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Author Topic: strange high pitched sound from installed system  (Read 1957 times)

Gary Fitzpatrick

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strange high pitched sound from installed system
« on: December 23, 2015, 02:37:42 pm »

Hi, I have a problem with an installed system in a chapel and I'm looking for some help in diagnosing the problem.

 The system in question is in a traditional church....Soundweb Blu-16, QSC ISA amplifier driving several Bose 402 70v speakers. All microphones are AKG GN series on the Altar, and an AKG D5 for the choir.

Anyway, the priest has been complaining of a high pitched intermittent sound appearing occasionally. I have been down to the church several times and the system has always behaved itself perfectly. He called me back down today, and was able to demonstrate the sound to me. He discovered that when he touches the pins of the socket in the choir area, this high pitched sound is produced.  (all the mic sockets in this church are male rather than female....dont know why the original installer done that). It is a high pitched sound...maybe around 1.5-2k whenever you touch pin 1 and pin 2 or 3 at the same time. I put a multimeter across the pins to see was there any of the pins touching and everything was perfect. However, I did notice that when i touched pin 2 or pin 3 with one lead of the multimeter whilst leaving the other lead touching nothing, the high pitched sound sounded for maybe 3-4 seconds before stopping. I also discovered that if i disconnected the test lead from the multimeter and touched pin 2 or pin 3, the same thing happened...the high pitched sound was emitted for a brief period before stopping.

Although the priest did remind me that this sound was being emitted mid service whilst he was talking into one of the other microphones, and occurred when he was talking into both the altar and ambo microphones.

any suggestions as to the cause? or if you need any more detail i will try and fill you in :)

Thanks
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Ivan Beaver

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Re: strange high pitched sound from installed system
« Reply #1 on: December 23, 2015, 03:40:08 pm »

Years ago-it was "kinda standard" to have male XLRs as the inputs.

Why I don't know-but I have seen it a number of times.

There was even some gear made with male XLRs as inputs.

The installer of the new system "should" have changed this-unless all the Churches cables were setup as Female to female and they did not want to change it.

This sounds like an automix type system

I would suggest taking those jacks and redoing the processing so that they are muted or reduced in level when the primary mics are being used.

Maybe put an automixer in the DSP.

You could also try putting some gates on those channels in the DSP.

It sounds like what is happening is you are setting up an oscillation on those inputs.

If you don't want to redo the DSP, you could try putting some termination resistors on the back of the XLR jacks.

I would suggest starting with 20K from pins 2 to 3 and and the same for each of those pins to ground.

Of course the value might have to be changed a good bit-depending on the particulars of the system.
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Gary Fitzpatrick

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Re: strange high pitched sound from installed system
« Reply #2 on: December 23, 2015, 03:55:46 pm »

Years ago-it was "kinda standard" to have male XLRs as the inputs.

Why I don't know-but I have seen it a number of times.

There was even some gear made with male XLRs as inputs.

The installer of the new system "should" have changed this-unless all the Churches cables were setup as Female to female and they did not want to change it.

This sounds like an automix type system

I would suggest taking those jacks and redoing the processing so that they are muted or reduced in level when the primary mics are being used.

Maybe put an automixer in the DSP.

You could also try putting some gates on those channels in the DSP.

It sounds like what is happening is you are setting up an oscillation on those inputs.

If you don't want to redo the DSP, you could try putting some termination resistors on the back of the XLR jacks.

I would suggest starting with 20K from pins 2 to 3 and and the same for each of those pins to ground.

Of course the value might have to be changed a good bit-depending on the particulars of the system.

Yea in the new year I'm going to change all the sockets to female XLRs. The mad thing is that there are several AKG GN series mics that the original installer made female - female adaptors to convert them!

Re-doing the DSP is not a problem. Infact it is on the cards anyway as the DSP is locked down (The original installer password protected all his files and has now gone bust).

So you think that possibly gating the channels should stop the sound from developing?
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John Roberts {JR}

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Re: strange high pitched sound from installed system
« Reply #3 on: December 23, 2015, 04:30:10 pm »

Years ago-it was "kinda standard" to have male XLRs as the inputs.
kinda not... unless you had a sh_pile of male jacks to use up.
Quote
Why I don't know-but I have seen it a number of times.

There was even some gear made with male XLRs as inputs.

The installer of the new system "should" have changed this-unless all the Churches cables were setup as Female to female and they did not want to change it.

This sounds like an automix type system

I would suggest taking those jacks and redoing the processing so that they are muted or reduced in level when the primary mics are being used.

Maybe put an automixer in the DSP.

You could also try putting some gates on those channels in the DSP.

It sounds like what is happening is you are setting up an oscillation on those inputs.

If you don't want to redo the DSP, you could try putting some termination resistors on the back of the XLR jacks.

I would suggest starting with 20K from pins 2 to 3 and and the same for each of those pins to ground.
+1   properly designed instal gear will generally be quiet and stable even with no mic plugged in... sometimes there could be a 100' mic cord plugged in with no mic, acting as an antenna...  a termination resistance might help maybe even some C.
Quote
Of course the value might have to be changed a good bit-depending on the particulars of the system.
You can try muting unused inputs or shorting open inputs until the noise goes away. Figure out where it is coming in, and squash it like a bug. .

JR
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Ivan Beaver

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Re: strange high pitched sound from installed system
« Reply #4 on: December 23, 2015, 04:46:51 pm »

kinda not... unless you had a sh_pile of male jacks to use up.
I said "kinda" because I have seen it in a number of installs in different states-so I "Assumed" (you know what happens when you do that) that "somewhere/somehow" it happened for a reason.

Of course I have also seen AC power plugs (twist lock) used as mic inputs as well.

Often it is amazing what was done years ago-and not in a good way ;)
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Jason Lavoie

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Re: strange high pitched sound from installed system
« Reply #5 on: December 23, 2015, 05:16:43 pm »

Years ago-it was "kinda standard" to have male XLRs as the inputs.

Why I don't know-but I have seen it a number of times.

There was even some gear made with male XLRs as inputs.

I was told that one or two manufacturers a long time ago put male XLRs on their mixer/amplifiers because they were cheaper than females, and of course people wired systems to follow suit

Jason
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Mike Caldwell

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Re: strange high pitched sound from installed system
« Reply #6 on: January 09, 2016, 08:44:57 am »

Did you check and see if pin one is tied to the shell of the XLR's, check the wiring in the connectors on the cables as well. If you find one there will be others!!!

There was an era where male xlr inputs tried to become the standard, I have an old Shure mixer from that era as proof.

Charlie Tappa

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Re: strange high pitched sound from installed system
« Reply #7 on: January 11, 2016, 10:43:25 pm »

(all the mic sockets in this church are male rather than female....dont know why the original installer done that). 
 
 

I believe the inputs were male because a Male XLR connector had a far better chance of remaining useable after a period of time when mounted in a floor.   Female XLR's tend to fill up with dirt after a short time in a floor and become unuseable.  This was from a time before a wireless mic was a common item, wired mic's plugging into a floor were quite common in old systems.

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Gary-Fitzpatrick

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Re: strange high pitched sound from installed system
« Reply #8 on: January 12, 2016, 06:47:25 am »

Turns out it seems to be a problem with a socket at the back door...probably damp/corrosion related. Reprogrammed the system and took out any auto mixers and just gated the inputs.

In this particular church three sockets are on the floor...and the pins on the three male sockets had been misplaced leaving the female cable connector hard to get in and out


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Re: strange high pitched sound from installed system
« Reply #8 on: January 12, 2016, 06:47:25 am »


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