Frequently Asked Questions - Radial Engineering Pro48 User Manual

FREQUENTLY ASKED QUESTIONS

What is the diff erence 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 DI's, which can reduce ground hum
and noise in systems. The Pro48 features an isolation transformer in the power
supply to address this problem.
Which is better - active or passive?
Both have their place just like dynamic and condenser microphones. Passive
DI's are often easier to use because they do not require power while, active
ones 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.
What makes the Radial Pro48 so special?
Let's begin by understanding how active DI's work: active direct boxes are in fact
preamplifi ers. 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 specifi cation 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, it is no wonder guitars often sound harsh in a PA
system. The Radial Pro48 was specifi cally designed to solve this problem by
increasing the internal rail voltage so that these high output instruments would
not overload the DI's input.
How does Radial increase the rail voltage?
We take the phantom power voltage and drive it through a special custom made
DC-to-DC transformer. The transformer is coupled to a timing chip that essentially
drives the signal in the same way as the newer switch mode or digital power
amplifi ers work. This brings the current up to a workable level and creates a
higher internal rail voltage to handle the dynamics.
What is phantom power?
Phantom power is a 48 volt DC supply that comes from the mixing console that
was originally designed to provide power to condenser microphones. The Radial
Pro48 takes the phantom power and converts it using an internal switching power
supply. This allows the Pro48 to handle higher transients without the distortion
associated with most active direct boxes.
Radial Engineering Ltd Pro48 User Guide
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