Sansui 4000 Buzz Hum

pavement74

New Member
Hi. I just bought a 1969 Sansui 4000 and it sounds so sweet. Amazingly consistent from the bass to highs. I only use it play vinyl.
I noticed right away that it has a faint buzz/hum that gets louder as I turn up the volume. It's not noticeable when the music starts. This is my first vintage receiver, so I don't know if this is how all vintage receivers are or not. I didn't have the same noise in the receiver it replaced which was a newOnkyo A-9010. I use a Pro-ject turntable and Pioneer fs52 speakers.
I bought the Sansui from a seller on EBay who restored it. Here's what he did to it according to the listing:
  • replaced main filter capacitors and all capacitors on:
    • F1169 EQ Amplifier Block
    • F1150 Driver Amplifier Blocks
    • F1187 Ripple Filter Block
    • F1149 Tone Control Block
    • F1176 Protector Block
    • F1185 Multiplex Block
    • all replaced with audio grade Nichicon capacitors with like values unless an exact replacement was unavailable in which case I replaced it with one of equal uF but higher voltage.
  • replaced notoriously noisy 2SC458 transistors
  • cleaned all controls both knob and push button with contact cleaner and DeOxit so they move freely and without any static or sticking
  • cleaned inside surfaces with soft bristle brush and gentle compressed air
  • polished and cleaned face plate and knobs
  • replaced all lamps
  • adjusted bias per service manual
Any ideas? Even if I can't get rid of the noise, the Sansui sounds SO much better than my modern receiver that I will never go back!
 
Does the buzz continues if you switch the source to tape ? Wondering if this is related to the head amp (phono) or even to the wiring of the phono Jack to turntable - is their a ground wire from the turn table ? At any rate those circuits are far more sensitive to hum and interference than your other source inputs.
 
Thanks for the suggestion. Phono 2 is worse than Phono 1, but that has a coupler in the back. . Aux is better than Phonos. Yes, I have the turntable grounded. The noise completely goes away when I push tape monitor.
 
Ok - its not unreasonable to have a faint background hiss or hum in a 48 year old amp - even with some transistors replaced. You should not be able to hear it from a listening distance, but certainly if you turn up the volume and listen close to the tweeters - this will always be a bit more pronounced when selecting phono as you are engaging an additional amplifier circuit.

So if you select the source to either the AUX or tape the noise is largely gone (there shouldn't be much difference, but could be if the level adjust on the back is only for the aux and its turned down or dirty - do turn it up and work it several times) - But once you hook up your turntable the faint hum comes back ? Is the faint hum then dependent on whether the phono jacks are in or not ? and is it the same from L/R channel. If the hum is mostly pronounced with the jacks hooked up, it has to do with the cables/turntable/ground connection - I am no expert here. If the hum is the same with or without phono jacks inserted, the noise it likely from the the F-1169 phono board (EQ) - but again some hiss/hum to be picked up is not unreasonable if you crank the volume and listen carefully.
 
Thanks for the suggestion. The noise isn't very noticeable when I'm away from the speakers. I turned the amp up to 3/4 and the hum was 42db from 6" away from the speaker on phono. When I switched the phono plugs in the back to tape rec the noise went up to 46db at 3/4 volume. So I don't think the phono channel is a problem.
Thanks for the reminder that it is a 48 year-old amp! 3/4 volume is very high too. Thanks for your response and patience. I'm a newbie at this vintage receiver stuff!!:)
 
I don't think I would worry., 3/4 of the way up is full power or very close to - some noise at full hammer Is expected In an old design like that.

Still, give the level adjust screw on the back a really good work out and leave it all clockwise. Then with no Jack's connected, now set volume at you typical highest listening level, and let us know how the noise floor behaves between the tape, aux and phono and if it is even in each channel.

Tape and aux should be less than phono.
 
Thanks! Yes, phono has less noise than tape and aux. The level screw was very scratchy, so I'll work on it like you instructed.
I think you're right about the volume level. I turned the level screw to clockwise and the volume was so loud that I couldn't get it up to 1/4 without getting blasted. Boy, this thing has power!!
I backed the level screw the whole way counter clockwise and now it's a comfortable playing volume at 10:00 with very faint hum. Most of the hum I was hearing was probably from having the volume too high while testing it. Thanks again!!
 
You are welcome, enjoy the 4000, it's a great amp from the old school.

At some point you can buy a can of de-oxit on Amazon. Then take the cover off and give the level adjust pot a little squirt while turning it. These pots are almost never cleaned but they can easily cause trouble when gunked up.
 
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