Intermittent Hiss with Varying Volume

Question

We have a strange hissing sound that manifests occasionally in one of the channels of a church auditorium. Once it starts, it doesn't go away. Unplugging and replugging the microphone seems to make it go away perhaps every time. Briefly power cycling the pre-amp (in at least the most recent occurrence) does not make it go away.

It first started happening last year, once every several weeks. It started happening more often, and based on some comments on a forum somewhere I replaced the microphone in September. We had no more problems until mid April when it happened again.

Perhaps it is just the microphone again, but it's so new and the old one lasted so long (15 years) that I am concerned there may be something else in the system that is either the source of the issues or could be damaging the microphone.

It only happens on this one channel.

Here is a sample of the noise in a recent occurrence. We were playing with the volume a little at the beginning of the recording, hoping it would go away, and there's a pop when we turned off the power amp, but other than that it's exactly what our problem is.

Sound path:

• Audiotechnica U859Q condenser gooseneck mic (replaced Sep 2014)
• Audiotechnica AT8646 shock mount plate (replaced January 2015)
• ~6ft extension wire with XLR plug
• XLR jack and in-building wiring, approximately 100ft
• Peavy MMA 800T pre-amp

Answer 1

As you mentioned it could be the mic but there are some other things you can try to do.

It could be a bad ground in the system, if you have your pre and amps plugged right into wall outlets I would get a power conditioner and run them all of the same socket (assuming its fused for such operation) this will make sure your power is clean and in phase to all your gear,.

If you can get into the in-building wiring it may be worth checking out you may have a small short or shorted ground. On that note some times (even though its not correct) in building wiring is run over power conduits or even in the same conduit as power lines. This can create buzz in the system, not sure why this is only happening now but degraded cables could account for it. You can try getting a 100ft XLR cable and bypassing the in wall wire this would tell you if that is the bad spot.

the 6 ft extension xlr could have a short or be worn out.

You could be getting interference from wireless devices or possibly florescent lights if you have them.

Just some suggestions of things to look into.