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Radial Engineering JDI Passive Direct Box  From Radial

Passive DI Box

Radial Engineering


Retail:  $300.00

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The Radial JDI explained

Radial's Peter Janis explains key features of the JDI Jensen transformer equipped passive direct box.

  • Signal Chain
    • Radial Engineering JDI Passive Direct Box

Manufacturer's Description from Radial

  • Jensen Transformer equipped passive DI
  • Eliminates hum and buzz from ground loops
  • Virtually zero phase & harmonic distortion
  • Exceptional signal handling and noise rejection

The Radial JDI is a passive direct box designed to handle extreme signal levels without distortion of any kind. Unlike an active DI that is limited by the buffering amplifier’s rail voltage, the JDI employs a Jensen audio transformer as the engine. Jensen transformers are legendary in their ability to gracefully handle transients while delivering a smooth, warm sounding Bessel curve, reminiscent of the finest vintage gear. Ruler flat from 10Hz to 40kHz and with virtually zero phase deviation, the JDI delivers the natural, pure sound of the instrument without artifact.

The 100% passive circuitry inside the JDI is incredibly efficient. The transformer performs both high-to-low impedance conversion and signal balancing at the same time with minimal loading and does so without any power whatsoever. The transformer also introduces a magnetic bridge that passes signal while rejecting stray DC voltage. This makes the JDI particularly adept at eliminating hum and buzz caused by ground loops.

Features include input and throughput ¼” connectors, -15dB input pad, ground lift, and 180º degree polarity reverse to help phase align the instrument with the PA. A secondary circuit is added for direct interfacing with high output devices such as guitar or bass amp loudspeakers plus a unique merge function allows stereo sources such as keyboards to be summed mono, saving valuable input channels.

Built tough to handle the abuse of live touring, the JDI features a 14-gauge steel I-beam inner frame and a unique book-end outer shell. The innovative design eliminates stress on the PCB, reducing opportunity for solder joints to go ‘cold’ while the outer shell creates a protective zone around the switches and connectors. The steel casing resists noise-causing electromagnetic pollution and the transformer’s sensitive inner workings are further protected from magnetic fields with a mu-metal can. This ensures the signal transfer is quiet and free from hum.

These combined features have made the Radial JDI the most popular passive direct box in professional touring and an excellent choice for instrument interface in the studio!

The Radial JDI… the world's finest passive direct box.

Radial Engineering

About Manufacturer

Radial Engineering is a manufacturer and distributor of professional audio equipment, building tools for the working audio and audio-video professional. Radial is located on the Fraser River, just outside Vancouver, British Columbia in the municipality of Port Coquitlam. The company began operations in the fall of 1991 as the Canadian distributor of Mogami cable and Jensen Audio Transformers. In 1992, it became a limited corporation under the JP Cabletek Electronics Ltd. banner. The Radial name was first used on house branded cables and snake systems. The Radial name and logo represents a cross section of quad cable; Radial being round. In 1996 the Radial JDI direct box was launched. This led the way to the Radial JDV and today, over 50 electronic products are now being produced under the Radial, Tonebone and Forest Audio brands. In 2001, the Primacoustic brand was launched to address the growing demand for acoustic products for the burgeoning home recording market and in 2006, the company officially changed its name to Radial Engineering Ltd.


The Radial JDI is a phase coherent, passive direct box employing a nickel laminated Jensen™ audio transformer with virtually zero phase distortion, huge dynamics handling and ruler flat response from 10Hz to 40kHz. The Radial JDI™ is quite simply the world's finest passive direct box. With its heavy-duty steel shell and internal I-beam construction, the JDI is designed to work dependably for years in even the harshest of touring environments. Ideal for keyboards, bass and acoustic instruments of all kinds, the JDI Duplex™ and JD6™ are also available for stereo and multi-channel applications.




Audio circuit type: 

Passive, transformer based

Number of channels:

Single channel (mono)

Frequency response: 

20Hz ~ 20KHz (± 0.2dB)

Dynamic range: 


Maximum input: 

+21dB @ 20Hz ~ 20kHz 

Total harmonic distortion: 

0.05% from 20Hz ~ 20kHz @-10dB

Phase deviation: 

0.3° @ 100Hz; 3° @ 20Hz 

Input impedance: 

140k Ohms, unbalanced 

Output impedance: 

150 Ohms, balanced 





Jensen JT-DBE, 12:1 ratio


Dual Faraday, mu-metal can

Input pad: 



Sums left & right sources to mono

180° polarity reverse: 

Inverts absolute phase

Ground lift: 

Disconnects pin-1 at XLR output 

XLR configuration: 

AES standard (pin-2 hot) 

Speaker filter: 

-30dB pad and band-pass filter 


1/4" in & thru, XLR-M out





14 gauge steel chassis & outer shell


Baked enamel

Size:  (W x H x D)

 84 x 127 x 48mm (3.3" x 5.0" x 2")


0.70 kg (1.55 lbs) 

Shipping Size: W x H x D:

102 x 76 x 165mm (4" x 3" x 6.5")

Shipping Weight:

.87 kg (1.92 lbs)


Passive, no power required 


Radial 3-year, transferable

Specifications are subject to change without notice.





JDI Smart Sheet

JDI User Guide