In article , Sumatriptan
wrote:

TT mains off, hum/noise RMS -60 dB TT mains on, hum/noise RMS around
-55 dB but varies a lot, see below. Test track used at -20 dB RMS -6 dB
peaks (not worried about headroom for testing) Motor on/off made no
change. Tone arm position gives no change.

Moving tt position in this office/workshop gave large, up to 15 dB,
changes in hum/noise. Maybe due to lots of mains wiring underfloor as
well as trailing extension leads to PCs etc. So...

Interesting that tone arm position had no effect but moving the entire unit
did. Did the move require changing the mains socket used?

Here I can measure changes in hum+noise level as the arm is moved, but I
can't compare that with what you get as I don't know the details of your
'test track'. The hum here is inaudible, though, regardless of where I play
the recordings or if I use speakers or headphones. cf below.

I moved the tt to an acoustically and electrically quieter room and
tried it with my Pioneer amp (I had forgotten all about it in my earlier
posts). Result...hum not audible to me at normal listening levels.

A complication is that how audible 'hum' may be will depend on more than
its simple measured level at the amp.

A) Depends on the room acoustics, speakers, etc. One room setup may make it
higher in level at the listener's ears than another.

B) Is the hum pure 50Hz? Or does it have a lot of harmonics? That can make
a big difference to audibility.

Check the spectrum of the 'hum' and the above. Otherwise there might be a
risk that you make recordings with the hum level 'sounding low' but then
hear it when you play the results back elsewhere.

Jim

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