The Electro-Harmonix Knockout is an analog EQ pedal that Electro-Harmonix calls an Attack Equalizer. Instead of boosting or cutting fixed frequency bands, it splits your signal into three paths: one Low-Pass filter, one High-Pass filter, and a direct dry signal, each with its own level knob1. The result is a way to reshape the core character of a guitar, thinning a thick-sounding instrument or filling out a thin one.
Electro-Harmonix describes it as "one of the most specific and powerful tonal adjustment systems that you will ever use," and says the two-filter combination "can make your Les Paul sound like a Strat and your Strat sound like a Tele"1. The pedal was released in 2008 and discontinued in 2021, so it is now a secondhand buy1.
What the Knockout does to your sound
The Knockout is not a graphic EQ with sliders or a parametric EQ with sweepable frequencies. It is a pair of filters with a dry blend. The LOW knob is a volume control for the low or bass frequencies, the HIGH knob is a volume control for the high or treble frequencies, and the DRY knob controls the level of the untouched input signal1. Balancing the three is the whole game: more LOW and DRY gives a thicker, rounder tone, while more HIGH thins things out and adds bite.
Vintage Guitar, covering the reissue in 2012, described it as "a two-filter effect designed to help boost signal when used after a distortion box" and noted it uses "a six-pole filter to shape the high end of the mids"2. That steep six-pole filtering is what lets the pedal carve aggressively into the midrange rather than gently tilting the tone.
| Control | What it does |
|---|---|
| LOW knob | Volume control for the low or bass frequencies1 |
| HIGH knob | Volume control for the high or treble frequencies1 |
| DRY knob | Volume control for the signal present at the input jack1 |
| Footswitch and LED | Toggles between effect and bypass; lit LED means effect mode1 |
Power and connections
The Knockout runs on a 9V battery, which was included when the pedal was sold new, or on an optional 9.6VDC-200mA power adapter, which was not included. Current draw is 30mA1. Connections are simple: a 1/4" INPUT jack for your guitar and a 1/4" OUTPUT jack for your amp, with a single footswitch and status LED to toggle the effect on and off1. The pedal sits in a tough and compact die-cast chassis measuring 4.75 x 4 x 2.25 inches1.
The Knockout was discontinued in 20211, so it is found on the used market rather than new from Electro-Harmonix.
Where it came from
The version most players know was released in 20081. Vintage Guitar reported in June 2012 on the Knockout Attack Equalizer reissue, so the design predates the 2008 enclosure and has been through more than one run at Electro-Harmonix21. The reissue carried true-bypass switching, which the maker's page confirms for the final version as well12.
Where it sits in a signal chain
Electro-Harmonix says to "use after distortion to bring out the heavy weight punch of the metal masters"1. Vintage Guitar's description agrees, calling it a two-filter effect designed to help boost signal when used after a distortion box2. Placed after a distortion or overdrive pedal, it acts on the already-clipped signal, tightening the low end and shaping the high mids rather than changing what the distortion pedal itself sees.
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Questions
Is the Electro-Harmonix Knockout discontinued?
Yes. Electro-Harmonix discontinued the Knockout Attack Equalizer in 2021. It was originally released in 2008, and the version sold in the 2010s was a reissue of an earlier design. Used units are the way to find one now.
Does the EHX Knockout take a battery?
Yes. The Knockout runs on a 9V battery, and one was included when the pedal was sold new. It can also run on an optional 9.6VDC-200mA power adapter, which was not included. Current draw is 30mA.
Is the Electro-Harmonix Knockout true bypass?
Yes. Electro-Harmonix lists true bypass for the Knockout, and Vintage Guitar's coverage of the reissue also noted true-bypass switching. When the LED is lit, the pedal is in effect mode; when it is off, the signal passes through untouched.
Can the Knockout make a Les Paul sound like a Strat?
That is how Electro-Harmonix describes it. The maker says the two-filter combination can make your Les Paul sound like a Strat and your Strat sound like a Tele. It is a marketing claim, but the filters do let you thin or thicken a guitar's core tone considerably.
Should the Knockout go before or after distortion?
Electro-Harmonix says to use it after distortion to bring out the heavy weight punch of the metal masters. Vintage Guitar also described the reissue as a two-filter effect designed to help boost signal when used after a distortion box.
Sources (2)
- Knockout, Electro-Harmonix, 2021
- E-H Reissues Knockout Attack Equalizer, Vintage Guitar magazine, 2012-06-27
