In article , Dave Plowman (News)
scribeth thus
In article ,
tony sayer wrote:
In article , Dave Plowman (News)
scribeth thus
Had a bit more of a play. Disconneced the cartridge - hum goes. So it's
apparently being induced into the cartridge itself, rather than wiring.
No large transformers anywhere near - and it's more or less the same on
the workbench, in a different room. Next thing to try is removing the
mains to the turntable, I suppose.


Dave.. seriously suggest a small value resistor connected across the
inputs and that via a short bit of twin screened and see if the hum is
still there or not.

Then connect the cart to the same cable and move that around it
shouldn't under normal conditions "hum" unless its picking that up from
a transformer or motor. If so then you should be able to track that
easily.

In a way this is much the same as a moving coil microphone and they can
and do as I'm sure you know be used on rather long leads....

Had a play this morning before reading this. Turns out to have been caused
by the transformer in the PS - even although it's a weedy 6VA and 600mm or
so from the pickup. Nor does the hum change when moving the pickup around
- which is why I didn't go for this before. But running the pre-amp from
an external PS removes the hum totally. (the hum and noise on the output
of the original PS and external one are near identical on the scope)

I've ordered up a toroidal transformer and Eddystone box to put it in from
CPC. Still free carriage. ;-)



A Toriod tranny?, best bet for hum field reduction. Make sure there no
shorted turns thru it..

--
Tony Sayer