Radial JDI Duplex mk4 Stereo Direct Box Review

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(More customer reviews)There are better boxes out there, but they come with that tradition "better price" which could easily push you over $1000. This is Radial's top of the line stage class passive DI. It's the JDI (Jenson DIrect box) Duplex (for stereo applications.
What is it?
If your not familiar with DI's (aka Direct Boxes) they are a device that electricaly isolates an unbalanced line level input to a balanced line level output. It does this thru a transformer and (without getting into the physics) as such protects both lines from one another while at the same time elemintaing the possibility for problematic ground loops.
Why do you need one?
If you were to just "plug" an instrument such as a guitar (which uses unbalanced line level) into a mic line (which is a balanced AND in many cases POWERED line) the best thing that can happen is you'll get noise, hum, distorsion, ect. The worst that could happen is a powered line could cook your output on your instrument. This often the case where people plug iPods or laptops into powered stage or PA lines. The small voltage of a small electronic device becomes overwhelmed and shorts out due to the MUCH higher voltage and current of the PA's Phantom Powered lines.
This box is part of Radial's JDI line that uses genuine Jensen transformers for soft and subtle sound curves. Radial makes more affordable models that also sound terrific. However I wanted an "Any Situation" type box. This box is a stereo box which fits that bill nicely. It is acutally two seperate mono JDI's, each with their own transformer, in a single case. You could run two individual mono inputs and outputs if you wanted. But by pluging the individual right and left channels of a stereo device into each half of this box then running two output lines to the PA you preserve the stereo signal.
I/O
On the rear of the box each channel has a 1/4" input jack and a 1/4" thruput jack (for running a thru line to stage monitors). There's a "mix button" that will allow the thruput line to become a second input line for mixing stereo signals to mono. Each channel also two RCA inputs for mixing auido out of digital devices line CD/DVD, ipod, laptop, ect. The pairs for each channel are mixed to mono at output. Being a stereo box you might wonder why you would mix back to mono. Perhaps you only wish to run one line back to to PA mixer. The front of the unit has one XLR output and one XLR input for each channel. So as I said this can work as two standalone mono boxes. What if you want stereo? One the L channel to an input on channel 1 (1/4" in or RCA doesn't matter) then R channel to channel 2. Then run two XLR outputs to your PA mixer or console.
Other nice features
This unit features all metal construction which creates an electromanetic cage to shield it from outside interference. NICE if you standing next to HUGE stage moniters driving enormous magnets with tons of power. Each cannel has a high pass filter switch and a pad switch for devices. The pad is nice for digital devices like CD, ipod, ect. It also has a polarity flip switch for each output to eleminate hum caused by import sound devices. And lastly a ground lift switch to further isolate ground loops.
As I said this unit is about as good as it gets for passiv DI's. There are such things as Active DIs but that's a whole different animal. For most users, a passive is going to be the best choice. And as I said there are other models that aren't quite so pricey. I'll recommend a few. If your application like mine is primarily AV presentation then this box is actually a bit overkill. But like I said I wanted that "super utility" aka swiss army knife ablity coupled with true stereo and mono options. For just mono AV work I can recommend the Radial ProAV1. That line also contains several inexpensive stage type boxes. A step between this model and those I just mensioned is the Radial JDI. (Again this is the JDI duplex) It's the same technology and construction but at th same time is a mono box. It still has the stereo to mono mix feature as well. All will suit you well and sound great on systems big and small.

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