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Technics SL-5 Low Hum

C

csimone

New Member
Hi all,

I just acquired a Technics SL-5 turntable. All works well, except there is a low hum when playing music with or without a ground wire.

The hum only starts after the table unmutes itself and the stylus touches the record. It will continue after the table is switched off. Completely unplugging the table’s power cord will stop the hum.

I’m puzzled as to what is causing this hum. I’m considering doing a recap but am not sure that will solve the problem. RCA cables are shielded and have been ruled out.
 
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Interesting problem. Cartridge should be muted whenever cue is raised whether on or off. No signal path hum possible from table if fully muted. If not muted, it is always live on or off. There is no power draw when off. So pulling power cord doesn't make sense. Not doubting what your saying, just more info. Does it raise with volume? Is it gone when switching inputs? Some cartridges like to hum but none if muted. And why if power is off. Are you positive the table is shutting off? Are you certain the rca cables are well shielded? Video cables are fully shielded and can be used to test. Hum is a bitch at times...most times. Good luck.
 
That table is a P-Mount, so it should not be a grounding issue like you can get on a standard 1/2" mount.

Given the age, it might be generated in the turntable power supply and transferred via the ground, just takes some bad capacitors. They are 40 years old after all.
 
P mount needs ground same as H. Some tables are grounded thru left rca..but still grounded. Sometimes ground loop issues this way though depending on rest of system and source.
 
The SL5 I think has a plug-in ground wire that goes in the back. Its not grounded through one of the leads.

only thing that comes to mind, and I don't have a schematic in front of me to check, but if it has a line to chassis cap that is leaky you'll get 60hz hum through the chassis ground lead. Possible thats the issue.
 
Hi everyone! I have the exact same issue as OP here. My Technics SL-5 has a ground wire that is plugged in all the way, yet it still produces an awful 60hz hum when the needle is unmuted. I plugged in my friends SL-3 into the exact same setup, didn't change anything apart from the turntable and there was no humming. Also, when i touch (not press) the front panel buttons the hum gets louder, and it disappears when i close the circuit by touching the ground point on my preamp with my other hand. Could the ground wire connector be broken?
 
sounds like it. Either the wire itself is open for some reason, or the connection inside from the ground jack to whatever its supposed to be connected to is open. Ohm meter should tell the tale. If the lead itself is fine, pop the lid and have a look. Fair guess the problem will be obvious. Look for a wire hanging loose that looks like it ought to go somewhere.
 
gadget73 said:
sounds like it. Either the wire itself is open for some reason, or the connection inside from the ground jack to whatever its supposed to be connected to is open. Ohm meter should tell the tale. If the lead itself is fine, pop the lid and have a look. Fair guess the problem will be obvious. Look for a wire hanging loose that looks like it ought to go somewhere.
Click to expand...
will do the ohm meter test later, i opened the bottom lid a while back and i have a picture of the insides if that does any help :)
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nothing immediately jumps out but it may be under the board. Been a while since I had my SL-5 but I think the ground pin plugs in next to the RCA outputs? There ought to be a set of wires running from the output jacks to the board, four will be audio signal and one will be the ground. That needs to have low resistance from the ground jack to wherever it goes. It also should have low resistance to the metal plate underneath where the bearing is. You can see a wire from that metal plate to the board. That should make its way around to wherever the ground jack connects to.
 
I was just wrestling with the same issue. Replaced the substandard phono cables with high quality ones after cleaning all contacts with contact cleaner. No more buzz.
 
Just for the note:
  • the ON/OFF button is on the secondary transformer's winding, not on the primary, so it does not disconnect the transformer from the mains completely.
But the OP's hum problem is strange: an unplugeed TT should mute the pick-up coils, and the hum should - in theory - disappear.
 
If the unit has original caps, all bets are off. Those go bad and need replacing. After that, if it is still an issue, then maybe need to check connection from board to grounding plug and the grounding cable.
 
I've had a few Technics linear decks with hum problems. All were the plug-in ground wire type, the contact here has to be REALLY good. Even if you think you have a good, snug connection try contact cleaner and/or physically cleaning with metal polish.
 
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