[78-L] turntable hum mystery

[David Lennick]

At times I've had the opposite situation..hum disappears when I place the 
stylus in the groove. My Technics SP15 has a ground wire for the turntable and 
another for the tone arm and I found when I disconnected one of the grounds 
(can't remember which one), hum disappeared. Also when I stopped playing 
records by the Tuvan Throat Singers.

dl

On 11/8/2012 5:46 PM, neechevoneeznayou at gmail.com wrote:
> Listers,
>
> Last time I posted about hum on my turntable, it was solved by checking
> the ground connection. It was loose, and tightening it made a huge
> improvement.
>
> Later I was thinking I was hearing much hum from the records. Surely
> they didn't record that much hum in so many records did they? Upon
> further investigation, it appears not to be from the records. It is only
> when the table is on and the stylus in contact with the record. Lift the
> stylus even the tiniest bit and the hum goes away. Turn the thing off,
> even with the stylus on the record, and the hum goes away.
>
> So how is the hum getting into the system? Neither vinyl or diamond are
> conductors of electricity. So I've ruled that out. Bad p.s. caps giving
> off EMR that the cartridge is picking up? Seems unlikely, in that
> picking up the stylus even the tiniest bit causes the hum to cease. If
> the leak were in the air I would expect the hum to remain as long as the
> cart was within a certain proximity.
>
> Whaz goin' on here?