the crude method of halfing the output caps to the supple voltage, does not work on the 777a, however the schematics tells us what we need to be looking for - I think its 41V, but do check it out. This will probably be good enough, but I'd look for a shop or a friend with a scope to dial it in eventually.

2) I replaced all 16 signal transistors using the 1845's - the reason to use either 1815 or 945's is that the 458's you are replacing have a higher mA rating that the 1845's. Good practice is to never replace with transistors of a lesser mA rating. At the time I was unaware of it and 1845's was considered the goto for all signals. I've never has problems BUT do follow good practice !. I'd suggest you look up the specs for the 458's and compare to 1815 and 945 - look at mA, ft, hfe and cob and pick the closests match. Once you restore at the level of leestereo you can actually look at circuits and begin to differentiate if the 300 mhz 945's will be slightly better than the 80 mhz 1815's - but that is not for us mortals :-)
 
stereofun said:
1) It is best with a scope - the crude method of halfing the output caps to the supple voltage, does not work on the 777a, however the schematics tells us what we need to be looking for - I think its 41V, but do check it out. This will probably be good enough, but I'd look for a shop or a friend with a scope to dial it in eventually.
Click to expand...

Where exactly would I measure that half voltage? That crude method will have to do until I find someone with a scope. "halfing the output caps to the supple voltage" - where would I put the clamps of my meter -could you detail how exactly that would be measured? That would be really, really helpful :)

I took this picture from Leestereos thread, I hope he doesnt mind:

hsVpW8G.jpg


These are the two 1000uf output couplers. Does this picture help us in explaining the measurement points? :angel:
 
That method does not work on the 777a. There are at least one recent thread on adjusting the 777(a) - the best is to look for the value in the schematic, I think its 41v which ended up being very close to the value after a proper adjustment with a scope. 41vdc is what you adjust for between output caps c825/826 to chassis ground. Please verify this as I away from my usual pc where I can look up in detail.
 
stereofun said:
That method does not work on the 777a. There are at least one recent thread on adjusting the 777(a) - the best is to look for the value in the schematic, I think its 41v which ended up being very close to the value after a proper adjustment with a scope. 41vdc is what you adjust for between output caps c825/826 to chassis ground. Please verify this as I away from my usual pc where I can look up in detail.
Click to expand...

I just found this post of yours in another thread:
"The other adjustment requires a scope. If you don't have one, then put the black lead somewhere on the chassis and the red on the positive terminal of the large 4000 uf smoothing cap - make sure the DMM is now set to read vDC, look for a reading around 58'ish. Then place the red lead next on the positive terminal of the output caps (they are the two 2200 uf caps). Now adjust the appropriate pot to give you a reading 1/2 of that of the big supply cap. Keep in mind there is only one supply cap, but to output caps with each a corresponding pot to adjust."

This explains the doing! But c825/826 should be the 1000uf output caps, the 2200ufs are C819/C820 and should be the smoothing caps - which ones do I use for the dialing in? I would still expect c825/826 to be used for the reading, C819/C820 are only rated at 35v, too.
 
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Please disregard that post - This works on all cap coupled amps I have worked on except the 777's, which I only found out later. The output caps are C825/826 1000UF - the smoothing or supply cap is the single 4000. This is a single rail amp so there is only one, serving both channels. The C819/820 are not in the position to be output caps, but probably do some some kind of smoothing or pre-DC filtering - I've seen them referred to as pre-output caps - just another odd thing about the 777's design.

One good pratice is to see what voltage you get on the output caps before you adjust them. Your supply should read around 70V - but according to schematic you are looking for 40V on the outputs and not 35V as you'd expect. In fact your trimp pot wont allow you too adjust for 35v. Like others I found out the hard way, that the 777a is a different animal. Why dont you take a reading and let us know what you have on C825/826 plus to chassis ?
 
stereofun said:
Please disregard that post - This works on all cap coupled amps I have worked on except the 777's, which I only found out later. The output caps are C825/826 1000UF - the smoothing or supply cap is the single 4000. This is a single rail amp so there is only one, serving both channels. The C819/820 are not in the position to be output caps, but probably do some some kind of smoothing or pre-DC filtering - I've seen them referred to as pre-output caps - just another odd thing about the 777's design.

