The tonal differences between the DMM and Nano DMM have to do with input impedance. The older DMM has a lower input impedance equal to 100k. Depending on what is plugged into the unit, for example guitar straight into the pedal, lower input impedance might result in darker sounding dry and wet signals because the lower impedance might roll off some high end or treble.

The Nano DMM has a higher input impedance of 1M. Depending on what’s plugged in, for example guitar straight into the Nano DMM, the higher input impedance allows more high end to be retained.

Outside of the input circuit, LEVEL gain stage, and bypass circuit of the Nano DMM, the audio signal paths are identical between the two units.

Both the DMM and Nano DMM operate internally at 15VDC. The 24VDC DMM regulates the internal voltage down to 15VDC while the Nano DMM boosts the internal voltage to 15VDC. So the headroom is the same between the two.