AT831b problem with some PA systems

Craig Bumgarner

For the second or third time in the last couple years, I've encountered a problem using my AT831b with a house PA system. The sound was very brittle, tinny and thin, completely different than normal, awful and unusable. Okay, I'll stop ..... Plugged in an SM57, which sounded just fine (but had to give up to another guitarist).

I usually use the AT mic without phantom power into my own amp and this way, it sounds reliably good. A year ago when I had this problem going into a house PA, I had the sound tech turn off the phantom power on the house system and that seemed to help, but this weekend, turning off PP seemed to make things even worse. Sound tech could not resolve it, so I switched to a mag pickup which got it done. The AT specs say the mic is designed to accept phantom power.

What has solved the problem in every case has been switching to a different mic or pickup into the same line, same PA. So it would seem to be an interaction between the AT mic (or this particular AT mic) and the PA system.

Wondering if anyone else has had this problem. I have never heard of it from anyone and plenty of people use these mics on guitars with PA systems, so maybe mine is defective in some way. I'd be just as interested to hear if you are NOT having this problem.

CB

jscook777

Hey Craig,

Phantom power requires all three conductors in the mic signal to be intact. That includes the mic cable out of the AT transformer module, the snake line to the console, the break out mic cable in to the back of the console, and finally the wiring inside the XLR jack on the console itself. If one of the conductors becomes impaired anywhere in that chain you'll get that thin and brittle sound that you are talking about, in the audio world we would call it one-legged. A signal path like that will still sound decent with a dynamic mic like the SM57. A quick test in that case would be to grab another condenser and stab it into the mic cable to determine if it's the questionable condenser mic or the signal path. If you're in a rush or don't have another condenser laying around it's common to grab a new mic cable and start over on a different snake line and mic channel on the console to get you up and running quickly.

I'm sure you get an idea of how the problem can be anywhere in the building and I wouldn't trust a venue's wiring to determine if you're gear is funky. We were playing in a pub this weekend that had the beer cooler wired to the same circuit as the stage lighting, power, and P.A. Our stuff was behaving very wildly with noises popping up all over the place. If the wiring is really out of wack there can be actual A/C voltage passing through to the mics. I've seen this a few times, experiencing the jolt of stepping up to the mic to get to work and having my lips feel as though they were just burned off...yikes. It really ruins your day.

If I were you I would open up the power module and take a look at the solder joints on the XLR output and mini-xlr input as well as the circuit board. Just a couple of months ago I found a bad joint in an Audio-Technica power module at work, a quick solder and it was back in business. While you're poking around, try carefully unscrewing the barrel on the mini-xlr connecter on the mic side and inspect it for any fraying or arcing. After your satisfied the wiring is intact plug it in and carefully manipulate the mic and attached cable listening for any change or crackling. There is a possibility that the miniature mic cable can have a damaged conductor internally, but it doesn't sound like that is the problem. If I had to bet I would say that there was a bad signal path at the venue.

I hope this helps..

All the best,
Jason

Craig Bumgarner

Jason,

Thanks for your explanation, that all makes sense and seems to fit well with what is happening. That the mic sounds good all the time in my Acoustic Image amp suggests to me that the breakdown is in the house PA, or cables. The house PA systems I've worked with have all used dynamic mics, so they are likely unaware of this issue until someone plugs in a condensor mic. I seem to recall that I have alway used the house XLR cable provided, so right off, it would be interesting to try a known good cable.

I had a look inside the AT power supply box and things look good there, all the connections well soldered and tight. Mini-cable and connectors look good and don't crackle when wiggled. Though my AT is going on 3-4 years old, I've been fairly careful with the cable ends not to stress them.

The other guitarist I play with also has an AT, so the next time we have the problem, we'll A/B it with his mic in my channel.

Thanks again, very helpful indeed.

CB

jscook777

P.S. I'm liking that new avatar!