Keeley Electronics C4 4-Knob Compressor Review – Best Compression Pedal?

Review of: Keeley Electronics C4 4-Knob Compressor

Reviewed by: Rating:5On May 13, 2015Last modified:October 8, 2016



Reviewing the Keeley Electronics “4-Knob” Compressor almost seems redundant. After all, this is the pedal that put Keeley Electronics on the map and helped make Robert Keeley one of the most respected names in the boutique pedal industry. There’s no question as to whether the 4-Knob Compressor is a good pedal. It’s a certified classic in the realm of boutique guitar pedals. But with new pedal builders practically coming out of the woodwork and countless compression pedals released since Keeley’s classic “2-Knob” version came on the scene, it’s Best Guitar Effects’ continuing mission to discern which pedals remain at the top of the pecking order. Does the classic 4-Knob Compressor still hold up today? Is it the best guitar compression pedal around? We’ll help you answer that in our Keeley Electronics 4-Knob Compressor review.

Here’s a quick feature rundown before we jump right in with this one.


  • Controls for Sustain, Level, Clipping & Attack
  • Tone-tested components
  • True bypass switching circuit
  • Triple-pole double-throw switch
  • Powered by 9-volt battery or 9VDC power adapter (current draw: 5mA)

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Sound & Performance:

The Keeley C4 4-Knob Compressor is designed to do two things: compress your guitar signal and provide smooth sustain. It does that with four easy-to-use controls: Sustain, Level, Attack, & Clipping. The old 2-Knob Compressor (now discontinued) had the Attack & Clipping controls inside the pedal. The 4-Knob version, or “C4” as it’s now called, puts these essential controls on the outside as they’re quite useful for configuring the pedal to your current guitar and style of playing.

The Sustain and Level controls will be familiar to anyone who’s ever used or at least heard of the old Ross Compressor or Dyna Comp. The Sustain control essentially increases the amount of compression (ratio) and puts more of a squeeze on your guitar signal as you crank up the knob. The Level control sets your overall volume level. Easy enough.

Keeley-Electronics-C4-4-Knob-Compressor-Review-Best-Guitar-Compression-Pedal-02The Clipping and Attack controls are where things get interesting. The Clipping control limits the input signal going into the pedal before it hits the Sustain section. Think of it as a sort of pre-gain control. For lower level signals you may want to increase the setting or max it out. If you’re running a hotter signal or noticing additional noise or distortion, cut it back a bit. While the manual generally recommends leaving it all the way up, I find myself sometimes liking to pull it back a bit to decrease the amount of saturation produced from higher Sustain settings. What’s really interesting is how higher Clipping settings can liven up your tone and impart a very unique character on your overall sound. It adds to the vibe of the 4-Knob Compressor and contributes to why so many people love this pedal. The Keeley C4 Compressor has its own unique vibe and sound, a quality shared by the most famous studio compressors.

The Attack control adjusts the recovery time of the compressor, seeming almost more like a “release” control. Attack and release seem like both sides of the same coin here. A higher Attack setting gives your guitar a quicker, punchier sound, while lower settings make the sound “bloom” after your initial pick attack. The lower Attack settings are more useful for light chordal work and slower, fragmented playing for sounds that are lush and beautiful. The higher settings are preferable for quick, single note playing and when you’re using the pedal for singing solos that sustain at consistent volume levels.

And that’s part of what makes the 4-Knob Compressor so versatile. Whether you’re playing clean chords, dialing it in for searing leads, getting your funk on, or going for some country twang, there’s a setting here that’ll get the job done. This pedal is also the first stompbox I ever discovered was being used by studio engineers on a variety of instruments and audio signals. The Clipping knob comes into play here for handling higher line levels.

While Keeley Electronics have since released the GC-2 limiting Amplifier & Keeley Compressor Pro pedals, the classic 4-knobber is still going strong and stands out among other similarly Ross-inspired guitar compressors. I always look forward to seeing older designs reimagined. I’m one of those few guitarists that always think the best is still yet to come. But the 4-Knob Compressor got something right, and few pedals can even come close to the quality that Robert Keeley cooked up with this pedal.

The Keeley Electronics 4-Knob Compressor has still got it after all these years. It’s still up there with the best guitar compressor pedals. Let’s see the final result.



The Keeley Electronics C4 4-Knob Compressor lives up to its reputation and is still one of the best guitar compression pedals available today. While inspired by some classic compressors, Keeley’s pedal has become just as much a legend in its own right. Whether you want subtle compression or heavier squashing of your signal, the 4-Knob Compressor always remains musical while adding a pleasing sustain to your guitar. And it has a unique tone of its own among stompbox compressors. Nothing around sounds quite like it. And fewer pedals still can compete with this level of sheer overall quality.

That concludes our Keeley Electronics C4 4-Knob Compressor review. Thanks for reading.


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Gabriel Tanaka

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