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Earthing issues with Technics 1210/OL arm

K

kimmiles

pfm Member
I'm tearing what little hair I have left over this one!
I have 2 tt's, one of them a Technics 1210 Mk5G with an OL Alliance arm (and 2M Orange cartridge). I have no issues at all with the other tt set-up.
Even when the arm is earthed through the phono stage, there is still a hum, extremely noticeable!
When I contacted OL, the tech guy was all helpful and had many suggestions, until I mentioned that it was mounted on a Technics tt. Basically, he said that if there were going to be any earthing issues, it would be with a Technics!!!
He said that the earth lead from the arm would have to be attached to an earthing point on the tt chassis which would involve the removal of the base plate! Not a job for the faint-hearted!! Like me!!!
Any ideas?
 
The suggestion is not ureasonable.
Mains hum is most commonly caused by a series, or just two, earth wires that form a loop - a connection from an earthing point goes to point A, then to point B, then pont C, then.... and then back to the same earthing point.

Is there any hum when the arm earth is not connected to anything, or is what there is, tolerable? That would be the simplest answer, as the only other means following the suggestion. The fact that the arm earthing lead causes severe hum suggests that it is already earthed with no need for its own earth cable.
 
Does it hum all the time ? In my early 1200 / 1210 days I had a hum problem , When the arm was on the rest a very faint hum as I moved the arm inwards towards the centre spindle it got louder and louder , Turned out to be the inbuilt power supply causing the problem , I then fitted a external Power supply and hum gone .
 
I should have added that when the earth lead from the arm is disconnected from the phono stage, the hum is actually unbearable!!!
Trying to earth on other bits of the system, from the amp to the tuner (!!) reduces the hum to the same level as when earthed through the phono stage (obviously, I would think).
The hum is constant; no change when moving the arm.
How easy (and costly) is fitting an external power supply??
 
kimmiles said:
I should have added that when the earth lead from the arm is disconnected from the phono stage, the hum is actually unbearable!!!
Trying to earth on other bits of the system, from the amp to the tuner (!!) reduces the hum to the same level as when earthed through the phono stage (obviously, I would think).
The hum is constant; no change when moving the arm.
How easy (and costly) is fitting an external power supply??
Click to expand...

You are looking at a couple of hundred minimum but I can't see it making a difference in your case

Have you tried runnig the arm earth straight to the amp ?
 
I would and ask them to test it and point out the problem you are having
If it comes back as OK then you have eliminated the arm / wiring
 
Testing for short could not be simpler - it should take no more than 2-3 minutes. A cart' generate uV, so testing with a meter is serious, but safe, overkill.

Tried touching the arm earth to anything earth on the TT?
 
Vinny said:
Testing for short could not be simpler - it should take no more than 2-3 minutes. A cart' generate uV, so testing with a meter is serious, but safe, overkill.

Tried touching the arm earth to anything earth on the TT?
Click to expand...

You have lost me with this ?
 
AudioAl said:
I thought testing continuity was done using ohms
Click to expand...

No common or garden meter measures ohms, that is EXTREMELY difficult to do, they measure current at constant voltage and use V=IR.

A very serviceable, basic meter costs around £6-7, probably around what postage would cost, maybe less.
 
Vinny said:
No common or garden meter measures ohms, that is EXTREMELY difficult to do, they measure current at constant voltage and use V=IR.

A very serviceable, basic meter costs around £6-7, probably around what postage would cost, maybe less.
Click to expand...

Ohm's Law is V = IR, where V = voltage, I = current, and R = resistance. Ohm's Law allows you to determine characteristics of a circuit, such as how much current is flowing through it, if you know the voltage of the battery in the circuit and how much resistance is in the circuit.


:eek:o_O:confused:
 
AudioAl said:
Ohm's Law is V = IR, where V = voltage, I = current, and R = resistance. Ohm's Law allows you to determine characteristics of a circuit, such as how much current is flowing through it, if you know the voltage of the battery in the circuit and how much resistance is in the circuit.
Click to expand...

Correct, and your point is? I am more than fully aware of what Ohm's Law is and stated it in charcters above.

Repeating myself, no common or garden meter measures ohms. You switch any common or garden meter to a resistance/ohms range and a fixed voltage is applied across the probes and current is measured. In modern meters, a chip translates that to ohms, in older moving coil meters, the internal simple electronics does the job. In VERY old AVO meters, there was even a standard cell specifically for resistance measurement to ensure accuracy by providing a very stable voltage.
 
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