Doepfer MBP25 Midi Bass Pedal Electronics Kit - Manual (Page 9)

User's Guide page 9 MBP25
The potentiometer connected to ST3 generates midi volume data (control change
#7). If no potentiometer is connected to ST3 the center pin has to be connected to
+5V. For this ST3 is equipped with a jumper in the factory. An open center pin of ST3
will cause the transmission of random midi volume data !
By means of a trimming potentiometer the maximal voltage value for the
potentiometer connected to ST3 can be adjusted in a range of about +3.5V...+5V.
This value corresponds to midi data 127. This feature is useful if a potentiometer is
used which does not cover the whole rotating angle. This applies e.g. for some foot
controllers (e.g. Fatar FP5). In this case not the full midi data range 0...127 would be
covered without this feature.
The factory setting is +5V. In this case the trimming potentiometer is adjusted fully
clockwise. If a potentiometer is connected to ST3 that covers the full rotating angle
this setting remains unchanged. A normal rotating potentiometer with knob or a
slider/fader potentiometer meets these requirements.
If a potentiometer is connected to ST3 that does not cover the full rotating angle (e.g.
the foot controller FP5) the trimming potentiometer has to be adjusted. This is the
adjustment procedure:
• turn the potentiometer connected to ST3 to it's maximum position
• turn the trimming potentiometer beginning with the fully clockwise position until
the max. midi data (127) is transmitted. If the midi volume data cannot be
measured the adjustment can be done by ear too: turn the trimming potentiometer
until the max. loudness is reached.
If the trimming potentiometer is adjusted too far the volume function will no longer
work. Only about 30% of the adjustment angle (beginning from fully clockwise) are
allowed. The trimming potentiometer is connected to GND and +5V and the
adjustable voltage range has to be +3.5 ... +5V. Values less than 3.5V are not
allowed as the reference voltage of the ADC used (analog-to-digital converter) has to
be in the range +3.5 ... +5V. Otherwise the ADC will not work correctly.