Radial SB-2 Compact Passive Transformer DI Box

Radial SB-2: Pro-Grade Passive DI in a Palm-Sized Package

The Radial SB-2 is a compact, passive, transformer-isolated direct box (DI), a pocket-sized DI built for the traveling musician who wants full Radial performance without a full-size box on the floor. Inside its low-profile StageBug chassis sits a copper-shielded Eclipse ET-DB3 transformer that converts a high-impedance instrument into a clean, balanced signal and breaks the ground loops that cause hum, all with no power required. Designed for buffered sources like active acoustic guitars, keyboards, and basses, the SB-2 proves that size does not have to cost you sound, delivering the quiet, dependable direct box a club gig demands in something that fits in a gig-bag pocket.

What a DI Box Does and Why the Compact Form Matters

A direct box takes the high-impedance, unbalanced output of an instrument and converts it to a low-impedance, balanced signal that runs cleanly over long cable to a mixer, while isolating the grounds to stop hum. Most DI boxes are chunky steel bricks, and for a fly-date player or a singer-songwriter with a small pedalboard, that bulk is a burden. The SB-2 packs that exact functionality into a box just four and a half inches long and barely half a pound, so it disappears into a gig bag yet delivers the same clean, professional connection to the PA.

Passive by Design: Built for Buffered and Active Sources

The SB-2 is fully passive, using a transformer rather than a powered circuit, so it needs no battery and no phantom power. That passive design is happiest with buffered or active sources, which is exactly what it was built for: an active-electronics acoustic guitar, a keyboard, or an active bass all put out a strong, buffered signal that the SB-2's transformer converts beautifully. Because there is no active circuitry, there is nothing to switch on, nothing to run out of charge, and nothing to fail, it just works the moment you plug in.

Inside the Copper-Shielded Eclipse ET-DB3 Transformer

The heart of the SB-2 is a custom Eclipse ET-DB3 transformer with a 12:1 turns ratio, the same class of transformer engineering Radial builds into its larger boxes, shrunk to fit the StageBug form. The 12:1 ratio performs the impedance conversion, presenting a 140 kilohm input to your instrument and delivering a balanced output to the console. A copper shield wraps the core to reject stray hum, and the result is an exceptionally linear response from 20 Hz to 20 kHz with distortion of just 0.005 percent, performance that measures far beyond what a box this size has any right to deliver.

Stereo-to-Mono Merge: Saving Channels in the PA

The SB-2 hides a genuinely clever trick: a stereo-to-mono merge function. A stereo keyboard normally needs two DI boxes and two console channels, but the SB-2 accepts the keyboard's left and right outputs and sums them internally to a single mono XLR feed. That collapses a stereo source into one clean channel at the mixer, saving a precious console input at a small club or on a crowded festival stage where every channel counts. It is a small feature that solves a real, recurring headache for keyboard players.

Ground Lift and Pad: Beating Hum and Hot Signals

Despite its size, the SB-2 gives you the two switches that matter most on a real stage. A ground-lift switch lifts pin 1 on the XLR output to break the ground loop between your rig and the console, silencing the 60-cycle hum that shared power creates. And a 15 dB pad drops the input level so an extra-hot active pickup or a line-level keyboard cannot overload the transformer. Together they let you solve the two most common noise and level problems in the field without carrying anything larger.

On Acoustic, Keys, and Bass: Where the SB-2 Shines

This little box is built for the working performer. Plug an active acoustic-electric guitar into it and its pickup reaches the PA clean and hum-free through a long cable run. Feed a keyboard into it, use the merge to fold a stereo patch to mono, and save a channel. Run an active bass through it and the transformer handles the hot output with headroom to spare. And because it lives in a rugged 14-gauge steel chassis, the SB-2 survives the gig-bag-and-club-floor life that would dent a lesser box.

Who the SB-2 Is For

The SB-2 is for the singer-songwriter who plays fly dates and wants a pro DI that fits in a pocket; for the keyboard player who needs to fold a stereo rig to one channel at a small club; and for the gigging bassist or acoustic player who wants Radial-grade sound and build without a full-size box on the floor. If you carry an active instrument to gigs and need a clean, quiet, take-anywhere connection to the PA, the SB-2 is the compact passive direct box to keep in the bag.