JD•7 Development and Evolution

The quest for creating exciting new sounds has never been greater than today. Producers, engineers and musicians are constantly trying to bring something new to the musical landscape in effort to have their ‘sound’ stand out among the sea of ‘pre-packaged’ guitar tones. To this end, the Radial JD7 Injector allows the user to combine amplifiers, effect pedals and modeling devices to create new, never before sounds that excite the user and help spur on the creative process.

The concept of driving many amplifiers at the same time has been a dream for many. In fact, audio distribution amplifiers have been around for years. The problem is that they have for the most part, been designed to work with balanced line level signals and are unsuitable for guitar. Why? Simple: guitars are high impedance, noise generating, finicky instruments that range from vintage low level single coil pick-ups to high output active humbucking devices. And most challenging of all is the demands guitarists put on equipment manufacturers to produce the sound they want or in the case of the JD7 – to not change the original tone of the instrument.

We started developing the concept of a guitar signal distribution system in 1988. The 1st unit we built was a custom designed device that had 6 outputs. It was active, used op-amps and although it worked, sounded brittle and top-ended. When connecting this device to several amplifiers, one would encounter hum and noise problems due to ground loops.

In 1994 we produced a second custom unit that seemed to solve these problems. We changed the audio circuit to a Class-A and introduced transformer-isolated outputs. This unit featured off-the-shelf transformers and our 1st generation Class-A circuitry. It also sported 6 outputs and still today, works relatively well.

In the fall of 2000, we decided the time was right to look at building a production unit and developed the prototype JD6 that incorporated custom Jensen transformers. In 2001, the JD7 began to take shape. We reworked the circuit with our latest Class-A design, introduced a balanced output to use the JD7 like a direct injection box, introduced an active balanced input to allow pre-recorded tracks or line level devices to be connected and added a separate tuner output. We also invested a lot of time on the grounding system and introduced a full ground plane to the floating circuit. Keep in mind that guitars are notoriously bad for noise and noise-control is critical when boosting and distributing guitar signals.

We thought we had the JD7 licked until one early morning during tests, we found that the sound was not right. There was something odd… We checked the specs and double-checked our tests; the JD7 was perfect… yes perfect… Jensen Transformers, Class-A circuitry, super low noise… Perfect! In fact it became evident that it was too perfect. Here’s the problem…

When you connect a guitar to the JD7, the guitar signal is ‘buffered’ or amplified so that it can drive all of the outputs at the same time. What we and everyone else that has ever tried to build a guitar distribution system failed to realize is that distinct relationship that exists between a guitar pickup and the amplifier. The guitar and the amp couple together and form an electrical circuit. Put the JD7 in between and the guitar no longer ‘sees’ the amp. The guitar sees a perfect load and the amp sees a perfect source… the relationship is lost.

This is how we came to develop Drag Control, our proprietary load correction circuit. Drag reintroduces the relationship by loading down the pickup so that it thinks it is connected directly to the amplifier. This subtle control is both effective and musical and plays a tremendous role in achieving the ‘un-sound’ that has made the JD7 famous. The Drag Control feature is now employed in several of our products including the Radial JDV Super DI and the JD7’s little brother, the JX2 Switchbone.