JD7 Injector™ Using & Applications

This quick start is designed to give the experienced professional player and guitar tech an overview on how to use the Radial JD7. For complete details, we suggest you download this PDF manual

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The JD7 is a guitar splitter. The more appropriate name is a high-impedance unity-gain guitar signal distribution amplifier. It allows you to drive as many as six amplifiers; a tuner; two effects loops; and feed a recording system via the built-in direct box at the same time. Full Reamping capabilities means you can then run a dry track into the JD7 to feed the amps and effects and adjust the tone as needed.

Input connections

As with all electronic audio products, always ensure levels are turned down or equipment is turned off before making connections. This will ensure turn-on transients do not harm sensitive electronics or speakers. The JD7 comes with an external power supply. As soon as you connect it, the JD7 will turn on.

JD7 instrument input connection jacks and Drag Control™.

There are two inputs on the front panel designated as 1 and 2. Depressing the SELECT switch will engage the input-2 if a guitar is connected. If not, it will select the balanced XLR input on the rear panel for Reamping through the JD7.

Drag Control™

The Radial JD7 is equipped with Drag Control load correction. The adjustable circuit lets you reintroduce the load on the pickup so that it sounds as if connected directly to a tube guitar amp. Start by setting the Drag Control to 12 o'clock. Listen. As you move the control clockwise, it will sound brighter. Adjust to suit.

-8dB PAD

Input-2 is equipped with a PAD that can be switched in for 8dB of level reduction. This can be helpful to match the input level between two guitars. Active pickups tend to output a hotter signal compared to passive pickups. The PAD can be used to bring active and passive guitar closer to the same input level.

Clip LED

All inputs, including the balanced XLR Reamping input, are monitored for overload by the clip LED. If the LED illuminates while playing reducing the input level going into the JD7

Grounding and connecting amplifiers

A properly grounded amp must be connected to output-1 at all times.

There are six outputs on the front panel. Channel-1 is designated as a 'DIRECT' output and should always be connected to a grounded amplifier, even if not used. The reason is for any electronic system to work safely it needs a path to ground. The JD7 provides this through the direct output-1 and the amp connected to it.

This means the amp your choose to connect to output-1 must have a good connection to ground. To ensure a solid ground only connect modern amplifiers that display UL and CSA certification labels and use a grounded three prong power plug. If you plan on connecting vintage amplifiers to outputs 2 thru 6 ensure that they have been modified to bring the power cord and grounding up to modern electrical safety codes by a qualified technician.

Its important to note that even through a grounded amp must be connected to output-1 at all times it does not have to be active. All amplifier outputs are equipped with ON/OFF toggle switches. You can use the toggle switch to turn the amp off while still using it as the primary path to ground.

Channels 2, 3 & 4

Amplifier outputs 2, 3 & 4 are identical transformer isolated outputs.

Output channels two, three and four feature transformer isolated outputs, an ON/OFF switch with status LED, a ground lift and polarity reverse switches. There are no volume controls on the JD7 outputs. As a unity gain device, it is designed to take whatever signal you put in, buffer it and output the same level without signal boost.

Live stages are often plagued by very powerful electromagnetic fields that can induce hum and buzz into everything! High impedance guitar circuits are particularly prone to noise. The JD7's isolated outputs can be very helpful as they naturally block DC currents which often times will cause hum and buzz when various pieces of equipment are connected together.

Channel 5 & 6 effects loop

Outputs 5 & 6 are transformer isolated and feature an effects loop switch.
Effects loop send and receive jacks on the rear panel.

Channels five and six are equipped with the same features plus an effect loop with rear panel send and receive jacks. Simply connect your pedals to the SEND and RECEIVE jacks and activate the loop by depressing the associated EFX LOOP switch on the front panel.

The idea here is to allow you to quickly compare the sound on outputs 5 and 6 with or without the pedals. Effect placed in the loops will be dedicated to one amp.

