Synthesis Technology MOTM-850, Owner'S Manual

Page: 15 / 21

SYNTHESIS TECHNOLOGY PAGE 15
MOTM-850 ASSEMBLY 10/25/01
WWW.SYNTHTECH.COM
series resistance, R24 then enters into the overall transfer function to ‘warp’ the x/(1-x)
pedal output. Rather than go through 5 pages of algebra, let it be said this value was picked
empirically. That is, we stuck different values in there until satisfied. We may be
perfectionists, but know the value of a good resistor decade box :)
INTERFACING TO CV OUT PEDALS/MODULES
The third type of pedal runs off of batteries, and outputs a DC voltage directly. For these
pedal types, or to process external voltages such as the output of a MOTM-800 EG, the blue
jumper shunt is removed from JP3. You can also ‘park the shunt’ by sticking only one pin of
the header into the shunt, so the other half of the shunt is sticking out over the pc board.
See Figure 3. This prevents you from losing the shunt if you change pedal types.
With the shunt removed, the additional resistor R16 is added into the series resistance. If
you have a pedal with a 100K pot, this makes the total series resistance 199K so the output
voltage is again 0 to +5V.
Since CV out pedals use mono (2-conductor) plugs, the ‘ring’ connection is shorted to ground
through R16+R17+R18. This doesn’t matter. The CV out from the pedal is to the Tip
connection, which goes straight into R24. Since the output impedance of the CV pedal is
low, R24 has no effect. The CV can be mixed, scaled and offset with ease.
USING THE MOTM-850
This first thing is to determine which type of pedal you have. If you have a passive volume
pedal (like the Ernie Ball), these will NOT work. If the pedal plug is a 3-conductor, then it
is some sort of resistive pedal. With a DVM, measure the resistance between Tip and Ring
as you move the pedal up and down. Note the maximum resistance, usually when the pedal
is depressed all the way down. Use the following table to set the jumpers.
PEDAL RESISTANCE (MAX) JP3 SETTING
5K - 15K OHMS R
15K – 75K OHMS Y
75K – 150K OHMS OPEN/PARKED
It doesn’t matter if the Tip is the wiper of the pedal pot or not, the MOTM-850 circuitry will
compensate.
P A R K IN G T H E S H U N T