Boss EX-4

The Boss EX-4 Effects Expander is a compact effects processor from Boss, a maker that describes it as a unit that "expands the capabilities of any pedalboard"¹. Boss presents it as a complement to the pedals you already own rather than a replacement for them, a "compact inspiration machine" that adds new sound-shaping options and real-time performance tools to your current setup². Effects are controlled with dual multi-function footswitches with color LEDs¹, and two external footswitches or an expression pedal can be connected for more real-time control¹.

Where a full multi-effects workstation rebuilds your whole rig, the EX-4 is built to sit alongside it. Bass Gear Magazine described it at launch as "a powerful compact effects processor that infuses any pedalboard setup with a massive boost in sonic versatility"³.

A compact processor with 120 Boss effects

The core idea is simple: four effect slots, filled from a catalog of 120 Boss effects. Every major category is represented, including overdrive and distortion, modulation and delay¹⁵, and you can load multiple instances of the same effect, so two delays or two overdrives can stack in one unit¹. On top of the four effect blocks, the EX-4 carries six utility blocks: a divider/mixer, send/return, foot volume, two noise suppressors and a global EQ⁶¹.

The effect library is drawn from Boss's own back catalog. Guitar World's review notes the 120 effects are compiled from the GX series of multi-effects, classic stompboxes, and discontinued units such as the SG-1 Slow Gear⁷. Each effect type also offers multiple "Gear Suite" settings with professionally tuned parameters, selectable with a knob turn rather than deep menu diving⁴.

The EX-4 offers two ways to work with those effects. Manual mode behaves like a set of stompboxes, with each effect block switched on and off from the pedal. Memory mode works from presets, of which there are 128 factory memories covering both guitar and bass, plus 128 user memories for saving custom sounds¹. Guitar.com's reviewer confirmed the split: "there are 128 user presets to go with the 128 factory ones"⁸.

The controls and display

Editing and navigation center on a 2.4-inch color display that shows the full signal chain, individual effect blocks, editing options and menus⁹. Guitar.com's Josh Gardner found the screen "clear and sharp" and counted five rotary controls alongside it, showing the current preset and the four effects in the chain⁸. MusicRadar likewise highlighted the full-color 2.4-inch LCD as the feature that makes edits easy¹⁰¹.

The two onboard footswitches are assignable. Boss's documentation lists assignments including effect block on/off, memory up/down, master bypass, tap tempo and individual parameter control¹¹. Beyond the built-in switches, two external footswitches or an expression pedal can be connected to the EXP/CTRL input for more real-time control¹⁵.

Connections: stereo, effect loop and MIDI

The EX-4's four audio jacks support mono or stereo connectivity, with the option to use two of them as an effect loop for placing external pedals in the chain¹³. Guitar World's review spells out the trade-off: the effects loop is available when the unit runs in mono, and its full connectivity list covers stereo in and out, the mono-mode effects loop, MIDI in and out, the EXP/CTRL input and USB-C⁷.

MIDI is handled through space-saving TRS MIDI jacks rather than full-size DIN sockets, which Boss says unlocks integration with other MIDI pedals, switching systems and external clocking devices¹⁵. Power comes from an included Boss PSU⁶.

What reviewers said

Early coverage was positive. Guitar Pedal X's Stefan Karlsson called it "a fantastic intuitive Multi-FX Pedal" delivering four stereo effects at a time from the 120 on offer¹²⁶. Guitar World's verdict leaned on its breadth and footprint:

Guitar.com's review praised the display and the stereo I/O, half of which can double as effects send and return⁸.

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