Audacity Forum

This problem appears to have nothing to do with Audacity apart from stopping me using it.
After searching (please point me if I missed something) I’m asking for help with my set-up to use Audacity to try to record my stack of LPs.

Audacity version- 1.2.6
Software - XP Pro, SP3, Realtek HD Sound Effects.
Motherboard – Albatron KX600A [please don’t laugh <]:-}]
Sound system – turntable / Phono Preamp / Motherboard’s Line In.
I have already taken all wiring away from the power amplifier.

With everything connected and the turntable off there is a great deal of hum, evidenced by nasty fat lines where there should be just two skinny ones when no signal is being fired in Audacity’s direction. Disconnecting the turntable leads makes no difference.
DMM reading indicates 2mV across either pre-amp o/p while connected to the computer, nothing when disconnected from the computer.
Removing the computer Line In cable removes all trace of voltage at the Pre-amp’s O/P.
Measuring between the metal outside parts of the motherboard and the earth connection of its Line In jack shows . . . . 2 mV ac !
So, apparently the computer has a separate earth for the LI which floats about 2000 uV away from earth and presumably all I can do is go with recent advice for another forum member – buy a UCA202 or similar.
I am concerned that there may be something obvious I have missed ( hope I have been through all the set-ups and got them correct), all help will be much appreciated.

audioFILE wrote:Measuring between the metal outside parts of the motherboard and the earth connection of its Line In jack shows . . . . 2 mV ac !

Good fault finding - you've found a hardware problem.
Have you checked to see if there is any voltage (AC or DC) between chassis ground on the computer and ground on the pre-amp?
I presume that you have the turntable's ground wire connected to the pre-amp?

Quick response, thank you Steve.

DC AC
Earth-to-earth 18 mV 116 mV
Line In, pin-to-ring 63 mV 9 mV

The kitset/s preamp and it's power supply both seem OK. Have already had to by-pass the 0V track on the power supply board as it had some voltage generated between the in and out terminals!!!! Earth track is a bit skinny on that Jaycar kit.
Sound is half-reasonable in a 'normal' setup, without the pooder. Trouble is that they replaced the motherboard under warranty with something someone else had returned and I did not understand why they were so interested in my complete string of gripes with the returned one!!
TT was disconnected ages ago, in case things started flying out o' the cot.

audioFILE wrote:Have already had to by-pass the 0V track on the power supply board as it had some voltage generated between the in and out terminals

So the signal grounds on the pre-amp are floating?

A good point Steve.
No, I just disconnected the power supply output "0V", to the pre-. Popped the wire directly into the centre tap terminal where the power tranny wires meet the supply/regulator pcb. It probably should not have, but I am not about to complain. Designers appear to have gone to some trouble not to form an earth loop on the board. It's dead quiet,now!.

All HUMMmmm was breaking loose as soon as any of pooder's earthy bits got a bit close to the established audio system.

Arrived home from a long walk with a made-up twin RCA lead, each braid interrupted by a 1:1 miniature transformer. Poof !- no more problems in the hum department.
I am not sure I want to go any further with the original problem: I do not hold a lot of faith in this cobbled-up machine, and it's getting long in the tooth.
Your interest is appreciated and if you are curious about anything I will be glad to 'probe around' on the weekend.