Radial Engineering Pro D2

• Stereo direct box designed for keyboards
• Smooth, warm sound rounds out digital edge
• Able to handle huge transients without choking
• May be rack mounted for touring rigs

The Radial ProD2 is a compact stereo direct box developed specifically to address the needs and challenges of interfacing a stereo keyboard to a professional audio system. This passive DI features two independent channels with separate inputs and thru-puts for the artist's stage amp and two fully isolated outputs for the PA system.

At the heart of the design are two high performance Eclipse ET-DB2 transformers. These deliver 20Hz to 20kHz performance with less than 1.5dB deviation above 18kHz and are able to withstand tremendous signal levels without distortion. Unlike active circuits that overload when the signal exceeds the rail voltage, transformers saturate. This creates a pleasing effect that naturally rounds out the tone, acting like a subtle limiter which is particularly advantageous when interfacing the ProD2 with digital pianos, samplers and drum machines that can produce excessive dynamics. Transformers are particularly adept at eliminating hum and buzz caused by ground loops.

As with all Radial products, the ProD2 is built tough to handle the rigors of professional touring. A 14-gauge steel ultra rigid i-beam skeleton frame eliminates opportunity from outside stress to flex the sensitive PC board and cause premature solder joint failure. The innovative book-end design creates a protective zone around the connectors and switches further increasing lifespan. And a full bottom no-slip pad adds mechanical isolation and electrical insulation to further reduce opportunity for noise.

The Radial ProD2's warm sound, legendary build quality and compact design have made it the most popular stereo direct box made today.

This short guide is written for those who are experienced with pro-audio and direct boxes. Complete details about the many features built into the ProD2 and information about connecting it to your system can be found in the manual (PDF download).

The best feature of the ProD2 is its 'plug & play' ease of use. All you do is connect the instrument to the ¼” inputs, the ¼” through jacks to the stage amplifiers or local mixer and the XLR outputs 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 ProD2 will immediately eliminate troublesome ground loops while delivering solid dynamics with a full rich sound.

?Sometimes the output level of active pickups and devices like keyboards can be too hot for audio devices down stream in the signal chain. To prevent distortion the PAD switch introduces a 

-15dB attenuation at the instrument input.

The ProD2 features two PAD switches, one for each channel. When using the ProD2 in stereo both PADs should be set to the same position to keep the balance between channels. Separate PAD switches allow the ProD2 to be flexible when used as a dual mono direct box.

Start with the PAD switch in the outward position (disengaged) when doing your basic connection. If you detect distortion engage the PAD by pushing the switch inward. You may have to increase the gain at the console or preamp to compensate.

?As mentioned, the ProDI features 100% transformer isolation to protect against hum and buzz caused by ground loops. If you hear hum or buzz set the lift switch to the inward position.

Setting the switch to the inward position will disconnect signal ground at pin-1 on the XLR connector and allow the transformer to act as a bridge between the input and output.

 

The ProD2 is designed for stereo devices like keyboards. Simple, straight ahead hookup makes it easy to connect your keys to your recording system for great stereo sound!

 

Driving the output from a sampler or electronic drum machine to the PA system has never been easier. The ProD2 delivers plenty of headroom and lets you connect a local DJ mixer too.

 

Two Radial ProDI direct boxes in one, multi instrumentalists rejoice! The ProD2 is perfectly well suited for bass, acoustic guitar or just about any instrument with a pickup.

The Radial J48 has gained a tremendous following through the professional audio community. With significantly more headroom, lower distortion and unmatched durability, it is no wonder that the J48 has become the most specified direct box on stages around the world. As you will note with the specifications below, the J48 is exceptionally linear when tested both under laboratory conditions and when placed under the extra stress of 100 meters (300 feet) of cable. In the lab, the high frequency response actually exceeds 40kHz! This makes the J48 a perfect candidate for the most demanding studio recording while being the obvious choice for the artist on stage.