There are other options for effects pedals. You can dedicate an effect to one amp by placing it between the JD7 output and the amps input. You can share an effect will all amps by connecting your guitar to it before connecting to the JD7.

Connecting a tuner

The built-in direct box.

Auxiliary output number seven is another buffered output identical to output one except that it is always on and can not be turned off. It can be used to drive rack tuners, in-ear systems, alternate amplifiers, the 2 channel on an already connected amplifier, to drive monitors, another direct box, etc, etc... in fact, we would love to hear how you've used this output in a creative way on your own rig.

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Setting up several amps

180° Polarity on ch 2~6

You can drive a number of amplifiers on stage using the JD7. When connecting multiple amps it's very important to ensure your amps are phase aligned and all loudspeakers are moving in the same direction. This will allow more than one amp to play at a time with the best sound. The amp connected to output-1 is your "phase reference" amp. Amplifiers connected to the other outputs will be tested against your first amp and adjusted to match using the 180° polarity switch.

We recommend you add and test one amp at a time. The following checklist will guide you through the process of setting up each output to drive an amp without noise or phase problems.

  1. Always start by connecting output-1 to a grounded amplifier. Check to make sure your first amp is working normally. If so, you are ready add more amplifiers.
  2. Connect an amplifier to output-2 and turn it on at a low level. Listen for hum or buzz. If you hear noise depress the ground lift switch. This disconnects the ground to the amplifier and can often help eliminate noise from ground loops and magnetic interference.
  3. Set both amplifiers to the same volume to begin testing the phase of output-2.
  4. Toggle the 180° polarity switch on output-2 and compare the tone of the two settings. The in-phase setting will sound loud and full, the out-of-phase setting will sound hollow and weak. Choose the setting that sounds the best.
    The 180° control inverts the signal polarity of the output causing the amps speakers to move in the opposite direction. The idea is to choose the setting where the speakers in both amps are moving in the same direction.
  5. Once the output-2 is set up turn it off and move on to the next output and amp. Always test one amp at a time against the amp connected to output-1.
    Be aware that you may introduce a new polarity problem if you change an amp or add an effect pedal after setting up the outputs. This may happen because some effect pedals invert the polarity of the signal and some amps wire their speaker(s) opposite to others. If you change something its a good idea to check phase against your first amp.

 

Using the JD7 for studio Reamping

Record a dry track

Reamping is a two step process where the first thing is to record a clean dry track of the players performance. Set up the JD7 with the guitar connected to it and to an amp or two so that the guitarist is comfortable. Adjust the Drag control to make it 'just so' and mic up his amps as you would normally do. Record everything to separate tracks.

The direct box outputs a mic-level
signal to your mic preamp.

Then, connect an XLR cable from the JD7's direct box output to your recording system. This is a balanced mic-level output and should connect to a mixing console or mic preamp. Record the direct box output with no EQ or effects. This will capture the clean sound of the guitar while it feeds the amps.

This clean dry track will playback an exact copy of the players performance when Reamped back through the JD7. When the guitarist whales away with feedback, the dry signal will actually capture the sustaining strings. It will blow your mind.

The guitarist should be nice and fresh and ready to play. Do not worry too much about the recorded sound; capture the moment by concentrating on the performance. Once the track has been recorded, you can now send the guitarist to the beach.

 


The JD7 set up for recording a clean direct track for reamping later.

 

The built-in direct box.

Reamping the dry track

Take the clean dry track from the recording system and send it into the JD7 using the balanced line Reamp input. This is equipped with a level control that will let you adjust the signal level to replicate the original guitar level for your amps. You can connect as many amps and effects as you would like to the JD7 outputs.

Experiment with different amps and effects using various microphones and move them around the room until you get the sound you want. You can record track after track and the guitar player is no longer subjected to the painful technical details. This reduces stress for everyone! Best of all, you can always go back and Reamp the track again if later on you feel the track is not sitting quite right in the mix.

 


The JD7 routes the clean track from the multi-track to several amps.