BOSS EX-4 Effects Expander Multi-Effects Pedal

The BOSS EX-4 Effects Expander is for the player whose board is full but whose head is still full of sounds they can't reach. It doesn't ask you to pull up your drives and start again with a floor unit — it sits in beside them and adds four blocks of BOSS processing in a 117 x 138 mm box that weighs just 800 g. There is no amp or cab modelling on board at all; every bit of its brain goes to effects.

120 BOSS effects, four at a time

The library runs to 120 effect types. Overdrive and distortion, modulation, delay and reverb are all there, along with a set voiced specifically for bass and a few BOSS cult favourites — Slow Gear for violin-style volume swells and Slicer for chopped, rhythmic patterns among them. Load up to four into a patch in whatever order suits, and nothing stops you using the same type twice: two delays at different subdivisions, or a pair of pitch shifters on parallel paths. Under the hood it converts at 24-bit with BOSS's AF method on the way in, 32-bit on the way out, and processes in 32-bit floating point at 48 kHz.

Build the chain your way

The four effect blocks can be rearranged into any running order, set up in series, split into parallel paths, or run in a wet/dry layout that leaves your dry signal untouched while the effects sit alongside it. On top of those four you get six dedicated utility blocks that never cost you an effect slot: a foot volume, two separate noise suppressors, a send/return for outboard pedals, a divider and mixer for the parallel paths, and a global EQ to match the unit to different rigs and rooms. Because the send/return is a block like any other, the pedals you patch into it can be moved around the chain just as freely as the EX-4's own effects.

A 2.4-inch colour screen and a button for every block

The 320 x 240 colour display shows the entire chain at once, then drills down into individual blocks and menus when you need them. FX1 to FX4 buttons flank the screen, and each one lights up in the same colour its block wears on the display, so there is never any doubt which button runs which effect — tap to switch a block on or off, hold to jump straight into its settings. Three knobs sit under the screen for the parameters shown along its bottom edge, with SELECT and TYPE/VALUE up top. Gear Suite speeds things along further: every effect type carries several professionally dialled settings you can scroll through with a knob, and you can tweak any of them and store your own go-to version.

Manual or Memory: footswitches that work your way

Run the EX-4 in Manual mode and it behaves like a row of stomp boxes, each block on its own switch; flip to Memory mode and it becomes a preset machine, with 128 factory memories for guitar and bass and 128 slots for your own. Memory changes are seamless, and with suitable effect configurations the delay repeats and reverb decay ring on across the change instead of cutting off. The two heavy-duty footswitches are ringed with split-colour LEDs that show what each one is doing from standing height, and each can be given its own job: tap tempo, master bypass, switching single blocks, stepping through memories, or real-time control of individual parameters.

Connections for any size of board

Every jack lives on the rear edge, so the leads run back and away from your feet. Four 1/4" jacks give you full stereo in and out; run it mono and the right-hand pair become a send and return for an external effects loop. The 1/4" TRS CTL/EXP jack takes a BOSS FS-5U, FS-5L, FS-6 or FS-7 footswitch, or an expression pedal such as the EV-30 or FV-500, for hands-free control. TRS MIDI in and out on 3.5 mm jacks tie it into switchers, other MIDI pedals and external clock sources without eating space, and there is a USB-C port alongside.

Power and what's in the box

BOSS supplies a PSA-S series adaptor with the EX-4, along with four rubber feet and a startup guide. It draws 300 mA, so if you would rather run it from your pedalboard supply, make sure the outlet you give it is rated for that. Height is 65 mm with the feet fitted, or 63 mm without them for a low-profile board mount.