The original Radial JDI (1996)

The original Radial JDI (1996)

Primary winding transfers prevent DC noise from passing through

The primary winding transfers the audio signal to the secondary via the inductive magnetic bridge. Only AC (audio) can pass, DC noise cannot cross the magnetic bridge.

Problem: Ground loop creates DC hum and buzz

Problem: ground loop creates
DC hum and buzz.

Solved: transformer isolation eliminates DC noise

Solved: Transformer isolation disconnects the 'hard wire' electrical input from the output while allowing the audio signal to pass. Ground loops are eliminated.

ProD2™ Development

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.

Sound quality
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!

Feature Set
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.

ProDI uses a specially made custom audio transformer
ProDI uses a specially made custom audio transformer.
JDI uses the Jensen transformer
JDI uses the Jensen transformer
Frequency Response
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.
Phase Response
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.