please help with a "new" Sansui AU-9900

[sheiku]

Hi, sorry for my poor English..
First i want to thank you for this wonderful forum i watch for many years without posting on it..
But now i need your advice..

i am a big fan of the Sansui brand and i own (by few years in different shapes) the following
Sansui AU-505
Sansui AU-x701
Sansui 1000x
Sansui 317II
Sansui Au D5
Sansui Tu 217

Truth is that I am in loved with the sound of OLD sansuis like AU505 and 1000x despite having AU x701 ( this is sleeping in my wardrobe ) And i am listening on 1000x receiver
And yesterday i bought an Sansui AU-9900 in very good exterior shape. ( only a small dent and a little scratch) hoping to another good old sansui sound.
Quite expensive for the income from my country..

I picked it from the seller but with no possibility to hear it before. The seller tell me that he is original inside , no intervention. I will check this.

PROBLEM 1):
i have almost or tiny no bass even with bass pot switched to maximum. and no round, or warm sound . Mibe is also missing from the low middle some. Sincerely i do not recognize many songs i play daily on the other amplifiers i have. This is the tiniest bass from whatever sansui i have. Ok i understand that is not capacitor coupled as 505 or 1000x ( those two have very big bass ) but also AU x701 and AU D5 have bigger bass, and low frequencies than my new "baby".

PROBLEM 2)
There is hiss in the both channels no matter what filter i push on AU 9900. ( i hear it form about 1 meters if no music is involved)

Except those problems and the quite angry wife ( regarding the price of course i feel that is 9900 is exemplary in the middle, heights and separation..maybe also on sound stage.

What should i do now?
I do not have an repair technician/shop in my city, so if i have to recap or change some transistors i have to do on my own.

about 10 years ago i was able to construct from 0 to full an working Diy Gainclone amplifier , so even i am not good at all and i lost all my knowledge , i know ( maybe) how to recap or to do an solder work.
But i never tested electronics and do recaps..
I also have an good multi meter and i will buy again soldering gun.
So from what i read here on forum the missing low frequencies are from old capacitors ( the main/ big 4 capacitors) and the hiss is form the transistors.Is this correct?

Any tips, where to start..of course not to change all the electronic components inside..
Also after a recapping or replacing whatever will be necessary , an 9900 will be close enough form the sound of old seris as 1000x or capacitor coupled amplifiers instead of the new pure and cristal cleare as au x701? Will have strong bass and warm sound?

My speakers are Quadral Vulkan mk II. Real transmission line 150 w. even the little AU505 played admirably with excellent low end on this speakers ..but after one week started to develop an pop, or scratch , and i stopped pairing with those big speakers) But this is another story

Thank you
Regards
Dan

 

[slimecity]

For starters - clean all your controls.

Secondly - check that your speaker polarity is correct.

Thirdly - test each stage of the amplifier (pre section & power section) by using outboard amplifiers/music sources (thru the "pre out" and "main/power in" RCA sockets at the back) to test if this issue is in the power or the pre stage.

Is the issue in both channels? Its possible that it could be dirty/worn speaker relay contacts.

 

[sheiku]

Thank you,
I will do what you suggest and i will came back with results..maybe tomorrow.
I never test or used an pre and a main amplifier in this mode ..separate and now i see that the 9900 have some separate inputs..
Thank you,

PS: Maybe an answer to this..9900 is know as having good and strong bass? Or this very shy bass is his characteristic?

 

[KeithD]

PS: Maybe an answer to this..9900 is know as having good and strong bass? Or this very shy bass is his characteristic?

No, the AU-9900 should have good bass, no different than any other Sansui from that time frame such as 9090 or your AU-505. There is no Loudness switch to enhance the bass and treble, so if you want more bass you need to turn up the bass tone control. But it is not weak in this department in my experience with mine.

 

[sheiku]

Thank you KeithD. Good news. It give me hope..
Since i bought it i stay only with the bass tone controll and the medium tome controls pots to the maximum to make quite enjoyable the lower end a little..Even so it is the lower bass i have had from any of my sansui. i tested the same configuration on the other sansui amplifiers and ...at least on my 1000x and au-505 my bed and my windows are shaking and i feel the the air is vibrating in some passages..

UPDATE:
1) the hiss on the right speaker is bigger than the left speaker.
2) my speakers are connected ok and they have much more than necessary bass with other amplifiers
3) i discovered that i am not able to connect another amplifier as a pre amp. I must have another preamp or another amplifier with special RCA outputs to be used as preamp? I only have the amplifiers from my signature.
Thank you

 

[slimecity]

You can run any music source into the "power/main in" RCA terminals on your 9900.

If any of your existing amplifiers have "pre out" RCA terminals - use a normal pair of RCA cables to run from there to the "main in" RCA's on your 9900.

Ie: get a converter lead like that pictured. TURN THE VOLUME DOWN on your cellphone/mp3 player, connect to main in on the sansui.

