True to the Music
Radial Engineering
J48 User Guide
7
Dynamic headroom
Years ago when the first phantom powered active direct boxes came around, the “instrument” of the day was a passive
Fender Bass. These instruments would typically generate 1 or 2 peak volts at best. This seemed to work well. Then all of
a sudden, someone decided to put a battery powered pre-amp in the instrument and the output levels increased. Today
basses and acoustic guitars will easily output voltages as high as 7 volts. The result: overload!
With more input voltage, you need more dynamic handling to handle the transients. This means you need a higher inter-
nal rail voltage. The Radial J48 converts the 48V phantom using a similar approach to today’s super-high output power
amplifiers whereby a digital switching power supply is employed to raise the internal rail voltage from the typical 3 volts to
9 volts. Headroom!
Because the J48 is able to handle these transients without overloading, you eliminate square wave distortion. Because of
larger internal capacitors, the circuit is not constantly working at its peak. Harmonic distortion is reduced, inter-modulation
distortion goes down and phase distortion is minimized. The Radial J48 coasts along producing a less stressed and more
musical sound.
Buzz and hum caused by ground loops
Probably the most challenging aspect when setting up a sound system is reducing system noise. The most common problem
is buzz and hum due to ground loops. This is generally caused by two separate ground paths with different voltage poten-
tials interacting together, such as an AC powered keyboard connected through a DI to a mixer. Although lifting the ground
can help, this is often not sufficient. Often times, engineers will revert to passive direct boxes such as the Radial JDI just
to avoid ground loops. The Radial J48 employs a transformer as part of the internal switching power supply design. The
transformer isolates the current from the phantom power supply, eliminating the ground loop. Clever.
Plug and play easy
Ultimately, a good direct box should be plug and play easy to use. The J48 is a sophisticated device on the inside that
is designed to be easy to use on the outside. By understanding the design, we feel that you can make better use of the
features that are built into this marvelous direct box.
