this tour life

troubleshooting a hum and why it exists.

June 11, 2014
by

have a hum?

a hum is one of the most common problems in live music and there are many possible causes for this, most of them involve the ground connection. to eliminate the power source as the issue you can use an outlet tester. these will tell you if you have a problem at the outlet and what the problem is. you can get these at any hardware store and they are easy to fit in your workbox.

not that? the problem could be a ground loop, this creates a 60hz hum in an 110v system or 50hz hum in a 220v system. this happens when 2 or more devices are sharing a common ground. for example, a pedal board is plugged into the same outlet as the corresponding bass rig. they are both grounded at the same point and then the instrument cable completes the “loop” by connecting the ground from the pedal board output to the ground at the bass rig input. in an 110v environment one solution is to “lift” the ground of ONE of the devices, the one remaining ground would function for both. this is done using a “ground lift”; these essentially remove the ground from the ac cable. These things are small and there is no reason not to have them in your workbox.  another solution that can help in both 110v and 220v situations is using a D.I. box that has a “ground switch” in-between the pedal board and the amplifier. you can use this to break the loop that the instrument cable was completing.

have a hum coming from the guitar?

does it change when you touch anything metal on the guitar? its probably that one of the grounds between the metal components isn’t connected correctly. all of the switches, pickups, pots and even the bridge of your guitar share a common ground and if one isn’t connected it affects all of them. if this is your problem you will probably also notice some signal loss, might sound a little “thin”. instead of taking everything apart to visually see if there is a problem, you can use a multi meter between the components and if you see that one of them isn’t connected to another- you found it.

its also possible that you might be hearing EMI (electromagnetic interference). this is electrical radiation in the air being amplified along with everything else. a single coil pickup is usually the culprit on this one. if this is the case, try another pickup configuration on the guitar, change guitars, or deal with it.

still have a hum?

at this point the problem could be a bad cable somewhere in the chaining of the setup,a bad tube or some component inside your amplifier. if you suspect its coming from the amp itself, first inspect the tubes by tapping on the them and listening to see if one is “harmonic” or much hotter to the touch then the other tubes. if replacing suspicious tubes doesn’t resolve your hum issue, it might be time to open the amplifier up.

always unplug the amplifier, or any electronic equipment, before opening it up! its also a good idea to drain the capacitors to avoid any electrical shocks during your inspection. If you are unfamiliar with amp repair, it is probably best to take it to a professional repair person. Make friends and see what you can learn from him. This most certainly will not be the last time you need to tackle this commonly occurring situation.

electricity is strange.

 


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