Alternatively it may be a better idea for you to take this to a technician to diagnose & fix. This is a very complicated amplifier and not suited to a beginner to fix.

 

[sheiku]

Yes,
Very explicit. Now i understand.
I have this sort of cable, i will do the test.
Thank you slimecity

 

[sheiku]

I tested as you advised..:
1) I used an android phone as preamp for my 9900. The result is clear better, i was happy with the sound ( from a poor phone feeding the sansui). More open, more clear, more separated, a better bass and punchier, even compared with bass tone to the max of my amp.
2) Also i realized that if i simply switch the button (pre-main) of my 9900 amp to the "Separate" position , the hiss on the right speaker is becoming very low at the same level with the left speaker hiss.
First time i hear the hiss in my left speaker i thought the outside were raining( the right speaker is near the window)
I have audible hiss ( but) near the speakers also in this position of the button ( pre-main > Separate ) but incomparable lower than before, and it is equal in both speakers as intensity level. Maybe I can live with this..if there is not fix for it)
So i suppose that there are some problems in the preamp section of my amplifier. It is ok my supposition?

What will be the next step?
Thank you for your help..

PS..i readed in a post regarding the hiss of a 11000 sansui that the grounding may be the problem.
I just saw in a youtube video that 9900 of the owner has something in the GND hole ( in the right lateral of the amplifier)
Or in this picture https://img.ukaudiomart.com/uploads/large/2046217-sansui-au9900-integrated-power-amplifier.jpg My amplifier do not have that piece inside the gnd hole...I am missing something ?( please see the attached pictures. Mine is the clearer one)

 

[KeithD]

That's the ground for the phonograph if you connect one. Missing that connector has no bearing on your amplifier problems.

 

[sheiku]

Pff...starting today i have almost no sound from left speaker when i connect phono input , no mater what phono ( 1 or 2 ) is connected...
I hear some sound very close from the speaker, but very very low barely imperceptible, and the right is loud.
I tested all the other inputs and all is ok between channels..
Lots of problems..
Also , regarding my main question, supposing that my preamp is defective. what should i look about:

-are responsable for weak bass some capacitors? There are involved those 4 big from main supply?
-are responsable for the hiss transistors or diodes..?
Thank you

 

[DAnny45acp]

As Slimecity stated did you get a good deoxit and clean all ALL the controls - just to start with the basics I'd clean all the controls (signal is going thru all your controls) and measure all the fusible resistors as they more than likely drifted and check your bias current as a starting point and set filters switch to "defeat" to eliminate a little in the pre-amp.

 

[sheiku]

Hi,
I followed the procedure from here http://www.vintageaudioaddict.com/sansui_au9900/sansui_au-9900.htm and deoxided and cleaned all necesary..
Very minor improvements especially in small cracks an pops..
But no improvments in the - fullness of bass
- hiss in the right speaker
- no regain sound in the left speaker when using phono.

I d like to restore the bass and the hiss firstly. From the tests suggested by slimecity results that my preamp is ..the "Achilles heel"
As a next step ..should i remove the preamp board and test the components of preamp board ( diodes..capacitors) ? Excepting the transistors i am able to do that.
I canot test the bias as i have no experience. I readed some posts about setting the bias in 11000 but , maybe because of my poor English i was not able to understand the procedure.
Regards

 

[sheiku]

Hi,
I have a strange but clear feeling that as long as i use the amplifier, and i use for about 5-8 hours/ day. ( yes .. ) the bass is becoming more powerful.
It is not about being use with it , because i compere with my known songs. In first 1..2 days there were very weak bass and now it is better.. Is still not enough for my taste or as my 1000x but it is ..more them before.

Question is : it is about a phenomena of burning in of the capacitors? Let say that last owner did not used the amplifier for long time and now if i use it again for extended periods the capacitors are recovering their " values" ..
It seems strange.
Any way i ordered an ESR multi-meter to test some components inside.
Thank you

 

[sheiku]

UPDATE --with bad news.
yesterday i made another deoxid bath, better than previous and for my surprise ...i had an wow to the sound and especially to the new bass. I listened yesterday few hours: the sound was more opened, with plenty of details , and more bassy , to the point i had to lower ( the bass on some songs) So this amplifier gave me yesterday some of his ( i hope original) sound. It has both from the 2 worlds of a newer alpha > au x701 and older cap coupled au-505. details, clarity and also bass and warmth.
Hiss in the right channel still remain very bad..

The bad news: today morning i opened the amplifier and after 2-3 seconds it filled my room with 4-5 very loud pops and crack. So loud that my little daughter start crying. I switched it of. After few minutes i tried to open again and again those violent and loud pops/cracks in both my speakers to the point i was afraid to be damage my speakers. I tested after that my speakers with sabsui 1000x and all the speakers are ok, no damage to them .

