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Author Topic: Induction loop interference  (Read 384 times)

Gary Fitzpatrick

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Induction loop interference
« on: February 22, 2019, 02:35:55 pm »

I have a church where the hearing loop is causing interference with a submixer in the choir gallery.

The hearing loop cable runs close ish to the cable going to the gallery.

When the choir mixer is turned on (Sound craft epm12) all is fine, but if the mixer is powered off there is a high pitched sound through the system. Plug the xlr out of the mixer and all is fine. Mute the signal going to the induction loop amplifier and all is fine.

Any suggestions? I would like the choir to have as little do do as possible, so would rather not have them having to unplug the xlr when they are not using it. Like to keep it as simple as possible.

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Pete Erskine

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Re: Induction loop interference
« Reply #1 on: February 22, 2019, 05:54:48 pm »

I have a church where the hearing loop is causing interference with a submixer in the choir gallery.

The hearing loop cable runs close ish to the cable going to the gallery.

When the choir mixer is turned on (Sound craft epm12) all is fine, but if the mixer is powered off there is a high pitched sound through the system. Plug the xlr out of the mixer and all is fine. Mute the signal going to the induction loop amplifier and all is fine.

Any suggestions? I would like the choir to have as little do do as possible, so would rather not have them having to unplug the xlr when they are not using it. Like to keep it as simple as possible.

Sent from my EML-L09 using Tapatalk

Do you hear it when all inputs to the mixer are off?  If so it is pickup in the mixer.  Install ferrite filters on all power and in/out to the mixer and shield the mixer with Mu metal covering as much of it as possible.

If it goes away with an input off, use electret or phantom mics instead of dynamic.  they pickup loops.

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Gary Fitzpatrick

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Re: Induction loop interference
« Reply #2 on: February 22, 2019, 06:01:35 pm »

When the mixer is on, there is no noise at all.
It's only when the mixer is powered off that the noise presents.

Gary

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Pete Erskine

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Re: Induction loop interference
« Reply #3 on: February 23, 2019, 12:10:43 pm »

When the mixer is on, there is no noise at all.
It's only when the mixer is powered off that the noise presents.

Gary

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so in normal use it works fine.
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Gary Fitzpatrick

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Re: Induction loop interference
« Reply #4 on: February 24, 2019, 05:10:44 pm »

so in normal use it works fine.
I probably should have given a bit more background.

It's a Catholic Church, and has a service every day, but the choir is only present on Sundays, Weddings, funerals.

The choir mixer is normally only turned on when the choir is present.

However, I received complaints that the induction loop signal was very low. When I turned up the induction loop, it started interfering with the choir mixer, but only is the mixer is powered off.

Main system on, choir mixer on = no noise

Main system on, choir mixer off = noise



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Pete Erskine

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Re: Induction loop interference
« Reply #5 on: February 24, 2019, 08:06:19 pm »

I probably should have given a bit more background.

It's a Catholic Church, and has a service every day, but the choir is only present on Sundays, Weddings, funerals.

The choir mixer is normally only turned on when the choir is present.

However, I received complaints that the induction loop signal was very low. When I turned up the induction loop, it started interfering with the choir mixer, but only is the mixer is powered off.

Main system on, choir mixer on = no noise

Main system on, choir mixer off = noise



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Don't turn off choir mixer... problem solved.
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Mike Caldwell

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Re: Induction loop interference
« Reply #6 on: February 25, 2019, 11:41:55 pm »

Try putting a 1 to 1 isolation transformer between the output of the mixer and the cable going from the mixer.

Powering off the mixer basically removes the balanced line output driver from the cable.

The transformer iso should maintain the balanced connection to the cable when the mixer is turned off........or it will act like a pickup from the loop system!!

If the transformer iso makes it worse connected at the mixer try putting it inline at the other end of the cable where it connects to the system input.

An inline mute switch that shorts pin 2 and 3 together may work, but they would have to remember to un mute the switch or they will be calling you on Sunday morning saying there is no sound from the choir mics.

Leaving the mixer on and the inputs muted would be fine until someone forgets and turns it off and then you get called about the noise in the system.
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