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Sansui 661 HUM problem

Zeus12 said:
I have been advised to "change high value carbon resistors with metal films". Would that change the tonal quality of the Sansui? Can I check them first and if not out of speck, leave them in there?
Click to expand...
It might do, Sansui have a habit of putting Carbon Composition resistors (those with dark brown bodies), as distinct from 'Carbon Film' resistors, specifically to introduce a modified tonal quality. Unfortunately they are known to be a bit noisy, sometimes a lot noisy - this is especially true for the high value examples - which can also drift in value by some percentage points. But changing them is very unlikely to alter the hum situation, although it might reduce background 'hiss'.
 
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@moeffuz

As I was posting my message, your 2nd message came in.

Yes it is 50Hz. I just sprayed the Driver board with WD-40 Contact Kleaner but then I cleaned it thoroughly with acetone (both sides) and also the other boards (PSU and Tone board). Don´t know how many "Q-tips" I used but I can tell you that it´s spotless and shiny.

You mention, "lift the grounds between input/tape/phono etc. just to see if their is a ground loop sneaking in somewhere.". You are referring to the screws? From the design in the other Sansuis that I have, they all have some wire (ground wire) that is soldered on a point on the chassis. The 661 has no such thing. The screws are the ONLY grounding (that I can see). From the article:
"ideally, a single point ground is used for sensitive analog circuits to be sure everything is operating at the same potential."

Maybe down the road, when I get some more experience, I will give it a shot and try to do it. I just don´t fee comfortable and to be honest, I don´t want to put any more money and time in it.

I´m keeping the AU-5500 for my room and for the living room the 5050. They are both SWEET sounding and with the typical Sansui balanced sound!!!

Cheers!!!
 
@Hyperion

Thanks for you help, as always! I don´t have any background hiss. If "changing them [resistors] is very unlikely to alter the hum situation"., to be honest, I don´t want to put more time and effort into it.

Will just have to learn from it and in the meantime I will start concentrating on the recap of the AU-5500. Oh, what a nice sounding amp!!! I´m slowly moving up the wattage in the Sansui line and I have to say that you were absolutely right! The higher you go, the better, richer and fuller the sound!

Cheers!!!
 
@moefuzz

"Good to hear that you've been able to keep your spirits up during this long haul
and trudge on thru. These kind of growing pains just make a guy better in the long run.
Good job and congrates on making it this far,"

Thank you Moe!!! You helped me lift my spirits!!! :):):)

To love only what happens, what was destined. No greater harmony. Marcus Aurelius
 
Zeus12 said:
Hi MBZ,

Thank you for you reply. HUM is equally present on both channels. Makes no difference what Input Selector I choose. I just use the AUX and FM Stereo by the way. The hum I have sounds EXACTLY like this:

Regards,
Click to expand...
I had a similar hum. I moved my land line phone further from the amp. The hum is gone. Check devices around the amp.
 
Also I reduced the noise connecting the ground of the preamp board and the ground screw of the power amp with a wire (blue line).

screenshot_20210426_180507.jpg
 
@olegau

Thanks again buddy! Yes, this series definitely has a grounding problem. Great workaround you found. Where exactly on the "Preamp" board did you solder the wire?

Cheers!!!:beerchug:
 
Zeus12 said:
@olegau

Thanks again buddy! Yes, this series definitely has a grounding problem. Great workaround you found. Where exactly on the "Preamp" board did you solder the wire?

Cheers!!!:beerchug:
Click to expand...
It is shown on the pic. Just remove the paint between the C601/602 and then solder wire there. Another end of the wire should be soldered or screwed on the ground of the power amp.
 
@olegau

Tried to upload an .m4a file but it was impossible through the site you gave me. I can send it by email if you prefer.

Cheers!!
 
https://radikal.ru/ supports video files. Upload a video file without music, only hum rotating the Volume from zero to full level.
It is possible that one of flat capacitors in the unit work as the antenna attracting noise from outside the unit.

1. Similar low frequency hum (Sansui 222) I fixed putting a small steel plate under my land line phone base.
2. Similar hum I had when I took off the Sansui 661 bottom cover. When the cover on place the hum significantly reduced. I fixed it adding one more wire connecting the pre amp board with the amp frame. See my letter above.
3. Similar hum I had fixing a tube amplifier. The problem was the 6V AC cables feeding tube filaments was located too close to the Volume pot. I wrapped the 6V AC wires with aluminium foil. Hum gone. Try to move with your finger the 6V AC wires in your unit and listen the hum either changed or not.
4. Similar hum I had fixing a subwoofer. I cut off the ground green/yellow wire in the power cord leaving only neutral and phase cables. Also try to connect the amp to another power socket in home. 5. Also Try to turn the power plug to 180 degree and then connect it to the power socket.

6. Take something made of steel, a comp hard drive or small steel plate for example, and then move it around the unit. Listen. If the hum is changing problem is coming outside the unit.
 
@olegau

Big thanks for your help buddy!! :):) HUM is from inside the amp. Many people have had problems with HUM with the XX1 series from what I have seen. I think option No. 2 is the one.

I love the SWEET sound of it and the bass is almost tubular. Can listen to it all day with no listening fatigue. I use it with Fishers XP7 + XP55B speakers (inverted stacked). Amazing how well they go together.

Cheers!!:beerchug::beerchug:
 
Hiho,

I worked on a sansui 661 during the last days and my unit also hat a little bit of hum.
I resolved the issue by modifying the ground connection which goes to the negative speaker terminals:
In my unit they where attached to the ground terminal at the back plate below the speaker terminals.
I removed the cables and soldered them to the point where olegau connected the ground wire for the pre-amp (see post above, screw near the main filter caps...)
...now the hum is completely gone...
 
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