I first built a standard one (from MUSIKDING kit here in Europe) and lent it to a friend. He came back asking me to build another one for him, and explained that he had found an interesting feature : he mainly uses it as a slap-back echo with head #1, and observed that just flipping the head #4 on gave hime the other effect he was after, without any other change.
I then figured out that if I simply replace the little toggle switch of head #4 by a foot switch, he would be able to switch to this effect on the fly. I therefore built the attached variant.
I had initially expected to be able to make a pre-selection of heads # 2-3-4 (choose on or off) and validate/actuate this choice with the footswitch. Unfortunately, head 4 uses another input of the FV-1 than the three other heads, so it is not possible.
In order to achieve that, it would be necessary to modify the effect selection bank so that head 1 would use the input which now serves for head 4, so that heads 2, 3 and 4 would use the inputs on pins 16, 17 & 18 of the chip. Reverse the order of the selection, in other words.
But this is beyond my abilities.