VTDB-2B | Frets Magazine (December 1988)

Frets Magazine (December 1988) By Larry Cragg

Finding the ultimate natural sounding amplification system for acoustic string instruments is a never ending struggle. But acoustic sound reinforcement seems to have taken another step toward that goal with the introduction of the Tube Direct Box by James Demeter of Innovative Audio Systems. Our review unit was shipped directly to Frets from the factory. The purpose of a direct box is to help correct impedance mismatches between two pieces of equipment, such as a musical instrument pickup and a mixing console or amplifier. Also, direct boxes can, if they have an onboard preamp, step up the signal from a pickup. Most direct boxes on the market are transistorized, but the Tube Direct Box uses a vacuum tube for the input stage, instead of transistors. Inherent with a vacuum tube is its ability to provide extremely high input impedance, to prevent "loading" of a pickup ("Loading" is a frequency-sensitive form of attenuation). It also provides substantial headroom, allowing for a wide dynamic range without distortion. The Tube Direct Box uses a Jensen transformer for the balanced output (lo Z, 3 pin cannon). This transformer produces a "transparent" sound, with excellent distortion and phase characteristics. Another feature is a 1/4" output jack for connecting the direct box to a guitar amplifier. The signal exiting this jack also is buffered through the tube circuit, making long cable-runs possible without loss of high frequencies. Complete ground isolation is attainable with the Tube Direct Box by using the ground lift switch. Also, there is a boost switch that increases the output to the board by 9 dB. This is useful for instruments with low output volume (voltage). The Tube Direct Box measures 8" X 5" X 2", and weighs 4 pounds. It is housed in a heavy-gauge black anodized case of brushed aluminum and steel. The retail price is $399.00. Critique When the Tube Direct Box was tested with a magnetic pickup mounted in an acoustic guitar, to my ear the high frequencies became clearer, and the overall tone got sweeter and more natural sounding, as compared to the sound of the guitar with the pickup plugged straight into the amplification system. When tested with a piezo-electric pickup in an acoustic guitar, the result was a much warmer and richer sounding instrument. This is due to the extra-high input impedance of the direct box, which causes the low frequencies to increase because of the lack of pickup loading. When the Tube Direct Box was compared to a transistorized direct box that is considered a current standard of the industry, it produced a smoother, more natural sound with both types of pickups. Not only did the Tube Direct Box sound better when comparing the two direct boxes low impedance outputs sent to a mixing console, but also when comparing the 1/4" outputs (high impedance) sent to a guitar amplifier. The only possible inconvenience of the Tube Direct Box is that it must be plugged into an AC outlet, instead of using a battery or phantom power from the mixing board. But it passes every other test with flying colors. In fact, many studio musicians appreciate the sound of the Tube Direct Box so much that they have bought their own unit and carry it with them to recording sessions.