Abstrakt Instruments Avalon Reference Manual page 38

Once the bottom cover is removed the DIP switch can be viewed through the hole in the PCB.
The ON position for these DIP switches is towards the top of the unit (all switches in the graphic above are in the ON position).
a) SWITCH 1: CUTOFF low end range. This switch sets the low end of the cutoff range allowed by the CUTOFF knob. The TB-303 low cutoff range is
limited. This switch allows for extended range.

OFF: TB-303 setting (minimal range)

ON: Extended range (*default)
b) SWITCH 2: ENV MOD minimum depth. This switch sets the ENV MOD depth when the control is at the minimum position. The TB-303 doesn't
allow the filter envelope modulation to be turned all the way off, and there's still some modulation when the control is at the minimum setting.
This switch allows for ENV MOD to extend to "off" when the ENV MOD knob is at its minimum setting.

OFF: ENV MOD goes to "off" (*default)

ON: TB-303 range
c) SWITCH 3: ENV MOD maximum amount. This switch sets the maximum filter envelope modulation amount when the control is at the maximum
setting. When enabled the maximum modulation depth is doubled versus the default setting.

OFF: TB-303 setting (*default)

ON: Extended amount
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AVALON - Reference Manual