One good pratice is to see what voltage you get on the output caps before you adjust them. Your supply should read around 70V - but according to schematic you are looking for 40V on the outputs and not 35V as you'd expect. In fact your trimp pot wont allow you too adjust for 35v. Like others I found out the hard way, that the 777a is a different animal. Why dont you take a reading and let us know what you have on C825/826 plus to chassis ?
Click to expand...

Thank you Tom! I have currently readings of ~38V and ~37V. As far as I know this amp has never been serviced, so its basically factory settings on old components. Bit low, but not too far off and readings are very stable. Schematic says 40V indeed.

Vb9p7sY.jpg

I needed to add this image, because my mind gets a bit blown by actually having the original schematic at hand to check this. :banana:

From the inside, very tidy after removing a bit of dust. Will clean thorougly, when I get to work on the individual boards. Next step will be carefully compiling a mouser order.
WhxNB2l.jpg
 
Congrats! My units I've had in the past ( only one now) both dialed in to around 40.5v-41v regarding the center voltage adjustment. Dunno why it's not half of the main filter voltage like any other amp is....btw love the wood case! Very envious....
 
Thanks Fuxtor for verifying the 40'ish Vdc. ... yes all other Cap coupled amps follows the 1/2 supply scheme (in leu of a scope)
 
On 10D1 Diode replacement: this Diode can be found on the power and protector board F-1153. Direct replacement would be the 1N5393, which is a 1,5A type. Leestereo however suggests using a 2A soft recovery type, but doesnt name the specific diode he used. I'd like to go that route, too.
I have seen EGB20B elsewhere as a sub for 10D1. EGB20B is 2A and will probably be my pick.
 
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I have finished the parts list and now wait for my order to arrive. Link to Mouser project, might be helpful as a starting point for someone organizing a 777A restoration:
https://www.mouser.de/ProjectManager/ProjectDetail.aspx?AccessID=d2079fd73b

The list is complete and only missing a few smaller caps that I still have here and dont need to order. Key locations include upgrades taken from smurfers and leestereos projects. All C458 transistors are replaced with KSC1815.
I did not go all the way everywhere though. I only choose to replace/upgrade resistors in key locations in power supply and driver boards. Most of the Mylar caps are not touched, too, with only a few being upgraded to PP versions. For many smaller caps I stick to high quality electrolytics instead of upgrading everything to stacked film. My speakers are very revealing Yamaha monitors and I dont need the last bit of brightness and absolute neutrality in the source gear, too. I also like mixing Nichicon FG, Elna Silmic and Nichicon ES Muse. For power amp locations and similar tasks I stick to Nichicon PW.
As usual: YMMV!! :)

All chassis mounted large caps are upgraded in capacitance Nichicon KGs following Lees recipe. The 4000uf supply cap will be upgraded to a 10000uf Kemet (formerly BHC) Slit Foil. Partly, to add a bit of a different flavour to the massive capacitance accumulation of Nichicon KGs and partly, because I have been wanting to try those slit foils for quite a while!

As a minor annoyance both front lamps (protector and power) are not working. I was hoping they just dont have proper contact in their mountings, as the filaments look fine actually. But no success, I will have to find suitable replacements now. :dunno:

MhlMaR2.jpg
 
toneriderMUC said:
As a minor annoyance both front lamps (protector and power) are not working. I was hoping they just dont have proper contact in their mountings, as the filaments look fine actually. But no success, I will have to find suitable replacements now. :dunno:
Click to expand...

Re the Protector lamp, this lamp will only illuminate if the protection circuit is triggered (it is off in normal operation)

Cheers

John
 
skippy124 said:
Re the Protector lamp, this lamp will only illuminate if the protection circuit is triggered (it is off in normal operation)

Cheers

John
Click to expand...

Good Point! I was somehow still expecting the protection lamp to light up when starting up the amplifier - will still replace it to have to light up when there really is an issue. I started working on the amp now, will first do the power section and large chassis mounted capacitors. Pics will follow.
To avoid damage during work I already removed the faceplate and knobs. As the amp arrived here already being very clean there was only a little finger smear and old grime on the knobs and front to remove. I cleaned the knobs with warm water and a little soap, same with the faceplate. The knobs look like new now, but I wasnt happy with the faceplate after that treatment though and I also gave it a careful run with WD40 on a cloth. That worked like a charm and the result is really pretty:

7A7XOmD.jpg
 
Power and Protector board F-1153 & chassis mounted caps

Lifting tracks are a quite thing in the Au 777A! It's even worse than in the BA-F1, which so far had the doubtful fame of being my personal queen of lifting tracks. Being careful here is not enough. The larger solder blobs on F1153 do require some heat to melt and those tracks are soon happy to rise. But luckily the tracks are fairly wide too and in two damaged places I could solve the problem by just carefully hand-drilling new holes a few mm away and set the new contact there.

