Tuesday, March 6, 2012

Kill The Hum

So I got a call from by good friend Pauly who currently has the house sound contract at a venue inside a skate park in Buffalo, NY.  He did some reconfiguring and in the process of cleaning up his amp racks came up with a ton of buzz in his wedges.

We talked about it for a while and he thought the only thing different was that instead of using an XLR to 1/4" adapter to get from a crossover to his drum fill he's now using a cable of the same configuration.  He was also getting the same buzz on a pair of front line wedges that were fed directly from the racks at FOH.

The first thing that came to mind was to question those adapter cables.  This is where the dreaded XLR to 1/4" cable is OK to use.  You never NEVER want to use one to introduce a mic level signal to a line level input or vice versa.  But that's another post.  When you come from a line level XLR output to a line level 1/4" input, you want to make sure that the 1/4" connector is a TRS and not just TS.  TS connectors are tip-sleeve and are sometimes called "mono" because they just have a signal and a ground.  TRS or tip-ring-sleeve connectors can carry a stereo signal if they're on your cans (headphones) or they can do all three conductors needed for a balanced connection.  If you send a balanced signal to a TS connector you start out with the hot signal on the tip, but then you wind up with the cold or negative (not the same as ground) and ground on the sleeve.  It'll pass audio but you're going to loose about 6dB of level and open yourself up to all kinds of hum.

While he should probably get after fixing those cables there were some other issues that should also be addressed and may actually be able to be taken care of more easily.  He's fortunate enough to have an electrical sub-panel right by the stage that's dedicated to his sound system.  That's great but even with its own panel, if some of the gear is plugged into outlets fed from one leg of the service and the rest plugged into another, you have a potential for noise.  I'm not going to get into that in detail here because that's a lengthy post all by itself.  But to put it briefly, by using circuits 1 and 2, 5 and 6, and skipping the ones in between, he's using power that's all from the same buss bar for his amps.  With that done, you can do scary things like plug in ancient SCR dimmer packs to the other circuits and only get minimal noise from the lighting rig.

The last thing we got to may actually be the most important.  His FOH gear is on a circuit that comes from God knows where.  That right there is a big no-no and most guys with portable systems will always carry extra cable so they can power their mix off the same circuits as their stage gear.  Easy enough to check with a 100 foot extension cord.  That and re-plugging the amp power should go a long way toward killing the buzz.  Although even if it does he should still get after those TRS connectors because a 6dB boost from five minutes of soldering is well worth the fumes.

As always it was good to talk to ya Pauly.  Glad to hear you've been reading and sharing from the blog and I'm looking forward to having you post up some club sound guy stories.  Hope you get the better of that buzz and on that note I'll bid a fond farewell to all my fellow Brethren of the Knob and Fader.

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