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Reply To: Buzzing, hissing

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#133551
parsky1
Member

The places to start looking is where you are using 3-prong plugs.  Generally, 2 prong supplies like wallwarts don't have the the secondary side ground of the transformer tied to AC ground (output is floating).  When I speak of "AC Ground" I'm speaking of the green wire in household wiring.  The reason why we love those Fat walwarts is because the transformer has 4000 volts of isolation and therefore there is almost a zero chance of a short from the primary to secondary side.  In the case of switching power supplies (3 prong type like those with laptops, televisions, etc) it is difficult to obtain 4000 volt isolation because these supplies have very high switching frequencies which usually have smaller transformers with lower primary to secondary isolation.  If there is a short between primary to secondary, then it gets shorted to ground and trips a fuse.  Saving you from an unpleasant shock or death.

I would usually start looking for 3-prong type adapters.  Most amps, as far as I can tell, have the secondary side ground tied to AC ground just like laptop supplies.  Therefore if you want zero hum you can' thave any other supplies that are wired this way.  That is why I put every effect on its own FAT walwart (none of those junky switching walwarts) or each on a separate output of a Pedal Power 2+, Cioks DC10, or PowerFactor.   

You could also buy an Ebtech Humx which basically uses an old back to back diode trick to tie the secondary side ground to ac ground.  Basically in normal operation the diodes prevent the "hum" current from flowing.  If there is a primary to secondary side short, the secondary side voltage exceeds the 0.7V drop of the diode and it begins to conduct thus blowing the fuse and protecting you from getting shocked. 

You can try diagnosing with a 2-prong "cheater" plug, but this is at your own risk and I would not use it as a long term solution.  It may at least tell you where you have a ground loop.  This is at your own risk and I take no responsibility for it.

My suspicion is that both the amplifier and macbook are the sources of the ground loop and one of those needs to get lifted.  Basically some of the ground current from your amp with a slight 60hz component on it is not going back to its original ground as it going through the audiopath ground to your macbook, or viceversa.   It could also be the fact that you have other FX pedals daisy chained to the same supply.  Usually what happens is there has always been a ground loop but as people add more fx pedals the problem becomes amplified due to various reasons.

 I have also seen it where the shell of a patch cable is touching the metal of your pedalboard and causing a hum.  This is probably because the chasis of my Voodoo labs pedal power is tied to AC ground and since it is screwed into the pedalboard, it ties the entire pedalboard chasis to AC ground.  Therefore whenever the metal plug of a patch cable touches it, some AC current flows through the patchcable shield.  If this is on a cable on the input side of a guitar amp and you run a high gain channel you will definately notice it.

Also, whenever possible, plug your pedalboard and amp into the same outlet.  Actually just always do this to lessen the chances of hum issues.