Road Test: Radial Engineering ProD8 Rackmount Passive DI

Optimized for use with keyboards, but it has many other uses at gigs as well

By Craig Leerman July 31, 2012

A view of the “front” of the Pro8D, with 1/4-inch jacks and PAD switches.

The Radial Engineering ProD8 is an 8-channel, rack-mountable passive direct box that is optimized for use with keyboards, but it has many other uses at gigs as well.

The eight channels can each be used with mono sources, or with stereo sources that it can merge to mono.

The unit also offers loop-through routing capabilities, as well as an effects loop on every channel.

Like all Radial units I’ve worked with over the years, the ProD8 is very well built.

The outer chassis is constructed of 14-gauge steel, covered with a baked enamel finish. It measures 1RU high by 6.2 inches deep, and weighs about 8 pounds.

Frequency response is specified as 20 Hz to 18.5 kHz (+ or – 0.2 dB) with total harmonic distortion at 0.01 percent from 20 Hz to 20 kHz (-10 dB) Input impedance is stated as 140k Ohms (unbalanced), while output impedance is 150 Ohms (balanced).

Each channel uses a shielded Eclipse ET-DB1 transformer with a 12:1 turn ratio.

The front panel offers 1/4-inch inputs and outputs, as well as PAD switches. For each channel there are two 1/4-inch jacks for inputs A and B that will auto merge to mono, a single 1/4-inch jack for loop-through output, and a TRS 1/4-inch jack for the effects loop.

Each channel also has a -15 dB PAD switch to accommodate higher output devices.

On the rear panel, meanwhile, each channel has an XLR output, a ground-lift switch, and a polarity switch that reverses pins 2 and 3 on the XLR. Internally, there are individual channel switches for chassis ground set in the “lift” position at the factory.

Full view of both ProD8 panels. (click to enlarge)

Also inside, pre/post switches allow the through output to be either pre or post the effects loop. (These are factory set to the post effects loop position.)

User’s Choice

Earlier I referenced the front and rear of the unit, but it offers reversible (pivoting) rack ears so either can face the front of a rack. This is a great feature for those who are going to rack the unit with other gear and may want more convenient access to the XLRs to interconnect with the PA.

Many of us in production, however, probably would choose to have the 1/4-inch connectors facing front so we can easily interface different setups, and then use a fan-to-fan XLR snake connected to the back for the hookup to the PA.

There are four different ways to use the ProD8:

1) For eight mono sources or keyboards. By plugging into just one of the A or B input jacks the unit behaves like eight separate mono DIs. 

2) With eight mono keyboards. Plug a stereo signal or keyboard into the A and B inputs on a channel, and the ProD8 merges the signals to a mono output, and a mono “thru” output for onstage monitoring. This is a great feature to have if you have a limited number of snake or mixer channels available.

3) With four stereo sources or keyboards by simply using two channels in the ProD8 per keyboard. Of course you can always use any combination of stereo and mono sources together as each channel is fully isolated from the others.

4) With eight merged stereo keyboards. This requires splitting a keyboard’s outputs between two separate channels using the A input on one channel and the B input on a second channel. By using both inputs this way, two keyboards can share two channels and while they will be merged together, they will both output a stereo signal.

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About Craig

Craig Leerman
Craig Leerman

Senior Contributing Editor, ProSoundWeb & Live Sound International
Craig has worked in a wide range of roles in professional audio for more than 25 years in a dynamic career that encompasses touring, theater, live televised broadcast events and even concerts at the White House. Currently he owns and operates Tech Works, a regional production company that focuses on corporate events based in Las Vegas and Reno.


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