# XLR to RCA cable causes hum,buzz.



## Guest

I had a noise coming from my amp, and I've narrowed it down to XLR to RCA cables going from a Crown XLS 402 to a Emotiva USP-1. I've narrowed it down to the cables because if I unplug them from the amp, it goes silent. The amp is not putting out a 60hz hum turned on and plugged in. The only time noise is picked up is when I plug a cable in to it. They look kind of cheap and I got them off of amazon.com

I wanted to try a set from monoprice, but before I do, is their something else I should be checking? Anyone know anything else that could be causing this?


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## mechman

I'd stick with the cable. It sounds like that is the problem and it's probably the cheapest fix.


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## Anthony

Sounds like you are getting a ground loop. Common for a pro-amp and consumer preamp setup.

Are they plugged into the same power strip (sometimes that helps)?
Try unhooking your cable/sat feed from the box.
Also try using a cheater plug to lift the ground on the amp (temporarily, just to diagnose the problem).

It may just be a bad cable, but those are two quick checks to see if it's a power issue or a signal issue.

Can the Emotiva do an XLR output to the Crown inputs? Keeping it balanced all the way should help with the grounding problem. 

Good luck.


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## Guest

Anthony said:


> Sounds like you are getting a ground loop. Common for a pro-amp and consumer preamp setup.
> 
> Are they plugged into the same power strip (sometimes that helps)?
> Try unhooking your cable/sat feed from the box.
> Also try using a cheater plug to lift the ground on the amp (temporarily, just to diagnose the problem).
> 
> It may just be a bad cable, but those are two quick checks to see if it's a power issue or a signal issue.
> 
> Can the Emotiva do an XLR output to the Crown inputs? Keeping it balanced all the way should help with the grounding problem.
> 
> Good luck.


I'm not sure what a cheater plug is. Do you know of a link or picture that could help explain that?

The emotiva does not have XLR out for the mains. Not sure why, the have that option for the sub out. The amp is not plugged in to the same strip as the pre-amp. I have all the low power stuff on a power strip and the main amp and sub is plugged in to the same outlet on the wall. I tried changing some stuff around, but it didn't change anything. I do believe they are all on the same circuit. The emotiva actually does a pretty good job of cutting the noise down, once I turn it on, but I just want to fix the hum/buzz that exist when everything else is turned off, but the crown

Just to clarify, the buzz/hum happens as soon as I plug a XLR cable in to the Crown, even if the other end is not connected to the emotiva. So, if pro and consumer products have this problem, its a problem with the emotiva out of the picture. The crown can be on, speakers connected, gain up with zero noise. As soon as I plug in a XLR in the back, nasty noise. It does seem to be interference noise, but I can't figure out what is causing it. I actually took the cover off the RCA side of the cable and put some electrical tape around the red wire, making sure nothing was grounding out, and nothing changed.


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## Andre

Your cables probably "think" your connecting a Balanced XLR output to a Balanced RCA input. The Emotiva's RCA's are probably not balanced. You can fix the problem if you don't mind working with your cables. 

the connectors on either side of the cable. The XLR end (3pin) all three pins will be connected. If on the RCA end all three wires are connected that is your problem. Find the pin 1 wire color on the XLR, trace it back to the RCA, that wire shouldn't be connected to anything on the RCA end, only the XLR end.


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## StephenRyan

It seems like this should be a simple problem but it's surprisingly complex. Connecting unbalanced connections to balanced presents a myriad of different scenarios depending on the devices at each end and the wiring of the cable. Noise can be picked up in a number of way's. Here are a few...

The crown amp has a differential input. This means there are two signal inputs and a ground used for shielding the inputs. One of the signal conductors is designated positive and propagated through the device in a way that a positive signal on this input presents a positive signal to the output (this preserves the phase of the signal as it runs through the amp). In a balanced scenario neither of the input signal conductors are connected to the ground/shield. In an xlr connector pins 2 & 3 carry the signal with pin 2 usually being positive (some #%!& gear reverses this). There is another conductor within an xlr cable (pin 1) that is designated signal ground. The fourth 'conductor' in an xlr cable is the shield. Conventional cabling will connect the shield to the connector metal case and rely on the device to make any connection between the shield and pin 1. The crown amp does this.

An adapter like the one you describe can be build in several ways. The rca end can be connected only to the signal pairs with no connection to the shield or signal ground wire in the xlr. This is more expensive to do because it requires that the rca connection be 'floated' using some insulating material.

More typically, the rca ground is tied to either or both the negative signal (xlr pin 3) and the signal ground (xlr pin 1). Use an ohm meter to check your adapter. When you connect this type of adapter to the input of the amp it grounds one side of the balanced connector to earth. The other end (in the case of the crown amp) goes directly into a very high impedance buffer amp (tl072). With no other connection it becomes a very sensitive antenna. Hence... noise. Connecting the rca cable to the Emotiva ties this line to the output impedance of the Emotiva (around 10k ohms) which converts it from an antenna to a quiet line.

