Radial ProDI Passive Transformer-Isolated DI Direct Box

Radial ProDI: The Compact Passive DI That Never Runs Out of Headroom

The Radial ProDI is a passive, transformer-isolated direct box (DI), a compact single-channel passive DI box that turns a high-impedance instrument into a clean, balanced signal without needing any power at all. At its heart sits Radial's own Eclipse ET-DB2 transformer, which drops the signal to mic level, breaks the ground loops that cause hum, and does it with enough headroom to swallow the hottest active bass or line-level keyboard. When you need a direct box that just works, plug after plug and load-in after load-in, the ProDI is the quiet, bulletproof answer.

What a DI Box Actually Does

A direct box does three jobs at once, and understanding them explains why you need one. First, impedance conversion: it takes the high-impedance output of a bass or keyboard and drops it to the low impedance a mixer wants, so the tone stays full instead of thin. Second, it converts an unbalanced signal to a balanced one, so noise picked up along a long cable run cancels itself out and arrives clean. Third, it provides ground isolation, breaking the loop between your rig and the console that causes 60-cycle hum. The ProDI does all three, and does them silently.

Passive vs Active: Why the ProDI Needs No Power

The ProDI is a passive DI, which means it uses a transformer rather than a powered buffer. A passive design needs no battery and no phantom power, and its transformer thrives on hot, high-level signals: the more voltage an active bass or a line-level keyboard throws at it, the happier it is. An active DI uses a powered buffer with very high input impedance and is the better choice for delicate, low-output pickups, but for strong signals the ProDI's transformer delivers rich, natural tone with nothing to power, nothing to fail, and nothing to think about.

Inside the Eclipse ET-DB2 Transformer

The single most important part of any passive DI is its transformer, and the ProDI uses Radial's own Eclipse ET-DB2. Its 12:1 turns ratio is what performs the impedance conversion, presenting a 140 kilohm input to your instrument while delivering a 150 ohm balanced output to the console. Just as important, the core is wrapped in MuMETAL, a nickel-iron alloy that shields the transformer from the stray magnetic fields thrown off by lighting dimmers, power amps, and transformers, so the signal that leaves the box is free of induced hum.

Headroom to Spare: +18 dB and 128 dB of Dynamic Range

Here is where the ProDI earns its reputation. It accepts a maximum input of +18 dB before the transformer saturates, and it delivers a 128 dB dynamic range with total harmonic distortion of just 0.01 percent across a 20 Hz to 18.5 kHz response that stays flat within a tenth of a decibel. Active basses that peak hard and keyboards that run hot slam into a lesser box and crackle; the ProDI simply takes it, staying clean and punchy from the deepest low string to the airiest high.

Ground Lift and Pad: Beating Hum and Hot Pickups

Two switches handle the two problems every DI faces on a real stage. The ground-lift switch breaks the ground loop between your rig and the mixer, silencing the 60-cycle buzz that plagues shared power. The 15 dB pad drops the input level so the hottest active pickup or line output cannot overload the transformer. And a 1/4-inch Thru jack passes the unbalanced signal straight through to an onstage amp or tuner while the balanced XLR runs the long distance to front of house.

On Bass, Keys, and Acoustic: Where the ProDI Shines

This is the box's home turf. On active electric bass, the high headroom captures every bit of slap and string detail without a hint of clipping. On digital keyboards and synths, it cleanly tames line-level output down to mic level for the console. On an acoustic-electric guitar running an active onboard preamp, it flatters the pickup and drives a hum-free run to the stage box. The 1/4-inch Thru feeds your onstage amp at the same time, so both the room and the mix get a clean signal in stage and studio alike.

Who the ProDI Is For

The ProDI is for the touring bassist who wants a bomb-proof passive DI with nothing to power and nothing to break; for the keyboard player feeding hot line-level signals to a busy console; and for the studio engineer who needs a transparent, high-headroom direct box that sounds the same take after take. If you plug a strong-output instrument into a mixer and the signal has to be clean, quiet, and utterly reliable, the ProDI is the passive direct box to standardize on.