User Manual

FREQUENTLY ASKED QUESTIONS
What is the difference between active & passive?
Active DI’s have a built-in pre-amp requiring power to run while passive DI’s use a transformer to convert the signal. Both
transform or convert the instrument’s high-impedance output to a low impedance balanced microphone level. This allows
long cable runs without adding unwanted noise. Passive boxes have the advantage of providing isolation over typical DIs,
which can reduce ground hum and noise in systems. The J48 features an isolation transformer in the power supply to ad-
dress this problem.
Which is better - active or passive?
Both have their place just like dynamic and condenser microphones. Passive DIs are often easier to use because they do
not require power while, active DIs tend to have more reach. As a rule, passive direct boxes are best suited for electrically
powered devices like keyboards, while active boxes are often preferred for instruments like acoustic guitars and basses.
Can you explain loading?
Years ago, most bass guitars used low output pick-ups such as those found on Fender basses, while acoustic guitars used
piezos. Musicians found that connecting the instrument ‘thru’ a passive direct box to their amplifier and then to a mixer
caused the sound to change. Splitting the signal to the instrument amplifier and the mixer created the added second load.
This of course would reduce the level going to the instrument amplifier and cause the sound to change. Active DIs like the
Radial J48 buffer or pre-amplify the signal so that loading is never a problem.
What makes the Radial J48 so special?
Let’s begin by understanding how active DI’s work: active direct boxes are in fact preamplifiers. They boost the instrument’s
signal to a manageable level. This means that active direct boxes require power to run. As such, they must either get their
power from batteries or phantom power from the console.
When using batteries, they must be fresh for the direct box to work properly. As soon as the power is low, the direct box
will distort. This is why engineers hate batteries and prefer phantom power. But phantom has limitations; phantom power
was originally developed to supply low-current condenser microphones. The AES specification for phantom is 48 volts with
only a few milliamps of current. We tested a popular acoustic guitar with built-in pre-amp and found that when pushed to
the max, the output peaked at 7 volts. Considering that most DI’s can barely manage 3 volts, its no wonder guitars often
sound harsh in a PA system. The Radial J48 was specifically designed to solve this problem by increasing the internal rail
voltage so that these high output instruments would not overload the DI’s input.
True to the Music
Radial Engineering J48 User Guide
13