Motor hum? Electromagnetic Interference ? Ground issue?

[WaynerN]

something else you can do with aluminum. spin it in a magnetic field, and it will also become partially magnetic. That's how the old speedometers worked

Ah, but several aluminum alloys have iron in them......which is magnetic and can be magnetically induced by an induction coil..........

So we have that going for us......which is nice!

 

[marcmorin]

I always thought that worked by some sort of electrical induction. The magnet spun into what amounted to a shorted turn and that was what drug the needle along.

the speedo cable drove an aluminum disk. near that disk was a magnet, the faster the disk spins the more magnetic the aluminum disk becomes. the pointer just followed the field.

 

[doctor fuse]

An old thread, but this might be helpful.

I had the same issue with a low level hum that would appear when the tonearm moved near the spindle (where the motor lies).

I had thought it was the flimsy headshell/cartridge wires on the Rega and Grace arms that I had tried with the Mission 775S table, with the increased impedance making the cartridge sensitive to induced hum from the motor (this didn’t turn out to be the case).

Today I decided to do a thorough cleaning of the Mission, cleaning and relubing the spindle bearing, and exposing the motor to check it and clean it.

Mission used some sort of black goop around the motor, evidently as resonance and vibration control (it works well). Either they squirted this black goo in sloppily or it has melting and oozed around in its 4 decades of life.

This black goo was all over what appeared to be the ground wire going to the motor. I cleaned the goo off the wire until the bare wire and insulation was clean, then sprayed alcohol on it and the circuit board and wiped them clean. I reassembled and did a sound check.

No more hum!

I bet this is the same cause of the OP’s hum.

 

[cmcguire]

An old thread, but this might be helpful.

I had the same issue with a low level hum that would appear when the tonearm moved near the spindle (where the motor lies).

I had thought it was the flimsy headshell/cartridge wires on the Rega and Grace arms that I had tried with the Mission 775S table, with the increased impedance making the cartridge sensitive to induced hum from the motor (this didn’t turn out to be the case).

Today I decided to do a thorough cleaning of the Mission, cleaning and relubing the spindle bearing, and exposing the motor to check it and clean it.

Mission used some sort of black goop around the motor, evidently as resonance and vibration control (it works well). Either they squirted this black goo in sloppily or it has melting and oozed around in its 4 decades of life.

This black goo was all over what appeared to be the ground wire going to the motor. I cleaned the goo off the wire until the bare wire and insulation was clean, then sprayed alcohol on it and the circuit board and wiped them clean. I reassembled and did a sound check.

No more hum!

I bet this is the same cause of the OP’s hum.

Amazing! Your resurrection of this thread means I’ll be resurrecting my 775 from the basement tomorrow to give this a shot. I’m very much betting it’ll work. Cheers!

 

[tnsilver]

An old thread, but this might be helpful.

I had the same issue with a low level hum that would appear when the tonearm moved near the spindle (where the motor lies).

I had thought it was the flimsy headshell/cartridge wires on the Rega and Grace arms that I had tried with the Mission 775S table, with the increased impedance making the cartridge sensitive to induced hum from the motor (this didn’t turn out to be the case).

Today I decided to do a thorough cleaning of the Mission, cleaning and relubing the spindle bearing, and exposing the motor to check it and clean it.

Mission used some sort of black goop around the motor, evidently as resonance and vibration control (it works well). Either they squirted this black goo in sloppily or it has melting and oozed around in its 4 decades of life.

This black goo was all over what appeared to be the ground wire going to the motor. I cleaned the goo off the wire until the bare wire and insulation was clean, then sprayed alcohol on it and the circuit board and wiped them clean. I reassembled and did a sound check.

No more hum!

I bet this is the same cause of the OP’s hum.

I've seen this sort of crap in many vintage turntables. An AKAI AP-001 even uses it on the transformer mounts to reduce vibrations. It's nasty, sticky, and it won't easily desolve in alcohol, but rather in Naphta, lighter fluid, turpentine and other petrol based solvents and it's a serious bitch to clean up. Unfortunately, I don't think it has anything to do with the hum issue. I think, coincidentally, you've just improved a possibly tarnished ground lead contact.

 

[gadget73]

if it won't go in alcohol but does in a petroleum solvent, its probably something tar-adjacent like butyl. Older cars used this for sealing glass to the body and sometimes to stick plastic lenses into the rest of the light assembly. Its semi-soft when new but turns hard with time. Heat will make it ooze though.

What I've found works best is to heat it gently with a hair dryer on low and scrape the bulk of it away, then wipe the remains with solvent.