Sansui AU D11 Transformer Hum

[Zoeden71]

Hi, I am hoping someone can help me with a bit of info. I have a Sansui AU D11 and it has an audible hum that can be heard through my speakers. It is independent of the volume, component or power outlet. I took it to a service tech and he said it was 100% the transformer and it had more than likely blown a winding? Everything I read about Sansui transformers tells me they are bullet proof and it is an unusual for them to play up.
I can hear it humming when I have taken the cover off the amp. It is definitely making a bit of noise, nothing major but there is a little bit of hum.
I have tried dampening the transformers connection to the amp with vibration deadening material... no joy.
I have switched it to 120V and ran it through a step down transformer... no joy.
The low hum through the speaker remains.
I am reluctant to keep throwing coin at this amp, however would it be worth getting a second opinion on this blown winding?

 

[GrisPato]

Interesting story, and know I am not an expert, so take what I say with a grain of salt. By the way, beautiful amplifier that is, one of Sansui's finest and really underappreciated. I am working just now on an AU-D907G Extra, which is in a certain way the third iteration of your D11 ( Japanese domestic product D907F)

I would imagen that hum from your transformer would not be one on one noticeable in the output of your amplifier. When your transformer blows a winding my guess is you would know!
What I would look at is the really elaborate regulated power supply for the input and VA stage of your D11.
This produces a lot of heat and your decoupling caps there could be worn out.



PS

Although I don't know your repair man.
And Sansui transformers can and do fail at times too.
The transformer story is often the long version of to complicated, no motivation to solve this, and transformer is end of story.

PS number 2
This transformers in this series are attached to the chassis with some kind of rubber / silicon pad between. They are known to dry out and harden and can be replaced. There is at least one thread on that here.
Will not solve the hum in your output but it can solve the mechanical vibrations you're hearing.

 

[Zoeden71]

Interesting story, and know I am not an expert, so take what I say with a grain of salt. By the way, beautiful amplifier that is, one of Sansui's finest and really underappreciated. I am working just now on an AU-D907G Extra, which is in a certain way the third iteration of your D11 ( Japanese domestic product D907F)

I would imagen that hum from your transformer would not be one on one noticeable in the output of your amplifier. When your transformer blows a winding my guess is you would know!
What I would look at is the really elaborate regulated power supply for the input and VA stage of your D11.
This produces a lot of heat and your decoupling caps there could be worn out.

View attachment 2536745

PS

Although I don't know your repair man.
And Sansui transformers can and do fail at times too.
The transformer story is often the long version of to complicated, no motivation to solve this, and transformer is end of story.

Thanks for that. I kind of have the same impression in regards to the last paragraph of yours. I might take it to someone else to look at. Cheers mate.

 

[Zoeden71]

Interesting story, and know I am not an expert, so take what I say with a grain of salt. By the way, beautiful amplifier that is, one of Sansui's finest and really underappreciated. I am working just now on an AU-D907G Extra, which is in a certain way the third iteration of your D11 ( Japanese domestic product D907F)

I would imagen that hum from your transformer would not be one on one noticeable in the output of your amplifier. When your transformer blows a winding my guess is you would know!
What I would look at is the really elaborate regulated power supply for the input and VA stage of your D11.
This produces a lot of heat and your decoupling caps there could be worn out.

View attachment 2536745

PS

Although I don't know your repair man.
And Sansui transformers can and do fail at times too.
The transformer story is often the long version of to complicated, no motivation to solve this, and transformer is end of story.

PS number 2
This transformers in this series are attached to the chassis with some kind of rubber / silicon pad between. They are known to dry out and harden and can be replaced. There is at least one thread on that here.
Will not solve the hum in your output but it can solve the mechanical vibrations you're hearing.

I have tried to isolate any vibration with some antivibration material. It did nothing much to my disappointment

 

[GrisPato]

have tried dampening the transformers connection to the amp with vibration deadening material... no joy.

Sorry, missed that reading your post the first time.
Is this amplifier new to you, and doing this as long as you have it. Or did it develop over time being in your possession?

 

[Zoeden71]

Sorry, missed that reading your post the first time.
Is this amplifier new to you, and doing this as long as you have it. Or did it develop over time being in your possession?