I couldn't tell from your post if you were getting noise with the Emotiva connected or not.. Getting noise with it connected could be due to a number of things. If the noise changes when the Emotiva is powered off/on (either a thump, or buzz/hum) this means that either the Emotiva or the Crown power supply is the likely source of the noise. It the noise is constant then the noise is probably a result of the overall routing of the cabling and/or it being near power lines or other interference. A better (isolating) adapter might fix the problem as well.

Good luck, hope some of this helps, noise is quite complex..
Steve


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## StephenRyan

When connecting devices using unbalanced connections it's best to keep them nearby each other and connected to the same power using the shortest signal AND power cables you can. An unavoidable ground loop is created between the devices and keeping that loop as small as possible reduces it's vulnerability to noise. Think of the 'loop' created by the devices power and signal connections as an antenna. Shrinking the size of this loop reduces it's sensitivity.


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## Andre

Stephen is correct about the lenght being as short as possible. Long interconnect lenghts will require a transformer based converter


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## Tonto

How are you surge protecting your sub & amp? If you just plug them into the wall & you get a surge, it could pass to all your equipment through the connections. That type of event is not covered by your strips insurance policy. You can get small ones that cover just the outlet.


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## Andre

Personnaly I had an electrician install a whole home surge protector at the panel. Unit is made by Square D


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## Anthony

I have a whole house surge, but I still use power units at the equipment. For one, it ties all the third prong (and cable/SAT shield) to the same ground, which can help eliminate sources of hum/buzz. You can never have too much surge protection. 

I agree with a lot of what was said as to possible causes and solutions.

Oh, and here's an explanation of a cheater plug: http://en.wikipedia.org/wiki/Cheater_plug
Again: not for full time use, but if the third prong is causing a ground loop, this will help diagnose it.


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## Tonto

Nice, I've heard some discussion on the whole home surge protection @ the main box. Maybe someone more knowledgeable can chime in. The issue becomes, does your strip constitute daisy chaining or is it OK to add another one in line like that? Does the main box surge protector handle to cable coming into the house if there is a lightning strike. I remember having my equipment for like 2 years. The week I bought a surge protector, I was watching a DVD & saw a lightning strike in the field through my window. Everything turned off & I could hear my surge protector ringing. Talk about timing! Reset it & everything was fine.


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## gdstupak

Here is a very good article from Rane about noise and ground loops (it has good drawings of cable wiring):

http://www.rane.com/note110.html


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## Guest

A little bit of an update. I went on a last minuet road trip, so I've been gone awhile.

Anyway, I've done some trouble shooting and I'm pretty sure the cables are just acting as an antenna, picking up noise. I'm going to order 1.5" ones from monoprice (half the length of what I have). They look like they are higher quality, better shielded, ect. I ended up unplugging a lot of things to make sure nothing else in my stereo was causing it.

How things are plugged up: All the low power stuff, turn table, pre-amp, cd player etc, are plugged in to a power strip that is suppose to equalize the ground. The last house I lived in had two power boxes and the inspector warned that the ground might have some noise in it, so I got the strip. It seems to work. At the moment, I'm living in a newer place, one box, everything plugged in to the same line (two different outlets).

I went ahead and plugged the crown amp and sub in to a spare UPS I had. It is plugged in to a different outlet from the other strip, but I didn't think a simple power strip could support everything I had.

I am NOT getting a 60hz hum from a bad ground, but as soon as a XLR to RCA cable is plugged in, I start to get a little background noise. I actually ended up turning the gain down on the crown and sub to help cut it. Now, I don't notice it unless I put my ear to the speakers, but I still want to try shorter, better cables to clean it up even more.


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## Anthony

Seems like you have it narrowed down. Sorry you are getting interference. RF interference is really hard to nail down (it can be intermittent). Shielding will help some. If you are picking up one specific radio station (or baby monitor, phone, etc), just changing the length a little bit could make it go away.

Good luck and let us know how it turns out.


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## Guest

Well, monoprice was out of their shortest XLR to RCA cables for awhile, but I did finally get them in. I went from 6' random Amazon.com cable to a 1.5' mono price cable. The monoprice looked like a much higher quality unit. Better shielding, better looking connections...

Overall, it probably cleaned up about 95% of my problem. If I stick my ear up to the speaker, I can hear a tiny bit of noise, but nothing from listening distance.

So if anyone else wants to go pro amp and needs a XLR to RCA cable, try and go as short as possible. I think this is actually the first cable I got from mono price, but I'm a fan. They sell nice, really cheap stuff.


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