In article , Java Jive
wrote:
On Wed, 04 Mar 2015 19:09:58 +0000, Sumatriptan
wrote:

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.

Yes, it certainly doesn't look like a neat 50Hz physical loop!


My suspicions would now rest on the deck or the PC's PSU.

Mine tend to be that the cartridge or its wiring are picking up stray
magnetic fields from currents elsewhere. i.e. that the coils in the
cartridge and its wiring are having currents inducted from nearby mains
wirings. This tends to be supported by finding that moving things around
alters the hum. But I don't know enough about the deck, etc, and can't
experiment from here.

Jim

--
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