Loud Hum sansui AU111

ger56

New Member
Hello ,

I have a loud hum on my right channel tube amp Sansui Au111. volum at 0 and any device ( phono - aux- tuner ... )

- It comes form the preamp section as I test the amp section with an other pre and it works fine .

- I have tried to change one by one the (5) 12Ax7 with a brand new ecc83 but the problem remain ( unless there would be 2 tube or more defect ) .

Any idea would be welcome , I have the manual but I am not a technician .

Regards

Ger56
 
Best guess ( without you being a tech ) a cap has opened up or broken OR a lead wire in the input stage has broken. Is this amp new to you or has it been working for a LONG time and not moved? If the power amp is fine that almost rules out the power supply.
Let me look at the schematic… BRB
 
Do you still get the hum, when you separate the pre-amp from the power-amp by pulling the U connectors at the back of the Amp.?
If it stops, then its the pre-amp. If it does not its in the output stages. Hope none of the valves are red-plating.

I had a similar problem, hum on one channel, took me absolutely ages, if yours is one of the earlier model, it was due to lack of shielding around the pre-amp section near the power-switch. I will dig out a pic tonight and post

It was not loud, but there.
 
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OH… there are hum nulling pots for the filament supplies…
Left VR-16
Right VR-15
AND
VR-14 for the first V-1 pre amp tube ( phono pre ).
I would try these ( one at a time ) twist for minimum audible hum with headphones and see where that gets you.

Flip the unit into tape monitor, that will remove some of the front end.
Do you have an RCA shorting plug?

Is the unit near anything that generates an hi voltage field ( power panel, computer tube style CRT / TV ) ?

Have YOU had the amp serviced.. at all, or do you know it's history??
 
Hello and thank you for the answers ...

To resume , I bought this amp some years ago and was not working .

I had the chance to find a nice fellow who rebuild as he said the power section .

Amp was working at that time but I only use it as backup so it stays for 4 years as it is .

I needed to use the sansui as I had an issue with one of my audio mirror amp and use the sansui for a week then one morning when power up the loud hum came ( very loud like 60% power )

The preamp section was connection to a behringer active filter abck to the sansui amp section .

When I got the hum I connected my preamp ( van alstine ) to the sansui amp section and it works .

So I am quiet sure the preamp section has an issue .

Regards

Ger56
 
Hmmmmm so the unit had the power supply rebuilt but the front end is " original ".
The unit sat for 4 years
The hum is almost 2/3rds power. Not good…
Where are you located ?
 
AND with the amp disconnected from everything in your other system ( headphones only ) does it still do it…? I would still take a shot at twisting the hum null pots… they get crusty over time and might have opened up… If that doesn't do it… send it out for service ( or sell it to me ! )
 
hi ,

The power supply ( transfo ) is original , only some components were rebuild I believe ( caps etc ... )

I live in casablanca , Morocco .

What is a null pot ?

Regards

ger56
 
It's similar to a volume control with no knob…
Can you send a pix of the back and the insides ( top removed ) if possible…
Morocco… is VERY far away from the US...

Mike
 
ger56,
Yep, Morrocco is far and across a big pond for me as well. If its 60% loud and its been in storage, any number of things as its only on one channel. Similar possibilities as per Vigman, may be the odd bug sack or insects got fried when powered up that morning and caused a mess.
 
Hello ,

Casablanca , Morocco is only 7 hours from NYC and 3 hours from London ...

Anyway here are some picture attached ( if it works ) .
Just in case I can make some picture on specific arera if needed .

regards
 

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Ger… Nice unit ( drool ) …
Give me a pix from the top looking into the unit so I can see the chassis…
AND
If you have the time… remove the bottom and a pix of the components
( might be able to see … SOMETHING )
 
Hello ,

Casablanca , Morocco is only 7 hours from NYC and 3 hours from London ...

Anyway here are some picture attached ( if it works ) .
Just in case I can make some picture on specific arera if needed .

regards

I have a very similar problem for 1 of mine.

the hum is on the right channel. I have to put my ear on the speaker to hear it. Even at zero volume. the left side is OK. I have not have time to track this down.

by the way your knobs are not original.
 
YellowBee,
I had a slight hum on 1 channel and it was due to lack of shielding by the pre-amp section near the power-switch. It may have been quite at 110V but at 240V, it was very noticeable. May be the same with yours. On later models, this area was shielded.

Ended up using a piece of plastic from a tough ice-cream case, cut it to size and used aluminium sticky foil (just on one side, as its close to the powerswitch wiring!!!) as used in air-con systems to make a shield and held it down with the screw from the wiring strip. Took me ages to find it.
You can see the shiny aluminium just on the right hand side about qtr of th way down.
IMG_0030_zpsf419ded2.jpg
 
Sansui AU-111 hum null pots

Mano I believe this is correct
 

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Mano I believe this is correct
I marked it up after verifying it with a set of headphones connected. Unfortunately I had to sell this unit to pay off the cost of a newer version 2001 G version. The buyer is more adventures than me, he is very very very pleased with the purchase and the sound/sonics and now wants to experiment with tube roll. Will wait on his findings.
 
Just wanted to make sure your " mark's " were the correct function….
But those are the filament hum null, correct?
 
Just wanted to make sure your " mark's " were the correct function….
But those are the filament hum null, correct?

Yes, works very well, set with no input signal. Found setting by Ears to be better than trying to use scope.
 
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