JDI™ Using & Applications

This short guide is written for those who are experienced with pro-audio and direct boxes. Complete details about the many features built into the JDI and information on connecting your direct box can be found in the manual (PDF download).

The Radial JDI is a passive direct box and as such does not require any external power such as phantom or batteries to make it work. Just plug-in and play! Before you begin, make sure all switches are in the outward position and the audio levels of your system are turned all the way down.

Input Connections

The JDI features two ¼" jacks on the input panel. These are designed to accept instrument inputs from basses, guitars, keyboards, drum machines, etc. The ¼" input jack is normally connected to the instrument. The ¼" thru jack is a parallel 'thru-put' connection that feeds the instrument signal to the musician's on-stage amplifier.

Using the 'thru' jack with an on-stage amplifier allows both the musician and the engineer to work with the original signal direct from the instrument. This way, the musician can set up his stage sound with his own EQ while the audio engineer can process the instrument to sound good in the venue through the PA system.

Some instruments do not use on-stage amplification. It is common for instruments such as acoustic guitar to be connected directly to the PA system through the JDI using only the balanced XLR output. This allows the signal to feed the stage snakes, monitor mixer for foldback and main PA, just like a microphone.

Typical bass guitar setup using an on-stage amp
Typical bass guitar setup using an on-stage amp.
Typical acoustic guitar setup with no on-stage amp
Typical acoustic guitar setup with no on-stage amp.


Output Connections and Settings

The JDI features a mic-level, balanced output jack that uses a standard XLR male connector. The XLR out jack is wired to the AES (Audio Engineering Society) standard with pin-1 ground, pin-2 hot and pin-3 cold. Connect the XLR OUTPUT to the PA or recording console using a balanced XLR cable.

-15dB PAD

Depressing the PAD switch (located on the input panel side) inserts a -15dB attenuation circuit into the signal path before the transformer. This PAD is used to prevent transformer core saturation by very loud signal sources such as keyboards, drum machines and CD players. If you hear distortion at the XLR output try depressing the PAD switch. The ¼" THRU output is not affected by the PAD setting.

Ground Switch

Once connected, slowly turn up the system levels. If you hear hum or buzz try depressing the GROUND switch. This is a ground lift that disconnects pin-1 at the XLR output when set to its inward position.

REV 180º Switch

The REV 180º switch is a polarity reverse that inverts pin-2 and pin-3 at the XLR output. This provides several operational benefits: interfacing with older mixing consoles that have pin-3 hot is simply a matter of depressing the polarity reverse.

When combining mic and JDI signals from the same instrument to one track one can sometimes encounters 'phase' problems. Reversing the DI signal polarity can correct phase between two transducers. On-stage, the polarity reverse can sometimes reduce feedback from acoustic instruments. This same process, while recording, provides the engineer with another 'tonal palette' and experimenting with different settings can lead to some very pleasing results.


Special Features - MERGE

The JDI features an innovative 'MERGE' function that turns the ¼" INPUT and THRU jacks into a 'sum-to-mono' mixer. Depressing the merge switch introduces a resistive mixer circuit that will sum a stereo input to mono at the XLR output. This function allows stereo sources such as a stereo keyboard or CD players to 'merge-to-mono', saving valuable channels on the snake and the mixer when you have more sources than available inputs.

To 'merge' simply connect two instruments with similar output levels into the IN and THRU jacks, depress the MERGE switch and you are set to go. The internal resistive mixer is set up to do this without introducing any problems such as phase cancellation.


Merge function used to sum a stereo keyboard to mono
Merge function used to sum a stereo keyboard to mono.
Outputs of two keyboards merged to save mixer inputs
Outputs of two keyboards merged to save mixer inputs.