Electro-Harmonix Cntl Knob review

A pedalboard-friendly alternative to an expression pedal

Electro-Harmonix Cntl Knob
(Image: © Future / Phil Barker)

Guitar World Verdict

An inexpensive, clever utility stompbox that will expand your pedalboard possibilities while saving space.


  • +

    Very cheap.

  • +

    Very compact.

  • +

    Very effective.


  • -

    Nothing, unless you need the treadle.

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We’ve probably all got one or more pedals that have an input for expression pedal control… and we’ve probably all got one or more reasons why we don’t always use them. 

Maybe we don’t own an expression pedal or we think it’s too much of a faff to set up. Or maybe it’s simply that an expression pedal (or indeed multiple expression pedals) can take up valuable real estate on our pedalboards

Now, there are instances when an expression pedal’s treadle action is essential: you’d definitely need one if you wanted to have real physical control over the wahs found in the Boss GT-1000Core reviewed in this issue, for example, or maybe to get some Whammy-style action from a pitch shifter such as the recently reviewed Electro-Harmonix Pitch Fork+

However, there are also instances where that treadle action of incrementally morphing through the full range of expression values is not required, and that’s where EHX has come up with an elegant solution that will slot into your pedalboard much more easily than a treadle-based pedal.

Also try...

Mooer Expline

(Image credit: Mooer)

• Mooer Expline
If you need an expression pedal but don’t have the space for a full-size one, this one is micro-sized at 128mm deep by 55mm wide and 48mm high.

• Old Blood Noise Endeavors Expression Slider
How about using a fader to change expression values? This will easily slot into your ’board or could perhaps be strapped to your mic stand.

• Mission Engineering Expressionator
A programmable multi-expression controller that lets one expression pedal control up to three expression-enabled effects.

The Cntl Knob is a micro-sized stompbox that lets you instantly switch between two different user-set expression pedal values; effectively, you get to toggle between two positions of a traditional expression pedal with its footswitch. The two values are set by a pair of knobs (EXP 1 and EXP 2), each with an associated LED to show which is currently active.

With both knobs, the fully anti-clockwise start point represents the heel-down position of an expression pedal, while the fully right clockwise position corresponds to the toe position, so you can set them to cover the full 0 to 127 heel-to-toe range or to switch between any two values in between.

The possibilities are many, including effectively giving you switching between two ‘presets’ in the case of pedals that allow multiple parameters to be mapped to expression values, toggling between two gain values on a drive pedal or two different pitches on a pitch shifter pedal. And, as the Cntl Knob has switchable polarity, it is compatible with many manufacturer’s pedals, not just those from Electro-Harmonix.


A clever utility item that will expand your pedalboard possibilities and is inexpensive and space-saving.

Electro-Harmonix Cntl Knob

(Image credit: Future / Phil Barker)


  • PRICE: $39 / £35
  • TYPE: Static expression pedal
  • FEATURES: Supplied 6ft cable
  • CONTROLS: Exp 1, Exp 2, TRS+/- Button, Bypass footswitch
  • CONNECTIONS: Standard Exp Out
  • POWER: 9V DC adaptor – pedal requires 5mA
  • DIMENSIONS: 40 (w) x 92 (d) x 45mm (h)
  • CONTACT: Electro-Harmonix

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Trevor Curwen

Trevor Curwen has played guitar for several decades – he's also mimed it on the UK's Top of the Pops. Much of his working life, though, has been spent behind the mixing desk, during which time he has built up a solid collection of the guitars, amps and pedals needed to cover just about any studio session. He writes pedal reviews for Guitarist and has contributed to Total Guitar, MusicRadar and Future Music among others.