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Retail: $220.00, Our Price: $199.99

Radial JDI Passive Direct Box

• Jensen Transformer equipped passive DI
• 100% isolation eliminates ground loops
• Virtually zero phase & harmonic distortion
• Exceptional signal handling
• High common mode noise rejection

The Radial JDI is considered by many to be the world’s finest direct box. It is a passive DI that employs a Jensen isolation transformer for optimum audio performance offering outstanding linearity at all frequencies, combined with extraordinary level handling without introducing distortion. Being completely passive, the plug & play JDI does not require any powering and has the unique advantage of eliminating 60-cycle ground loops. This makes the JDI a definite favorite with informed audio engineers. The JDI is great for guitars, bass, and keyboards and is particularly adept with high-output, broadband instruments such as active instruments and digital keyboards. The JDI may be rack-mounted using the J-Rak and is also available in a stereo (2-channel) version called the JDI Duplex and the 6-channel rack-mountable JD6.

Radial J-Rack Direct Box Rack-Mount Adaptor
The J-Rack is a unique direct box shelf and 19” rack adaptor that allows up to 8 JDI or J48 direct boxes to be rack-mounted in 2 rack spaces. This unique adaptor allows improved inventory management for sound companies allowing DI inventory to be used as stand-alone or rack mount depending on tour needs. Our Price: $119.99, special order. Lead time is about 1-2 weeks.

JDI Development and Evolution

Jensen JT-DBE audio transformer

The original JDI Mk1 Direct Box

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Radial JDI's Construction features a 14 gauge welded steel I-beam internal chassis and 14 gauge steel book cover shell to protect switches and connectors.

Direct boxes have the primary function of interfacing musical instruments with sound systems by converting unbalanced high impedance signals to 600 Ohm low impedance balanced mic levels. Proper impedance matching significantly improves the audio performance while balancing allows long cable runs without adding appreciable noise.

Passive direct boxes employ a transformer to isolate the input (primary) from the output (secondary) using only electro-magnetic induction to transfer the signal. The term ‘passive’ refers to the fact that these direct boxes do not require power such as a battery or 48V phantom to make them work. Because isolation transformers have the unique ability to bridge the signal without a ‘hard’ electrical junction, DC noise and stray ground currents are eliminated, thus 60-cycle hum caused by ground loops are removed.

Although passive direct boxes have been around for years, the liberal use of inexpensive, low quality transformers have the not so obvious consequence of compromising the sound. This is caused by the use of low-permeability steel in the transformer core which has the adverse effect of causing group-delay (phase distortion) and a lower saturation point (harmonic distortion), which of course are most prevalent at lower frequencies.

With the advent of better sound systems and recording techniques, the demand for quality grew. This spawned the development of active direct boxes as a means to improve the performance of these lesser passive DI’s without adding cost. The active DI herald in a new generation of improved sonic performance but alas, did so at the expense of isolation.

Evolution of the Radial JDI

The Radial JDI was introduced in 1996 as means to reintroduce the advantages of isolation while raising the bar for sonic performance. The use of a high quality Jensen® DBE Transformer is critical and is easily justified when one considers the hundreds of thousands of dollars spent on the sound system in the quest for great sound.

The 1st version of the JDI was a simple device that was made using an extruded aluminum shell and an inner ‘drawer’ or frame that contained the PC board and electronics. A dual recessed control panel was developed to protect the more fragile toggle switches. This was quickly upgraded to the JDI Mk2 with the introduction of the ‘merge’ function in 1997. This handy feature has become a staple of the Radial direct box feature set ever since.

In 2001, the JDI was given a major face-lift and redesigned using our innovative bookend enclosure. The bookend design provided several major advantages: The I-beam construction increased the inner frame strength thus reducing potential for outside stress; we were able to employ higher duty cycle push switches instead of the more fragile toggles; and manufacturing time was reduced from 45 minutes per unit down to under 5 minutes, thus reducing cost.

The Radial JDI Mk3 employs the same audio signal path as the original, yet is both more durable and more affordable.

