SW8™ Using & Applications

The Radial SW8 is a backing rack switcher that lets you select between two 8-channel audio sources and either switch them automatically or manually, depending on your preference. This page outlines how to approach using the SW8 in a typical concert stage environment. For more details, feel free to download the full SW8 manual by clicking on the icon at left.

Connecting the SW8

Always ensure the audio levels on the PA system are turned off before making connections. This will prevent turn-on or plug-in transients from damaging more sensitive components such as tweeters. There is no power switch on the SW8. Simply plug in the 15VDC supply and it will automatically spring to life. Once connected, either the A or B front-panel LED will illuminate depending on how the SW8 was last used. A handy power supply cable lock has been provided to screw the cable down for safety.

Most backing track systems will employ two identical multitrack playback systems. These will produce either balanced or unbalanced signals. To address both worlds, the SW8 is equipped with a choice of a 25 pin D-sub input connectors on the rear or two sets of eight ¼" TRS input connectors on the rear panel. The 8-channel D-Subs are wired following the ProTools/Tascam standard while the TRS connectors follow convention with Tip- (+), Ring (-) and Sleeve (Ground). Unbalanced ¼" cables may also be used as a source.

The SW8 has two sets of outputs: The rear panel D-subs are 'straight wire' and typically used if you are connecting to a +4dB professional balanced line level device. The front panel XLRs are arranged like a direct box with eight Eclipse transformers that isolate the outputs and produce a lower mic-level signal. These are generally used on stage to send the output of the SW8 to a snake system and mic splitter. For extra convenience, you can go inside the SW8 and re-assign the transformer isolated signal path to the D-sub output by simply moving a jumper cable.

Testing your connections

Make sure you are in manual mode by ensuring the AUTO switch is in the out position and the LED off. You should also make sure the JR-2 remote switch is disengaged (out position). For safety, always test your audio system at a low level before turning up. Begin testing the playback connections by playing a signal through input-A. If the audio signal is passing, the LED under the threshold depress the front panel A-B switch and this will turn off the input-A set and turn on thne input-B set. Activate the second playback machine. If you plan to use the transformer isolation output option, a global -20dB pad is available. This is typically used if the audio source is a line level device. During playback, if you notice distortion, you are likely overloading the transformers. Simply depress the pad switch to reduce the input sensitivity.

Switching options

There are several ways to switch the SW8: This includes manual switching using the front panel selector, remote switching using a dedicated footswitch or standard latching switch, or you can have the SW8 automatically switch using the built-in gate.

  • Front panel A-B Selector
    You can use the front panel AB switch as described above. This is usually used when setting up the system and testing. This is the most basic form of switching as it provides the convenience of front panel access right where the switching occurs.
  • Remote with contact closure
    You can switch the SW8 remotely by simply shorting out the tip and the ground on the contact closure port. This ¼" jack can also be switched using a standard latching footswitch as commonly used to switch channels or turn on effects on a guitar amp.
  • Remote with Radial JR-2 The Radial JR2 is a dual function footswitch that can be used to remotely control the A~B function or set the SW8 into standby mode. The advantage with using the JR2 is that it has LED indicators to let you know the status. Use the JR2 ON switch to activate.
  • Automatic via signal gate
    You can also set the SW8 to switch automatically by using the internal gate. To do this, record a steady 1kHz tone on your primary recorder on ether channel-1 or channel-8. The SW8 will draw the tone from either track depending on how you set the ALT (alternate) source select switch. You can also separate out a track and feed it directly into the dedicated auto-switcher gate input.

    Activate the auto-switching circuit by depressing the front panel switch. The LED indicator will illuminate. Once on, the SW8 will switch automatically as soon as the signal level going into the auto-switch circuit drops below a pre-determined level. This level is adjusted using the threshold control on the front panel. It is recessed and made hard to get to so that once set, it will not be altered by mistake.

    Set the gate at 12 o'clock and activate the primary playback machine. Test the gate function by reducing the threshold – turning the control counter clockwise. When the test tone falls below the threshold, the SW8 will
  • Using SMPTE as audio
    For setups where playback channels are all being used, a SMPTE time code signal can be used as an audio source by feeding it into the auto-switch gate input and setting the 3 position filter as needed. The filter serves to smooth out the digital binary code to produce a more stable signal.

Using the Standby function

When in auto-switch mode, stopping the primary (A) recorder will invariably stop the drone track from playing. This will cause the SW8 to switch inputs as soon as the drone disappears. Although on the surface this may not appear to be a big deal, a problem occurs when the artist decides to pause between songs, forcing an abrupt change to the show. The standby switch is used to hold the gate and input into the A position. When ready, activate your playback system and then switch off the standby. This will release the gate for normal operation. Connecting the optional Radial JR2 enables you to remotely turn on or off the standby function.

Using the mute function

Many shows require preparing playback tracks to follow last minute set changes. This means that the playback technician must search for tracks, listen and cue them up so that they are ready when needed. To assist, a mute function has been added to the SW8 that when depressed, mutes the front panel XLR outputs that are typically sent to the PA system. This leaves the D-Sub active for local monitoring.

Linking to other SW8s

To expand the system for 16 or more channels, the SW8 is equipped with a JR2 link function that enables you to connect one SW8 into another using a TRS cable. This employs a typical master-slave configuration whereby the first SW8 will be assigned as master which in turn will control the slave units. Once linked, any A~B status changes will automatically be transferred to the following units along with the standby function. In auto-switch mode, the drone track would connect to the master SW8 and the salves would follow. For those that are using a second generation SW8 with an older first generation unit, the new SW8 would be set as master and top panel switches would be arranged to properly control the older generation unit.

Sounding the alarm!

In busy setups where auto-switching may not be immediately obvious, an alarm may be connected in the form of a light or alarm tone using a special 24 volt relay. When the SW8 switches from A to B, the relay contacts are automatically closed, enabling the system engineer to rig up an appropriate alarm.

Eliminating noise

For the most part, audio playback systems are very quiet. But sometimes, switching can introduce a pop which could be annoying. This is usually caused by a DC offset in the recording system. The SW8 incorporates a series of filters that are designed to bleed off excess DC and reduce switching noise. This is augmented with transformer isolated XLRs and ground lift switches to reduce hum and buzz caused by ground loops.