if one of these circuit is out of phase with the other,then the adder circuit becomes a subtraction circuit--just what we need to complete our Karaoke circuit.
build the Op Amp adder using three 10k resistors and another TL0211C.
TO theck out its operation,wire up the left and right OP Amp signals to the two adder input .
use the scope to monitor the input signal (AO 0)on channel 0 and the adder output on channel 1.