The thing are getting worse..I do not know what to do from here..I had an old tech specialist who used to repair my stuff in the past but he died few years ago ..I also have in my city an company specialized in this repairs but i do not trust in them based on my previous experience with them.

i will order an digital osciloscope and an esr meter , maybe i will remember something from my youth, but i must confess that even i restored and recapped my sansui au 101 ( without having to trace some problems) , ...the 9900 is another level of complexity..

The led is switching from red to green if important this..
Any suggestions please..

 

[Mr. Nick]

The bad news: today morning i opened the amplifier and after 2-3 seconds it filled my room with 4-5 very loud pops and crack. So loud that my little daughter start crying. I switched it of. After few minutes i tried to open again and again those violent and loud pops/cracks in both my speakers to the point i was afraid to be damage my speakers. .

Any suggestions please..

If the amp did sit many years in the storage earlier it could be the case that electrolytics are forming again thus giving you better bass output.
Are you sure the loud pops came from both speakers, were they standing closely to each other? I believe one or more power amp transistors may have failed.
If you are sure both speakers crackled, then it may indicate a problem on the power supply section.
You can test with your external source to the power amp. I'd only connect *test* speakers to the amp.

It's often the scenario, when you turn on an amp that's been stored away for a year or more, may work fine for a day or a week, but in short time perioid one or more transistor fails.
I guess it's the result of the electrolytics that fail to work in the given specs.
I have some experience of this. Crackling occured on the second day I got the amp and until that it worked fine.

I have a lower middle of the line AU 4900 that has phenomenal rich bass performance.
Your AU 9900 should really be able to put same performance at least.

 

[sheiku]

Hello and thank you Mr. Nick. Happy to see again an answer on this thread..
( sorry for my poor english in explaining this)
i am 90% that it was from both speakers because when the pops were i was right between the speakers..and it seems that were from both speakers. But for the rest of 10%is unsure because there was so loud the pops that maybe i heard the sound so loud from all my room, all direction.

1) Let suppose power amp transistors...are they hard to obtain? There are some exotic components?
2) And i do not understand: power supply section problem is equal with failing power amp transistors ?
3) i do not understand the meaning of : "You can test with your external source to the power amp." I must to test separate the pre and main? ( this is the mean?)
4) "the result of the electrolytics". When you speak about electrolytic, it is about transistors or capacitors being aged? Or both?
Thank you

PS: it seems that i must to learn seriously how to deal with such problems because..sadly , this week 3 of my amplifiers developed each bad problems..pops, distortion hiss.
I started to learn about esr meters, oscilloscopes, and other electronics from my youth ...maybe i have a chance to repair them..

 

[Mr. Nick]

1) You can most likely replace a transistor in the unit with a modern substitute.
2) Power supply is often a separated section in an amplifier. A separate board with components layout. See block diagram on the service manual, page 3.
3) I refer to what user slimecity explained earlier in post #6 in this topic. Doing this you can identify better, if there's a problem on the preamp or power amp section of the amp. You did this earlier as you explained in the post #8.
As another option you can connect your AU 9900 preamp RCA outputs to your 1000x Main in RCA inputs to test, if the preamp works without crackles. Make sure you have volume control all the way down to no volume.
Run signal into your AU 9900 and hook up test speakers to your 1000x to see, if the preamp works fine.
Slowly increase volume to see if crackle is present.

4) Sorry I referred to the electrolytics as electrolytic capacitors (=caps).

See, service manual and boards are illustrated in the service manual, which is available here on AK:
http://akdatabase.org/AKview/displayimage.php?album=28&pos=114

 

[sheiku]

Mr. Nick you have made my day better.
I will read again what you wrote to fully understand and to apply.
THANK you

 

[slimecity]

3) I refer to what user slimecity explained earlier in post #6 in this topic. Doing this you can identify better, if there's a problem on the preamp or power amp section of the amp. You did this earlier as you explained in the post #8.
As another option you can connect your AU 9900 preamp RCA outputs to your 1000x Main in RCA inputs to test, if the preamp works without crackles. Make sure you have volume control all the way down to no volume.
Run signal into your AU 9900 and hook up test speakers to your 1000x to see, if the preamp works fine.
Slowly increase volume to see if crackle is present.

Yes, this.

As Mr Nick says - use some test speakers - run each section of the amplifier for a while to see where/when the problem starts again.

There is something sending DC thru to the protect circuit and causing it to trigger.

I agree that I'd be looking at the powersupply section for the preamp - pretty sure that in this amplifier there are seperate pre-power amp section powersupplies. Yes, it could well be failing transistors. It could also be a dirty connection or bad solder joint however. Note the conditions when the issue starts - does it start after a certain period of time - once the amplifier has warmed up?

 

[sheiku]

Thank you, it pops right after i switch on..maximum 1 second.. I tried twice, and it was the same. Start to strongly pop after pop like ..fireworks