Part 7 - FAQ’s or Frequently Asked Questions
Q: What is the difference between active & passive?
A: Active DI’s have a built-in pre-amp that requires battery or 48V phantom power to run, while passive DI’s use a transformer
to convert the signal and do not require any power supply. 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, which can reduce ground hum and noise in systems.
Q: Which is better – active or passive?
A: 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 DI’s tend to have more reach. As a rule, passive direct boxes are preferred for electrically
powered devices such as keyboards and electronic drums.
Q: Why do people use passive direct boxes?
Passive direct boxes are often chosen as they are ‘plug & play’ easy to use. When equipped with a high quality transformer,
they can handle exceptionally high signal levels without harmonic distortion and a good one like the JDI will process the
signal without introducing artifacts such as phase distortion. Best of all, passive DI’s eliminate ground loops!
Q: Why do people use active direct boxes?
A: There are two reasons that active DI boxes like the Radial J48 have become popular. To get good sound with a passive
direct box, you need to use a high quality transformer like a Jensen, which can be quite expensive. This cost dissuades many
manufacturers from building passive DI’s; a basic
active
direct box can be made much more cheaply. The other reason is
that back in the 1970’s and 1980’s when DIs first showed up, most instruments used passive pickups and these generally
had very low output levels. Passive DI’s with inefficient transformers would ‘load’ down the pickup and cause the sound to
change. Active (buffered or amplified) direct boxes could be made with a high input impedance that would not load down
the pickups, which solved the loading issue.
Q: Can you explain loading?
A: Years ago, most bass guitars used low output pickups such as those found on Fender basses, while acoustic guitars
used piezos. Musicians found that connecting the instrument to a direct box, then the DI to their amplifier and also to a
mixer caused the sound to change. Splitting the signal to the instrument amplifier and the mixer added a second load. This
of course would reduce the level going to the instrument amplifier, thinning and colouring the sound.
Radial Engineering
JDI User Guide
12
True to the Music
