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Hum from Empire 698

Hi guys.

I'm having a hum problem with a 698 that was given to me. The motor is not completely quiet either.

When it was given to me the headshell was broken so I replaced it with a standard removable type. This required trimming the length of the arm about a .5 inch and rewiring the arm. The internal wire was replaced with van den Hul. The arm works great and is quiet on it's own. I did have to add a ground wire from the chassis to the tonearm ground to stop a loud hum from occurring.

When playing a record there is a constant hum until the arm is returned to the armrest. As long as the arm is in the rest it is quiet. As soon as the arm is raised from the rest there is a hum. There is also some noise from the motor but it can't be heard from a couple of feet away.

I took the circuit board out and looked at the caps and it appears the power switch capacitor has been changed to a Sprague .2uf 600v.

Any ideas?
rwwear
6 responses Add your response
normansizemore
601 posts
 
rwwear,

Sounds like the cartridge is picking up a open ground loop from the motor.  
When the stylus is moved over the platter (i.e. in closer proximity to the motor) your getting hum. 60hz I would imagine.  Try placing an additional rubber matt on the platter and see if the hum is reduced or disappears.  I am flying blind here, but I would think that your issue is in the motor, since you properly rewired the arm.

If the hum experiment above is sucessful, then a motor rebuild or replacement is in order. Being that it's making noise (is should be dead quiet), that is where I would look. 

Good luck, the 698 is a wonderful table and worth the effort to sort matters out.
Norman
rwwear OP
2,871 posts
 
Thanks Norman. I have ordered new grommets for the motor. I also plan to lube it. I'll try your remedy also.
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cleeds
5,957 posts
 
normansizemore283 posts"Sounds like the cartridge is picking up a open ground loop..."

That doesn't make any sense. A ground loop and an open ground are completely opposite things. A ground loop is the result of two or more paths to ground with different voltage potentials. An open ground is an open (incomplete) circuit.

The most likely cause is a cartridge that susceptible to motor hum. Grados are especially vulnerable to hum fields.

You might also check your arm wiring. That there is no hum when it is at rest is no assurance the wiring is ok, because of course the wiring must twist to some extent as the arm pivots.


rwwear OP
2,871 posts
 
I have connected the tonearm to the preamp before installing it into the turntable and there is no noise. I have taken the arm apart and reinstalled the wiring and can find nothing wrong. The turntable only hums when the arm is lifted from the rest. I haven't replaced the grommets yet.
atmasphere's avatar
atmasphere
11,841 posts
 
The motor grommets often cause hum- but usually when the needle is on the LP surface (we have new grommets BTW).

So if you lift the arm from the arm rest and then lower it in such a way that it does not touch the platter or the arm rest, does it still hum?

Does it hum with the motor switched off?
rwwear OP
2,871 posts
 
Thanks for replying Atmasphere.
I can’t recall if it hums with the motor off but I think it does. I’ll re-check.
I have new grommets but have not installed them yet.
There is hum as soon as the arm is removed from the rest even before it’s placed on the platter.
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