Sansui 661 speaker hiss and unit buzzing

Got to think about this some more. In the meantime, go with Lee's suggestion on better feedback parts. Any imperfection in a feedback divider becomes part of the amplifier. You usually get the most improvement replacing high value carbon composition resistors with metal films, say anything above 20 kohms, but only if their noise contribution is actually being amplified. Bleeder resistors and such don't matter. Much less improvement replacing carbon films, which are pretty good to start with. My guess is the noise is coming from the tone amp, so changes in the power section may not accomplish much, but I've been wrong before. IMO, the impedances in the tone amp are all pretty high, so the hiss might be inherent in the design.
 
Listen to the hiss. Is it a smooth hiss, or is there some underlying thing that sounds like frying bacon and/or popping popcorn? If the latter, you probably need a better transistor in the tone amp. If not, it's probably mostly thermal and unless better resistors in a few strategic locations improve it, it's inherent in the circuit.
 
It's a very smooth hiss. No popping or other noise. I'm going to redo the feedback parts and see if that makes any improvement. It won't take much to make me very happy with it. Thanks again for the help.
 
Very smooth is likely just Johnson noise and results from high resistances in locations with a lot of gain. Very hard to get rid of, as the unit probably already has carbon film resistors. Metals are better, but the difference is often unmeasurable. One of the poorer things is pot tracks, but you can't do anything about that. A last resort trick, if you have excess gain, is to cut the gain down to the minimum needed, so the noise is amplified less, but that can take both experience and experimentation.
 
Thanks for that explanation. Seems like it's inherent to the amplification. I may still try the feedback resistors but it's still a great sounding little receiver.
 
Thanks for that explanation. Seems like it's inherent to the amplification. I may still try the feedback resistors but it's still a great sounding little receiver.

Hi bberkom, I know this is a very old posting but wondering if you were able to fix the hum finally? I have the same receiver which I recapped and replaced some transistors, it sounds very nice, but I have hum on both speakers all the time at zero volume and I would like to fix it someday as it is sitting in my closet due to this problem. thanks,
 
Hi bberkom, I know this is a very old posting but wondering if you were able to fix the hum finally? I have the same receiver which I recapped and replaced some transistors, it sounds very nice, but I have hum on both speakers all the time at zero volume and I would like to fix it someday as it is sitting in my closet due to this problem. thanks,

Have you seen this thread?

There was supposed to be a link to the 881 ground problem fixing...sorry.
 
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I see it now! I had some leaky caps in the power supply, and that could cause a hum on both channels that is independent of volume. There could be a myraid of other issues, like a bad ground, etc. You could start by checking or replacing capacitors in the power supply, but you'd need some basic equipment like a digital multi-meter, soldering iron, and so on. Schematics are available on hifiengine, and signup is free.

Edit: I just reread your post and see that you already recapped it. I would still suspect power supply cap or bad ground. Did it hum before the recap, or did it just start after the recap? Did you replace the main filter caps?
 
Hi bberkom, I know this is a very old posting but wondering if you were able to fix the hum finally? I have the same receiver which I recapped and replaced some transistors, it sounds very nice, but I have hum on both speakers all the time at zero volume and I would like to fix it someday as it is sitting in my closet due to this problem. thanks,
You may want to start a new thread about your problem. The problem could be related to what I was hearing, but it'll get more response if you start a new thread with details on what work you did to the receiver and what the exact symptoms are. Good luck.
 
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