On Wed, 04 Mar 2015 19:09:58 +0000, Sumatriptan
wrote:

Mick..thnks for cartridge wiring details, actually 5 wires including the
black earth wire from the tt metalwork to the headshell via the tone arm.

If you are prepared to lose the right to return the unit, I would say
detach that black lead from the TT metalwork and take it out the back
to the amp earth. Can you simply unscrew it, or would it be a matter
of cutting the connection? The former gives you some possibility of a
reversible test without losing the ability to return it, as long as
you're careful not to leave marks on the screw.

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Notes
1) The spectrum was obtained before I normalised the audio track to
examine the waveform.

2) Hum is with mains on at tt, motor off, tonearm in resting position.

3) As explained, I can reduce the Audacity measured RMS hum level to
around -55dB in this room by repositioning...moving it around while
looking at the levels.

Wow, that's real dirty! I'm no expert at electronics, and would
always bow to the greater experience of those in this ng such as Jim,
but this suggests to me that this is not just a straightforward earth
loop problem.

My suspicions would now rest on the deck or the PC's PSU. It would be
useful to know:

1) Is the deck powered by a wall-wart or an inline unit and
low-voltage DC actually coming into the deck, or is it mains coming in
and its motor works directly off it? If the former, I'd suspect the
PSU.

2) What sort of PC is it? A desktop, or a laptop powered by a
wall-wart or inline unit as described for the deck? If the latter, I
had some weird my experiences comparing between using a laptop's
inline PSU and powered via its docking station, and would again
suspect the PSU:

"... I got the normal PSU for the laptop, and removed the
docking station. Big, big hum! Replaced the docking station. Back
to normal. Removed it again. Big, big hum! Replaced it again. Back
to normal.

I conclude that the DS has a decent PSU, while that supplied for the
laptop is crap."

If you want or need to read all of the original very long post
covering a wide range of points about digitising analogue sound
sources, including some concerning hum that I've already mentioned in
these recent posts in reply to you, the original post is he

Java Jive: ROT: PC Audio Recording & Playback (was: Holst and a
Headache), 6/12/11
https://groups.google.com/d/msg/uk.t...k/a7R64KmusM8J
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