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Radial Pro D2 Passive Stereo Direct Box

Radial Pro D2 Passive Stereo Direct Box

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The Radial Pro D2 is a high-quality, full-range passive direct box equipped with custom-made audio transformers for exceptional signal handling without saturation and with extremely low phase distortion in the critical bass and mid regions. The result is exceptional clarity and definition at an attractive price point. Ultra-compact and made of 14-gauge steel, the ProD2 features internal I-beam construction with a 'book-end' outer shell for extreme durability in the most demanding environments. The Pro D2 shares the same features as the ProDI, but the Pro D2 offers stereo connectivity. These exceptional direct boxes offer performance superior to any other DIs in their price range and are ideally suited for use with acoustic guitar, bass and keyboards.


- Full range passive direct boxes
- Isolation transformer eliminates noise
- Very low harmonic and phase distortion
- Compact and rugged design
- Ideal for live sound and studio

ProDI/ProD2 Development

When the Radial JDI was introduced in 1996, it revolutionized many preconceived concepts of what a direct box is and how a passive DI can, in many instances, be a better choice than it's active counterpart.The central task of a direct box is to convert an instrument's signal from high impedance to balanced low impedance. This enables the signal to travel long distances without adding noise and provides a proper load to the mixing console input for improved audio performance.Active direct boxes employ electronic circuits to change the impedance from hi-Z to lo-Z and balance the signal. Passive DIs employ a simple passive transformer to do the work. Active DIs require batteries, 48V phantom-power or external power supplies to power their circuits. Passive transformer-equipped direct boxes do not require any power to perform their task. The advantage of a transformer over typical active circuits can be summarized as 'a great device to reduce system noise' in a sound system.A transformer is an ingenious device that works by converting an electronic impulse, generally referred to as a current, into a magnetic field and then back again into a current. This 'magnetic bridge' has the distinct advantage of decoupling the source instrument from the receiving mixing console or mic preamp. When you hear a hum or buzz in the sound system, this is usually caused by stray voltages traveling through the wire causing havoc at the receiving end. This effect is commonly referred to as a ground loop. The most effective solution to this common malady is to place a transformer between the two offending devices.If the solution is so easy, why aren't all direct boxes passive? The trick lies in the quality of the transformer. The Radial JDI, the Duplex, and the JD6 all employ the world's finest audio transformer, Jensen, to manage the task. The problem lies in the fact that high quality transformers are expensive. These employ hand-stacked and laminated nickel core materials, precise winding schemes and expensive mu-metal Faraday shielding, all of which adds up to big bucks. Cheap transformers employ iron core materials and as a result, tend to saturate quickly, causing harmonic distortion and phase shift resulting in groups of frequencies exiting the transformer at different intervals or out of phase. Bottom line -
- cheap transformers sound bad.The quick solution is to employ an active circuit to balance and convert the impedance. Although this works and active DIs have their advantages, they do not provide any isolation and therefore are ill-equipped to eliminate ground loops.The Radial ProDI and ProD2 direct boxes employ a custom-made transformer that is fashioned around the Jensen transformer they use in the more expensive Radial JDI. No, the ProDI is not quite as good as the industry standard JDI (see comparison below), but considering it is half the price, the performance is nothing short of impressive.

Using the ProDI and ProD2

The best feature of the ProDI (and ProD2) is 'plug & play' ease of use. All you do is connect the instrument to the 1/4" input(s), the 1/4" through jack(s) to the stage amplifier(s) or mixer and the XLR output(s) to the mixing console and you are done. Any distortion? Hit the -10dB pad. Any noise? Just depress the ground lift switch.You will find that with acoustic guitars and basses, the natural tone of the instrument will shine through with a smooth and musical rendering. For electrically powered devices such as keyboards, the ProDI will immediately eliminate troublesome ground loops while delivering solid dynamics with a full rich sound.Look inside a ProDI or ProD2 and you will find the build quality and components to be of only the highest professional standards. Radial's proven construction methods and materials ensure years of trouble-free service. The ProDI and ProD2 feature audio transformers custom made to exacting standards to achieve the highest possible audio quality while maintaining an affordable price. The ProDI and ProD2 easily outperform all other direct boxes in their price range in both signal integrity and features

Inside the ProDI and ProD2

- Isolated XLR connectors to eliminate chassis ground potential.
- Custom audio transformer on input provides 100% isolation to eliminate hum and noise causing ground loops while maintaining signal integrity.
- Military spec PC board with full surface ground plane to reduce susceptibility to RF noise.
- High grade switches -
- long life, high cycle for reliable performance.
- 14-gauge steel welded I-beam construction makes it virtually impossible to torque the PC board.

