I’m trying to locate a disturbing ground hum and have tried everything from testing my wall outlets to swapping out keyboards. I’ve moved equipment around the room and swapped out gear one piece at a time.  No luck.

The only thing I have left to try is changing out cables.  I would have done so but don’t have any balanced TRS instrument cables here.  Before I buy cables that I may not need I’d like to ask a few simple questions. 

Are the line level L & R outs of a Yamaha S70XS balanced or unbalanced?
Should I run balanced cables all the way through?

Here’s my set-up:
• Yamaha S70XS out L & R to Rapco Horizon stereo/mono DI box.
• DI box to small Behringer mixer with three band EQ. (maybe upgrade mixer later)
• Mixer Main outs to two Yamaha DXR10s
• DI to FOH stereo or mono (depending on the engineer)

Note: I still get the hum when not using the DI Box in the chain

Kevin

kevin - 24 February 2016 11:27 AM

I’m trying to locate a disturbing ground hum and have tried everything from testing my wall outlets to swapping out keyboards. I’ve moved equipment around the room and swapped out gear one piece at a time.  No luck....

The outputs are unbalanced.

I solved initial noise levels in my DXR setup with proper gain staging.  I found that with the very high power output of the DXR it was easy to get sloppy with a weak signal up the line because the amp/speaker could produce plenty of sound with less than optimum gain staging. However, the end result was a poor signal to noise ratio at the speaker.  I carefully maximized the signal output from the keyboards on down.  The result was an extremely clean, powerful sound at the DXRs, with the DXR level control set at a real loafer number.

Hopefully you have optimized your gain strategy all the way through the routing.

With regard to the DI:  I ended up with a Radial ProD2 Passive Stereo DI Box straight out of my stereo keyboard mixer feed, which I have to say completely eliminated annoying ground buzzes for me.  And I don’t even run it with the ground lift engaged.  I’m a real fan of the box.

cmayhle - I think you’re right. Right now I’m running the DXRs and the main out on the mixer at about half.  That’s probably way too much.  I’m heading down to the rehearsal dungeon in a few minutes and will try tweaking the gain structure.

Ok – so I can run unbalanced cables from the S70XS to the DI.  Should I maybe be running balanced lines from the box to the mixer and balanced again from the mixer to the DXRs?  All of the cables I have are around 12 to 15’.

I own a Radial JDI mono DI box and love it. Now, needing stereo, I did look at the Radial ProD2 but it doesn’t sum to mono. I’d like to have that option in case the FOH guy doesn’t feel like running a second mic cable.

kevin - 24 February 2016 06:46 PM

Ok – so I can run unbalanced cables from the S70XS to the DI.  Should I maybe be running balanced lines from the box to the mixer and balanced again from the mixer to the DXRs?

Depends on the output of the box (DI). If it’s unbalanced nothing is gained. I don’t mix TRS cables with unbalanced outputs as I’ve had some instruments with unbalanced outputs create a boatload of noise probably due to intolerances in the connections. Not always, but for me, once is enough.

Thus for me; unbalanced keys to mixer, TS cable. Balanced out of mixer to DXRs. I’d probably be okay unbalanced as it"s a short run but I usually end up with a horde of wires around me carrying who knows what. FOH receives from me balanced outputs from Control Room out or Assignable Outputs (balanced) depending on the mixer. This allows for simple control of my stage volume without affecting FOH, and vice versa. Usually I have a stage drop near me and I’ll hit it without a DI. I rarely have gain or noise problems at all, if I do Radial Pro takes care of it.

As noted by cmayhle, proper gain staging is crucial.

Stone

I adjusted the gain staging starting with the keyboard at about 80% then the mixer channel levels and main out at unity.  I brought down the output level on the DXRs to about 35%.  This eliminated all but a very slight but very livable “noise”. 

The band showed up for rehearsal, I turned everything on and all was quite ….. until about an hour in when the “buzz” showed up again and was pretty loud.  I stood up from behind my keyboard and accidentally bumped into the electrical conduit connected to the outlet box where my gear is plugged in.  The buzz stopped!  The problem was that the nut on the fitting that holds the pipe to the box had come loose.  (in Chicago the metal conduit is used as ground) I opened the box and tightened the nut. Problem gone! Until about another hour or so when the buzz came back.

Yesterday, someone told me that the way to tell if the problem is in the house electric or gear is to plug one end of a ¼” cable into the powered speaker and hold the other end in your hand not allowing the open ends to touch anything.  If there is buzz, the problem is in the house electric, if not it’s on the gear side.  This test showed no buzz when holding the ends in my hand. 

So, my new theory is that more than one thing is causing the noise. I think I fixed two. 1) Gain structure 2) House ground by tightening that electrical conduit to the box.  I still have a slight buzz. My next step is to buy new cables.  Sheesh!!

Kevin

kevin - 29 February 2016 02:54 PM

I adjusted the gain staging starting with the keyboard at about 80% then the mixer channel levels and main out at unity.  I brought down the output level on the DXRs to about 35%.  This eliminated all but a very slight but very livable “noise”. 

The band showed up for rehearsal, I turned everything on and all was quite ….. until about an hour in when the “buzz” showed up again and was pretty loud.  I stood up from behind my keyboard and accidentally bumped into the electrical conduit connected to the outlet box where my gear is plugged in.  The buzz stopped!  The problem was that the nut on the fitting that holds the pipe to the box had come loose.  (in Chicago the metal conduit is used as ground) I opened the box and tightened the nut. Problem gone! Until about another hour or so when the buzz came back.

Yesterday, someone told me that the way to tell if the problem is in the house electric or gear is to plug one end of a ¼” cable into the powered speaker and hold the other end in your hand not allowing the open ends to touch anything.  If there is buzz, the problem is in the house electric, if not it’s on the gear side.  This test showed no buzz when holding the ends in my hand. 

So, my new theory is that more than one thing is causing the noise. I think I fixed two. 1) Gain structure 2) House ground by tightening that electrical conduit to the box.  I still have a slight buzz. My next step is to buy new cables.  Sheesh!!

Kevin

Rightfully so, use of rigid conduit as a bond is no longer acceptable. NEC requires a separate bond (ground) wire installed with each attached metal device also properly bonded. Having your electrical delivery system evaluated would be highly recommended. At the very least perhaps you can provide an isolated, properly installed line to your rehearsal area?

Holding a wire in your hand is not a practical way of telling you anything of value about your electrical system. Try not to touch a water line while doing so, that is, if it’s properly bonded.

Wish I was there man, I’d help you out.

Stone

You could try taking the mixer out of the equation temporarily, that is the Motif is connected only to the DI and the powered speakers. If there is no buzz, then you have some sort of grounding issue with the mixer.

Thanks for the replies.  I found the problem!

Yesterday afternoon an electrician friend of mine stopped by after work to check things out.  He couldn’t find anything out of the ordinary so we decided that we’d run a separate circuit to the rehearsal area with a dedicated ground after work today. 

Yesterday evening my brother in law, a musician with a background in electronics, brought over an Allen & Heath ZED. We started from scratch and when it got to the point to add the mixer we ran the ZED using the XLR balanced outs to the DXRs with XLR mic cable.  The annoying buzz was gone. We then added the DI box to the chain without a problem. 

Even though I cancelled my electrician I think we still may some day run that separate circuit with the dedicated ground. The conduit is already there and it would just be a matter of buying and pulling wire. 

This is a great forum.  Thanks for the replies.  I hope this helps someone else who may be experiencing the same issue.