Motion Sound PRO-145 User Manual
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reduce any ground loop “hum”. Standard ¼” cords can be used but ground loop rejection will
not operate.
Gain Control – “Gain” control affects both inputs and adjusts the drive into the 12AX7EH tube
pre-amplifier, lower settings provide clean transparent sound while higher settings produce over
drive distortion. The gain control works in conjunction with your keyboards volume control and
volume control pedal if used. Do not use analog volume pedals made for guitars, the impedance
of such pedals will produce a large loss in volume and over drive.
Pre-Amp Mode – Classic tube circuits typically have resistive or inductive plate loads that
provide different audio “color” to sound. You can vary the type of load from resistive “R”
through inductive “I” to find the sound that’s right for you. The sonic difference between modes
is more noticeable at higher overdrive levels but some tonal change and harmonics are present at
all volume levels, above and below tube overdrive point.
Resistive Mode – “R” has a sharper onset knee into distortion with overdrive rising rapidly as
gain is increased. The overdrive harmonics sound hasher and brighter. The resistive mode
provides the cleanest sound when not overdriven.
Inductive Mode – “I” has a softer onset knee into distortion with a more gradual rise into
overdrive. The overdrive harmonics are mellow and somewhat compressed with less volume and
bass. You can add the bass and volume back in with the EQ controls.
12AX7EH Tube and Bias – Every tube is different and even a selected tube can be finely adjusted
with the bias trim. We recommend 12AX7EH and 5751 tubes only. If you replace the tube,
adjust the bias for the loudest signal without distortion; use the gain control to gradually adjust
the volume while "tweeking" the bias. Other brands of 12AX7 may not work correctly and
reduced power may result. (Refer
legacy page for more tube
information).
Volume Control – After the pre-amp mode and gain are adjusted, the overall volume of the PRO-
145 can be set. This control also allows gain variation between tubes to be compensated. For
clean sound, set the volume higher and gain lower. For overdrive, set the volume lower and gain
higher. Too much volume may produce unwanted “tube” hiss, and settings will vary some if
tubes are changed.
-EQ Controls-
The PRO-145 EQ controls are of 100% attenuation design. If a control is set to zero, frequencies
outside of its range will drop at 6 Db/octave to a zero level. If the bass, middle, and treble are set
to zero no sound will pass through the EQ section. All controls set to “N” provides flat response.
Bass – Frequencies at 150Hz and below are adjusted. Bass uses a great deal of power so we
recommend a setting of “N” or less if you work with a bass player. If you use a subwoofer
amplifier set the bass at “N” or less and adjust the subwoofer amplifier as needed.
Middle – Covers a range from 150Hz to 3kHz. Middle frequencies are fundamental to the classic
147 type sound. Start with a setting of “N” to 8 and then experiment.