The Radial JX•2 Switchbone is an AB-Y box that is designed for an electric a guitar to drive two guitar amplifiers at the same time without introducing noise, hum or coloration. All of the features on the Switchbone have been optimized for maximum performance while eliminating clutter and unnecessary controls and it’s compact size.
Primary Audio Path It is important to understand that the Switchbone is in fact a unity gain amplifier or pre-amplifier that takes the input signal from the guitar and duplicates this signal at the two amplifier outputs while also sending a signal to the tuner output. In technical terms, one would call this a high-impedance signal distribution amplifier. Without amplifying the signal, the guitar would sound weak, lack punch and body. Based on the critically acclaimed Radial JD7 Injector, the Switchbone’s primary signal path is pure Class-A for minimal coloration. Class-A circuits are the preferred choice in tube amplifiers and audiophile stereo systems due to their natural sound. Radial doesn’t use chips or op-amps in the primary audio circuit. Class-A circuits are less ‘efficient’ than typical AB (push-pull) circuits but with Radial Switchbone, Radial primary concern is sound quality. When amplifying high impedance guitar signals, noise is a major concern. To reduce noise and interference, the Switchbone comes with an external 15-Volt power supply. Keeping the power supply away from the circuit significantly lowers interference. The Switchbone also incorporates a floating circuit and ground plane to further suppress internal and external stray magnetic fields.
Drag™ Control When a guitar is connected directly to an amplifier, the pickup and the amp join to form an electrical circuit. The length of the guitar cable; the cable’s resistance and impedance; and the amplifier’s input impedance and the load it exhorts on the pickup combine to affect the pickup’s tone. This relationship is part of the magic that makes a great guitar and amp combination sound so good. As detailed in the previous section, the Switchbone amplifies the guitar signal so that the incoming level from the guitar is duplicated at both guitar amplifier outputs and the tuner output. The problem here is that the natural relationship between the pickup and amplifier is lost. The Switchbone’s exceptionally clean circuit is in fact too perfect: It provides a perfect load on the pick-up and a perfect source to the amp. Drag Control solves the problem by allowing the user to reintroduce a load on the pickup, which in essence, fools the pickup into thinking it is connected to the amplifier. This simple control is easy to use and is extremely musical. Simply set the Drag at 12 o’clock and listen. Each pickup is slightly different. For instance a Fender® Strat® ™ connected to a Twin™ sounds right at around 10 o’clock.
Amplifier Outputs The Switchbone has two amplifier outputs. Output 1 (A) is a direct out and should be connected to the newest amplifier, as this is where the Switchbone will be grounded. Output 2 (B) is transformer isolated and is equipped with a ground lift switch and polarity reverse. Transformer isolation removes hum and buzz caused by so-called ‘ground-loops’. The Switchbone’s custom designed transformer isolates the current between the two amplifiers while the ground-lift switch disconnects the ground path between the Switchbone’s output-2 and the amp for 100% isolation. The polarity reverse switch allows one to ‘align’ your amplifiers in-phase to compensate for the way the amplifiers have been designed. Keep in mind every amplifier company does things differently and the Switchbone has been designed to work with any set-up! Switching and LED indicators AB-Y amp switching is performed with two foot-switches that are optimized to do away with ‘tap-dancing’. The center switch is an A-B ‘amp toggle’ selector while the left-hand switch is a ‘both’ or ‘Y’ selector. A series of LED’s provide quick and intuitive amp status read-out allowing the player to toggle between amps or between one or two amps quickly. The Switchbone’s LED (light emitting diode) status indicators are large and easy to see. In AB toggle mode, the light goes on when the amp output is on. Simple. However when ‘Both’ amps are turned on, one LED will be illuminated while the other will flash. This lets the player know that the flashing output will go off when going back to single amp operation. To eradicate switch noise, the Switchbone employs a series of lighting-fast opto-couplers instead of relays. The opto-couplers are in fact, electronic switches that are controlled by the foot switch and perform the same function as a relay. Although more expensive, these do not suffer from contact degradation, mechanical failure or arcing, typical problems that relays introduce. The biggest advantage is zero switching noise as these eliminate any mechanically induced electronic contact spark. The result is whisper quiet switching even when used with saturated amplifiers.
Power Booster Circuit The Switchbone incorporates a simple yet extremely effective power booster. This has been added for several reasons, the most obvious being that when using two amplifiers, boosting the level of both amps at the same time for solos would be practically impossible. The Power Boost also serves another important function by allowing the user to compensate for volume when going from two amps down to one. There are three controls plus an activating foot switch for the Power Booster. These include a variable gain control; a function switch that selects between gain boost, mid and gain boost or mute. The mute turns off the amp outputs while still sending signal to the tuner out. The mid selector switch features bypass, and two mid boost intensities.
Tuner Out The Switchbone is equipped with a separate tuner out that is always on. This has been designed to allow on-the-fly tuning no matter what the settings on the Switchbone. The Switchbone lets you mute the amplifiers by setting the Power Booster selector switch to the mute position, and depressing the ’BOOST’ footswitch. This allows quiet tuning.