The Walrus Audio Mako Series MKII ACS1 Amp + Cab Simulator is a digital pedal that replaces an amplifier and speaker cabinet in your signal chain. Walrus Audio describes it as "an amplifier and speaker cab simulator delivering the sound and feel of world-class amplifiers"12. It carries six amplifier models and twelve cabinet impulse responses (IRs), plus a room reverb section, so a pedalboard can go straight to a PA, interface or headphones without an amp in the room. It is part of the same speaker simulation family as the Strymon Iridium and Universal Audio UAFX Ox Stomp.
The MKII is the second generation of the ACS1, which Walrus Audio launched in January 2021 as the third pedal in its Mako series3. The original is covered on its own page, the Walrus Audio Mako ACS1 Amp + Cab Simulator.
An amp and cab simulator with room reverb
The ACS1 MKII does two jobs in one box. The amp side models six amplifiers that Walrus Audio calls "fan-favorite amps, each with its place in music history"5. The cab side runs twelve speaker cabinet IRs, including complimentary sets created by Tone Factor and York Audio1. Both halves can be switched off independently: Walrus Audio notes that "cab IRs as well as amp models can both be bypassed with the ACS1, making it more flexible for ampless rigs"2, which matters if you want the pedal to serve only as an amp front end into a real cab, or only as a cab sim after your drive pedals.
On top of the amp and cab simulation sits a reverb built around the Room knob. There are three reverb types5:
| Reverb type | What it simulates |
|---|---|
| Room | The size of a room |
| Hall | The acoustics of a large, live sound space |
| Spring | Spring reverb tanks found in tube amps |
Turning the Room knob clockwise gives you a bigger room or more reverb, and the room decay is adjustable in the Global Sound menu1. That makes the reverb part of the simulated amp environment rather than a separate effect, closer to how a real amp's spring reverb sits in its sound.
The controls
The MKII moved from the original's knob-and-switch panel to a screen-based interface, a change Guitar Pedal X described as the Mako series "really coming of age with its extra features and new MKII screen-based control interface"7. MusicRadar's coverage of the MKII series noted the new OLED display and added controls, features and sounds8.
The top row of knobs handles the core amp settings1:
| Control | What it does |
|---|---|
| Volume | Sets output level; works together with gain |
| Gain | Sets amp drive; as gain is increased and made louder, volume compensates |
| Room | Increases room size or reverb amount; further clockwise is a bigger room |
Below that, the left encoder knob controls bass, the middle controls mids and the right controls treble, adjustable on the home screen for the L, R, and L+R channels1. Presence and resonance controls sit in the Amp EQ Settings menu for finer shaping of the simulated amp's response1. The original ACS1 handled cab and amp selection with A/B/C and named amp switches (Fullerton, London, Dartford)4; the MKII's encoders and screen replace that with menu-driven selection of the six amps and twelve cabs.
The 300mA current draw rules out a battery, and the pedal needs a 9V DC output that can supply at least that much current. A small daisy-chain output rated well below 300mA is not enough14.
Presets, MIDI and stereo
The ACS1 MKII is fully programmable. Up to three presets can be saved and recalled onboard, reached from the two footswitches, and using MIDI that expands to up to 128 presets514. MIDI in and MIDI out connections sit at the top of the unit4, so the pedal can sit in a larger MIDI-controlled rig, and MusicRadar listed MIDI controllability among the original's reasons to buy4.
The pedal runs in full stereo, with stereo inputs and outputs giving you the choice of running it in mono or stereo4. Guitar World's MKII review lists full stereo operation among its features, alongside the six amp models, twelve cabinet sims, an independent boost and MIDI compatibility9. Connections also include a mini-jack headphone output and USB4, which makes the pedal usable as a complete practice and recording setup on its own.
What the MKII added over the original ACS1
The MkII update, reported in late 2024, was more than a cosmetic refresh. MusicRadar called the ACS1 "a good example of how this is not just a spit and polish refresh of the lineup"8. Reported additions include81011:
- A screen-based control interface with an OLED display and more controls
- Three new amp models and six new cab simulations
- Custom IR upload
- A boost footswitch
- A noise gate
- Presets
The MKII also ships with complimentary cabinet IRs created by Tone Factor and York Audio, and controllable room size1. The enclosure comes in an anodized gold finish with black and green ink1.
What reviewers said
"surely makes the most persuasive case yet for using a digital pedal to replace real amps and cabs"12
Richard Purvis, Guitar.com12
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Questions
Is the Walrus Audio ACS1 MKII analog or digital?
It is digital, using 32-bit floating point processing for its six amp models and twelve cab IRs1. Guitar.com's reviewer found it "makes the most persuasive case yet for using a digital pedal to replace real amps and cabs"12.
Does the ACS1 MKII have true bypass?
Yes. Walrus Audio lists both True Bypass and Buffered Bypass, so you can run the pedal fully out of the circuit or keep a buffer in the chain when it is disengaged5.
How many presets does the ACS1 MKII store?
Up to three presets are saved onboard and accessed via the footswitches, and up to 128 presets can be saved and recalled using MIDI14.
What power does the Mako ACS1 MKII need?
A 9V DC supply delivering at least 300mA, not included with the pedal14.
What did the MKII add over the original ACS1?
A screen-based control interface with an OLED display, three new amp models, six new cab simulations, custom IR upload, a boost footswitch, a noise gate and presets81011.
Can you load your own cab IRs into the ACS1 MKII?
Yes. IR loading was already a feature of the original ACS14, and custom IR upload was one of the reported MkII additions4. The MKII ships with twelve cab IRs, including complimentary sets from Tone Factor and York Audio52.
Sources (12)
- Voyager Preamp/Overdrive, Walrus Audio
- Mako Series MKII: ACS1 Amp + Cab Simulator, Walrus Audio
- Walrus Audio unveils its third Mako Series pedal, the ACS1 Amp + Cab Simulator, Guitar World, 2021-01-22
- Walrus Audio Mako Series ACS1 Amp + Cab Simulator review, MusicRadar, 2021-09-25
- Mako Series MKII: ACS1 Amp + Cab Simulator, Walrus Audio
- Mako Series MKII, Walrus Audio
- Guitar Pedal X, Guitar Pedal X, 2024-09-27
- “Dialling in these inspiring studio grade tones has never been easier and has never sounded better”: Walrus Audio adds OLED display, more controls, features and sounds on its new and improved flagship Mako MkII series pedals, MusicRadar, 2024-09-25
- Walrus Audio Mako Series MKII ACS1 review, Guitar World, 2025-01-25
- Walrus Audio ACS1 MkII Amp & Cab Simulator, Delicious Audio, 2024-12-03
- Walrus Audio overhauls Mako pedal line with new MkII series, Guitar World, 2024-09-25
- Walrus Audio Mako Series MkII ACS1 review, Guitar.com, 2025-08-18
