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 our decision to use a Jensen.


The JDI's internal I-beam shell 		     
  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. An innovative ‘slide-in-place’ XLR trace makes it possible to use I-Beam girder construction.
  3. The JDI uses a Jensen transformer for distortion-free performance. The Jensen features a nickel core for best signal transfer and minimal loading.
  4. A military-grade PC board is employed for maximum wear and tear in abusive environments. Welded steel standoffs ensure the PC board will not shift.
The Radial JDI is characterized by a distinctive book-end design. This has the advantage of protecting the switches against damage from abuse by providing a protective zone on both input and output panels. A heavy duty baked enamel finish resists scratching while a full-bottom no-slip rubberized pad stops the JDI from moving around and ads both mechanical and electrical isolation.

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 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.

JDI input panel

  
 
  5. A -15dB pad allows super hot inputs such as that from a CD player to be connected and balanced for long runs.
  6. The 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!
  7. The input connects to the instrument.
  8. The thru-put is connected to the instrument amplifier. The JDI has a high input impedance to reduce loading.


JDI output panel		   9. Our book-end design creates a protective zone around the switches & connectors for best protection!
  10. A heavy-duty baked enamel finish for excellent durability and great looks for years! 100% 14-gauge steel construction.
  11. The XLR balanced mic level output provides 100% isolation for runs to 1000 feet without appreciable noise.
  12. A 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.
  13. The 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.
  14. The parallel speaker interface option introduces a second -30dB pad with band-pass filter to emulate a 12” guitar speaker.
  15. A no-slip full bottom pad reduces mechanical vibration, improves electrical isolation and keeps the JDI from moving around on busy stages!
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.
 


Construction

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.

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

 

 

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.
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.
 

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.


Summary

 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.
     
 email: info@radialeng.com  << Back | Top | Next >> ©2003 JP Cabletek Electronics Ltd.