Thorens TD 125 - Strange Hum

[buckshotcharlie]

I have a Thorens TD 125 turntable, an SME tone arm, and an MA3002 cartridge. I purchased the Thorens and the SME in the early 1970's. They are as good today as when they were new. The MA 3002 is eight years old.

I have a problem. I get a low level hum when playing a record. It is faintly noticeable on the lead in groove and end of record groove. When I lift the needle from the record, the hum goes away. When I place the needle on the record with the turntable off there is no hum, and if I rotate the turntable with my finger there is no hum. If the turntable is on and the turntable is not turning (I remove the drive belt), there is no hum.

What follows is a summary of test conditions.

[TD="align: center"]Turntable On/Off[/TD]
[TD="align: center"]Platter Turning[/TD]
[TD="align: center"]Needle On/Off Record[/TD]
[TD="align: center"]Hum?[/TD]

[TD="align: center"]
[/TD]
[TD="align: center"]
[/TD]
[TD="align: center"]
[/TD]
[TD="align: center"]
[/TD]

[TD="align: center"]on[/TD]
[TD="align: center"]yes[/TD]
[TD="align: center"]on[/TD]
[TD="align: center"]Yes[/TD]

[TD="align: center"]on[/TD]
[TD="align: center"]yes[/TD]
[TD="align: center"]off[/TD]
[TD="align: center"]No[/TD]

[TD="align: center"]on[/TD]
[TD="align: center"]no[/TD]
[TD="align: center"]on[/TD]
[TD="align: center"]No[/TD]

[TD="align: center"]on[/TD]
[TD="align: center"]no[/TD]
[TD="align: center"]off[/TD]
[TD="align: center"]No[/TD]

[TD="align: center"]off[/TD]
[TD="align: center"]yes[/TD]
[TD="align: center"]on[/TD]
[TD="align: center"]No[/TD]

[TD="align: center"]off[/TD]
[TD="align: center"]yes[/TD]
[TD="align: center"]off[/TD]
[TD="align: center"]No[/TD]

[TD="align: center"]off[/TD]
[TD="align: center"]no[/TD]
[TD="align: center"]on[/TD]
[TD="align: center"]No[/TD]

[TD="align: center"]off[/TD]
[TD="align: center"]no[/TD]
[TD="align: center"]off[/TD]
[TD="align: center"]No[/TD]

Might you have any idea what is causing this problem?

I don't think it is a grounding issue as the hum goes away when the needle comes off the record.

I don't think it is a cartridge issue as there is no hum when the turntable is off and the needle is on the record.

Interestingly, if the turntable is on but the platter is not turning (I remove the belt), and the needle is on the record, there is no hum.

Any thoughts or suggestions?

Thank you.

 

[joeinid]

Welcome to the forum buckshotcharlie!

Thank you for joining.

 

[Petro85]

wow thats an interesting situation and i like the chart you added.lol.!!! i instantly would have said ground, but it would have a humm all the time i think.
only thing i can think of is your headshell wires, maybe a problem there? i had a humm once and it was a loose headshell. but i didnt test in in all the ways you did. i just always start with the connections when i hear a problem and go from there.
good luck and welcome to the forum