ProD2 Input and Output Panels

- Pad -
- 15dB pad for left channel reduces the level going in from loud sources that could overload the circuit and cause distortion.
- Left input and thru -
- instrument 1/4" input and thru-put to amplifier.
- Right input and thru -
- instrument 1/4" input and thru-put to amplifier.
- Pad -
- 15dB pad for right channel reduces the level going in from loud sources that could overload the circuit and cause distortion.
- Book-end design creates a protective zone around the switches & connectors, indestructible 14-gauge steel construction.
- Full no-slip rubber bottom pad provides mechanical isolation, electrical insulation and prevents unit from sliding around.
- Left -
- balanced male XLR output connector, AES standard with pin-1 ground and pin-2 hot.
- Lift ground pin-1 -
- switch lifts the ground to pin-1 on both channels.
- Right
- balanced male XLR output connector, AES standard with pin-1 ground and pin-2 hot.
- Heavy-duty baked enamel finish for excellent durability and great looks for years!


The ProDI and ProD2 are designed to withstand the rigors of the most demanding high-use professional environments. Radial pioneered the use of it's innovative 'book cover' design, which provides a protective zone around the switches and connectors that keeps these components safe.Stress on circuitboards causes broken and intermittent solder joints, a common cause of failure in commercial rental and other high-use environments. Radial's 14-gauge welded I-beam inner chassis and 14-gauge outer shell greatly reduce the possibility of torque stresses being applied to the PC board.A full-bottom no-slip rubber pad works double-duty by providing protection from electrical shock and making sure these DIs stay put.


Q: Why do some people feel active direct boxes are better than passive DIsA: Comparing active DIs to passive ones is akin to comparing condenser mics to dynamics.Condensers tend to have more 'reach' and upper end clarity, while dynamics tend to be bolder and better suited to handling transients without distortion. Active direct boxes are signal preamplifiers that draw very little current from the instrument and because of their higher input impedance, tend to have more reach and sparkle. The high input impedance results in less loading on the pickup, an effect that can cause passive pickups, as found on vintage basses and electric guitars, to sound thinner. Today, most basses and acoustic guitars employ battery-powered preamps that buffer the signal and are not affected by loading. Most pros have some of each depending on the tone they are looking for or the problem they are trying to solve.Q: If the Radial DI is the best, should I spend more money to buy it?A: This depends entirely on the sound system you are using. Most PA systems are not capable of producing the bandwidth that comes out of the Radial JDI and therefore, the Radial ProDI is a good solution.Q: What causes ground loops?A: When manufacturers build their products, the internal circuit and outer shells are teaming with electrical currents traveling all over the place and returning to the safety ground. This ground reference voltage varies between manufacturers and when two devices are connected together, these 'stray' voltages can often combine to create 60 cycle hum commonly known as a ground loop. A good transformer provides an effective solution in reducing this 'common mode' noise and is the reason why passive direct boxes are often preferred for live concert touring.Q: Is the ProD2 two separate DIs in one?A: Yes. Each channel inside a ProD2 is completely isolated from the other and is the same as having two ProDIs in a single box. The ProD2 was designed for stereo keyboards and devices (such as CD players) that need to be balanced.Q: Can I rack-mount the ProDI or ProD2A: The ProDI is not rack-mountable while the ProD2 is. In fact, with the J-Rak, you can jam in 16 separate channels (8 x ProD2) in two rack spaces, making it ideal for large keyboard rigs on tour.Q: Can I use a headphone out into the ProDIA: Yes. Keep volume low and use the pad. Listen for distortion as overly high levels can saturate the transformer.Q: Can I use a ProDI backwards for reamping?A: Yes. Careful on the level as it should be very low: mic level -
- not line level!Q: Will phantom-power hurt the ProDIA: No, phantom-power is DC and very low current. The ProDI will ignore it.Q: Can I run a guitar into effects and then into the ProDI for direct recording?A: Yes! The ProDI will eliminate noise caused by stray voltages and provide a smooth, natural response.