The Radial JX2 Switchbone is an ABY 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 pedal-board users will truly appreciate the Switchboneﾒs compact size. You will be amazed at the circuitry required to make this unique AB/Y box work. The Switchbone is a true engineering marvel.
Primary Audio PathIt 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ﾒ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 does not use chips or op-amps in the primary audio circuit. Class-A circuits are less ﾑefficientﾒ than typical AB (push-pull) circuits but with Radial Switchbone, their 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ﾙ ControlWhen 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ﾒs resistance and impedance; and the amplifierﾒs input impedance and the load it exhorts on the pickup combine to affect the pickupﾒ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ﾒ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ﾒclock and listen. Each pickup is slightly different. For instance a Fender Stratﾙ connected to a Twinﾙ sounds right at around 10 oﾒclock.
Amplifier OutputsThe 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ﾒ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 indicatorsAB/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 ﾑamp toggleﾒ selector while the left-hand switch is a "both" or "Y" selector. A series of LEDs provide quick and intuitive amp status read-out allowing you to toggle between amps or between one or two amps quickly.
The Switchboneﾒ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 you 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 CircuitThe 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 OutThe 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. Muting of the amplifiers may also be accomplished by setting the Power Booster foot switch to the mute position.Radial Tonebone JXﾕ2 Switchbone Development
For years, guitarists have been searching for a real solution for ABY amp switching and combining. One would think that in this day of unbelievable technology, that building this type of device would be easy. And of course it is easyﾅ. unless you are intent on retaining the original sound of the guitarﾅ.
For those that have tried connecting two amplifiers together using Y-cords or some of the other AB-Y boxes that have come before, you are familiar with the many challenges: Drop in gain, tone changes, buzz and hum just to name a few. The Radial Switchbone is a remarkable device that deals with all of these problems and brings forth a design that is easy to use, musical and truly effective. The Radial Switchbone has been optimized for stage use and allows a guitar to drive two amplifiers and do it while retaining the natural sound of the instrument without introducing buzz, hum, distortion or switching noise.
The Radial Switchbone begins with the concept that most "tone crazy" players will generally use two amps on stage. When driving two amplifiers with one guitar, the signal from the pickup is divided in two and the sound changes. To get around this problem, the Switchbone employs a unique Class-A amplifier circuit that has been optimized for use with guitars. With Radial customers like Eric Johnson, Steve Lukather, Carlos Santana, Steve Stevens and Neal Schon, we are not allowed to alter the sound of their favorite vintage axe. The sound must be real!
This leads to the next problem: Your guitar has now gone from being passive to essentially becoming active. Your pickup is no longer connected directly to the amplifier. It is being ﾑbufferedﾒ (amplified) by the Switchbone. The natural relationship is lost. To compensate for this, we have introduced a feature called Dragﾙ control to allow you to reintroduce the natural loading that is lost. With load-correction, the instrument goes back to normal. It breathes!
Then, as soon as you connect your two amplifiers together they hum, they buzz and sometimes even spark with hundreds of volts! This is due to the way that each manufacturer builds their amplifiers. Some use positive ground, others negative. Some use the chassis as a ground plane while old designs from the 50ﾒs and 60ﾒs do not even have proper 3-pin safety U-grounds! To solve these problems, the Radial Switchbone incorporates a transformer-isolated output, a ground lift switch, and a polarity reverse switch. This isolates the electrical current flow of each amplifier and eliminates ground loops.
Of course, once you get these amps connected together, you have to control them! This is where the Switchbone also shines! The Switchbone is easy to use. The foot switch layout and LED readout follows a ﾑcommon senseﾒ and intuitive approach that is very natural. We have also added a boost circuit to allow you to ﾑstep-upﾒ the output to both amps simultaneously for a solo or extra saturation when playing through a distorted sound. For icing on the cake, we added a separate output for your tuner. This takes the tuner out of the audio circuit, thus ensuring you get the direct tone of your guitar without extra loading.
- Input impedance: 1meg ohm at input jack
- Drag control: Variable matching network
- Circuit topology: Class-A primary audio circuit
- Switching: Opto-coupler assisted, 5msec Rise time
- LED indicators: Large 3 mm OD ultra-bright light emitting diodes
- Boost level: 0dB to +15dB
- Mid boost: +5dB @ 1KHz and +9dB @ 800Hz
- Output 1: Direct coupled
- Output 2: Transformer isolated
- Ground lift: Lifts ground at output 2
- Polarity reverse: 180ﾺ polarity (phase) reverse at output 2
- Construction: 14 guage steel, baked enamel finish
- Power supply: 15VDC 400mA, center pole negative