JDI Features & Functions

The Radial JDI is a passive direct box that employs the world’s finest Jensen JT-DBE transformer as its main drive engine. The Jensen DBE transformer employs a laminated nickel core that has the distinct advantage of low-permeability. Permeability (see 'Transformer Distortion' side bar) is a term that describes the metals ability to become magnetized and demagnetized without retaining any magnetic memory. When one considers that full bandwidth audio is made up of a series of fundamentals and harmonics that range from 20Hz to 20kHz all of which ‘move’ in tandem, disrupting their relationship is not a desired effect! This underscores the importance of a very high quality transformer and the decision to use a Jensen.

The JDI's internal I-beam shell
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1. Welded I-beam construction makes it impossible to torque the PC board. This virtually eliminates cold solder joints - the No.1 cause of system failure in the field.

2. ‘Slide-in-place’ XLR trace makes it possible to use I-Beam girder construction.

3. Jensen transformer is used for distortion-free performance. The Jensen features a nickel core for best signal transfer and minimal loading.

4. Military-grade PC board is employed for maximum wear and tear in abusive environments. Welded steel standoffs ensure the PC board will not shift.

Inside, the JDI features a compound, welded ‘I beam’ construction that protects the sensitive electronics from outside stress. This makes it impossible to torque the PC board, assuring years of trouble-free performance. The internal skeletal frame is locked together with 4 hex screws.

The output panel features balanced 600 Ohm XLR connector with pin-2 hot following the AES specification. A polarity reverse switch toggles pin-2 and pin-3 to allow the JDI to interface with older non-AES equipment and for creative tinkering. The ground lift switch disconnects the XLR pin-1 ground from the JDI for 100% input-to-output isolation.

Finally, a second -30dB pad may be engaged that, when used in tandem with the -15dB input pad, allows the JDI to be connected in parallel with a speaker. This, for instance, allows the engineer to ‘tap’ the sound coming from a guitar amplifier speaker ‘post distortion’ thus adding another creative dimension. This unique function incorporates a speaker emulation filter circuit that rolls off highs and lows to more closely approximate the sound of a 12” driver.

5. XLR balanced mic level output provides 100% isolation for runs to 1000 feet without appreciable noise.

6. Polarity reverse switch flips the polarity from the AES standard Pin-2 to Pin-3 on the XLR and is used when combining sounds that may be out of phase.

7. Ground-lift disconnects the ground path to the transformer at the XLR output. This is used when a ground path is made at the input side such as with a keyboard.

8. Parallel speaker interface option introduces a second -30dB pad with band-pass filter to emulate a 12” guitar speaker.

9. -15dB pad allows super hot inputs such as that from a CD player to be connected and balanced for long runs.

10. Merge function turns the input and thru into a passive mixer to sum stereo feeds to mono at the XLR output. This saves valuable inputs on the mixer!

11. Input connects to the instrument.

12. Thru-put is connected to the instrument amplifier. The JDI has a high input impedance to reduce loading.

13. Book-end design creates a protective zone around the switches & connectors for best protection!

14. Heavy-duty baked enamel finish for excellent durability and great looks for years! 100% 14-gauge steel construction.

15. No-slip full bottom pad reduces mechanical vibration, improves electrical isolation and keeps the JDI from moving around on busy stages! Mounting this with Velcro to a pedalboard enhances this function.

The input panel features a ¼” instrument input and traditional thru-put. An innovative ‘merge’ function allows the thru-put to be converted to a second input to allow stereo to mono summing. This is often used to interface stereo sources such as keyboards or CD players in live shows where audio channels may be not always be plentiful. The JDI also sports a -15dB pad to interface with higher output levels.

Construction

All Radial DI's feature a 14 guage internal I-beam chassis and 14 gauge 'bookend' outer shell to protect connectors and switches.

As with all Radial direct box, the Radial J48 is designed for use in abusive environments such as on fast-paced stages of concert touring. An innovative book-end design provides a protective zone around the switches and connectors that makes it practically impossible to damage these components.

The inner skeletal frame features a unique 14-gauge welded I-beam construction that makes it impossible to torque the PC board. Stress on the printed circuit board can introduce intermittent solder joints, which by all accounts is the primary cause of direct box failure.

An innovative full-bottom no-slip rubberized pad works double duty by assuring the J48 won’t slip and slide around when placed on an amplifier. The protective pad also ads an element of electrical shock resistance by providing a mechanical shield from guitar amp handles that are often directly coupled to the amp chassis.

