Hum with SM57

[mGeorgeStuv]

Hi,

I just finished building an A12 and it passes audio OK. B supplies are +/-18V with SC25. I gave it a listen while at the bench (without installing in chassis yet). There is more hum/buzz (sounds like 60 Hz) with SM57 than with a condenser mic w/ phantom power. Is this just something that will go away when shielded in the chassis, or anything I should look at before that? There are fluorescent lights and so forth at the bench so there's probably lots of 60Hz there.

THanks

[tpryan]

viewtopic.php?f=2&t=1728

[mGeorgeStuv]

Thanks, sorry to post on something already covered. I only searched the A12 section. It seems my problem was mostly the SM57 itself. It generates a bit of hum (location and orientation dependent) which is also true through an off-the-shelf mixer. Some of my other dynamic mics are quieter. There's hardly any hum with the condenser with the +48 off and I can't hear it at all with the power on.