Q: What is a direct box anyway?
A: A direct box is an impedance matching and signal-balancing device. DI's convert hi-impedance instrument signals to mic-level balanced lines for interface with pro-audio equipment such as mixing consoles. A good direct box will ensure proper electrical signals are maintained throughout the signal chain and allow long cable runs without added noise. A good DI box is just as important as a good microphone.

Q: What is the difference between Active & Passive?
A: This is somewhat similar to comparing dynamic mics to condensers. Active DI’s have a built-in pre-amp that requires 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 and will improve the instrument’s sound quality. The J48 uses phantom power to derive its power source.

Q: What is phantom power and will it harm my other equipment ?
A: Phantom power is a DC supply that comes from the mixing console on pins 1 and 2 of the XLR connector. It was originally designed to provide power to condenser microphones. It is usually 48 volts and about 5mA. All equipment used in pro-audio is designed to interface when phantom is on. As such, phantom will not harm your equipment.

Q: Why do people use active direct boxes?
A: Active direct boxes tend to have more ‘reach’ in that they can capture harmonics and dynamics that can be lost with cheap passive direct boxes with steel core transformers. They are also less prone to loading the instrument, which can change the instrument’s tone

Q: Can you explain loading?
A: Years ago, most bass guitars used regular output pick-ups such as those found on Fender basses. Musicians found that connecting the bass ‘thru’ a direct box and then to their amplifier caused the sound to change. This was caused by the added load of the direct box driving the signal to the mixer (and cable) that could be as far as 200 feet away. This would reduce the level going to the amplifier.

Q: Why is loading no longer the main concern?
A: Back in the 1970’s and 1980’s, acoustic guitars did not have the sophisticated pick-ups and built-in pre-amps that are standard today. Electric basses now incorporate high-output pick-ups or have active electronics built in. Keyboards inherently have high output levels. These high output levels are so powerful; loading is no longer the concern. This ‘fix’ has in fact caused a new problem; input distortion or saturation.

Q: What makes the Radial J48 so special?
A: Let’s begin by understanding how active DI’s work: Active direct boxes are in fact signal 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, for the direct box to work properly, the batteries must be fresh. 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. Back then, no one ever figured that we would have to manage the high dynamic levels of today’s active instruments. We recently tested a Takamine 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 2 to 3 volts, its no wonder guitars often sound harsh in a PA system. Active basses push the DI’s further due to their powerful low frequency content and keyboards (especially digital pianos) are even more demanding.

The Radial J48™ was specifically designed to solve this problem by boosting the internal rail voltage so that these instruments would not be able to overload the input. The J48™ can be hit with as much as 10 volts and still sound great! This is called headroom.

Q: Why does the LED not stay on?
A: We felt that every milliwatt of available power should be diverted to provide maximum sound quality since phantom power has very little available current, we felt that lighting up an LED that requires almost as much current as the whole J48™ circuit would not be wise. For the most part, direct boxes tend to be placed under keyboard racks or behind amplifiers and you can’t see the light anyway.

Q: Why do people use passive direct boxes?
A: 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. A good one like the Radial JDI™ will process the signal without introducing artifacts such as phase distortion. This is achieved because the Jensen Transformer we use is extremely well made.

Q: What is phase distortion?
A: Keeping your signal in-phase is akin to making sure that when you play guitar, the sound coming from the low E string plays at the same time as the G string when it comes out of your amp. You may take this for granted but the fact is, phase distortion can cause an instrument to get lost in the mix and make a bass sound muddy. Phase distortion can occur at all frequencies but is most noticeable in the bass or low frequencies. Try facing your stereo speakers close together and reverse the wires on one cabinet so that it is wired ‘out of phase’ and you will immediately become an ‘in-phase disciple’.

When we tested several popular direct boxes, we found that most were fine at 1kHz. What surprised us is how they performed at 20Hz from absolute phase. One popular box was 40º out of phase, while another was 20º out. The best was the Radial JDI™ at a mere 4º while the J48™ comes in at a very respectable 9.8º. We spend thousands of dollars on PA systems to ensure they are time aligned (in phase) while lesser direct boxes ruin the sound even before it gets to the mix position!

Q: Is a flat frequency response better than a colored response?
A: This is a good question. When buying a large diaphragm condenser microphone, you are not getting a flat mic, but getting a color or flavor for your sound palette. Most studios boast a selection of mics and the sign of a good engineer is ‘knowing’ which mic to use on what in order to get a particular tone. With direct boxes, it is usually not the case. If the sound of the guitar is not right, one will usually change the guitar not the direct box. Therefore, we believe the role of the direct box is to transport the original signal as faithfully as possible from the instrument to the destination and allow the engineer and producer to make the artistic choices.

Here’s more food for thought… Should the direct box manufacturer change the tone? If it makes your Strat sound fat, will it make your Les Paul muddy? We think a properly designed DI should be faithful to the source. The Radial J48™ direct box is natural and uncolored.

Q: What about tube direct boxes?
A: Tube direct boxes are cool and there is a definite place for them in the recording world. Tube DI’s introduce personality to the sound and should be viewed in the same way as one views a large diaphragm microphone.

Q: What is the difference between phase and polarity?
A: This is often confused. Reversing the polarity means switching the (+) wire with the (-) wire and is an electrical connection. Reversing the phase has to do with the time domain. When a frequency is delayed by 180º and played with the original, it has the audible effect of being out of phase and causing cancellation. Reversing the polarity of a speaker has the same audible effect but at all frequencies.

Q: What makes the J48™ better than the rest?
A: A good direct box needs to address several facets to be functional: The sound, the feature-set and construction are all essential parts that make up the whole. Let’s start with the construction. The Radial J48™ is in fact two boxes in one. The inner skeleton features a 14-guage welded construction in which the PC board, circuit, transformer and switches are housed. Pick up the J48™ and you know you are dealing with quality. The rigid design ensures that there will not be any stress on the PC board and the solder joints will remain intact even after years of use. The outer book-end design provides easy access to the connectors while creating a natural protective zone for the switches. In the real world of concert touring, DI boxes are stepped on and abused. Radial direct boxes must be able to stand up to the abuse. No other DI box offers as many features. This makes the J48™ practical in pretty much any application. Finally, the sound of the J48™ is ‘not’. Check out the specification and you will find that it is extremely linear from 20Hz to 20kHz, it exhibits almost no distortion in the most rigorous and demanding 20Hz region and with extremely low phase distortion throughout the audio bandwidth, what you put in – you get out. Nothing added, nothing changed.

Q: Why choose a Radial direct box?
A: Passion and quality. We believe that today, what is missing in many products is a passion to build the product right. We are passionate about producing products that not only exceed the sonic norms, but also exceed the durability expectations.

Radial - True to the Music™