Thanks for the explantion Paul
As i see in this circuit the output is out of phase with the input. That means that even at bypass mode the signal will be inverted. Also the input
impedance of the circuit is 100K,(the 100K at the inverting input of IC1A is the input impedance at an inverting op amp) which is low for guitar signals.
This can be solved by changing the connections at IC1A to make it a non inverting amplifier.This can be done easily by removing the 100K resistors which connect at IC1A pins 1,2. Place a jumper to connect pins 1 and 2 in the place of the 100K which was removed. Remove the 0.047uF capacitor which connect to pin 3 and replace the 100K which connects
to pin3 with an 1M resistor. Finally use a jumper to connect the 0.1uF cap with pin 3 of the ic. The jumpers can be placed to the empty pads of the components that were removed.
This an image of what i mean
Now we have a non inverting phase circuit with 1 Meg input impedance. This may even solve the problem of volume drop when the effect is true bypassed. I don't know if this mod will change the character of the effect. But i think that it will not cause any additional problems like cancelations at the signal adders of feedback, blend etc.
It can also be modified to provide a little gain if the volume drop insists.