midwayfair
Well-known member
I've got a Line Audio OM1. Recently I started having some trouble when I plug it directly into the interface (RME FF 400). It's mains hum, at 60Hz. It goes away/diminishes when I touch the cable (more so the closer I am to the mic) or the microphone body.
It's a fairly basic balanced circuit using an 8" electret (with built-in FET), a single transistor providing some gain, and a pair of BJTs for a transformerless output. I don't have the circuit traced, but everything is solid inside and the mic is working the same as it always has.
-If I plug the mic into ANY OTHER preamp on the shelf and then into the interface, I don't get the hum. This includes any number of other pres running off the same power strip, even the ones without three-prong plugs.
-I have changed cables.
-I have connected a different microphone using the same cable and interface input and I don't get the hum with other microphones of various stripes under the exact same circumstances (multiple schoeps style, transformer balanced, and transformerless mics).
Since it's not a buzz, I'm not suspecting a ground loop. The output appears to be balanced (there's no other reason to have that many devices in there if weren't), but the fact that I can kill the hum with the presence of my body has me wondering if I'm not overlooking something. Since it only happens with this mic and this preamp (direct to the interface), it's not unusable, but I am definitely stumped.
Can anyone think of something else to test to identify the problem?
It's a fairly basic balanced circuit using an 8" electret (with built-in FET), a single transistor providing some gain, and a pair of BJTs for a transformerless output. I don't have the circuit traced, but everything is solid inside and the mic is working the same as it always has.
-If I plug the mic into ANY OTHER preamp on the shelf and then into the interface, I don't get the hum. This includes any number of other pres running off the same power strip, even the ones without three-prong plugs.
-I have changed cables.
-I have connected a different microphone using the same cable and interface input and I don't get the hum with other microphones of various stripes under the exact same circumstances (multiple schoeps style, transformer balanced, and transformerless mics).
Since it's not a buzz, I'm not suspecting a ground loop. The output appears to be balanced (there's no other reason to have that many devices in there if weren't), but the fact that I can kill the hum with the presence of my body has me wondering if I'm not overlooking something. Since it only happens with this mic and this preamp (direct to the interface), it's not unusable, but I am definitely stumped.
Can anyone think of something else to test to identify the problem?