Sansui 771 - Humming Noise from Speakers

P

peterfranks

Super Member
Good afternoon - I picked up a beautiful 771 for cheap - shows little wear and is very clean. Hook up a pair of 8ohm speakers (tried several different pairs) and I get a hum from both speakers.

The hum isn't too loud and I can't detect it when there is volume. No volume and the hum is noticeable. I tried all three speaker inputs and still the same.

As soon as the receiver comes out of protection the hum begins regardless of any knob or switch setting. Balance has no affect. The sound and power are wonderful. Just that hum with no volume.

Is this a simple DeOxit cleaning issue or something that needs to be looked into? Common issue? Sound familiar?

Much appreciated!
 
Hate to say this but the 661 and 771 are known to develop that hum.
I never did get it figured out on my 661. Even after a re-cap, it was there.

You can try the connector cleaning on the driver board, but don't hold your breath.

My last theory was tired diodes but I never did change them.
 
blhagstrom said:
Hate to say this but the 661 and 771 are known to develop that hum.
I never did get it figured out on my 661. Even after a re-cap, it was there.

You can try the connector cleaning on the driver board, but don't hold your breath.

My last theory was tired diodes but I never did change them.
Click to expand...

thanks - actually its good to hear this isn't too uncommon. OK - off with the case and in with DeOxit - will report back.

I have a pretty clean low use receiver here - I'd like to use it.
thanks!
 
CKeeler said:
The 881 also seems to be prone to the dreaded "hum".
Click to expand...

I thought I saw some threads about the 881 also.

SOMEDAY, one of use will figure it out.
I finally got a decent scope, but now I don't have a Sansui xx1 with a hum.
 
I fixed it on my 881, but it's been so long ago I don't remember EXACTLY how, and I don't have it anymore to open up and refresh my memory.

I do remember it was a ground problem though. After a complete recap, and still having a pretty horrible hum I looked into it more. I eventualy ended up running some new grounds off of some of the boards using copper braid and the hum was gone. I dont remember which boards now though, sorry.

And after weeks of measuring resistance, and looking, and trying to find the source of the hum with my scope, I still could not find where I had lost a ground anywhere. I eventually gave up in a fit of rage and ran the new grounds. When the hum went away, I threw my hands in the air and said forget it, and called it good. Other than that pesky hum it was a good sounding unit.
 
CKeeler said:
I fixed it on my 881, but it's been so long ago I don't remember EXACTLY how, and I don't have it anymore to open up and refresh my memory.

I do remember it was a ground problem though. After a complete recap, and still having a pretty horrible hum I looked into it more. I eventualy ended up running some new grounds off of some of the boards using copper braid and the hum was gone. I dont remember which boards now though, sorry.

And after weeks of measuring resistance, and looking, and trying to find the source of the hum with my scope, I still could not find where I had lost a ground anywhere. I eventually gave up in a fit of rage and ran the new grounds. When the hum went away, I threw my hands in the air and said forget it, and called it good. Other than that pesky hum it was a good sounding unit.
Click to expand...

Actually - that is a very good point about the grounds. I will poke around when I have it open.
 
CKeeler said:
I fixed it on my 881, but it's been so long ago I don't remember EXACTLY how, and I don't have it anymore to open up and refresh my memory.

I do remember it was a ground problem though. After a complete recap, and still having a pretty horrible hum I looked into it more. I eventualy ended up running some new grounds off of some of the boards using copper braid and the hum was gone. I dont remember which boards now though, sorry.

And after weeks of measuring resistance, and looking, and trying to find the source of the hum with my scope, I still could not find where I had lost a ground anywhere. I eventually gave up in a fit of rage and ran the new grounds. When the hum went away, I threw my hands in the air and said forget it, and called it good. Other than that pesky hum it was a good sounding unit.
Click to expand...

I did trace all the grounds and added some on my 661...no joy.
BUT, it is good to know that someone, somewhere actually fixed a hum on one of them.
 
Recently I acquired Sansui 661. I checked inside out and listen a little before I got it. I remember that, while in thrift store I noticed a little hum.

When I bring it home, inside was full of dust, so i decided to do little cleaning, it turns out full washing squence. After that I did complete recap & offset - bias adjustments..
661 is on my main system for a while and its quiet as a mouse!

Is it possible to be this hum caused by mains supply?
 
Starbender said:
Recently I acquired Sansui 661. I checked inside out and listen a little before I got it. I remember that, while in thrift store I noticed a little hum.

When I bring it home, inside was full of dust, so i decided to do little cleaning, it turns out full washing squence. After that I did complete recap & offset - bias adjustments..
661 is on my main system for a while and its quiet as a mouse!

Is it possible to be this hum caused by mains supply?
Click to expand...

You bet -that and/or the caps in the power supply. Hum can get introduced thru you house circuit specially with 2 prong AC plug.

Most likely was the power supply caps that you replaced.

Glad to see you got it fixed, sometimes hum issues can be very hard to track down.

Cheers,
Bob
 
Use grounding plugs on the Phono input rcas, and ensure there are no florescent lamps near the receiver. I use solder braid and run extra grounds...

Someone once told me it can also be the power switch, use the other side of it and replace the little gumdrop cap.
 
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