MOTM

From: Speth, John <john.speth@...>
Can anyone tell me if the MOTM-850 is capable of gaining the pedal voltage?
If so, what is the gain when the range pot is full CW?

LH:
John, the 850 is designed to for a +/- 5 volt output with resistive and CV
pedals (assuming 5 V CV pedal).  So, without changes, the normal output will
only be up to +/- 5 volts which can be biased up or down up to 2.5 volts
each direction.  You can also bias the voltage up or down using a separate
voltage input at the "mix" input.

Now, if you simply want to expand the range of the CV pedal, and take
advantage of the 850's range, scale, and gate extraction, you can do that
several ways with very little modification to your 850.

Here are some ways you could make that work:

1.  No module modification.  Run the pedal to both the pedal input AND the
mix IN.  If you do not get enough voltage with the range control at full
scale, you can add to the scale with the mix control.  You could get +/- 10
volts that way if you wish.

There are 2 ways to accomplish this:
A - "Y" cable (mono plugs are best)
B - clip out the jumper on the "mix in" jack that goes from top to bevel
(switch to ground) if it was installed. (it shows in the schematic but not
the instructions)  Connect a jumper from the top (switch) lug on the mix IN
jack to the LEFT lug on the pedal jack (same place the white wire is).

A or B above will allow the mix control to add to the CV pedal range.
However, if something else is jacked into the mix, the extra pedal CV is cut
off.

2.  You could change the master scaling resistor R21. That changes the scale
of the entire output.  So, it increases the voltage form the pedal, the mix
and the bias.  currently it is a 715K resistor.  If you changes it to about
half that size, all values would double.  That would make the pedal +/- 10
and the bias +/- 5.  Of course, you could have error if you tried to add
both of those together (+/- 15) at their extremes.  The op amps cannot have
voltage output that close to the supply voltage.  I think about  13 1/2 is
all you will get out of it.

3.  You could get a second 715 K resistor and parallel the original too to
double that range also.  You could install a switch for normal and 2X scale
and use it to switch one end of that parallel 715K resistor.

Larry Hendry