Alexander Alexander Graham Bell
with first telephone

SGI™ Development

One of the most challenging problems common to both studio and stage is noise. Noise is particularly troublesome when it comes to high-impedance sources and as we all know, electric guitars are particularly problematic. Surround the guitar with noise emitting devices like amplifiers, transformers, lighting systems and dimmers, it is no wonder that our high-impedance guitar circuits are constantly being attacked!

It all started with the telephone
Although balanced wires are commonly used in today's recording studios and live concert systems, the development actually followed the invention of the telephone by Alexander Graham Bell in 1876. Balancing an audio signal consists of splitting the signal into two halves and transmitting it over using two wires that are out of phase or of opposing polarity. When the signals arrive, the two halves are recombined while the noise gets cancelled out. The noise cancelling technology afforded by balanced transmission allowed telephone wires to be suspended adjacent to electrical wires using the same telephone poles and were in general use by 1884. Even then, distances of 1500kms (930 miles) were possible without the use of booster amplifiers which serves to underline how effective a balanced system can be.

Balancing Guitar Signals
It is common knowledge that when you employ a guitar cable that is longer than 8 or 9 meters (25 or 30 feet) the signal not only degrades, but noise tends to increased significantly. This is caused by the capacitance in the cable and of course the susceptibility to outside interference from radio frequencies and electromagnetic fields..

For years, electronic engineers have attempted to present guitarists with a viable solution in the form of a buffer. A buffer is in fact a unity gain amplifier that lowers the impedance thus reducing susceptibility to noise while driving the signal further will less of a load on the pickup. The problem: guitarists hate the sound and feel of a buffer. As soon as you plug it, you get a sense of detachment. It just does not feel right. We discovered this problem when developing the Radial JD7 Injector.

Designing the SGI
We thought about it and asked ourselves if we could use the technology we had developed in the Radial JD7 and reapply it in a balanced drive system. Since the SGI would need to convert a high impedance unbalanced signal to a low impedance balanced signal and then back again to an unbalanced circuit, it seemed evident that one box would be needed at each end: a transmit (TX) and receive (RX). In between, a common XLR cable would be used. This would allow the SGI to adapt to standard studio wiring while being compatible with large scale concert system snakes. jd7

The SGI-TX circuit design begins with the same award-winning class-A active buffer as the JD7 and incorporates Drag Control™ load correction. For those that are not familiar, Drag Control lets you adjust the load on the pickup so that it replicates the sound as if connecting a regular guitar cable to a tube amplifier. You just close your eyes and dial it in until it feels right. At the other end, the RX is completely passive. In other words, it does not require any form of AC or DC power. Instead it employs a transformer coupled input and 'snubbing' circuits that optimize the output for natural tone.

The send-receive design is ideally suited for recording where a guitarist can sit in the control room and play his amp some distance away in an isolation booth. This way, he can hear exactly what is being recorded as he lays down his tracks. Live, the SGI can be used to route signals from wireless systems to pedalboards, to under-the-stage amps or to isolation cabinets.

Today, the Radial SGI is used in studios everywhere, in houses of worship to keep the stage noise down and on concert stages by major artists including Carlos Santana, Jeff Beck, Eric Clapton and many other greats. And if we can 'fool' these guys into believing that they are connected to their amps… we figure we have done a pretty good job!