Walrus Audio ACS1 MkII

The Walrus Audio ACS1 MkII is an amplifier and speaker cabinet simulator pedal: a digital box that replaces an amp and cab on a pedalboard, feeding a PA, an interface or a pair of headphones. Walrus Audio describes it as "an amplifier and speaker cab simulator delivering the sound and feel of world-class amplifiers"¹²³. It is the second version of the ACS1, part of the Walrus Audio Mako Series, and it holds six amp models and twelve cabinet IRs (impulse responses, the recorded snapshots of a speaker cabinet used to simulate it digitally)⁴.

What it does: digital amp models with IR cabinets

The ACS1 MkII carries six amplifier models. The three carried over from the original ACS1 emulate the Fender Deluxe Reverb, Marshall Bluesbreaker and Vox AC30; the MkII adds three high-gain models inspired by the Mesa Boogie Dual Rectifier, Orange Rockerverb and Peavey 5150, the last emulating that amp's red channel³. Premier Guitar reported that the three new models were "all inspired by high-gain amps for heavy-style players"⁹.

Each amp pairs with any of the twelve cabinet IRs, and the cab slots can take user-loaded IRs managed over USB¹⁰⁴¹¹. The signal path is digital, with 24-bit 48kHz A/D and D/A converters and 32-bit floating point processing¹². There is also onboard reverb in three types, Room, Hall and Spring, set from the Room knob¹².

Volume and Gain interact the way they do on a real amp: raising the gain also raises the overall output level, so balancing the two is part of dialing in a sound³.

The controls and footswitches

The MkII replaces the original's toggle switches with an OLED menu screen, and the bottom three dials double as push controls for navigating it⁸. Guitar World's reviewer called the screen "a massive difference between this new version and the previous MK1"⁸.

There are two footswitches. One engages and bypasses the pedal; the other is a Boost switch that calls up a second, user-defined volume and gain setting¹³¹⁴. The pedal cycles through its three onboard presets, shown as red, green and blue, from a footswitch².

Power and connections

Power requirements are 9V DC at 300 mA minimum². The original ACS1 used a 9V DC center-negative supply with the same 300 mA minimum, and the supply is not included¹⁴¹³.

Connections are left and right inputs, left and right outputs, a headphone output, USB-C, and MIDI in and thru⁸. The headphone output is a mini-jack⁷. With MIDI connected, up to 128 presets can be saved and recalled⁴.

The stereo routing is flexible. The two outputs can be configured in Stereo, with the same amp and cab on both sides, or in Dual mode, with a different amp and cab simulation on each channel³. The stereo inputs also allow two guitars to be plugged in at once, each running through its own independent amp and cab⁵.

How the MkII differs from the original ACS1

The original Mako Series ACS1 predates the MkII by a full generation, and the biggest change between the two is on the surface: the MkII replaces the original's toggle switches with an OLED menu screen, a difference one reviewer called "a massive difference between this new version and the previous MK1"⁸¹⁰. Under the hood, the MkII also expands the amp modeling from the original's selection to six amp model emulations in total, adding the Mesa Boogie Dual Rectifier, Orange Rockerverb and Peavey 5150 (emulating the amp's red channel) alongside the Fender Deluxe Reverb, Marshall Bluesbreaker and Vox AC30³.

The MkII, announced in September 2024, changes most of that:

• Three new high-gain amp models added to the original three, for six total⁹
• Twelve cab IRs, up from six, with custom IR upload⁴
• An OLED menu screen replacing toggle switches, with push functions on the bottom three dials⁸
• A noise gate added as a program control⁹¹⁵
• An extra Boost footswitch for a second volume and gain setting³
• A mini-jack headphone output⁷
• Increased headroom and a lower noise floor, as Guitar World's reviewer reported⁸

What reviewers said

Guitar.com's review of the MkII centered on how it moves the pedal on from the original, with the reviewer highlighting the OLED menu screen and the secondary push controls on the bottom three dials as the headline changes over the Mk1⁸. The same review noted that the London model "doesn't have the same level of gain as other Marshall-in-a-box type overdrives," and listed cheaper and more versatile options being available among its reasons to avoid, placing the pedal at the more premium end of the spectrum⁸.

Guitar World's 2026 review praised the OLED screen and the quieter, higher-headroom design, but flagged two drawbacks: the London model "doesn't have the same level of gain as other Marshall-in-a-box type overdrives," and the pedal "sits at the more premium end of the spectrum" on price, with cheaper and more versatile options available⁸.

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