Help with a noisy XLR Out on Nashville 112

Jerry Knapper · From: Lakeland, Florida , USA

I have an older Nashville 112 that I recently acquired and have read the topics on mic or no mic. I play in an Opry where I can run through the Phonic box head that they use, but using a mic has not worked well since it is unmaned. When I use the direct XLR out, I get a loud hum that I can't reduce by adjusting any of the amp controls. Are any of you other NV112 owners having that problem or does anyone know a quick fix. I have notified Peavey, but have no response as of the last week. (Over Christmas!!!). I have a Wharfedale PA system and it seems to be less loud through it, but still quite noticable.

robert kramer · From: Nashville TN

Sounds like a ground loop problem. Try this:

http://www.sweetwater.com/store/detail/HumX/?gclid=CIPSuKuT-J4CFQOdnAodTH9RJw

This is also essential if you are using two amps or - if you are going into an amp and into a board at the same time.

Jack Stoner · From: Kansas City, MO

I would agree it's probably a ground loop problem.

One source of problems in XLR cables is that some add the cable's shield to the ground connection in the connector and if that's done there is potential for a ground loop hum. I bought some Musicians Friend XLR cables and every one of them had the shield connected to the ground lug in the XLR connector. My friend (and forumite)Blake Hawkins, who is an EE and worked in Radio and TV gave me the advice about the grounds.

Jerry Knapper · From: Lakeland, Florida , USA

There is no question that the ground loop problem has exixted. I had tried to use a profex II or a GFX1000 effects processor and every time I pluged the power supply in from either one, I received a horrible ground loop noise problem through the amp. I did purchase a Hum X which helped that problem to some degree, but it has not improved the line out noise through the XLR. While here in Florida, I did pull the chassis to see if there was anything out of the ordinary, but did not find anything. I will change XLR cables and see if that helps. I surely appreciate the suggestions and feedback.

Georg Sørtun · From: Mandal, Agder, Norway

Agree on the probable cause - ground loop.
This is more frequent/problematic on equipment run on American mains than on our European/Norwegian ones, but cause and solutions are basically the same.

Problem is that true balanced, low-impedance/high-level line outputs are rare in such equipment these days, and the NV 112 doesn't have one. What it has is a quite normal quasi-balanced, medium-impedance/low-level output that is almost as open to level-offsets and ground-loops and the resulting noise/hum as the usual non-balanced ones.

I run all such quasi-balanced and unbalanced outputs, including that in an NV 112, through a true line-driver, that brings down the impedance, raises the level, and breaks the connection - including ground - via a single-end shielded 600/600 ohm line-trafo. No ground-loop or direct signal connections means the mains conditions and equipment at both ends don't matter anymore. As a result one can drive cables that are several hundred yards long with such line-drivers, and it doesn't matter how mains are wired at both ends.

FWIW: the longest I've driven audio-signals with proper line-drivers is 8 kilometers - through phone wires - with frequency correction to compensate for non-linear line-loss.

Balanced, XLR, cables, for microphones etc., have ground connections in order to deliver phantom-feed voltage/current to drive microphones, and because they are also frequently used for unbalanced mics that use the ground. Balanced cables for line-level signals don't need that ground connection, but ground is usually connected anyway since same cables are used both for mics and line.

Usually not a good idea to cut the ground connection in the XLR cable to get rid of the hum, since the result may be broken quasi-balanced line-drivers and input circuits at the other end as the equipment lose common ground. Only line-trafos can eliminate the need for common ground.
Lifting the mains ground at the NV 112 will definitely work better, if its quasi-balanced line-output isn't damaged already.

Jack Stoner · From: Kansas City, MO

To clarify, what I was referring to is removing the ground jumper between the ground tab on the XLR shell connector and Pin 1 in the XLR connector (the ground connection).

