why does tt need external gnd. wire

leftwinger57

I knew that tt for the most part have a seperate ground wire to be atteched to the chassi of your pre/amp. My old Dual had one ,now my Denon DP-11F has one and I do use it. What is reason for this device alone to have a seperate ground wire. No other device I have has one and for the most part they are all polarized plugs.My apt about 40 yrs old does have grounded outlets, with my Samson sp15 plug strip being the only device w/ a 3 pronged plug,not even the Adcom.

nspindel

Someone a lot more knowledgable than me may have a better explanation, but I believe the reason is that a turntable's power supply feeds the motor, it is not electrically connected to the tone arm or cartridge. The vibration of the stylus in the grooves of the record is generating electrical signals in the cartridge, which flow through the tone arm wiring into the phono preamp, and therefore needs to be grounded to the preamp.

quadzilla

It's to ground the metal parts of the tonearm/turntable and keep them at the same potential as the phono stage in order to prevent noise from being capacitively coupled into the leads. This is needed because while other devices put out a signal, assuming 0 db, of 1 v, the signal from a cartridge to a phono stage is measured in millivolts, usually between .3-.5 millivolts for low-output moving coils, to around 4-5 millivolts for moving magnet cartridges.

dromunds

Right now, I'm using a Thorens TD-150 which has no apparent ground wire. I put a cherry wood arm on it and I get some hum. The arm has RCAs at the end of the arm, and I attached a wire to the red RCA connection and ran that wire to the phono pre ground connection. It reduced the hum considerably but not entirely. Is there a better way to eliminate the hum? I'm in the process of modding a Denon DP-72L with a Grace arm, that had a bad cable. So the Thorens is temporary so to speak but I'd like to get rid of the hum entirely. Thanks.

[Deleted User]

Hello,
It might be helpful if you thought of your turntable connection as a balanced signal, with the right channel signal being sent via the red and green wires and the left channel being sent as the white and blue signal, none of these wires at ground potential. Then the separate grounding wire establishes the ground connection between the turntable and your phono stage. There used to be an audiophile tweak of connecting one channel of an amplifier opposite in polarity to the other channel to the speakers (wiring them out-of-phase) then reversing one channel of the phono cartridge. Many people felt it improved the sound especially during high demands.
Regards, Ken