Radial ProDI Caixa DI

Radial ProDI Passive Direct Box for Stage and Studio

The Radial ProDI is a compact, full-range passive direct box designed to convert high-impedance, unbalanced instrument signals into low-impedance, balanced output for a mixing console or audio interface. Built around a custom-wound Radial transformer with an exceptionally high 140 kΩ input impedance, it reduces loading on the pickup while handling extreme signal levels without distortion. Pro musicians rely on the ProDI passive direct box to deliver clean, hum-free bass, keyboard, and acoustic guitar signal to front-of-house mixers and recording systems alike.

Custom Transformer and MuMETAL Shielding for Noiseless Signal Transfer

At the heart of the ProDI sits a custom-made audio transformer wound specifically for full-range musical performance, offering 100% electrical isolation between input and output to eliminate the ground-loop hum that plagues live rigs. An internal MuMETAL shield protects the transformer core from stray electromagnetic fields that would otherwise drive unshielded windings into distortion. This combination lets the unit tolerate the loud output of active bass pickups, active acoustic preamps, and wide-dynamic-range digital keyboards without phase shift or saturation in the bass and mid bands.

Signal Handling — Headroom for Active Instruments

Engineers choose a passive DI like this model when they need bulletproof headroom from active instruments with no external power supply to fail mid-show. The high input impedance keeps the pickup's natural character intact, while the transformer ratio drops the level to a safe, balanced line signal that survives 100-meter XLR runs.

• Design Type: Passive mono direct box — single-channel, requires no batteries or phantom power
• Input Impedance: 140 kΩ — preserves the natural tone of passive and active pickups without loading them down
• Pad: -15 dB — engages for hot active pickups and excess stage level to prevent internal saturation
• A ground lift switch on the rear disconnects pin-1 ground on the XLR to silence ground-loop buzz between a stage amp and the PA.

Connectivity — Inputs, Thru, and Balanced Output

As a hard-working utility for any rig, the ProDI needs to route signal in, pass it through to a stage amp, and deliver a balanced feed to the desk simultaneously. The chassis houses all three connections plus pad and ground-lift switches in a layout that survives dark-stage cable swaps and rental-house abuse.

• Inputs: 1 × 1/4" TS instrument input — accepts guitar, bass, keyboard, or piezo pickup output
• Outputs: 1 × male XLR (balanced, pin-2 hot) and 1 × 1/4" thru — sends balanced feed to the mixer and parallel feed to a stage amp
• Construction: 14-gauge welded steel I-beam inner chassis with 14-gauge outer shell, book-end switch guards, baked-enamel finish
• A military-spec board with a full surface ground plane reduces RF susceptibility for quiet operation near wireless racks.

Dimensions and Weight — Tour-Ready Footprint

Compact form factor matters when DIs are mounted under pedalboards, strapped to mic stands, or buried deep in rack drawers. A no-slip rubber base pad keeps the box stationary on amp tops and adds electrical isolation from chassis ground.

• Dimensions (H × W × D): 45 × 70 × 108 mm
• Weight: 0.54 kg — dense enough to feel road-worthy without bogging a pedalboard down

Who This Model Is Built For

The ProDI is the right choice for gigging bassists, keyboard players, and acoustic guitarists with active pickups who need hum-free balanced signal going to the PA without any power supply or battery to manage. It suits front-of-house engineers feeding acoustic acts, small-format rental houses that need a workhorse DI for daily cycles, and home-studio owners wanting a transparent mono path from a keyboard or bass rig to an audio interface. Touring players who already run Radial pedals and need one more DI in the case will also recognize its build and finish as matching the rest of their setup.

Radial Engineering — A Canadian Pro Audio Brand Trusted on World Tours

Radial Engineering designs and manufactures its direct boxes in Vancouver, Canada, focusing on road-ready construction and transformer-isolated signal paths for live sound. Alan Parsons and his production team have toured for years with this model, ProD2, and JDI units on stage for keyboards, acoustic guitars, and computer interfaces, citing their rugged build as a key reason they never see breakdowns on the road. Front of House magazine reviewer Mark Amundson put the ProDI on keyboards and acoustic guitars and noted its transparency was so clear that other popular passive DIs in his collection were retired in its favor.