Fn0Pwtq.jpg


F-1153 sits tightly surrounded by a lot of wires on the chassis. To be able to loosen and actually work on it, removing the five wires connecting on left side did the trick for me. F1153 covers the outermost section of the driver amp (F-1183-1) and it's a good idea to work on that one too, while F-1153 is still loose. With all the wires there, replacing some of the large chassis mounted caps is also easier before reattaching the power amp board here.
As seen in the picture resistors were mostly replaced by larger wattage variants following Leestereos restoration, also upgrading cement resistors to wirewound vitrous enamel types. Resistors were all installed in elevated position to allow better heat dissipation. Nichicon PW cap values also are increased in all four cases. Rectifier diodes have been upgraded to Vishay SBYV27-200.

Before mounting the larger caps, I like installing cable shoes on the lugs. Nichicon KGs here unfortunately come with fairly small (lets face it, they are tiny!) solder legs which dont easily allow connecting two or three cables at once. With these cable shoes it is a lot easier!
78w4CMQ.jpg



All large caps in place. Lots of Nichicon KG Gold Tune and the slim 10.000 uf Slit Foil on the right:
6xktNjA.jpg
 
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Tone control F-1207

Slowly making my way through the amplifier and finished the tone board today. This board is not directly accessable, as you need to remove the front plate first (should be removed anyway while working on the amp) and also a few wires have to be unsoldered to make working on the board possible. I only removed the black and red wires on the bottom side as it allowed me to pull out the board far enough. Working like that is still not optimal and if I had to do it again, I'd take out the board completely.

Replacements on the board are mostly straight forward. I replaced all electrolytics and the four C458 transistors. Mylars all stayed. They are known to be generally reliable (in the end, they are just polyester caps) and I am somehow concerned, that they might contribute a bit to that sweet Sansui sound that this 777A delivers in spades, and so they stay. I also couldnt see any visual indication of detoriation such as cracks or other signs of stress.

On the back of the board you can find this questionable construction:
CoKbbxB.jpg


I am no engineer, but I do wonder if there was really no better way of including those resistors and the two coupling caps. The two resistors have to be unsoldered to give access to a few of the caps. The process of replacing the two 3,3uf caps connecting the wires would be correctly described as tinkering :angel:

The finished tone board:
IbMxQQy.jpg
 
Driver boards F-1170 & Driver amp block F-11831

Driver amp stage completed. Recapping those boards has been very straight forward. F1170 is duplicated for both channels and mounted upright towards the back. Working on it again requires removal of a few wires. The original open frame trimmers measured and looked fine but have been upgraded to modern Bourns equivalents. All necessary adjustments could be done easily now and readings are stable and in spec.


Done except two caps that I missed putting in my order. Are ordered now and will be thrown in, once here.
MW8koTg.jpg



First Listening on 80% completion
I have been checking functionality after every board finished. No issues, the amp each time powered up just fine and clean sound coming from the small test speakers on my workdesk. With the finished work on the driver section and successful adjustments made I couldnt wait to give this a listen on my main speakers, even though the preamp board F-1194 is yet to be completed. The arrival of Neil Youngs Archive Vol. II on his website for hi-res streaming certainly didnt help my impatience! :angel:

First impressions are very, very good - with a small caveat. The sound has improved in authority clarity, detail and high and low frequency response. Especially bass is more defined. It was punchy before, now there is more control and and texture. Complex passages are handled more easily. Really nice! The whole sound cleared up quite a bit while retaining the original character mostly. But what I also noticed: the unrestored unit had a certain forward "magic" in the midrange, that is now partly lost. The sound was very rich and full bodied. It is still full bodied but has lost a bit of that gorgeous textured midrange that just filled the room. It subtly went from a lets call it "tubelike" sound to a more "modern"/refined presentation, so to say. I still wouldnt want to trade it back, as everything else has improved so much and I now feel safe running the unit. I might try a few other coupling cap options out of curiosity in a few weeks, after things had time to settle a bit and I still feel something is missing somehow.
 
would you say it sounds a little brighter after the new caps? I have noticed that after a recap it can sound bright but warms up after a burn in of a 100 or so hours.
 
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