3
Speed Control: Connect the supplied dual button foot switch here. This is a TRS connector
where the sleeve is common or ground, the “tip” controls fast/slow operation and the
“ring” determines whether slow or stop is enabled.
Fast overrides all:
When the fast speed is on (yellow fast indicator on the KBR-3D is lit), the
stop button does not have effect. When the fast button is pressed again (yellow indicator
off) the slow speed or stop is enabled depending on the position of the stop switch button.
This enables the horn motor and low rotor simulator to cycle between fast to slow, fast to
stop and slow to stop. The rotors will follow the acceleration times as set internally.
Disable Stop: If the stop function is not desired, a single contact switch can be used with a mono ¼’ jack.
The stop is disabled by the sleeve of the ¼” connector and the switch button then controls
fast/slow only.
Pre-Gain: Inputs 1 and 2 are fed to this control before reaching the 12AX7EH tube circuit. The pre-gain is
actually an attenuator allowing input levels to be virtually unlimited.
Contour: This knob controls the high frequency response of the rotary channel. The 147 position (approx.
5 kHz role off) is similar to many older rotating speakers. If you would like a brighter sound,
choose the PRO-3 (approx. 7 kHz roll off) setting. The control also provides positions in between
to allow for today’s keyboards and personal taste in high frequency response.
12AX7EH Pre-Amp: There are no solid state devices in this unique tube circuit which utilizes a 12AX7EH
(or any of its derivatives) in a self-biased symmetrical clipping topology that behaves like a 147
tube output stage when overdriven. This design provides silky-smooth sound until pushed into
clipping, at first crunchy and at extremes provides a gnarly massive tube grind! A combination of
keyboard volume X volume pedal X pre-gain settings determines the overall drive of the
12AX7EH.
Post-Gain: This control allows silky-smooth, clean tube sound with settings of 8-10 and utilizes the full
output range of the 45-watt RMS horn power amplifier. When turned down and used in
conjunction with the pre-gain and keyboard volume controls, the post-gain allows all levels of
overdrive to be played at any volume below the 45-watt amplifier’s clipping point and can provide
tube only overdrive at loud to very soft levels.
Many users like to set a level or “ceiling” with the pre-gain around 5 and about 50% volume on their
keyboard, a point where the 12AX7EH runs fairly clean and then be able to push the tube into clipping by
conveniently raising the volume on the keyboard. Again, overall volume can be changed with the post-gain
without affecting this “ceiling” level.
pre-gain
post-gain
Clean Sound
1-5
8-9
Crunch
5-8
3-7
Gnarl
8-10
1-7
Settings depend on a signal source level of approximately 300 mV RMS fed into the KBR-3D rotary
channel input 1 only (input 2 not used).
Low Rotor Volume: The balance between sound from the rotating horn (> 800 Hz) and that of the low
simulator is adjusted here. Set the balance to default or to match your favorite classic rotating
speaker or personal taste.
Bass:
The control effects bass frequencies below approx. 150 Hz. Generally set to “0”, this is also a
personal taste control. If you play with a bas player, leave the control between –10 to 0. If you
play solo and use pedals, try a settings of 0- +5. Bass reproduction uses a great deal of power—
use only what seems needed in each situation.
