Using The Pro48™

The Radial Pro48 is an exceptionally great sounding direct box that has been specifically developed to be easy to use. But don't let the straight forward feature set fool you... the Pro48 employs the same world class active circuit as the industry standard Radial J48. The following page covers basic functionality. For more details, we invite you to download the complete manual by clicking on the icon at left.


The Radial Pro48 is a professional direct box that is equally useful for studio as it is for performance. It serves the purpose by converting the high impedance output of an instrument to a low input impedance, microphone level signal that is compatible with mixing console inputs. It also balances the signal to allow long runs to upwards of 1000 feet (300 meters) without appreciable signal loss or noise.

Unlike typical direct boxes that simply use phantom power to drive an internal buffer, the Pro48 actually converts phantom power from DC to AC, then uses a unique internal switching power supply to increase the internal working voltage in order to achieve much greater headroom. Because of this process, the active amplifier (buffer) is not constantly red lining. This means we do not have to trade off frequency response for dynamic range. The result is a response curve that starts at 10Hz and extends well above 40kHz! This assures the natural tone of the instrument is retained without degradation or introducing artifact.

So what does this have to do with using the Pro48? Simply put – with the Pro48 active direct box you have less to worry about. Although the Pro48 is extremely easy to use, there is a ton of technology built inside that makes it so.

Making connections

Begin by making sure the PA system is turned down before connecting the Pro48. This practice will assure that transients from powering up the active circuit do not enter the sound system. This good safe approach will help keep those tweeters working for years!

Basic Instrument Setup

  1. Connect a ¼" cable from your instrument to the Pro48 input.
  2. Connect the ¼" thru connector to your instrument amplifier. This 'straight through' parallel connection is easily tested by turning up your amp. Always test at a low volume to make sure connections and cables are working properly.
  3. Connect an XLR cable from the Pro48 output to a mic-preamp input on your mixing console. Make sure you turn the 48V phantom power on. Today pretty much all mixers are equipped with 48V phantom powering. This ingenious system sends a DC signal back to the Pro48 that powers the internal amplifier that does not interfere with the AC audio signal path. The Phantom LED indicator will illuminate to let you know if the Pro48 is getting power.
  4. Slowly turn the volume up on your mixer to a low level and test to make sure signal is present. If you encounter any buzz or hum, try lifting the ground. Begin playing. If you encounter any distortion, lower the source volume or hit the input pad.
  5. It's that easy! You are set to go!

Using the Pro48 with Acoustic Guitar

One of the most common applications for the Radial Pro48 is with an acoustic guitar on stage. The Pro48 is designed to be used alone, with the PA and monitoring system, or in combination with the PA system and on-stage instrument amplifier.

On large professional concert stages, the monitors or sound on the stage is typically controlled by a monitor engineer or the front-of-house (FOH) engineer working double duty. In this case, the Pro48 is basically invisible whereby the guitar connects to the Pro48 and the rest is handled much in the same way as a microphone would be.

Using the Radial Pro48 with Bass Guitar

As described above, just like an acoustic guitar, a bass guitar can either be used 'direct' or be used along with a bass amplifier. This applies to both recording in the studio and playing live. The advantage of a direct set-up is simplicity. No amps to carry around, no phase issues… just plug and play.

Combining the direct feed from the Radial Pro48 with the sound of a mic'd amplifier is a common approach, particularly in a live event. Here, the bass player can create the sound and feel he wants on stage which is extremely important when laying down grooves with the drummer. But the same applies when it comes to EQ… what may sound great on stage, may not necessarily sound good in the hall. This is why most players take a direct feed from the bass before it goes to the amp, thus allowing the FOH engineer to work with an unprocessed sound and optimize the EQ for the room. Reversing the polarity on the bas can sometimes help time-align the low frequencies to reduce resonance and make mixing easier.