Specifications  

• Audio circuit type : Proprietary analog circuit with low-noise op-amp
• Frequency response : 20Hz ~ 20kHz
• Dynamic range : 109dB
• Noise floor : -99dB below 0dBu
• Equivalent input noise : -103dBu
• Maximum input : +10dBu
• Phase deviation : +10º at 20Hz | 0º at 1kHz | -1º at 20kHz
• Total harmonic distortion : 0.002 % @ -5dBu
• Inter-modulation distortion : 0.003% @ -3dBu
• Input impedance : 220kΩ - ¼" input
• Output impedance : 600Ω - XLR output

Features  

• Merge function : IN and THRU jacks are summed to mono
• Input pad : -15dB
• Polarity : 180º signal polarity reverse switch
• Low-cut filter : -3 dB @ 80Hz
• Ground lift : Disconnects pin-1 at XLR output
• XLR configuration : AES standard (pin-2 hot)

• Power : 48V phantom - proprietary digital switching
• Construction : 14 gauge steel chassis and outer shell
• Finish : Durable powder coat
• FCC approval : Complies with section 15 of the FCC Rules
• Conditions : For use in dry locations only between 5°C and 40°C

When developing the ProD2 direct box our primary concerns included optimizing sound quality by extending the frequency response and dynamic handling, making sure construction was sufficiently solid to stand up to being kicked around on stage and of course it had to have a simple yet effective feature set to address the needs of today's professional touring keyboard player.

Today, most keyboards are digital. This means that they employ buffers or internal gain stages to produce the output signal. As such, they can generate a ton of signal. In fact the most common problem with keyboards is that they will often overload the input stage of most devices. This is particularly acute with digital pianos. These not only have a very wide frequency range, they are exceedingly dynamic.

To address the higher output and dynamics of today's keyboards, the decision was made to employ a passive signal path. In other words, instead of using an active buffer that could potentially distort, the 'engine' inside the ProD2 is a transformer. You can hit the ProD2 real hard with tons of signal and it still sounds great! This is due to the way transformers distort. Unlike active circuits that 'square wave' once you exceed the rail voltage, transformers saturate. This means that the onset of distortion is more gradual. This creates a natural limiting effect that is often referred to as 'vintage' sounding.

Because the Radial ProD2 is passive, it does not require any powering whatsoever. A specially designed transformer does the high-to-low impedance transfer and balances the signal so that it can drive the signal well over 300 meters (1000 feet). The custom wound Radial transformers employ a special nickel core that produces an exceptionally linear response from 20Hz to 18.5kHz. This is sufficiently broad to handle the most demanding artist and of course wider than the frequency response that is available from most PA systems.

Transformers also benefit by eliminating the buzz and hum caused by ground loops. These are more prevalent when interfacing two AC powered devices such as a keyboard and a mixer that share the same earth ground. By lifting the audio ground and isolating the two devices, noise magically disappears!

When developing the ProD2, we wanted to combine high performance with simplicity. In other words, we really wanted it to be plug & play easy to use. And because so many keyboards are stereo, it of course had to address this need.

Each channel is equipped with a separate ¼" input for the instrument and a ¼" thru-put to allow local monitoring. The 3 pin XLR-male balanced output connects to the mixer. Because all of the connectors are electrically isolated from the metal shell, both channels are completely independent. This enables the ProD2 to be used with two completely different instruments without worry of cross-talk or contamination. This is furthered with separate -15dB pads on each channel that enable you to optimize the signal path should two different instruments be connected.

Transformers are particularly effective at eliminating hum and buzz caused by ground loops. Because audio is passed via a magnetic bridge, the electrical connection between the input and output is completely disconnected. A single dual channel ground lift switch allows the user to also disconnect the ground for 100% isolation.

As with all Radial gear, the ProD2 is built tough to handle the rigors of professional touring. DI boxes get particularly harsh treatment as they are often tossed on the stage floor, kicked around and of course cables are tripped on further increasing stress. The internal I-beam skeleton provides maximum rigidity to avoid PC board stress that could cause solder joints to prematurely fail. The book-end design further protects the connectors and switches from abuse. And because the ProD2 can be rack-mounted using the J-Rak, as many as 16 channels can be set up in two rack spaces for unequaled flexibility.

The ProD2 frequency response is almost ruler flat from 20Hz to 20kHz. In fact with less than 1dB deviation at 20kHz, human hearing is unable to detect any fault. Considering most PA systems barely produce audio above 17kHz, the ProD2 is exceptionally well suited for live touring.

Critical to delivering natural sound is the ProD2's ability to retain the phase coherence across the audio spectrum. This basically means that what you put in, comes out. Considering the exceptional fidelity of today's digitally sampled keyboards, it is good to know the ProD2 can deliver your sound without artefact.