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Author Topic: Likely cause for mixer noise?  (Read 3088 times)

Mike Caldwell

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Re: Likely cause for mixer noise?
« Reply #10 on: June 10, 2018, 12:07:14 PM »

Make sure that your XLR cables do not have pin 1 (ground) tied to the outer shell of the XLR connector.

Do you get the hum if you only connect to one of the mixers XLR outputs?

As JR mentioned check with headphones connected to the XLR, you will need to use some clip leads or a creative adapter.
To take that further check pins two and three individually with headphones on the XLR output. Connect XLR pin one to the sleeve of the headphone plug and connect XLR pin 2 to the tip of the headphone plug ( the tip is the left headphone channel) you should hear sound, now connect XLR pin 3 to the headphone plug tip, you should hear sound.
If you don't hear sound on one or the other XLR pins you may have a problem with the output amp or connection in the mixer.

If you mixer uses what has been called an impedance balanced output you would not hear sound on the output of XLR pin 3.

David Allred

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Re: Likely cause for mixer noise?
« Reply #11 on: June 10, 2018, 08:25:40 PM »

Make sure that your XLR cables do not have pin 1 (ground) tied to the outer shell of the XLR connector.

Do you get the hum if you only connect to one of the mixers XLR outputs?

As JR mentioned check with headphones connected to the XLR, you will need to use some clip leads or a creative adapter.
To take that further check pins two and three individually with headphones on the XLR output. Connect XLR pin one to the sleeve of the headphone plug and connect XLR pin 2 to the tip of the headphone plug ( the tip is the left headphone channel) you should hear sound, now connect XLR pin 3 to the headphone plug tip, you should hear sound.
If you don't hear sound on one or the other XLR pins you may have a problem with the output amp or connection in the mixer.

If you mixer uses what has been called an impedance balanced output you would not hear sound on the output of XLR pin 3.

Shells not ground.  I connected an xlr-rca barrel adaptor, then an rca to 1/4",  then a 1/4" barrel to connect to the headphones.  No buz.   The xlr-rca adaptor shorts pin1 to 3.
« Last Edit: June 10, 2018, 08:38:34 PM by David Allred »
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David Allred

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Re: Likely cause for mixer noise?
« Reply #12 on: June 14, 2018, 10:16:22 AM »

Let's add some strangeness to this.
I connected XLR from the noisy mixer to a powered speaker(NX25P) - clean (ground lift NOT engaged).  Connected back to 3 different PLX amps (2 in one rack, one in another).  All buzzed, but the single buzzed less.
In the rack with the mixer is a Driverack PA... not connected and not on.  Turned on the PA... no change (not connected).  I unplugged power cord to the PA and the buzz stopped (80-90% reduction).  I wish I had patched through the PA, but the wife called me to supper, so I called it a night.
Thoughts?
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Ike Zimbel

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Re: Likely cause for mixer noise?
« Reply #13 on: June 14, 2018, 02:57:05 PM »

Let's add some strangeness to this.
I connected XLR from the noisy mixer to a powered speaker(NX25P) - clean (ground lift NOT engaged).  Connected back to 3 different PLX amps (2 in one rack, one in another).  All buzzed, but the single buzzed less.
In the rack with the mixer is a Driverack PA... not connected and not on.  Turned on the PA... no change (not connected).  I unplugged power cord to the PA and the buzz stopped (80-90% reduction).  I wish I had patched through the PA, but the wife called me to supper, so I called it a night.
Thoughts?
Tighten all of the rack screws, both in the amp racks and in the rack with the mixer and Drive Rack.
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~Ike Zimbel~
Wireless frequency coordination specialist and educator.
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Radio Active Designs
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Mike Caldwell

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Re: Likely cause for mixer noise?
« Reply #14 on: June 14, 2018, 04:09:16 PM »

Let's add some strangeness to this.
I connected XLR from the noisy mixer to a powered speaker(NX25P) - clean (ground lift NOT engaged).  Connected back to 3 different PLX amps (2 in one rack, one in another).  All buzzed, but the single buzzed less.
In the rack with the mixer is a Driverack PA... not connected and not on.  Turned on the PA... no change (not connected).  I unplugged power cord to the PA and the buzz stopped (80-90% reduction).  I wish I had patched through the PA, but the wife called me to supper, so I called it a night.
Thoughts?

Have any of the power cords had new plugs put on them?

David Allred

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Re: Likely cause for mixer noise?
« Reply #15 on: June 14, 2018, 04:33:13 PM »

Have any of the power cords had new plugs put on them?
No.  The only non factory cord is a quad box.  I will eliminate it from the chain this afternoon.
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David Allred

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Re: Likely cause for mixer noise?
« Reply #16 on: June 14, 2018, 07:29:22 PM »

No.  The only non factory cord is a quad box.  I will eliminate it from the chain this afternoon.
I must have only tried one output when I connected to the powered speaker.  After much back and forth with amp and  cables,  only the right output  has the noise, but every amp and powered speaker buzzes.  Removed the mixer from the rack and the buzz remains.  I brought I to the house and in the quieter room the  buzz does increase as the master is raised.  Not a great amount,  but definitely noticeable.
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Ike Zimbel

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Re: Likely cause for mixer noise?
« Reply #17 on: June 15, 2018, 11:47:30 AM »

I must have only tried one output when I connected to the powered speaker.  After much back and forth with amp and  cables,  only the right output  has the noise, but every amp and powered speaker buzzes.  Removed the mixer from the rack and the buzz remains.  I brought I to the house and in the quieter room the  buzz does increase as the master is raised.  Not a great amount,  but definitely noticeable.
What frequency is the dominant one? If it is 120Hz, you almost certainly have a power supply issue, usually either a failed filter capacitor, or a good one with a broken solder joint.
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~Ike Zimbel~
Wireless frequency coordination specialist and educator.
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Radio Active Designs
Pro Audio equipment repair and upgrades.
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Mike Caldwell

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Re: Likely cause for mixer noise?
« Reply #18 on: June 15, 2018, 12:17:44 PM »

Did you ever try head phones directly connected to the xlr outputs?
A battery powered headphone amp could be used as well for a test.

David Allred

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Re: Likely cause for mixer noise?
« Reply #19 on: June 15, 2018, 12:55:16 PM »

Did you ever try head phones directly connected to the xlr outputs?
A battery powered headphone amp could be used as well for a test.

I did, but using an XLR to RCA non-transformer adaptor.  Also can't remember if I checked both channels for sure.  I plan to re-visit this and make a pig tail to make checking more trustworthy.  Should I try 1 with 2 and 1 with 3 to the headphone?  Both must work, right? 
Can I also use the pigtail to measure voltage between 1/3 and 2/3?  They should be the same, right?  2-ish volts each?  Or will that tell me anything?
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Re: Likely cause for mixer noise?
« Reply #19 on: June 15, 2018, 12:55:16 PM »


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