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Road Test: Radial PZ-DI Piezo-Optimized Active Direct Box
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The new Radial Engineering PZ-DI. Note the control and switch labels on the case.

Related Tags
  Craig Leerman, Road Test, Di Boxes, Reviews

The Radial Engineering PZ-DI active direct box provides several features that come in very handy if you work with piezo-equipped instruments, and it can also be used in any application where a quality DI is needed.

The PZ-DI incorporates a proprietary analog circuit with low-noise FET op-amp, and has a stated frequency response is 20 Hz to 20 kHz with total harmonic distortion less than 0.02 percent.

The enclosure has the standard “book-end” shape found with most Radial DI boxes, made of 14-gauge steel and tough as nails. Combined with simple yet smart protection of the knobs and switches, it’s rugged enough to survive the abuse of any stage crew. And, it also includes shielding that guards against interference caused by electromagnetic fields.

The enclosure bottom has a non-slip pad that helps keep the unit in place. One end offers a 1/4-inch input and 1/4-inch loop-through jacks, -15 dB pad switch, variable lo-cut knob, hi-cut switch, and 3-position load switch.

The other end sports an XLR-balanced output connector, 180-degree phase invert switch, ground lift switch, and 48-volt phantom power LED that visually confirms the unit is receiving phantom power. (There is no battery required, the unit runs only on phantom power even when the ground is lifted.)

The load switch allows the user to adjust the input impedance and optimize the load for the type of pickup being used, minimizing distortion and maximizing the frequency response. The 220k Ohm setting is designed for use with magnetic pickups, the 10M Ohm position is geared toward piezo pickups, and the 1M Ohm setting is a traditional setting for input impedance.

A look at the various capabilities provided at both ends of the unit. (click to enlarge)


The variable lo-cut (high-pass) filter is adjustable between 5 Hz and 500 Hz, and can help eliminate unwanted resonances and low-end rumble. The hi-cut filter switch rolls off high frequencies above 3 kHz.

Getting Familiar
I pulled the unit out of the box and put it on my bench to check out. As noted earlier, like all Radial products I’ve used, the PZ-DI is built well. All controls and jacks feel solid and will last for a very long time. Controls are labeled on the end faces as well as on the top of the unit.

One minor negative is that the lo-cut filter knob isn’t accompanied by corresponding frequency markings on the unit. While I make audio adjustments based on how something sounds, I do like to know where things are set. The user guide says to start with the knob fully counter-clockwise (set at 5 Hz), rotate it until you hear the bass roll off, and then turn it back just a bit, and it’s set. That’s a good way to do it, but I would like to know the actual frequency setting.


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