Having trouble with a thumping noise when you activate your killswitch? Not to worry – it’s a very common problem, and is very easily fixed.
The Most Likely Cause of Killswitch Pedal Thump
A proper guitar killswitch pedal mutes the signal to ground, and if the noise-to-signal ratio is large enough, this can manifest as an audible thump whenever signal is grounded. When ground planes are shared between pedals, noise and hiss cascades from one pedal to the next, markedly degrading your guitar signal.
If you’re experiencing killswitch pedal thump, 99/100 times, that sound is caused by your pedal power supply. Many pedal power supplies are available, and they are not all equal.
In order to offer superior tone and prevent signal noise, each pedal in your chain needs to be connected to its own output on a transformer-isolated pedal power supply. We’ll find out what that means in a moment, but first, let’s find out which pedal power supplies don’t isolate their outputs, and thus, share ground planes.
Old Pedal Power Supplies
Many old style pedal power supplies, including some older models from trusted names like Roland, T-Rex and others (I’ve got an old Arion one from my teenage years somewhere around here at Vein-Tap.com HQ) use shared ground outputs to power pedals.
Even if (and it’s not a guarantee) each power output is filtered, you’ve still got the problem of a shared ground plane. This means that the added noise from each pedal adds up, each one loading up the next, leading to a massive helping of unwanted hiss and noise.
If you’re still using a shared ground pedal power supply, t’s time to upgrade. It was time to upgrade 10 years ago. The difference a proper, transformer-isolated power supply with have on your sound is amazing. Spend the money. You’ll be glad you did.
Wallwart / Daisy Chain Power Supplies
These. These are, without exception, utterly useless. They will ruin your tone. Always. Every time. Do not use them.
Falsely Advertised Isolated Power Supplies
Many pedal power supplies claim to be isolated, without offering transformer ground isolated outputs. They are merely “short-circuit” isolated – which isn’t good enough. Short circuit isolation means that, if a pedal is shorted somehow, that short is prevented from affecting the other pedals in your chain. This can be acheived by adding a single diode to each power output.
You see these advertised on eBay and Amazon a lot. Many do have filtered power outputs, but these outputs share a ground plane, and as such, there’s only so much they can do to prevent hiss, noise, and an impared noise to signal ratio.
Do not allow yourself to fall for this dodgy marketing trick. You need a true, transformer-isolated pedal power supply.
How to Cure Pedal Thump
Transformer-isolated pedal power supplies cure ground thump. It’s that simple.
Transformer ground isolated pedal power supplies use small electronic devices known as transformers on each and every power output. By connecting each pedal in your chain to its own output on these power supplies, you give it its own individual ground plane – stopping the noise, hiss and gain from cascading from one pedal to the next. This keeps the noise to signal ratio of your chain as low as possible, and makes sure that the thump you hear from engaging a guitar killswitch pedal is almost inaudible.
These superior pedal power supplies aren’t even that expensive these days. Many power supply models in Thomann’s Harley Benton range, including the £30 (£30!) PowerPlant JR, boast full, true transformer-isolated outputs. For the cost, it’s a no brainer.
Fender’s Engine Room series, Strymon’s Zuma series, T Rex’s Fuel Tank JR as well as Voodoo Lab’s range of pedal supplies also feature transformer-isolation. There’s loads available, and they’re well worth their price.
The Second Most Likely Cause of Pedal Thump
There is another common reason for audible guitar killswitch pedal thump, and can even show up when using transformer-isolated pedal power supplies, and that’s static build-up. Fortunately, this is very easy to cure – simply leave your amp on standby as it powers up, and give your guitar killswitch pedal a few dozen stomps in quick succession. This disperses the static build up. From there, you and switch your amp on from Standby, and the problem should be gone.
I hope this short article helps you cure guitar killswitch pedal thump, and helps to improve your tone as well. Thanks for reading!