Hello. I want to mod my PT-80 delay so that I can hear the trail of Delays as I switch it off.
My research points to buffered bypasses and not "true bypass" which is the one I am using on all effects.
What I did was route the output of the delay to the pedal output and ground the input in the "off" position of the FS. So I get what I need. I can hear the fading delays as I turn it off and I can keep playing my guitar. Though when I turn it off I get a huge volume drop on my guitar. It seems as if the guitar soundwave flows into the output of the effect so I get a much reduced amplitude in the amplifier. That is how I perceive it.
I found a ton load of references to buffered bypass switching circuits but I can't make anything out of it. I did try to use a buffer on the input of my circuit but that seemed to ruin all. Maybe I did something wrong.
Replace your FS with an SPST between point A and the 1u at pin 11 of the SA571. (You can keep your current FS, but only use two adjacent lugs of one pole.)*
Point A is the dry path between the input buffer (first half of TL072) and the output mixer (2nd half) that combines the wet and dry paths. The proposed SPST acts as an on/off switch for the delay path input without affecting the output of the wet path that provides the tails. Your bypass signal will sound the same as your dry path signal without any delay.
*Edit: Now that I think about it, you'll probably want to use the third lug of one pole to add a pulldown resistor between the 1u and Vref so it doesn't pop.