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Author Topic: Help trouble shoot speaker voltage leak.  (Read 4688 times)

Nitin Sidhu

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Help trouble shoot speaker voltage leak.
« on: October 31, 2015, 02:32:22 am »

Hello!

Im a tad stumped here and would appreciate some direction.

We have with us 4 boxes of the FM12 active wedges.

The FM12's will measure a live voltage in excess of 80-100v across its line in terminals in some venues. Other venues they would be absolutely fine. And will measure the difference without any audio connections made.
This is recurring, as in we know venues where the FM12's work flawless and others where they dont.

We measure all circuits using a multimeter and ensure that we have a good ground, and no leak in the N conductor.
My assumption is that this could be caused due to dirty electricity, but honestly I have no clue.

Electricity here is 220-240volts.


Regards,
Sidhu
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Steve M Smith

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Re: Help trouble shoot speaker voltage leak.
« Reply #1 on: October 31, 2015, 06:08:39 am »

Do you mean between pins 2 and 3 of the audio input?


Steve.
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John Roberts {JR}

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Re: Help trouble shoot speaker voltage leak.
« Reply #2 on: October 31, 2015, 08:56:15 am »

You need to talk to the speaker manufacturer.

Could be a line-neutral reversed mains, but that still should never energize inputs.

JR
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Nitin Sidhu

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Re: Help trouble shoot speaker voltage leak.
« Reply #3 on: October 31, 2015, 01:07:56 pm »

Do you mean between pins 2 and 3 of the audio input?


Steve.
Thank you gentlemen for your time.

I have been trying, without success, to have multiple queries answered by the manufacture. No response ever. And I am considering a time span of over a year.

These db boxes were retired and left in the warehouse for almost a yr, well replaced with the stx812's. However, they are great sounding and work excellent. When they do.
We needed them again at a venue where we knew they worked well. So deployed them.

Steve. I am going to find time and do another analysis before I answer your query. Thank you.

Sidhu

Sent from my Moto G using Tapatalk

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John Roberts {JR}

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Re: Help trouble shoot speaker voltage leak.
« Reply #4 on: October 31, 2015, 01:32:55 pm »

With unit unplugged measure between mains cord plug blades and audio input pins. There should be no measurable resistance, and if your VOM has a capacitance scale check that too.

Note: a sensitive, high input impedance VOM could measure significant voltage while still very low current, so not really dangerous. Perhaps a 10K ohm resistor across the VOM input when measuring the voltage would absorb some harmless leakage.

Both the hot and neutral power inlets should be well insulated from anything the customer could touch. If not take it out of service before it hurts somebody.

JR
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Mike Sokol

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Re: Help trouble shoot speaker voltage leak.
« Reply #5 on: October 31, 2015, 04:22:29 pm »

Sidhu

Refresh my memory, but India uses British power voltages and pin-outs, correct. That is, 230 volts at 60 Hz with a Brown (hot), Blue (neutral) and Green-Yellow (EGC Ground) wire. Do these boxes have standard XLR connections with pin-2 hot, pin-3 cold, and pin-1 shield? Are you using any kind of pin-1 lifts on these XLR cables, or perhaps any audio isolation transformer in the signal path. Do you have any kind of AC power transformers in the system, for instance to step 230-volts down to 120-volt to run "American" gear?

I want to make sure we all understand exactly what we're measuring before we jump to any conclusions or make dangerous suggestions.

Mike Sokol
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Nitin Sidhu

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Re: Help trouble shoot speaker voltage leak.
« Reply #6 on: October 31, 2015, 09:36:24 pm »

Yes Mike. British voltages. Red-Hot, Black-Neutral and green Earth. Anywhere between 220-240v
Standard XLR's, no ground lifts or transformers. Most small venues will be shore power, single phase powering both FOH and Stage.

We had a run of outputs on our consoles being burnt and found these boxes to be leaking voltage. Then we found them to leak voltage only in certain venues, and not in others.
I have measured in detail in the past, but as its been a while, im going to remeasure it all and return with what I find. I know they leak voltage in the warehouse. By Thursday I should have it done in two venues, with and without the leak.

There is another box in our inventory. The Alto SXM112a, 2 of which, also give us an issue (like a ground hum when connected to an audio source), but this too only does so at certain venues. I want to see if both the Voltage leak in the FM12's, and the noise with the SXm112a are consistent with the venue.

Again, like i said. We measure our electricity to best of our capabilities at every gig every time. I was almost considering getting an oscilloscope to 'see' the voltage. But then read that I dont plug in mains to an oscilloscope if I dont know what im doing. Which i dont.

Thank you JR, will do so.

Regards,
Sidhu
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John Roberts {JR}

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Re: Help trouble shoot speaker voltage leak.
« Reply #7 on: October 31, 2015, 09:53:47 pm »

If it's eating console output stages there is a good chance it's faulty... the fact that it might not do that all the time does not mean it's OK...

JR
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Jonathan Johnson

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Re: Help trouble shoot speaker voltage leak.
« Reply #8 on: October 31, 2015, 11:47:37 pm »

I wonder if you have a reverse polarity bootleg ground in the problematic venues. Standard test procedures where you meter the receptacle only with itself will not reveal this problem; you must meter against a known, tested external reference ground.

If this is the case, pin 1 could have voltage present, but I don't really know how that would measure between pin 1 and the signal pins. If it's not a true balanced input, but pin  3 is referenced to ground/pin 1 then that could explain what's going on.

Mike is the expert on RPBG, I'll defer to him.
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Nitin Sidhu

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Re: Help trouble shoot speaker voltage leak.
« Reply #9 on: November 01, 2015, 02:00:16 am »

I wonder if you have a reverse polarity bootleg ground in the problematic venues. Standard test procedures where you meter the receptacle only with itself will not reveal this problem; you must meter against a known, tested external reference ground.

We measure to ensure that the Hot-Neutral wires are not swapped. So...
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ProSoundWeb Community

Re: Help trouble shoot speaker voltage leak.
« Reply #9 on: November 01, 2015, 02:00:16 am »


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