Jerry Knapper · From: Lakeland, Florida , USA

This is good info. I have some transforming items that I will work with and see what happens. Jack, I am sorry we couldn't make it down for your Dec 9th jam. I had it in mind, but we arrived that day and I just couldn't fit it into my schedule. We could have discussed this face to face then.

Jack Stoner · From: Kansas City, MO

Jerry, too bad as we had a good jam and a Christmas party. Too bad too as the weather here is much better than it is in OK. I talked to my daughter in KC and they got dumped on with snow and blowing snow Christmas eve.

Georg Sørtun · From: Mandal, Agder, Norway

Jerry, if you by "transforming items" mean "line-trafos" for the line-out, remember that the NV 112's XLR line-out should be loaded with 5 Kohm or higher. Too low load-impedance may ruin the balance, the sound, or (worst case scenario) blow up the NV 112's line-out driver.

Eddie Harper · From: Fairfield, Ohio

Hi Jack
I have the same problem with my Nashville 1000. Would the same fix as the 112 be for me also. I use a DI Box at church that is supposed to eliminate the ground loop problem but it doesn't. I finally just disconnected the XLR from the back of the 1000 and not running thru the PA at present.

thanks Eddie

Jerry Knapper · From: Lakeland, Florida , USA

I have a couple of DI boxes that I was thinking about trying when we get home. According to Eddie they may not work. It is good to know the essential load required though. As I stated, I contacted Peavey but did not hear from them. I have just downloaded a manual with the schematics in it and hope that will help with your info.

Jonathan Cullifer · From: Gallatin, TN

Just run out of the preamp out into a real DI with a ground lift on it. Remember that you are putting out a line level signal so it will be fairly hot at the board.

Jerry Knapper · From: Lakeland, Florida , USA

I need the amp for a monitor. Doesn't that cut out the amp?

Jack Stoner · From: Kansas City, MO

The NV112 and 1000 have the same (identical) preamp section and XLR output.

I don't have any problem with either my NV112 or 1000 running out of the XLR to my recording board. The potential for a ground loop hum is the same there as it would be to a mixer. I've run direct with an XLR cable and I've also run through a DI box.

Jonathan Cullifer · From: Gallatin, TN

Jerry Knapper · From: Lakeland, Florida , USA

Thanks Jonathan

Randy Waldo · From: Memphis,TN, USA

Jerry,
I have engineered a lot of live recordings
in the past. I usually keep a stick of
ground lift adapters in my gear for just this
type of situation. This usually is most common
in hooking up a DI on the bass rig. Some
keyboard rigs as well. Not the correct fix but
you can usually lift the AC ground and it will
go away. In some strange situations, I will start
with the guitar amp that I am trying to fix
the hum problem with, if that doesn't work, I start
at the console and try each piece of gear in
the chain until I find the culprit. I
have found that u could lift the ground on the power amp or EQ
on the house system. By doing this, you break
the power ground which is not good, but it
help troubleshoot where the loop is and can
get you through an emergency situaltion.
Grounding problems can make you chase
your tail sometimes and make you want to
pull your hair out. Hope this helps.

Be Blessed,
Randy.

Gary Chiappetta · From: San Bruno, California, USA

Jerry,
About 5-years ago I acquired a Radial JDI passive direct box and always carry it with me in my gig bag. It has solved a lot of problems for me in the field because of the features it has (including ground lift). The JDI is expensive at $199, but I am glad I have it in my equipment inventory even though I don't use it very often. The main reason I bought it was that it gave me a way to put a DI on my Twin Reverb. I just run a cable from the extension speaker output to the JDI and I have a way to go directly to a mixing board with the same signal that is going to my speakers.
http://www.radialeng.com/di-jdi.htm
I have a Nashville 112 myself and have run into the same problem you have with a ground-loop hum when I tried to use the direct-out. My solution at the time was to use my Twin Reverb and the JDI. After reading this thread I am going to make an adapter cable for XLR-to-1/4" and keep it with the JDI.

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