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Bumper™ Using & Applications

The following page describes how to use the Radial Bumper. For more details, feel free to download the full manual by clicking the icon at left.

Making connections

As with all audio gear, always turn the volume down on your stage amp before making connections as this will avoid connection transients from damaging more sensitive components. The Bumper requires a 9V power adaptor or connection from a 9V pedalboard power brick using a standard Boss® style supply. The power supply is not included. Make sure you check the polarity of the supply to ensure it is center negative. There is no power switch. As soon as you connect the power, the Bumper will spring to life.


A handy cable lock can be used to secure the power from accidental disconnection. To use, simply unscrew using a hex key and then pass the power cable through the access hole and re-tighten.


Upon power-up, the Bumper will automatically be set to input-1 and the input-1 LED will illuminate. Connect your first instrument to input-1. Then connect the Bumper's output jack to your amp. Slowly increase the level on your amp while playing to make sure the connections are working. It is good practice to always test at a low volume. This way, should a connection not be right, plug-in transients will not harm your speaker or shorten their life.
If all is well, connect your second instrument to the Bumper. Using the selector footswitch, you can now 'bump' between inputs 1 and 2. The LED indicators will follow the active instrument input. Adding a 3rd or 4th instrument can now be done. The switching jacks automatically set the selector switch to advance incrementally and then rotate back to input-1.

Using the Drag Control

Each input on the Bumper is equipped with a slider switch and a 'set & forget' potentiometer. The slider can be set to Drag or to Trim. Drag control is used to adjust the load on a passive pickup to counteract the effect of the buffer, while the trim setting is used to reduce the input sensitivity or loudness of the instrument.

The buffer inside the Bumper is basically a unity gain amplifier that lets us manipulate the audio signal inside the circuit. Once the signal is buffered, the impedance is lowered which allows cable lengths of up to 15 meters (50') without appreciable noise. Although Radial employs an exceptionally natural sounding Class-A buffer, it can in fact sound too clean. Drag control is used to replicate the tone and feel as if connected directly to your amp. This essentially lets you tame the top end by loading down the pickup to create a warmer, more natural tone. Drag has little or no effect on buffered or active circuits. Set the slider switch to Drag and then set the Drag control to 12 o'clock and listen. Rotate the Drag control using a guitar pick as a screwdriver - clockwise to brighten the tone or counter-clockwise to darken.



Using the Trim Control

Output levels can vary significantly between active and passive instruments. So when switching between them, you are usually forced to readjust the level on your amp to compensate. If the amp is being mic'd in the PA, the front of house and monitor engineers must also compensate. The Bumper solves the problem by allowing you to Trim or lower the volume on the louder instruments to match the output of the softer ones.

To audition the output levels of various instruments, set all of the Trim/Drag switches to the Drag position. Start by connecting all of your instruments and then rotate through each one using the selector footswitch to identify which instrument has the lowest output. Keep in mind the Bumper does not produce any gain – in other words, it will not boost the signal. You can only reduce the signal level of the louder instruments.

For those that are louder, set the Drag-Trim to the Trim position. Turn the 'set & forget' knob fully clockwise and then slowly turn it counter-clockwise until the output levels are matched. You will of course have to switch back and forth using the selector switch.