Transformer Distortion

Have you ever noticed how Dad’s old screwdriver can pick-up small nails? It has somehow become magnetized. In fact, the magnetic domains (sub-atomic particles) in the steel have become ‘aligned’ and have turned it into a magnet. By simply banging the steel screwdriver while surrounded by a magnetic field, the domains become realigned. Low permeability metals such as steel suffer from this and as a consequence, become polarized.

When passing an audio signal through a polarized transformer, the transfer of the signal becomes uneven. This causes certain groups of frequencies to become offset or delayed which of course results in phase distortion. Considering we spend thousands if not hundreds of thousands of dollars doing everything we can to time-align our sound systems, isn’t it perplexing that some engineers will allow the signal to be completely skewed before it even gets to the console?

Jensen transformers use high permeability nickel in the core material to solve this problem. Unfortunately, nickel is much more expensive than steel and furthermore, each transformer stack must be assembled by hand to ensure proper alignment of the nickel laminates. At Jensen, precision Swiss-made digital winders are employed to ensure exact wire placement on the bobbin and precise turn ratios are maintained. This is of particular importance when attempting to employ a series of matched transformers such as used in a snake splitter system.

When compared to other direct boxes, the JDI clearly measures above the others. These measurements were conducted by an independent engineer and derived from the Radial Green Report.

	Radial JDI	Country-man	BSS
Harmonic Distortion @ 20Hz	0.06%	0.5%	0.7%
Linearity 20Hz-20kHz	+/- 0.2dB	+/- 2.0dB	+/- 1.0dB
Phase distortion @ 20Hz	4.3°	19.8°	38.5°

Using the JDI

Being completely passive, the Radial JDI is ‘plug and play’ easy to use. Simply connect the instrument to the input, the amplifier to the thru-put and the mixer to the output and you are ready.

The JDI input features a high 10kOhm input impedance for minimal loading. This makes the JDI ideal for interface with all instruments. The 600-Ohm mic level output allows the JDI to be used with typical snake systems that incorporate bridging transformers (splitters) without fear of overloading them.

As a passive device, the JDI is particularly ideal for use with high output devices such as active or self-powered instruments such as acoustic and bass guitars with built-in battery powered preamps and keyboards. These devices tend to overload most active direct boxes making them sound thin and edgy. The JDI is capable of exceptionally high signal handling without distortion.
The real benefit of isolation is immediately realized when connecting two pieces of gear together that are electrically powered systems. These typically employ different reference to ground voltage schemes which will often result in what is commonly known as ground loops or an annoying 60 cycle hum. The JDI’s exceptionally high common mode noise rejection completely eliminates this problem. This of course has the benefit of making stage set-ups quick and effortless.

The Radial JDI is Jensen Transformer equipped, high quality passive direct box that has the advantage of providing complete isolation for reduced noise. The exceptionally low phase distortion, almost perfect linear response and low harmonic distortion make the JDI a superb choice for critical recording or live performance. The rugged construction allows the JDI to be used in the most abusive environments without concern for damage. The Radial JDI Mk3 is ideal for acoustic guitars, bass, and keyboards.

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Specifications:

Dynamic Range: 135db
Signal to Noise: 119db
Maximum Input Level: +19db
Frequency Response: 10Hz ~ 40kHz (+/- 1db)
Linearity Coherence: 4° at 20Hz, 0° at 1kHz
Distortion at 20Hz: 0.006%
CMR Rejection: 100db at 60Hz
Input Impedance: 10kOhms
Output Impedance: 600 Ohms
Input Connectors: Two 1/4" phone jacks
Construction: 14 gauge welded steel, baked enamel finish
Size: 3-5/16"W x 5”L x 1-7/8"D (84mm x 127mm x 48mm)
Weight: 2lb (1.3kg)

JDI Frequently Asked Questions

What is a direct box anyway?
A direct box is an impedance matching and signal-balancing device. DI's convert hi-impedance instrument signals to mic-level balanced lines for interface with pro-audio equipment such as mixing consoles. A good direct box will ensure proper electrical signals are maintained throughout the signal chain and allow long cable runs without added noise. A good DI box is just as important as a good microphone.

What is the difference between a passive and an active DI?
Passive direct boxes use a transformer to convert the electrical signals while active direct boxes use an amplifier circuit. Passive boxes have the advantage of providing isolation which can reduce ground hum in systems.

