Parallel Op amps (op amp stacking)
This may be one the more unique tweaks, and can be great for any pedal that uses an op amp. If you are very handy and neat with a soldering iron you can put this together simply, at times these are available from Barber (depends on work load)
For this tweak you should have a fine tipped soldering iron with temperature control 700 degrees works nicely (666-700 for lead free). I also recommend solder with a diameter less than .032". You will want to "stack" the op amps so that the pins align and have enough contact force to hold them together, lightly "pinching" the pins of the top op amp can help. after you have the op amps stacks simply solder the pins with a small amount of solder, be sure that the solder does not flow down the pins of the bottom op amp, these have to stay clear of solder so they will fit in the socket.
We have tried many configurations of parallel op amps, some sound great others barely work at all. You can stack more than two op amps. There are sonic changes when stacking same type op amps and when stacking mixed type op amps...If you listen carefully you can make your own op amp cocktail. You may also find a carefully soldered iso resistor on the output can help, along with some changes in a resistor value or two, but this is for the brave, the coloration without iso resistors can be very nice.
When you hit upon a nice combination expect a sound that is more muscular, thick, natural or rich. The cool part is how inexpensive and simple this tweak is!