Deane Jensen
The JDI as it was introduced circa 1996.
Twin-Servo advocate Frank Zappa in the studio
The original Jensen Twin-Servo
Radial Twin-Servo inside view

Twin-Servo Microphone Preamplifier™ Development

In the professional audio industry, there are a number of icons that have played significant roles in advancing the art of audio. Names such as Sidney Shure, Georg Neumann, Rupert Neve, Les Paul and Robert Moog all come to mind. Deane Jensen stands among them as the pioneer that reinvented the way that audio transformers were designed and built. Deane also brought about another significant advancement when he openly offered the industry free use of his patented 990 op-amp design. Today, the 990 continues to be used by many as the foundation for their preamp designs.

Radial began its relationship with Jensen in 1992 when it became Jensen’s Canadian distributor and over the coming years, Radial grew to the point where it became Jensen’s largest customer. Radial president Peter Janis explains: “I first heard about Jensen in 1981 when a tech that I was working with purchased one and remarked how much better it sounded. This stuck with me. When I started my own company, I contacted Jensen to represent them in Canada. We started by using Jensen mic bridging transformers in large custom snakes and in 1996, we launched the Radial JDI, the first commercially available direct box that used a Jensen transformer. As a manufacturer, one invariably buys parts from a number of sources and occasionally, one or two stand above the rest with respect to quality, accuracy and consistency. Jensen was and continues to be one of those companies.”

In recent years, the demand for Radial direct boxes exceeded Jensen’s capacity to produce, resulting in Radial purchasing Jensen in order to ensure a stable supply chain. With Radial’s manufacturing capacity and desire to add more modules for the 500 series format, the decision was made to bring back the original Deane Jensen 990 equipped Twin-Servo. Janis continues: “For those in the know, the Jensen Twin-Servo is considered by many to rank alongside offerings by Neve and API to be among the finest preamps ever made. Famous Twin-Servo customers include Frank Zappa, Kenny Loggins, Michael McDonald, Peter Frampton and Stanley Clarke. Tony Bennett even owned his own. When we discussed bringing back this original design to our customers, it got everyone really excited. So we brought our Radial engineering team together with the Jensen team and got to work.”

The Twin-Servo 500 is not a simplified version of the original. In other words, there are many companies that have used derivatives of the 990 op-amp in their designs with very good results. The Twin-Servo is different. As the name implies, the Twin-Servo employs two 990 op-amps that are cascaded in such a way that you get maximum horsepower and lowest noise at all signal levels. This combines with two servos to control feedback, eliminating the use of signal degrading capacitors in the audio path. Two oversized Jensen transformers frame the design - with one at the input and one at the output - to deliver maximum bandwidth. Janis adds: “From the moment we plugged in the first prototype, I was immediately struck with the bottom end. I have never heard anything like it. It is huge and solid - yet without hype. In other words, what Deane Jensen achieved is a design that truly marries transformers with a powerful gain stage while doing away with disruptive phase coloration.”

The Twin-Servo 500 has been meticulously designed to replicate the performance of the original, while working within the framework of the 500 series format. This includes 100% discrete parts to recreate the 990 topology, custom induction coil servos and of course the integration of Jensen’s finest transformers.

Made in Canada and distributed globally by Radial Engineering, the 100% discrete design follows Radial’s high standards with all-steel construction, rugged powder coat finish, a fully enclosed back box and dual-sided gold contacts for positive connection to the 500 series back-plane.