In article , Dave Plowman (News)
scribeth thus
In article ,
The Natural Philosopher wrote:
On 26/08/13 14:06, Dave Plowman (News) wrote:
In article ,
Tim Streater wrote:
The arm assembly is mounted on wood so it's not a ground loop.
Moving the arm over the deck makes no difference to the hum - so I'd
guess it isn't coming from the motor. The wiring within the arm is
single wires - but then the arm itself should screen them? I've
checked it is grounded to my star ground point.
Where the wires leave the arm to enter the cartridge?
I'm not sure where SME grounds the arm. There are five wires going to
the connector on the base of the assembly (other end from the
cartridge, as it were) - one of which is the arm ground. They all
disappear up the middle of the pivot.

what you SHOULD do is to ground everything at the amplifier INPUT.
traditionally that means that the arm carries a separate earth for the
metalwork back to the amp chassis, which should be the ONLY part of the
hifi stack that is actually attached to earth.

And that ONLY at the preamp input itself.

As I said, the arm is electrically isolated from the actual deck due to
being mounted on a wood board. It appears to make no audible difference if
the arm body is grounded or not. I've tried it direct to the main amp
ground terminal both on its own and also grounding the PS O volts rail

in order to reserve the safety niceties, what the means is that other
equipment is only grounded electronically to cases by a 100 ohm resistor
if the cases are to be earthed, and that the outer sheath of the
phono/DIN plugs are NOT directly connected to mais earth on peripherals.

It's the pick-up to on board pre-amp where the hum occurs. Pre-amp to main
amp control unit is fine.


Right..

You say this amp is a "balanced" input is that transformers or
electronically balanced?.

Either way what happens when you simply short out the inputs with a
total short then say 10 ohms then 100, any reduction or rise in the
"hum" level?. Do that at the input terminals presumably XLR or similar
then repeat the same on the cartridge leads on the SME arm where the
cart goes.

Of course each lead from each pickup coil left and right that is, is
connected via two isolated from any ground leads is it not?..


--
Tony Sayer