Guitar buzzing – Ground loop hum

A friend of mine is having issues with his guitar buzzing so I thought I would post some info on getting around it.

Guitars them selves are literately antennas. The pickup/s can pick up and then amplify Hz sound waves from near by devices such as 50/60Hz from your wall outlet or other devices that use wall warts, microwave ovens, phones and even a fridge. These wave forms are a byproduct of electromagnetic interference (EMI)..

There are a few ways to help suppress EMI in the guitar itself by double checking the bridge to see if it is properly grounded. Replace the tone capacitor if it is a vintage guitar. You can even add some copper foil to the inside the wiring compartment and under the pick guard to use as a filter (Faraday cage).

Now there are a few other places to check such as your cabling and most of all the amp and effect pedals.

Lets start with the effect pedals since these cause a lot of issues.
A effect pedal usually uses a 9V battery. They have a option for a DC adapter known as a wall wart. You might notice when you switch from a battery to a external voltage supply that you hear a hum. Well a wall wart is nothing more then a step down transformer converting high Alternating Current to a lower voltage then passes though a bridge rectifier that converts it to DC. They are not earth referenced ground and they’re not regulated. There are a few ways to rectify AC voltage into DC. You have the half bridge and a full bridge. From the rectifier there are some times inside a wall wart a smoothing capacitor but a lot of times it isn’t the right grade for the device you want to power. So you still end up with raw DC power.

Look at this diagram bellow, we have clean DC that is straight across that has the proper smoothing added. Batteries naturally are clean DC. Look bellow that you have rectified half bridge DC that has no smoothing and below that full bridge with no smoothing. When smoothing is applied it straights out the waveform.

250px-Current_rectification_diagram.svg

Now with the dirty raw DC you will probably hear it in a amp. A high pitch sound around 60Hz to 120Hz.

Now there are also switch mode wall warts and they use a even higher frequency but still audible to a human ear. Do not use switch mode wall warts.

In all your best bet is to stick with batteries since batteries are a clean Direct Current.

Now the amp can cause hum as well. Depending how old the amp is some use a three prong and some use a two prong. Tube amps use two prong and some early solid state amps also used two prong. Do not do something stupid like adding a third prong ground your amp. You will probably blow it up. Nine times out of ten it’s the smoothing capacitors and need to be changed out. Tube amps will still hum at a degree at idle. That’s just what tubes do.

Now if you have a modern amp that uses three prongs for a earth reference ground then chances are you’re running multiple amps, some one wired a outlet wrong or 60Hz is bleeding from the neutral to ground This is a form of ground loop. Almost everyone doesn’t know that the Earth ground is indeed connected the the neutral at the fuse panel in your home. It branches off to literately ground outside near your power meter. To fix this you can make a adapter or even include it inside your amp. It’s just a couple of diodes and a 1K resistor.

groudloop

Doesn’t matter what end is what. When I deploy this circuit I use it closest to the transformer. This will fix it most of the time. Comes in handy for multiple amp configurations. However since we are in the digital age and you’re brand new Line 6 might be using a switch mode power supply instead of linear so Just use a adapter box. (I’m not sure if modern amps use switch mode supplies.)

Also check the power supply to the amp or take it for a tech to check it out.

That is all the tips I got.

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