Interference with KM-184s

[ginridge]

Greeting all,

I have a reasonably professional home studio: 2 Tascam DA-30 8 track digital records (16 tracks total) Grace 101 pre amps, and a Mackie Digital 8 bus mixer. I recorded my last CD with this set up with excellent results. There was one problem however. I perform primarily acoustic music (guitars, resonators, bass, mandolin etc) and one of primary mic set ups is to use a pair of Neumann KM-184s in stereo. For reasons I cannot explain, I get an unusual interference with the KM 184s. It is a high end radio interference of some sort (NOT a 60 cycle hum) which is very sensitive to where the mic is placed in the room. The problem is so severe that I could only record in one very specific location. Moving even an inch to either side would create interference.

I've talked to numerous sound pro's including Neumann and have purchesed Neumann cables ($60.00 a pop!) and Blueberry Kiwi cables to no effect. These lesson the interference somewhat but do not remove it. I do not have this problem with the other mics in my collection (an AKG 460 mic, a B.L.U.E. Blueberry mic or a Rode large diaphram mic), but their sound isn't as good as the Neumann's. I'm beginning to suspect there might be magnetic field interference in the room. Does sanyone have any suggestions on where I might learn about magnetic field interference or have any other suggestions about how to deal with this?

Thanks!

[xstatic]

Is it both KM184's? Or is it possible that it is just one of them. I would imagine that to be either in the cable, the mic itself, or even somewhere in the preamp. However, you have tried different cables, so scratch the cable off. Most likely if it was the preamp, then other mics would have the problem as well. It seems more likely to me that it is the mic at fault based on a quick mental troubleshoot based on the information you provided. If it is just one of the two mics, I reccomend having it repaired or replaced. If it is both, than I would have to seriously give more consideration to possible outside interference.

Out of curiosity, how do you get 16 tracks out of two DA-30's? If memory serves, those are DAT machines which only offer 2 tracks each. Maybe you meant DA-38's?

[ginridge]

Yes, you got me, I meant DA-38. Also, yes, it's both mics and I have gone through a long series of tests trying to isolate the problem. I've isolated various pre-amps, killed circuits, switched grounds and cables. It is very location specific and changes as I move the mic chord in relation to the mic itself. The interference is on going with a variety of grounding options, a variety of pre amps, and occurs throughout all 3 floors of my house. I DO NOT get this interference when recording with these mics outside the house so I'm certain it's site specific. The engineer from my local Public radio stations who designed and installed their digital radio system can't find a problem and has declared it some form of RF or magnetic interference.

i managed to struggle through the last CD recordings with this problem, but don't want to go through that again!

Regards,

Ginridge

[blackdiscoball]

Sprinkle holy water around all four corners of your house and do an exercism.

[ginridge]

Do you know the prayers for a magnetic spirit excorcism?

[tourettes5139]

Originally Posted by blackdiscoball

Sprinkle holy water around all four corners of your house and do an exercism.

Is that where you make the evil spirits run on a treadmill in pink spandex and headbands while the TV is blaring those "Sit and Be Fit" ladies on PBS??




sorry!

[gordone]

Sorry you're having KM184 problems. They're my go-to mic for acoustic guitar recordings. Unfortunately I only have one of them (anyone want to lend me $600?)

Have you tried another pair of KM184s?

[ginridge]

No, I haven't tried another pair (anybody got an extra $1200.00 they care to lend?), but I have used this pair with stellar results and no ill effects in other locations. I've talked with Neumann engineers who say that the increased sensitivity of the 184's can cause this in some situations. They recamended the high end cables (Neumann's own, then B.L.U.E Kiwi's) which reduced but didn't eliminate the problem.

I've had the engineer that installed the digital radio set up for the local NPR affiliate come over and he feels it's an RF problem or magnetic field problem of some sort. I'd really like to learn more about that. Any ideas as to where I can look?

Thanks to all!