unknown buzz

[corban]

Over the weekend I had an interesting problem. I'm recording a guitar amp with two mics, an sm57 up close and a room SP B1 running into my DMP3. I find that there's an electric buzz on the 57 channel. So I take the mic cable from the 57 to the preamp, which is in Channel A, and put it in Channel B, and vice versa with the cable from the B1. The problem follows the 57. So it's the cable or the mic, right?

So, I swap the two cables completely. The problem has not moved to the B1, it stayed with the 57, so it must be the mic, right?

OK, so I swap in another 57. Same thing. I try another 57, same thing. Tried plugging the preamp into another power outlet, same thing. Couldn't figure it out. Any ideas on what this is? Since the DMP3 does not have individual channel controls for phantom power, I had to have phantom power on both mics to use the B1 at the same time. Could that be causing the buzz with the dynamic? Beyond that, I can't figure out what the problem might be. Obviously I have more troubleshooting to do, but any ideas are appreciated.

 

[SouthSIDE Glen]

Over the weekend I had an interesting problem. I'm recording a guitar amp with two mics, an sm57 up close and a room SP B1 running into my DMP3. I find that there's an electric buzz on the 57 channel. So I take the mic cable from the 57 to the preamp, which is in Channel A, and put it in Channel B, and vice versa with the cable from the B1. The problem follows the 57. So it's the cable or the mic, right?

So, I swap the two cables completely. The problem has not moved to the B1, it stayed with the 57, so it must be the mic, right?

OK, so I swap in another 57. Same thing. I try another 57, same thing. Tried plugging the preamp into another power outlet, same thing. Couldn't figure it out. Any ideas on what this is? Since the DMP3 does not have individual channel controls for phantom power, I had to have phantom power on both mics to use the B1 at the same time. Could that be causing the buzz with the dynamic? Beyond that, I can't figure out what the problem might be. Obviously I have more troubleshooting to do, but any ideas are appreciated.

Corban,

My first suspect based upon your description would be that it's the location and/or orientation of the mic and cable that's picking up RFI from an electrical (inductance or transformer) source somewhere. You might want to try any or all of the following:

- physically move the amp (and therefore also the mics and cables) to another location. Somethines even a 1-foot difference can matter, but it might take more than that.

- Change the orientation of the mic cable in question, E.g., instead of running it straight east-west, use some extra cable and angle it NE-SW.

- Make sure there are no electrical cables anywhere near the mic cables. Also make sure that any that are near are not running parallel to each other. Also make sure that electrical and mic cables are not coiled up anywhere, keep them as un-coiled as possible.

- Make sure there are no devices with AC transformers anywhere around. Things like refridgerators, humidifiers, neon signs, coin-operated vibrating beds, etc.

HTH,

G.

 

[Myriad_Rocker]

coin-operated vibrating beds

Nice......

 

[corban]

Nice......

Good call.

Glen, no there's nothing like that around, and I usually keep power and audio cables separate or perpendicular, but I'll double-check that and try different locations and wirings. Thanks for the word.

 

[stetto]

You mention that your phantom supply is suspect, but you didn't say whether you turned it off to find out....Seems to me a logical step...

Only thing I ever had trouble with re: phantom power was a horrific buzz that quit as soon as I disconnected my Bass VAmp from a channel strip (the -10dB line signal did not get along with 48v trying to sneak up it's ass)...