In article , Johny B Good
wrote:

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

Wow! That's impressively rich in HF harmonics which suggests the use
of an unscreened[1] transformer for powering the RIAA pre-amp[2]
allowing capacitive coupling of the higher frequency harmonics and
noise to dominate the mains hum interference.

Yes. It may also be that the transformer has a noticable external magnetic
field. I've come across mains transformers where you had to rotate the
transformer to find a 'minimum hum pickup' for nearby wires because of
external fields.



[2] I've assumed you're using an RIAA pre-amp of some sort in the TT
itself (quite honestly _the_ only place to do the RIAA
pre-amplification).

I think he's using the RIAA inside the Behringer - which is powered via the
5v line of its USB connection.

Which makes me wonder if it would also be wise to try using that via a
decent USB hub with its own external power. I've had problems with other
USB ADCs for such reasons. Not as bad as reported here, but then I only
used line level inputs not RIAA.

Echo the comments about choice of cable. But if changing this keep in mind
that the cable capacitance also matters for MM cartridges.

Jim

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