I heard active direct boxes are better?
This can be thought in terms of a dynamic mic compared to a condenser mic. There are good dynamic mics and there are good condenser mics. A good passive direct box depends entirely on the transformer that is being used. For instance, the Radial JDI uses the world's finest transformer, a Jensen. These DI's sound fabulous! In fact way better than most active direct boxes!

If the JDI is so good, why should one buy the JDV over the JDI?
It comes down to the application. For keyboards, and simple live set-ups, the JDI is fantastic. No power supply, no batteries to go dead. You just plug it in and it sounds great. The JDV on the other hand will give you more reach. You will enjoy more detail or as Khaliq Glover (Engineer for Marcus Miller and Herbie Hancock) said: “the JDV is almost holographic compared to the single dimension of most DIs.”

Why do people use active direct boxes?
Because a good passive direct box requires a good transformer and these are expensive. The Radial JDI uses a Jensen Transformer and these are considered the best in the world. Active boxes can be made for much less money and will generally sound better than a cheap passive box.

So why not simply buy an active direct box?
Active DI's can be good but they can have several disadvantages: First and foremost, active direct boxes require power. This means that they must either run off batteries, phantom power from the console or use a power source like a 'wall-wart' or AC/DC supply. When the power is low, they distort. This means that for the direct box to work well, you must keep the batteries at full charge which is impractical if not impossible.

What about phantom power?
Phantom power is a DC supply that comes from the mixing console. The phantom powered direct box draws its power from the console through the balanced mic cable. The problem is that phantom power is rarely sufficient to properly supply the direct box. This 'starves' the amplifier and limits its ability to handle dynamics without distortion. The Radial J48 is a low-power consumption DI that addresses this problem by ensuring maximum available power is diverted to the signal path so that full dynamics may be enjoyed without distortion.

Why use an active direct box at all?
Sound. Some active boxes like the Radial JDV have exceptional sound and a frequency response that is well beyond the norm. Furthermore, when using low output devices such as piezo pickups, these require the added 'gain' that an active box can supply. Finally, when using older vintage instruments that have low-output pick-ups, one can encounter a 'loading' effect whereby the pickup is not able to drive both the stage amplifier and the 300 feet of cable to the mix position. An active box will not load down the pickup where the passive box may. The JDI is extremely efficient but being passive, can cause loading on these rare occasions.

What else should I look for should I decide to go active?
Probably the most important specification to look for is IMD or inter-modulation distortion. The test beats two dissonant tones together to measure the robustness of the circuit design . This is akin to playing two dissonant notes on a piano. Some pianos when well tuned somehow manage to sound good, while others just plain sound bad. This test is rarely done on direct boxes as most fail miserably. Check out the Mix Magazine “Seven for the Road” direct box comparative test and review on our web site at www.radialeng.com for more details on IMD.

So I should go active? I'm confused!
No. The decision between active and passive is based on application. If you are using the DI primarily in live situations, we usually recommend the JDI as it is both trouble free and is adaptable to a wide range of applications. Today, most bass guitars have extremely powerful pick-ups or have built-in active circuits. Acoustics are the same. Keyboards have tons of gain. And who dares to use a vintage 1955 Pre-bass live anymore?

What makes the JDI better than the rest?
A good direct box needs to address several facets to be functional: The sound, the feature-set and construction are all essential parts that make up the whole.

Lets start with the construction. The JDI is in fact two boxes in one. The inner skeleton features a 14-gauge welded construction in which the PC board, circuit, transformer and switches are housed. Lift up the JDI and you know you are dealing with quality. The rigid design ensures that there will not be any stress on the PC board (mil spec 2-sided) and the solder joints will remain intact even after years of use. The outer book-end design provides easy access to the connectors while creating a protective zone for the switches. In the real world of touring, DI boxes are stepped on & abused. Radial DI’s must be able to stand-up to the abuse.

As for feature set, we know of no other DI box that offers as many features. This makes the JDI practical in pretty much any application. Finally, the sound. Check out the specifications and you will find that it is extremely linear from 20Hz to 20kHz, it exhibits almost no distortion in the most rigorous and demanding 20Hz region and with virtually zero-phase distortion throughout the audio bandwidth, what you put in - you get out. Nothing added, nothing changed.

Radial - True to the Music™