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Author Topic: Guitar Hum  (Read 1704 times)

Joel Colin

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Guitar Hum
« on: November 27, 2016, 10:39:50 pm »

Hi,
Before I start I am quite a newbie to sound so please do bear with me.
So I am currently connecting a acoustic guitar via a TS cable to an active DI(https://djcity.com.au/product/behringer-di20-di-box/). From there I would typically go to a snake and then to the front of house mixer.
I originally connected the guitar through a XLR male from the guitar and then into the DI but the port on the guitar broke for some reason. Now the guitarist has asked if I could take a TS cable instead out of the guitar.
Since then, I am getting this unwanted hum for some reason. I've looked into the http://www.swamp.net.au/alctron-hm-2-hum-eliminator-transformer-isolator-1, to see if I could get rid of that hum.
Would there be any other ways of eliminating this hum?
Thanks
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Ivan Beaver

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Re: Guitar Hum
« Reply #1 on: November 28, 2016, 07:27:05 am »


I originally connected the guitar through a XLR male from the guitar and then into the DI but the port on the guitar broke for some reason. Now the guitarist has asked if I could take a TS cable instead out of the guitar.
Since then, I am getting this unwanted hum for some reason.
Thanks
Are you saying that the guitar originally had an XLR output?

And then you put a TS jack on the guitar?

If so-how did you wire it?

XLR is typically balanced (not always), and TS is always unbalanced.

I suspect a wiring issue in the replacement of the jack.
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Ivan Beaver
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PHYSICS- NOT FADS!

Keith Broughton

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Re: Guitar Hum
« Reply #2 on: November 28, 2016, 07:41:26 am »


I suspect a wiring issue in the replacement of the jack.
I'm with Ivan on this one.
As it's not connected to an amp, it's not a ground loop hum.
Plug the bass guitar into your DI and see if it hums.
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Joel Colin

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Re: Guitar Hum
« Reply #3 on: November 29, 2016, 12:43:00 am »

Are you saying that the guitar originally had an XLR output?

And then you put a TS jack on the guitar?

If so-how did you wire it?

XLR is typically balanced (not always), and TS is always unbalanced.

I suspect a wiring issue in the replacement of the jack.
Hi Ivan,
To answer your question: yes there originally was an XLR port on the guitar but it broke for some reason. Now we are taking a TS out of the guitar and into the DI. The guitar port had one XLR out and one quarter inch out as well. From there we take XLR out of the DI.
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Don T. Williams

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Re: Guitar Hum
« Reply #4 on: November 29, 2016, 01:01:58 am »

Make certain you are only using a good quality "guitar cord" with shielded cable wired correctly.  TRS cables and unshielded speaker TS speaker cable won't work correctly.

Also make certain the DI isn't sitting on a guitar amp's or some other gear's power transformer.  Power transformers can radiate a strong 60Hz field.
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Sammy Barr

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Re: Guitar Hum
« Reply #5 on: November 29, 2016, 11:05:49 am »

It could be that the same wire problem internally that caused the xlr to stop working is causing the hum in the ts outlet.
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Josh Millward

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Re: Guitar Hum
« Reply #6 on: November 29, 2016, 05:36:49 pm »

I am somewhat surprised that no one has bothered to mention the ground lift button on the DI.

1. Be certain you are using a proper TS guitar cable to plug the guitar into the DI. Using a 1/4" speaker cable is no good at all and TRS cables are not for this purpose.

2. If you are certain you are using the right cable, then try flipping the Ground Lift switch on the DI box. It may help reduce the noise or it may make the noise worse. You won't know until you try. I always try to start with the switches in the Grounded position and switch them to the Lift position if there is noise.

3. Also, check any pad switches on the DI box and disengage them. For a typical acoustic guitar, you should not need any engaged, unless the guitar is outfitted with an active pickup of some flavor and is providing line level output instead of instrument level. If that is the case, then you will not be able to turn the console's input sensitivity down low enough to stop from clipping the input. You will need to engage the pad on the DI box.
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Josh Millward
Danley Sound Labs

Don T. Williams

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Re: Guitar Hum
« Reply #7 on: November 30, 2016, 04:39:17 pm »

+1 for Josh.  I just assumed the ground lift switch was tried. It may not have been!  Some DI boxes don't have ground lift switches, like the Rapco Blox series.  I see a lot of these in churches.  There is another (Rapco I think) DI box with two 1/4" inputs, one lifted and one grounded.  I haven't had much luck with these.  I like a physical switch better.
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Frank DeWitt

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Re: Guitar Hum
« Reply #8 on: December 03, 2016, 05:26:46 pm »

The DI box you are using has a ground lift but it doesn't really disconnect the ground.  It inserts a resistor.  On these less expensive active DI boxes they can't lift the ground because that is part of the power for the DI.

I would first find out if the guitar works well when plugged directly into a guitar amp.  If it does, and it has a battery, or if you are using a pedal board I would use a passive DI. 
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Luke Geis

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Re: Guitar Hum
« Reply #9 on: December 04, 2016, 10:43:20 pm »

First thing is to be sure you have an instrument cable and not a speaker cable for the TS connection. The fact that you know it's a TS connector leads me to believe you already know that much. Next is to figure out why the XLR connector is NG. They are always, as for as I can tell, part of the same circuit. This means if the XLR circuit is bad, why wouldn't the 1/4" have an issue as well? That being the case. I am not a fan of active DI's. I think they are technically and actually inferior to any decent passive DI. Some will argue, but lest face it, an active DI has circuity that is limited by its design, which means if any one thing goes wrong it won't work right. A passive DI has very few and significantly less parts to fail than any active DI. To confirm, plug said guitar and cable directly into the mixers 1/4" input. If the problem follows, it is the guitar. If the mixer has no such connection try another mixer that does. If the problem exists at the guitar and or cable it will follow it. If it is fine, then you need to move down the line to the snake, mixer or other factors.
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