Wednesday, June 30, 2021



One of my favorite guitars in the world is equipped with three single coil pickups. When I get this guitar too close to amplifiers or electrical wiring the guitar picks up hum and noise which gets magnifyed by my ampifier system. It is an age-old battle, great sound vs hum.

Fear not tone warriors, we’ve got modern weapons to deploy against the evil enemy of 60-cycle hum and noise. Meet the “Hum Debugger” from Electro-Harmonix.


It is a large size stomp box with a single input and output, one tiny toggle switch and an on-off pushbutton footswitch. A single LED tells you whether the unit is ON or OFF. It is not a glamourous looking box. With a $139 street price it’s not an inexpensive effect. You insert this pedal inline with your guitar at the beginning of your pedal effect chain, switch it on and the magic happens, hum disappears. The biggest caveat is that you must use the tiny 7.5-volt AC power supply (included with the Hum Debugger), it will NOT work with typical 9-volt DC stompbox power distribution systems.

In order for the Hum Debugger to do its hum-disappearing act the unit must sample the 60-cycle wall current, this is the reason you must use the special AC power supply provided with the Hum Debugger. 

The only user-adjustable control on the Hum Debugger is a mini two-position toggle switch labeled “Normal” and “Strong”. In use the Normal setting has done a fine job of dramatically reducing hum-induced noise with Strat-style guitars. 

I’ve been playing guitars equipped with single-coil pickups for 58 years so the effect from Hum Debugger really is a bit like magic to my ears. You turn this pedal ON and hum disappears. 


The circuitry inside the Hum Debugger needs access to the AC power that is powering your guitar and amplifier system. The Hum Debugger samples the existing AC source power through the custom power supply provided with the unit.  My guess is that after the offending hum signal is isolated, it is phase inverted and added back to your dry guitar sound before exiting the Hum Debugger output jack. The two inverted signals cancel each other out and hum just seems to disappear.

If you have ground-loop hum caused by inexpensive power supply distribution the Hum Debugger won’t get rid of that noise. You’ll need to know where your noise is coming from to get benefit from the Hum Debugger.


I read reviews before I buy gadgets. Reaction to the Hum Debugger seems mixed but the majority of reviews I could find were positive. The negative reviews seemed to ignor the advice from EHX in the manual for the Hum Debugger. 


“If you use more effects pedals than just the Hum Debugger we advise that the Hum Debugger be inserted at the beginning of the effects chain.” 


From the manual: “In NORMAL mode the Hum Debugger removes only the odd harmonics from the hum present in your signal. In STRONG mode the Hum Debugger removes both odd and even harmonics from your sighal’s hum content”.

Other than testing the “Strong” switch position to hear what it sounded like I keep the Hum Debugger on my main studio pedalboard in the “normal” position. 

The Hum Debugger gets rid of A LOT of hum when used correctly. 


I have noticed sonic degradation as a result of using the Hum Debugger. When it is processing clean guitar tones from a Line6 Variax guitarr running an acoustic model the high frequency harmonics are not as present. Running a Les Paul Special with any of my distortion system engaged was a huge disappointment. The Hum Debugger removes odd harmonics (Normal switch setting) or odd and even harmonics (Strong switch setting) relevent to the 60 cycle hum but it is very audible, especially with high gain distortion pedals.

To counteract the tone-sucking qualities of the Hum Debugger I have installed it in the number one slot of my Voodoo Lab pedal switching system so it can be easily added or subtracted from my guitar signal path. 

The Hum Debugger definitely changes the sound of distortion effects located downstream from the unit. Using the Hum Debugger results in reduced distortion leaving the upper harmonics of the tone altered in a way that is not appealing. I programmed my switching system to bypass the Hum Debugger when distortion effects are in use and when I’m using my acoustic guitar modeling system. 

The Hum Debugger excels at cleaning up hum in quiet guitar passages where any hum present is a distraction.

If your pedalboard is powered by a budget 9-volt power supply with ground-loop problems then the Hum Dedbugger will not get rid of the grinding, always-on hum you’re hearing. The only way to get rid of ground-loop HUM is through the use of a high-quality power supplies which provide total galvanic-isolation between the 9-volt output jacks.


In my day to day recording world I’m trying to record live tracks with as little noise and hum as possible. The EHX Hum Debugger is a tool for reducing annoying hum. It may not be right for every situation and combination of gadgets.  

In my personal quest for lower noise the Hum Debugger from Electro-Harmonix is a a useful tool to have in my toolbox, turn it on and hum disappears. Just make sure your tone does not disappear along with the hum lol.

I hope it works for you.

Thank you for reading High on Technology. Good music to you!

This article is ©May 2021 Mark King, it’s not ok to copy or quote without written permission.