In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:
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?.

Electronic. Uses an SSM 2017 at the front end.

OK...


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.

No XLRs. The pre-amp board is mounted only a few inches from the pickup
arm. The SME arm has a plug and socket connector, which is hard wired to
the PCB. Unplug that, and the hum totally disappears. No need to provide a
dummy load.

Well in the process of elimination it would be a good idea to try that
just in case that isn't as "Balanced" as it ought to be.

Then connect the pick-up by a short, well a few feet of balanced twin
screened, just wrap the inner wire very lightly round the pins. That
then should also be quiet at those frequencies at least then move that
around to see if its inducting a magnetic field from anywhere if it is
then sort that, if not then do check that the wiring of the SME arm is
exactly as it ought be..


Don't earth any of the 2017 input leads from that the only earth should
be a single lead from the arm back to a "tech" earth....





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?..

Each coil goes to a balanced input. No other connection.



What I might try is removing the internal wiring to the arm, and see if it
is twisted.

Shouldn't really matter..

I suspect not.


--
Tony Sayer