I have had it about 2 years. It went into protection mode about 6 months ago and it was fixed. I think it was the power supply board that was rebuilt? It worked fine for about a month then the hum started. I then took it to a second tech for his opinion and he said it was the transformer. He put it on an oscilloscope and said that he had disconnected everything to pin the hum down to the transformer.
It may well be truly the issue. I would rather not part this amp out if it can be helped.

 

[GrisPato]

Ah, good to know some background.
I think the mechanical vibrations you hear from the transformer and the hum in your output are not related.
Could you share a picture of the work done to the power supply? (Board is installed vertical in front of your transformer)
Hum mostly is power supply, decoupling capacitors and grounding related.

 

[Zoeden71]

Ah, good to know some background.
I think the mechanical vibrations you hear from the transformer and the hum in your output are not related.
Could you share a picture of the work done to the power supply?
Hum mostly is power supply, decoupling capacitors and grounding related.

I will have to get back to you with photos. The amp is boxed up atm. The buzz was doing my head in so I took it out of my system. I was told by the second tech that he isolated the power supply and the hum was directly from the transformer? I might have to bite the bullet and get another opinion.

 

[GrisPato]

Ah, I can understand that.
Just as a last remark.
Is unclear to me if there is made a connection between the mechanical humming of the transformer and the electronical hum in de output of the amplifier ( from the speakers).
To my knowledge there should not be any correlation between them.

 

[Hyperion]

I was told by the second tech that he isolated the power supply and the hum was directly from the transformer?

Sounds like a load of horse-feathers to me.

Is unclear to me if there is made a connection between the mechanical humming of the transformer and the electronical hum in de output of the amplifier ( from the speakers).

Absolutely right, this needs to be clarified - are we talking about audible hum directly from the transformer or hum heard (only) through the speakers?

 

[Zoeden71]

Sounds like a load of horse-feathers to me.
Absolutely right, this needs to be clarified - are we talking about audible hum directly from the transformer or hum heard (only) through the speakers?

It is through the speakers. Power on, no components connected. I can simply connect a speaker to a terminal and the hum is heard. You have to get close to the speaker but it is clearly audible. The amp sits quiet when powered on with no speakers connected.

 

[Hyperion]

It is through the speakers. Power on, no components connected. I can simply connect a speaker to a terminal and the hum is heard. You have to get close to the speaker but it is clearly audible. The amp sits quiet when powered on with no speakers connected.

In my opinion that pretty much confirms the horse-feathers assertion. The Tech's are likely saying it's the transformer because they know they are 'unobtanium', so they won't have to fix it. When actually the fault might be quite simple, I am thinking 'broken ground' or blown series pass transistor in one of the PSU's.

 

[Zoeden71]

In my opinion that pretty much confirms the horse-feathers assertion. The Tech's are likely saying it's the transformer because they know they are 'unobtanium', so they won't have to fix it. When actually the fault might be quite simple, I am thinking 'broken ground' or blown series pass transistor in one of the PSU's.

Thanks for the info. I will go and take it to someone else to have a look at. I was a bit suspicious of the quick diagnosis to be honest. I just wanted some feedback from people with real knowledge of Sansui amps.

 

[BeerLegs]

Mine has developed a slight hum like yours in both channels also. Not too loud, but it is there and you can hear it during quiet passages. It is for the most part original and I'm pretty sure it has some Black Flag caps, along with the Sansui glue. It's overdue for a makeover.

 

[Zoeden71]

Mine has developed a slight hum like yours in both channels also. Not too loud, but it is there and you can hear it during quiet passages. It is for the most part original and I'm pretty sure it has some Black Flag caps, along with the Sansui glue. It's overdue for a makeover.

Thanks, I can't imagine two seperate transformers developing exactly the same issue given how well built they are. I will find another more reputable tech and get them to check it out.

 

[DigitalDad]

Hi, I am hoping someone can help me with a bit of info. I have a Sansui AU D11 and it has an audible hum that can be heard through my speakers. It is independent of the volume, component or power outlet. I took it to a service tech and he said it was 100% the transformer and it had more than likely blown a winding? Everything I read about Sansui transformers tells me they are bullet proof and it is an unusual for them to play up.
I can hear it humming when I have taken the cover off the amp. It is definitely making a bit of noise, nothing major but there is a little bit of hum.
I have tried dampening the transformers connection to the amp with vibration deadening material... no joy.
I have switched it to 120V and ran it through a step down transformer... no joy.
The low hum through the speaker remains.
I am reluctant to keep throwing coin at this amp, however would it be worth getting a second opinion on this blown winding?

