JDI Duplex™ 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 Duplex and information on connecting your direct box can be found in the manual (PDF download).

The Radial JDI Duplex is a passive stereo 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.

The Duplex can be connected in many ways. In fact, it would be a lot faster to tell you what you can't connect to the JDI Duplex. The following is some of the more common configurations.

Guitar and bass

Probably the most common use for the Duplex is to use it with high impedance instruments such as bass and acoustic guitar. Connect your instrument to the ¼” input. Each channel features a ¼" THRU jacks allowing you to pass the instrument signal to a stage amp or electronic tuner. In all situations the XLR outputs connect to the PA or recording console.

Single channel connections using the ¼ phone jacks
 

Stereo Keyboard

Another common use is for connecting stereo instruments like electronic keyboards, drum machines and samplers. The left signals connect to channel-1 and the right to channel-2. Used this way the ¼" THRU jacks can be used to patch the instrument signal to a personal monitoring system or powered loudspeaker.

stereo keyboard connections
 

Dual Stereo Keyboard

You can retain full stereo operation with two keyboards by connecting the keyboard's left and right outputs as shown and engaging the MONO SUM switch on both channels. Pushing the MONO SUM switch inward turns the THRU jack into a second input that the Duplex mixes with the standard input. Connected this way, the left signals from both devices are summed to one Duplex channel and the right signals are summed to the other. You can adjust the relative levels using the keyboards volume controls.

stereo keyboard connections
Duplex control panel
The SUM MONO switch converts the THRU jack into an second input.
 

Dual mono keyboards

Engaging the MONO SUM also makes it possible to connect a stereo device to one channel and have the Duplex mix it down and deliver a mono signal to the PA system. Used this way you can connect one or two stereo devices in mono. The balanced XLR outputs connect back to the PA or recording system.

Single channel connections using the ¼ phone jacks
 

Smart phones and tablets

Today, smart phones and tablets have become part of the band and DJ setups. The Duplex is equipped with a variety of connectors to meet the challenge and this includes a 3.5mm TRS connector to match up with the headphone output commonly found on laptops, smart phones and tablets. To use a music player or laptop using it's 3.5mm headphone output, connect the device to the stereo 3.5mm mini jack input. As described earlier, the balanced XLR outputs connect back to your PA or recording system.

Single channel connections using the ¼ phone jacks
 

DJ mixers and CD/DVD players

The Duplex features RCA INPUT and THRU jacks for each channel. You can connect stereo devices like DJ mixers and use the THRU jack to patch in to a personal monitor or recoding system. As described earlier, the balanced XLR outputs connect the stereo signals to the PA or recording system..

Single channel connections using the ¼ phone jacks
 

Dual stereo using the RCA jacks

Just like with the ¼" jacks, you can retain full stereo operation with two devices by connecting the left and right outputs as shown and pushing the MONO SUM switch inward on both channels. Connected this way, the left signals from both devices are summed to one Duplex channel and the right signals are summed to the other. You can adjust the relative levels using the device's volume controls. You can even connect a personal monitor to the ¼" THRU jacks.

Single channel connections using the ¼ phone jacks
 

Balanced +4dB line input

You may run into a situation where you need to take a +4dB balanced line-level source and convert it to a mic-level. This is particularly important in snake systems where the signal path is optimized for a microphone between -40dB and -20dB. If one were to connect a +4dB signal, the mic splitting transformers would likely overload and crosstalk would likely be introduced due to the +4dB line-level signal being significantly louder than the mic-level signal.

To address this situation, each Duplex channel is equipped with a female XLR input labeled Line-In that is pre-padded to bring a +4dB level down to mic-level. To use the XLR LINE-IN set the XLR SEL switch to it's inward position. The switch is recessed to prevent accidental use. a small screwdriver can be used to access the switch. When the balanced XLR input is active, the ¼", RCA and 3.5mm input jacks are disabled.

Single channel connections using the ¼ phone jacks