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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Ted Christensen on June 27, 2012, 03:29:16 am

Title: "Buzz"
Post by: Ted Christensen on June 27, 2012, 03:29:16 am
I searched buzz and didnt find to much.

Heres my problem.

I have two amp racks.

Amp rack one is to power only kf850 tops.

XTI4002
MA5000i
MA9000i


Amp rack two powers subs and monitors for 850 rig

OR

Amp rack two powers subs and biamp qrx 212 plus monitors

Amp rack two has

2 PLX3102 (monitors)
1 GX5 (highs)
1 Lab Gruppen FP14000 (subs)
1 Lab Gruppen 6000x (mids)

I have a motion labs rac pack in each with a L14-30 twist lock out. 4 breakers on each rack.

I plug everything in and run sound. mind you i only have the left and right output coming from the mixer. no other cables but ac and ipod are in the mixer.

No buzz at all.

I know plug in mixes from XLR out on mixer to input on PLX3102s to drive a signal to monitors.

The second that gets plugged in, buzzzz.

The buzz came from the horns on the xti4002 to power highs on the 850s and also monitors.

I have gotten this before without a generator.

When i really noticed this buzz was when i was using the most recent generator from united rentals which was a whisperwatt 25kw.

I had FOH power which drove both FOH and monitors line pluged in on a seperate motion labs stinger box on a seperate breaker from amps and still had buzz. i moved the FOH power cable to the amp rack with the plx amps and still had buzz.

I tried putting the foh power and plx power on the same leg and differnt leg of power, still had buzz.

Even with lights dimmer boxes had to be full up or off otherwise noticed an intance buzz inbetween 99 and 1 percent.

never had this problem as much before having motion labs. I dont think its the motion lab but the only thing i switched on my distro was going to only a few twist locks to the same power panel as before, nothing changed there but switching breakers and the twist locks going to breakers.

Any thoughts as to why i get this buzz with generators, or i general? i know i shouldnt have a buzz. I didnt get it as bad from 220 wall power. but i felt it was there enough to bother me.

i noticed the buzz is from the board and monitor amps. What gives? any cures?

Thanks!                 
Title: Re: "Buzz"
Post by: Ivan Beaver on June 27, 2012, 07:38:54 am
Try lifting the shield on the male XLR where it plugs into the monitor amp.

Leave it connected on the output of the console.
Title: Re: "Buzz"
Post by: Nick Enright on June 27, 2012, 04:58:24 pm
I searched buzz and didnt find to much.

Heres my problem.

<<content deleted>>

i noticed the buzz is from the board and monitor amps. What gives? any cures?

Thanks!               

Does one of the signal lines need around 6db more gain than the other? check to see if the cabling has all signal lines intact. I've had broken pin 2 or 3 cause weird buzzing issues that dont go away.