Good morning.
i had same problem on my AU-D11 and took some time to fix. Check the solder joints to the 8 TO-220 transistors on the F-3265 Power Amp Circuit Board. Transistors Q20, Q21, Q24, Q25. I found one transistor leg that did not extend through circuit board fully. I had to remove, straighten leg, and remount. When i restored, I remounted all of the TO-220 transistors.

When I got my amp, there was a low level buzz or hum in both channels. It would come and go, very difficult to nail down. On scope, it was actually a 76MHz sine wave.


To access the top of the board you need to remove the heat sink. The foil side can be accessed by removing the bottom panel.
In the picture, it is the transistors mounted on the silver heatsinks. Check the entire board for bad solder joints, mine had many but it was solder joint on one transistor that was at fault.



Also, there is glue on the Power Supply Circuit Board that will need to be removed. There are a couple of pass transistors without heatsinks that had legs cut short and were mounted low. The heat was causing the board to burn up and turning it to charcoal. This needed fixing as well but was not the hum issue. You'll find something like this in picture. board is easy to remove from amp and service.


(EDIT) I found no black flags in my amp. Had to use schematic for AU-907F when working on the driver board, AU-D11 schematic on HiFi Engine is terrible! Amp was very easy to work on and restore.

(EDIT 2) A quick tip for setting bias: I bought a plug at parts store that fit the pins down inside amp and added a length of wire to extend test points outside of amp. Do not attempt to attach mini grippers or probes directly to the test points. There is a thread on AK where someone did much damage to their amp when they shorted the test points!

Blue wire next to amp has four pin connector I used for setting bias.

 

[jfzea]

I have the same amp and I had the same problem, two sources of hum : cold soldering in many places like power supply, phono card and so on. The solution resolder all points above all near to the parts that generate heat. The other source was a connector with bad contact, a good cleaning with a contact cleaner was the solution. In this case you have to move all conectors and listen through the speakers.

By the way this is one my fav amplifiers with very good sound.

 

[Zoeden71]

Good morning.
i had same problem on my AU-D11 and took some time to fix. Check the solder joints to the 8 TO-220 transistors on the F-3265 Power Amp Circuit Board. Transistors Q20, Q21, Q24, Q25. I found one transistor leg that did not extend through circuit board fully. I had to remove, straighten leg, and remount. When i restored, I remounted all of the TO-220 transistors.

When I got my amp, there was a low level buzz or hum in both channels. It would come and go, very difficult to nail down. On scope, it was actually a 76MHz sine wave.


To access the top of the board you need to remove the heat sink. The foil side can be accessed by removing the bottom panel.
In the picture, it is the transistors mounted on the silver heatsinks. Check the entire board for bad solder joints, mine had many but it was solder joint on one transistor that was at fault.

View attachment 2537642

Also, there is glue on the Power Supply Circuit Board that will need to be removed. There are a couple of pass transistors without heatsinks that had legs cut short and were mounted low. The heat was causing the board to burn up and turning it to charcoal. This needed fixing as well but was not the hum issue. You'll find something like this in picture. board is easy to remove from amp and service.
View attachment 2537657

(EDIT) I found no black flags in my amp. Had to use schematic for AU-907F when working on the driver board, AU-D11 schematic on HiFi Engine is terrible! Amp was very easy to work on and restore.

(EDIT 2) A quick tip for setting bias: I bought a plug at parts store that fit the pins down inside amp and added a length of wire to extend test points outside of amp. Do not attempt to attach mini grippers or probes directly to the test points. There is a thread on AK where someone did much damage to their amp when they shorted the test points!
View attachment 2537678
Blue wire next to amp has four pin connector I used for setting bias.

Thank you so much for this, I am taking it to another tech and I will supply this information to him . Cheers!

 

[Zoeden71]

I have the same amp and I had the same problem, two sources of hum : cold soldering in many places like power supply, phono card and so on. The solution resolder all points above all near to the parts that generate heat. The other source was a connector with bad contact, a good cleaning with a contact cleaner was the solution. In this case you have to move all conectors and listen through the speakers.

By the way this is one my fav amplifiers with very good sound.

Thanks, by the sounds of it, it is a common problem. Which is good to hear. Thanks for the info !

 

[momolou]

what big difference between D11 and D11 ii ?