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Author Topic: Help trouble shoot speaker voltage leak.  (Read 4514 times)

David Buckley

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Re: Help trouble shoot speaker voltage leak.
« Reply #20 on: November 05, 2015, 10:41:58 pm »

There are things not adding up here.  When you are in the venue tomorrow, hold one probe of the DVM in your fingers, and the other probe in the ground pin of the outlet, and note the voltage.
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Mike Sokol

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Re: Help trouble shoot speaker voltage leak.
« Reply #21 on: November 06, 2015, 02:25:48 am »

The speaker is powered up, no audio link.
The FM12 across pins 2-3 would light up my contact voltage tester (one contact neon test light), and cause the speaker to buzz.

The FM when measured with a multimeter (VOM I think for the west) measured 112v across any of the 3 XLR pins on the FM12 and the ground on the power drop. Mike says this could be because of a floating ground. Within the speaker Electronics ? (Note, across all 3 pins)

*Edit : I will ensure our IEC power cables are good tomorrow. Afterthough.

Is there some sort of ground lift switch on the speaker's built-in amplifier? Either that, or the IEC cable has an open ground pin. That's the only thing that makes sense for this measurement. If either is the case, then the chassis of the speaker amp will try to float up to 1/2 line voltage if it's not connected to the mixing console ground via pin-1.

So do you have a pin-1 lift in your XLR cable feeding the speakers? Do you hook up all speakers first before powering up everything? That's best practice on most stages for initial setup, but during festival changeover I just make sure individual power switches on speakers are off before plugging in speakers to extra feeds. Heck, we sometimes yank XLR cables out and move to different console outputs while the speakers are still powered up. In the middle of battle things get hectic and shortcuts are sometimes taken. But I could see that doing hot patching could cause a voltage pulse back into the outputs of the mixing console. Is that what's causing your console outputs to fail? Are you hot ptaching without powering down your monitors?
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Mike Sokol
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Peter Morris

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Re: Help trouble shoot speaker voltage leak.
« Reply #22 on: November 16, 2015, 06:27:31 am »

I know you mentioned that you have a good ground, but it sounds a lot like the venues' grounds are not actually connected to anything and are floating.  The capacitance in the windings of the speaker's power transformer will cause its chassis to float up to about half the line voltage, in your case, 100V.  There shouldn't be very much current available, but the high static voltage might be able to destroy output circuits connected to it.

GTD

I think you are on the right track.

Usually when you see around 120 volts appearing in strange situations like this its caused by a missing earth.

For example where the earth wire is disconnected at the start of a cable it can act as a centre tapped capacitor think in terms of the Active being on plate of a capacitor, the Neutral another,  and the Earth as a middle plate.  You can try it with an extension cord disconnect the earth at the plug end and then measure the voltages at the socket end.
There will be (about) 120V between the earth wire and active and the earth wire and neutral.

If your speaker has the metal parts/ input connector earthed, the supply has 3 wires and the earth is not connect at the start of the cable this can happen.  When you plug it into your mixer (which is earthed) you will find 120V with enough current to give you a noticeable shock.

I would be looking for something like this.
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ProSoundWeb Community

Re: Help trouble shoot speaker voltage leak.
« Reply #22 on: November 16, 2015, 06:27:31 am »


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