Radial ProDI Passive Direct Box — Mint in Box, Custom Transformer, Ground Lift

No sales tax for US customers outside California.

Ask any working FOH engineer or touring bassist what DI box they trust and the answer comes back Radial more often than not. The ProDI is Radial's passive workhorse — a single-channel direct box built around a custom-wound transformer with a MuMETAL electromagnetic shield, a 140kΩ input impedance that doesn't load down active pickups, a -15dB pad for hot sources, and a ground lift switch that solves the hum problems that cheap DIs create. This example is mint in box — unplayed, ready to go straight to work. For acoustic guitarists, bassists, keyboard players, or any engineer building out a reliable live or studio rig, this is the straightforward right answer at a fair price.

The Details

• Manufacturer: Radial Engineering, Vancouver, British Columbia, Canada
• Model: ProDI — 1-channel passive direct box
• Type: Passive — no power required, no batteries
• Transformer: Custom-wound Radial transformer, MuMETAL shielded against electromagnetic interference
• Input impedance: 140kΩ — high enough to avoid loading active pickups or buffered pedal outputs
• Frequency response: 20Hz–18.5kHz, linear — full range with virtually zero phase distortion
• Connections: 1/4" instrument input, 1/4" thru output (to amp), XLR balanced output (to console or interface)
• Pad: -15dB switchable — handles hot active instruments and line-level sources
• Ground lift: Yes — eliminates hum from ground loops between stage and FOH
• Output impedance: 600Ω balanced
• Chassis: 14-gauge welded steel I-beam inner frame, baked enamel outer shell — genuinely road-proof construction
• Dimensions: 2.5" x 4.25"
• Condition: Mint, unplayed, in original box

A Bit of History

Radial Engineering was founded in 1992 in Vancouver, Canada by Peter Janis, who had spent years watching professional touring rigs struggle with the kind of ground loop hum, signal degradation, and cheap transformer failures that plagued the budget DI boxes of the era. The company's founding premise was simple: build DI boxes the way they should be built — with premium transformers, serious chassis construction, and enough engineering rigor to survive daily life on a major tour. That premise resonated immediately with touring engineers and session players, and Radial built a reputation through the 1990s as the brand that the professionals actually trusted. The ProDI became their accessible flagship — the same transformer-quality philosophy as the premium JDI, at a price that working musicians and smaller venues could justify. The MuMETAL shield inside the ProDI is a detail borrowed from scientific instrument design: it's the same material used in electron microscopes and MRI machines to block electromagnetic fields, and in a DI box it prevents the transformer from picking up interference from nearby power supplies, lighting dimmers, and other stage electronics that cause the low-level hum that drives engineers crazy. Notable ProDI users documented on Equipboard include Kim Gordon of Sonic Youth, Reeves Gabrels — the guitarist in David Bowie's band throughout the '90s and current Cure member — Scott Shriner of Weezer, and engineers on the Alan Parsons Live Project, whose production team specifically noted switching to Radial DIs on the road and never looking back. The ProDI has become one of the most widely used passive DI boxes in professional live sound — seen on stages from club tours to arena shows — and its used-market value holds unusually well precisely because of that reputation.

Excerpts from real online user forums and reviews

• "I want a DI? I just get a Radial, I don't bother with anything else. If I see any other DI rather than Radial in my touring case, I just don't touch it." — Sweetwater Verified Customer Review
• "I put the ProDI on keyboards and acoustic guitars, the prime usage for passive direct boxes. The transparency was noticeable. I am sorry to say, my other popular brand passive DIs are going to collect some dust from here on." — Radial Engineering / Pro endorser quote
• "Never thought our direct boxes were that big of a deal until I went to buy a new one. I thought the $30–$50 ones would give you what you needed. I was so wrong — a professional musician friend convinced me to give this a try, and I'll never go back to cheap DIs. The difference was startling, and made me feel really foolish for using the cheap ones for so long." — Sweetwater Verified Customer Review
• "I've used my ProDI for bass and guitar for live shows and non-pro recording. I love it. It sounds great to me, built like a tank — typical Radial." — TalkBass.com
• "Our lives changed when we started carrying our own Radial DIs on the road and we have never had a single issue or breakdown. Our Radial Direct Boxes are rugged, reliable, and sound great — so much better than the competition. In fact there is no competition." — Alan Parsons Live Project production team, via Radial Engineering

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