Electro-Harmonix Knockout

By Phil O'Keefe | August 8, 2014

Attack Equalizer reissue

By Phil O'Keefe

Back in the mid to late 1970s, I remember seeing print ads for the Electro-Harmonix Attack Equalizer pedal in various magazines. It promised to "convert your Les Paul to a Fender" and "your Fender to a Les Paul", and all for only $69.95. At the time it seemed like a pretty far-fetched idea to me; after all, there are some significant differences between a Les Paul and most Fender guitars, and the two typically sound quite a bit different from each other. However, when I finally had the chance to try one, I was surprised by how drastically the Attack Equalizer could bend and warp the basic sonic character of whatever was running through it. Fast forward a few decades, and EHX has re-issued the Attack Equalizer as the Knockout Attack Equalizer reissue, or Knockout for short. Let's take a look and see how faithful it is to the original units, and how it stacks up as a tone shaper.

What You Need To Know

The Knockout is a somewhat unusual pedal. It's an equalizer, which are fairly common in pedal form, but it's not your typical graphic or parametric type, which are what you'll normally find when shopping for equalizer pedals. Instead, it uses multi-pole high and low pass filters and a blend control to work its magic.

Housed in Electro-Harmonix's rugged XO-sized die cast metal enclosure, the Knockout measures approximately 4 5/8" L x 3 7/8" W x 2 1/8" H, including the jacks, knobs, and switch.

Speaking of switching, the Knockout features true bypass switching. A red LED illuminates when the effect is active.

The Knockout can be powered by an internal 9V battery (and one is included with the pedal), or from an optional external 9VDC power supply. The power jack uses the industry standard 2.1mm center negative plug format, and is located at the top of the pedal. Battery compartment access is achieved by removing the four screws that hold the bottom plate in place.

There are no internal switches or trim pots inside the Knockout.

The input and output jacks are mounted on the sides of the pedal. The 1/4" input jack is a switching type unit, and plugging into it functions as a "power on" switch for the pedal, making it important to unplug it whenever a battery is installed and the pedal is not being used in order to prolong battery life.

Input impedance is 390k Ohm.

The Knockout has three knobs, just as the original EHX Attack Equalizer pedal did, but they're labeled differently on the reissue. On the original, the controls were labeled Fundamental, Blend and Attack. The Knockout instead labels them Low, Dry and High. While the names have changed, their functions remain the same as they were previously.

The Low knob controls the output from the Knockout's 7-pole low pass filter. Turning this knob clockwise results in more bass. The cutoff frequency is 85Hz.

The High knob has a similar effect on high frequencies, and controls the Knockout's 6-pole high pass filter. The filter's cutoff frequency is 6.5kHz. Turning this knob clockwise results in a brighter sound.

The Dry knob is one of the keys to the power and flexibility of the Knockout Attack Equalizer reissue. It allows you to blend in as little or as much of the dry, pre-equalized sound as you want. By blending the unprocessed signal with various amounts of high and/or low pass filtering, a wide range of different tones is possible.

Limitations

The Knockout is better suited to tonal shaping duties, and less so as a corrective, problem-solving equalizer. For corrective duties, such as notch filtering out a 60Hz hum, a parametric EQ may be a better choice.

A bit more experimentation may be required to achieve the desired results than you'd need with a graphic EQ, and you don't get the same visual feedback, but the results are worth the slightly increased time required. Once you have a handle on how the controls interact, dialing up the sound you want is much faster and easier.

Conclusions

It's smaller, arguably better-built and physically tougher, and has the true bypass switching and effect-active LED indicator that the vintage originals lacked, so while the Knockout is not 100% true to the original EHX Attack Equalizer, all of the changes are welcome improvements over the earlier models. Sound-wise, this pedal - like the originals - is a sleeper. While equalizers are never going to be the stars of anyone's pedal collection, their usefulness is hard to deny, and the Electro-Harmonix Knockout can provide a lot of cool sounds that you would be hard-pressed to duplicate with other EQ pedals.

Although it might be overstating it just a bit to say that the EHX Knockout converts a Les Paul into a Tele, or a Strat into a Les Paul, you really can fundamentally and significantly change the basic tone and character of your instrument with the Knockout, and while it won't make your Tele sound exactly the same as your Les Paul in every way, that's still a good analogy, and a reasonable way of describing the effect and overall capabilities of this pedal. While it is very useful for guitar, I found it to be even more indispensable for processing bass guitar; it makes getting a great bass tone much easier, and allowed me to add note definition and clarity while retaining great low end support at the same time. If you're a bass player, this pedal should not be missed! Considering the "street" price of the Knockout is about the same today as it was in the mid-1970s, the modern price is a real bargain - it's inexpensive enough that every guitar and bass player should add one to their pedal collection. Your tonal options will increase significantly if you do.