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Author Topic: strange hummmmmmm  (Read 2203 times)

Gary Fitzpatrick

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strange hummmmmmm
« on: November 05, 2013, 12:05:03 pm »

help needed!

background : im installing a soundcraft epm6 mixing desk in the gallery of a church, feeding into main system which is controlled by a soundweb 3088.

problem : when I connected all up, and turned on there was quite a loud hum. when I disconnected the mixing desk the hum seemed to disappear...or nearly disappear. I can plug a dynamic or condensor mix into the socket in the gallery and no problem. works perfectly. as soon as I plug the mixing desk into the socket the hum appears.
checked wiring in socket and all leads and everything seems to be ok. went into the back of the sohndweb, and disconnected the shield on the input coming from the gallery...now the hum when the mixing desk is connected in the gallery has disappeared. BUT if I turn off the power to the mixing desk in the gallery, the hum returns.

any ideas???
any solutions??

thanks Gary
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Lee Buckalew

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Re: strange hummmmmmm
« Reply #1 on: November 05, 2013, 06:28:55 pm »

help needed!

background : im installing a soundcraft epm6 mixing desk in the gallery of a church, feeding into main system which is controlled by a soundweb 3088.

problem : when I connected all up, and turned on there was quite a loud hum. when I disconnected the mixing desk the hum seemed to disappear...or nearly disappear. I can plug a dynamic or condensor mix into the socket in the gallery and no problem. works perfectly. as soon as I plug the mixing desk into the socket the hum appears.
checked wiring in socket and all leads and everything seems to be ok. went into the back of the sohndweb, and disconnected the shield on the input coming from the gallery...now the hum when the mixing desk is connected in the gallery has disappeared. BUT if I turn off the power to the mixing desk in the gallery, the hum returns.

any ideas???
any solutions??

thanks Gary

Are you certain that you are connecting to a line level XLR input and not mic level.  Also possibly mic level with phantom power on? 

Try lifting pin 1 of the cable that you are connecting from the console to the wall plate.

Lee
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Hal Bissinger/COMSYSTEC

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Re: strange hummmmmmm
« Reply #2 on: November 05, 2013, 09:09:39 pm »

The 3088 is located in another part of the church than the gallery epm6? Sounds like you have power ground loop problems.

-Hal
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Brad Weber

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Re: strange hummmmmmm
« Reply #3 on: November 06, 2013, 09:09:28 am »

background : im installing a soundcraft epm6 mixing desk in the gallery of a church, feeding into main system which is controlled by a soundweb 3088.

problem : when I connected all up, and turned on there was quite a loud hum. when I disconnected the mixing desk the hum seemed to disappear...or nearly disappear. I can plug a dynamic or condensor mix into the socket in the gallery and no problem. works perfectly. as soon as I plug the mixing desk into the socket the hum appears.
Are you replacing an existing mixer in the gallery/balcony and, if so, what are you replacing and has anything else changed?  Or are you adding a new mixer using existing inputs in the gallery/balcony?  The fact that you can direct connect dynamic or condenser microphones into the galley/balcony connections being used and they with those mics work suggests those are likely configured as microphone inputs with phantom power.  Do you have any documentation of the existing system and/or the Soundweb configuration and settings?

If that is the case then you may be driving microphone inputs with a +4dBu nominal, +20dBu maximum line level output from the mixer.  You have a couple of options to address that.  If you will always be using the mixer then one option is to reprogram the related Soundweb 3088 inputs to be line level inputs with 0dB gain, which will then match the +20dBu maximum level of the mixer.  This is accomplished from the Soundweb Designer software.  One potential issue with this is that the 3088 addressed its eight inputs as two four channel groups; Inputs 1-4 and Inputs 5-8.  That includes for assigning them as either microphone or line level inputs, thus you would need to assign all four inputs in the related group as line inputs, you can't do that for just one or two inputs.
 
A second option, especially if you want to still be able to use the gallery/balcony system inputs for microphones as well as the mixer, would be to add a transformer style DI box between the mixer outputs and the system inputs.  That will drop the mixer outputs to mixcrophone level and address any possible phantom power related issues.  It should also help with any potential ground loop issues.
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Gary Fitzpatrick

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Re: strange hummmmmmm
« Reply #4 on: November 06, 2013, 06:19:46 pm »

Are you replacing an existing mixer in the gallery/balcony and, if so, what are you replacing and has anything else changed?  Or are you adding a new mixer using existing inputs in the gallery/balcony?  The fact that you can direct connect dynamic or condenser microphones into the galley/balcony connections being used and they with those mics work suggests those are likely configured as microphone inputs with phantom power.  Do you have any documentation of the existing system and/or the Soundweb configuration and settings?

If that is the case then you may be driving microphone inputs with a +4dBu nominal, +20dBu maximum line level output from the mixer.  You have a couple of options to address that.  If you will always be using the mixer then one option is to reprogram the related Soundweb 3088 inputs to be line level inputs with 0dB gain, which will then match the +20dBu maximum level of the mixer.  This is accomplished from the Soundweb Designer software.  One potential issue with this is that the 3088 addressed its eight inputs as two four channel groups; Inputs 1-4 and Inputs 5-8.  That includes for assigning them as either microphone or line level inputs, thus you would need to assign all four inputs in the related group as line inputs, you can't do that for just one or two inputs.
 
A second option, especially if you want to still be able to use the gallery/balcony system inputs for microphones as well as the mixer, would be to add a transformer style DI box between the mixer outputs and the system inputs.  That will drop the mixer outputs to mixcrophone level and address any possible phantom power related issues.  It should also help with any potential ground loop issues.

I actually run a new cable from the sacristy up to the balcony...there was never any microphone connection up there before. I need the other 7 inputs on the soundweb for mic level inputs so I cant assign one block to line level. I had phantom power turned off on this channel, and the gain turned right down to 0db so I didnt think it should be a problem. I actually redesigned the program myself in the soundweb as part of this job.

I will try attaching a DI box between the balcony mixing desk and the microphone point and hopefully it will cure my problems.

Thanks
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duane massey

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Re: strange hummmmmmm
« Reply #5 on: November 06, 2013, 06:53:57 pm »

Reconnect the shield at the Soundweb and lift it at the EPM6.
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Duane Massey
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Brad Weber

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Re: strange hummmmmmm
« Reply #6 on: November 07, 2013, 08:14:01 am »

I actually run a new cable from the sacristy up to the balcony...there was never any microphone connection up there before. I need the other 7 inputs on the soundweb for mic level inputs so I cant assign one block to line level. I had phantom power turned off on this channel, and the gain turned right down to 0db so I didnt think it should be a problem. I actually redesigned the program myself in the soundweb as part of this job.
You stated "I can plug a dynamic or condensor mix into the socket in the gallery and no problem. works perfectly."  Assuming you meant dynamic or condenser mic rather than "mix" that would seem to indicate that the related SW3088 input is set for microphone level and that phantom power is turned on.
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Gary Fitzpatrick

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Re: strange hummmmmmm
« Reply #7 on: November 07, 2013, 02:54:48 pm »

I had the soundweb software open so was able to turn phantom on and off as needbe. I got it solved anyway...put a cheap passive di box and humm gone.
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Re: strange hummmmmmm
« Reply #7 on: November 07, 2013, 02:54:48 pm »


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