J+4™ Using & Applications

The following page outlines how to use the J+4 in common applications. For complete details we suggest you download the manual by clicking here or on the icon at left.


The Radial J+4 is in fact a stereo preamplifier designed to accept an unbalanced consumer level device and boost the output so it can feed a professional +4dB balanced line input. Balancing the signal is particularly useful when driving long cable runs as the twisted pair configuration provides significantly greater noise rejection than a coaxial counterpart. Also, by increasing the signal level, pollution from outside electromagnetic fields is reduced.

The J+4 outputs are 100% transformer isolated. Transformers are particularly adept at eliminating noise caused by so-called ground loops. This type of noise is most common in the field where controlling the power grid is often compromised. Given the fact that many of our customers are in live touring, large system integration and broadcast, there is a certain expectation that a Radial product will not only do the job, but will actually help silence the system. The signal also passes through a high performance drive circuit that yields less than 0.004% distortion with better than 95dB signal-to-noise. This exceptional performance is particularly astonishing given the compact size.

Making Connections

Before making connections, always reduce signal levels and turn off audio equipment. This helps eliminate damage to more sensitive components such as tweeters that can occur due to turn-on transients. Always test at low levels before increasing the output.

J+4 Standard Instrument Setup
Click to view large image.
  1. J+4 is easy to use. Simply connect the source to the input panel of the J+4 by selecting the appropriate connector.
  2. Unused input jacks can also serve as an unbalanced throughput should the need occur.
  3. The output is a standard 3 pin XLR wired to the AES standard with pin-1 ground, pin-2 hot, and pin-3 cold.
  4. Slowly turn up the levels from the source and destination mixer and then bring up the level on the J+4.
  5. If you hear hum or buzz, try lifting the ground.
    You should be set to go!

Location and cable length

While balanced cables can be run great distances the rule for unbalanced cables is shorter is better. Because of this the J+4 is always located near your -10dB device. This helps prevent noise and signal loss.

Up to 300 meters
Up to 4 meters


The J+4 is one of those boxes that can be helpful in all types of situations. In live touring it can used to increase the level from a computer so that it can feed an auxiliary input. In the studio, you can use it to increase the level from an iPod® so that it can be connected to the mixer. In a commercial installation, it can be used to interface a CD player to the balanced input of a PA system.

To get a better grasp as to how it can best serve your particular need, the following table outlines typical signal levels and how they relate to the J+4.

The J+4 is designed to boost the signal from a low output device and bring it up to a +4dB professional standard. Keep in mind that you require twice the power to generate 3dB of gain. This means that the J+4 must generate at least +14dB to achieve this increased level. The real magic here is increasing the gain without adding noise. This is truly what separates the Radial J+4 from other devices.

J+4 input panel and level control.

Using the level control

The LEVEL control sets the output level for both XLR outputs. With a -10dB input signal this level control ranges from infinity to +10dB. The J+4 will produce a +4dB signal level when the control is at the
12 o'clock position.

Output level calibration with
a -10dB nominal input level.
Adjusting the filter and ground
settings with a tweaker tool.

Using the high pass filter

The Radial J+4 is equipped with a high-pass filter that is used to roll-off low frequencies below 100Hz. Bass frequencies contain significantly more energy than higher frequencies. When playing audio tracks through a PA system, reducing bass content with the high pass filter can increase the dynamic range of your audio system. When recording a -10dB source signal, the high pass filter can help clean up a muddy mix by reducing low frequencies.

Ground Lift

The J+4 is equipped with a dual ground lift switch that disconnects the pin-1 ground connection on both XLR outputs and prevents ground loops. If you hear hum or buzz, try toggling the ground lift switch.