In a CMoy, the op-amps are used in a very common non-inverting amplifier
configuration. This means that the input is connected to the non-inverting input (IN+) and the feedback loop is the output (OUT) fed through a voltage divider attached to the inverting input (IN-).
The voltage divider is comprised of two resistors. The formula for gain is 1+R2/R1, where R1 is the resistor between IN- and ground and R2 is the resistor between OUT and IN-.
You can easily adjust gain by replacing R1 or R2.
You can locate these resistors by determining which pins they are attached to. The pinouts depend on whether the amp uses one double op-amp or two single op-amps.
If there's one double op-amp, these are the pinouts:
OUTL┤1 8├ V+
IN-L┤2 7├ OUTR
IN+L┤3 6├ IN-R
V- ┤4 5├ IN+R
If there's two chips, one for each channel, these are the pinouts:
NC ┤1 8├ NC
IN- ┤2 7├ V+
IN+ ┤3 6├ OUT
V- ┤4 5├ NC
Pins 1, 5, and 8 might be used for offset adjustment,
but they can usually be left disconnected.