Mxr Carbon Copy Schematic -

The Deluxe version has tap tempo; the original does not. However, the schematic shows the Delay pot is just a variable resistor to ground. A savvy modder can:

The Carbon Copy’s modulation comes from a Low Frequency Oscillator (LFO) —usually a dual op-amp configured as a triangle wave generator. This LFO voltage is summed (added) to the "Delay" knob voltage. So, even if you don't touch the knob, the clock speed is subtly wobbling up and down. That wobble creates the pitch warble we call modulation. Mxr Carbon Copy Schematic