Quick question about ground loops - or using a input splitter...guitar content

[runonce]

I work a show with a guitarist who uses one of those plastic Radio Shack headphone splitters so he can have both his electric fiddle and guitar plugged into the same input on his Boss GT-6 pedal unit.

It is a mono splitter...two inputs combined to one 1/4 inch plug.

Reason I ask is - we have lingering hum issues...even when we work other venues.

I think the guy should have some sort of true A/B switch.

Is there the potential for ground loops in his current setup...? (he plays electric guitar and fiddle - Im assuming the fiddle has some sort of active pickup in it.)

The noise we get sounds like "bad electricity" - kinda comes and goes...an suddenly vanishes...

Sorry for the slightly off topic post...thanks!

[Patrick]

Troubleshoot the source of humming.  Plug guitar into amp, same with fiddle and see if the noise is there.  Try the same thing, but with the pedal in the chain.  Humming generally comes from an amplifier issue, but the intermittent crackling could be an entirely different issue.   

A more quality way of summing his inputs going into the pedal will certainly clean up his signal.  Especially since the impedances between the electric guitar and fiddle are most likely way different.

[kirk97132]

You can get that 60Hz hum from some instrument pickups and stages that have dimming and or not perfect AC wiring on stage.  I forget the brands but there are two or three pick ups that will do this more than others.  If it is a pick up on the instrument actually picking up the RFi noise then there is not much you can do.  Or at least that I know about.  I am basically ignorant of wiring in guitar/fiddle/mando pick ups.  Maybe someone knows of a shielding trick or something?  If you are trying to find the hum onstage make sure you have stage lighting on like you would at a show. 

[runonce]

Troubleshoot the source of humming.  Plug guitar into amp, same with fiddle and see if the noise is there.  Try the same thing, but with the pedal in the chain.  Humming generally comes from an amplifier issue, but the intermittent crackling could be an entirely different issue.   

A more quality way of summing his inputs going into the pedal will certainly clean up his signal.  Especially since the impedances between the electric guitar and fiddle are most likely way different.

The noise hasnt been as repeatable as I would like - seems to start in the middle of soundcheck (when ironically I have the least time to troubleshoot) - and then it seems to disappear once everybody is on stage and playing.

It sounds very electro-mechanical - swells up and down.

I should also mention we have 5 wireless units going as well - all different brands.

Most recently - this happened at the York Toyota Expo - except it was just in the monitors, the mains were clean...very nasty...the performers really had to suck it up for that one. When you spoke into a mic - it would have a electrical resonance - kind of like a feed back ring...except it was electric hum and not sound.

More or less the same sound on 3 different PAs...although the recent gigs at our home theatre seemed fine.

[runonce]

You can get that 60Hz hum from some instrument pickups and stages that have dimming and or not perfect AC wiring on stage.  I forget the brands but there are two or three pick ups that will do this more than others.  If it is a pick up on the instrument actually picking up the RFi noise then there is not much you can do.  Or at least that I know about.  I am basically ignorant of wiring in guitar/fiddle/mando pick ups.  Maybe someone knows of a shielding trick or something?  If you are trying to find the hum onstage make sure you have stage lighting on like you would at a show.

I think we should check our stage AC for sure...I have to plug my recording gear into the same rack strip that the PA uses - if I use another outlet, It often puts a buzz in the PA...(but this was an obvious one)

we did just get big new (to us) ENR 24 faderpack, but these problems predate that. And we have just completely rewired our lighting rig.

thanks for the replies guys...

[Patrick]

Troubleshoot the source of humming.  Plug guitar into amp, same with fiddle and see if the noise is there.  Try the same thing, but with the pedal in the chain.  Humming generally comes from an amplifier issue, but the intermittent crackling could be an entirely different issue.   

A more quality way of summing his inputs going into the pedal will certainly clean up his signal.  Especially since the impedances between the electric guitar and fiddle are most likely way different.

The noise hasnt been as repeatable as I would like - seems to start in the middle of soundcheck (when ironically I have the least time to troubleshoot) - and then it seems to disappear once everybody is on stage and playing.

It sounds very electro-mechanical - swells up and down.

I should also mention we have 5 wireless units going as well - all different brands.

Most recently - this happened at the York Toyota Expo - except it was just in the monitors, the mains were clean...very nasty...the performers really had to suck it up for that one. When you spoke into a mic - it would have a electrical resonance - kind of like a feed back ring...except it was electric hum and not sound.

More or less the same sound on 3 different PAs...although the recent gigs at our home theatre seemed fine.

Hmm. Are you guys carrying your own console for all these shows?

What wireless units are you using?  Handheld mics or instruments?

I have experienced the same noise that you are describing and it always comes back to dirty power or a loose ground connection.  Make sure to put your amps and console on different circuits, and if possible, keep your backline on as many different circuits as you can. 

[kirk97132]

another thing....you mentioned that you had a monitor issue but not mains.  That sounds like a line level cable was run parallel to an AC power cable most likely one connected to a dimmer.  if you have to get signal and power cords near each other they need to cross at a 90 degree angle to help eliminate inductive pickup of RFI.  The other thing is if you can get you lighting designer to run throw a quick set of lighting cues the buzz may be from a certian lighting instrument or set up so you'll want to try and find it

[Patrick]

another thing....you mentioned that you had a monitor issue but not mains.  That sounds like a line level cable was run parallel to an AC power cable most likely one connected to a dimmer.  if you have to get signal and power cords near each other they need to cross at a 90 degree angle to help eliminate inductive pickup of RFI.  The other thing is if you can get you lighting designer to run throw a quick set of lighting cues the buzz may be from a certian lighting instrument or set up so you'll want to try and find it

This is also great advice.

I recently was on a corporate show which we spent 3 hours troubleshooting (like fools!) why a video screen was showing "rolling lines."  Turns out our video cables were crossing paths with a simple 20amp dimmer in one spot.  We moved the cable and all was well!  Lots of time wasted on chasing grounds and moving circuits around.

[kirk97132]

JOn has a great point.  There are a lot of variables in your problem.  Eliminating the ones you can, like a splitter, then chasing ghosts is a little easier

[ghellquist]

Guessing - suggesting.

When the player puts down one of the instrument, it sometimes ends up near a power cable or other source of mains hum. The pickup in the instrument is sensitivy to magnetic fields. And depending on exactly where he places it och moves it, the hum may come or go.
  -- get an A/B switch

Other hum issues.
  -- check carefully for ground loops, you mentioned your recording rig creating problems. Get a few transformer isolated DI boxes to isolate problems.

// Gunnar

[andromedanwarmachine]

I would not have said the 1/4" mono y-adaptor was the source of the problem- unless the electric fiddle has a separate power connection.

I think you've got to differentiate between pick-up induction noise and a ground-loop. For a ground loop, your going to need a connection between gear which is seconded by a mains connection also.

For example; if you had two or three pieces of stage gear- (guitars, self powered pedals) running into one mixeramp (for the sake of argument) you couldn't have a mains loop as there's no second path to the source gear. You get a problem when a signal connection is shadowed by a mains connection of unequal impedance.

Plug everything in and power up and disconnect all I/P's. Reconnect one by one, establish the bad line and then run the power to the offending article from the mixer position.

Bottom line- try to run ALL power from the one position/area/source to aspire towards star-earthing...

have you got your own mains-distibution?

JimP