Tonearm wiring - Hum from hell...

[dlaloum]

When I first got my JVC QL-Y5F, I seemed to suffer serious Hum in one chanel, then I messed around with headshells and it was gone...

I assumed that it was just a poor connection with one of the headshells and moved on as everything seemed to be working fine.

(Famous last words...)

Tried to mount my AT150 today - the hum is back...

did some investigation

1) the Hum is limited to the left chanel
2) If the cartridge is connected but shielded from the Headshell there is no hum
3) the Left chanel ground is the ground that is connected to the cartridge body
4) Other cartridges I have been using have plastic screw mounting points, the AT150 is metal at the mounting point, so for the first time the cartridge body is in contact with the tonearm via the cartridge body ground.

So what I have happening is that the tonearm is picking up the hum, and feeding it through the cartridge body ground into the Left channel.

Is this a common problem?
What would cause this problem?

There's a whole bunch of cartridges that this will cause me trouble with...Having to Isolate every cartridge when mounting it will be difficult.... this TT is my Sandbox where I experiment with different cartridges and setups.... so this problem is a Royal PITA!!

Any suggestions?

thanks

David

[Dadimo]

I would check the back of the cartridge where the 4 leads connect to it. The AT might have smaller pins than the cartridge used previously. I had this problem one time, and had to slightly crimp the connectors to get a better connection, and the hum was gone.

[timeltel]

Hi, Dlaloum: "Sound" like a ground loop? The small grounding strap on the neg. pin is removable, with appropriate care of course. Should this not eliminate the hum, it is also replaceable.

Peace.

[dlaloum]

Hi Timeltel...

I see the strap... what I don't see is a reasonable way to remove it.

Short of open heart surgery that is....

And a short list of cartridges I've collected that I really don't feel comfortable doing open heart on...

Shure V15V
AT150
AT20
TK7su

It would feel criminal making a mistake on any of these.... (not to mention expensive - although that is relative of course)

My question was somewhat more focused on the tonearm.... and suggestions as to what/how this might be resolved at the arm level. - ie work on the cause rather than the symptom.

Even on insulated cartridges there is a noticeable hum component. (Not too bad when listening - but quite noticeable on any F/R measurements)

Makes me wonder whether a major sound upgrade could be achieved by shielding / grounding / ?Other?? the arm ?

Have I mentioned that I detest ground loups with a virulent passion?

bye for now

David

[timeltel]

Regards, David: You've listed some very good cartridges, your apprehension is understandable. For your consideration, I recently needed to do this with a Signet TK5ea, it too hummed, cartridge construction is comparable to your AT150. The ground strap is designed to accomodate removal for exactly this reason. It's a simple friction fit over the out pin, the tab is folded and then inserted between the cartridge engine and shroud establishing a contact ground to the shroud. If you have a "junk" cartridge you might try this on it first. Carefully work a precision screwdriver or hobby knife under the strap close to the pin, gently work one side then the other, it should start lifting off. There is no need to open the cartridge.

Peace,

[dlaloum]

Ahhh (great relief).... no open heart surgery.... band-aid lever first aid I can handle...

Will give this a try!

thank you

David