Over the past quarter century, sound systems have evolved as have the instruments that are now used. The listener has also evolved. CD quality sound is no longer a luxury, but expected. Only now are we beginning to hear and appreciate the advantages of a good direct box. But defining a good direct box is not just a matter of ease or use. A good DI must provide a wide distortion-free frequency response and the dynamic range to handle today’s powerful instruments. The Radial J48 is an active direct box that has been specifically designed to work around the limited current that is available with 48-Volt phantom power, and do so while delivering the pure and natural sound of the instrument. At Radial, we call it the “Un-Sound”™.

When direct boxes first came about, these were passive devices. They employed a transformer to convert the high impedance instrument level to a low impedance balanced line. Although transformers presented a formidable advantage in that they isolated the source and the destination, good passive DIs were expensive. Knowing that a more affordable DI would sell more readily, manufacturers introduced lower priced passive DIs using inexpensive steel core transformers. These cost much less but the trade off was objectionable sound quality. Inexpensive steel core transformers introduce problems such as group delay (phase distortion) and core saturation (harmonic distortion), which are most prevalent in the lower frequencies.

Another major setback with low quality transformers was an effect called loading. For instance when using a Fender Precision Bass (the typical bass of the day), the bass guitar output would connect to the DI which would then split the signal to the bass amplifier and then drive 200 feet of cable to the mixer. Since these passive DI’s did not boost the signal in any way, the lowly single coil pick-up would have to drive both the amp and mixer. The musicians complained that the sound was thin because the guitar pickups were being ‘loaded down’ with too much work.

The active direct box came about as a solution. Although active DIs no longer provided 100% isolation of the source and the destination (thus opening the door to ground loops) they had two distinct advantages: Active DIs could boost the signal without loading down the pick-up and they could be made for less money. Powering the DI came from batteries and eventually, from the 48V phantom power that was intended to supply condenser microphones.

Here in lies the problem: The standard specification for Phantom power is 48-volts with a mere 5 milliamps of current. This works perfectly fine with the intended application of powering the capacitive plates on a condenser microphone. But with a direct box, the problem is managing the dynamic headroom of today’s powerful active instruments. This relatively new problem has emerged with the advent of active guitars and bases and their built-in electronics.

It must be understood that for the most part, the ‘working model’ for the typical active DI is based around the Fender Precision Bass. Powering is derived from 48V phantom power, as phantom is both convenient and universal. A traditional passive bass such as a Precision, when played hard will develop between 2 and 3 volts peak. In this scenario, phantom power is sufficient to handle these transients. The problem is that today’s active instruments with their 9-Volt batteries and built-in pre-amps will easily produce anywhere from 5 to 8 volts of peak energy.

Those old direct box designs were never intended for this type of input level and the result is predictable: Overload the input and you get distortion. They choke. Bass guitars sound muddy and lack punch while acoustic guitars sound scratchy and have no body. Digital keyboards and in particular piano samplers produce huge harmonics and extreme dynamics, which unfortunately get lost in the mix.

The excessive instrument level saturates the direct box. The DI’s power supply is unable to manage the input level, and this causes overload distortion. The sound is compressed due to square wave distortion and the end result is lack of definition and natural dynamics.

The Radial J48 is designed specifically to solve the problem of 48V phantom’s limited current by increasing the internal rail voltage and signal handling capacity of the direct box so that it can handle these extreme transients without choking.

The J48 incorporates a digital switching supply; much the same as today’s lightweight high-current power amplifiers. One can ‘hit’ the J48 with as much as 9-Volts and it will cruise right along without a whimper. It took 3 years to develop the J48, but was worth the wait!