DIY | Voltage processing | Jim Patchell | Vladosh | PHOBoS
here's the Wave Wiper, a circuit that merges 2 waveforms together, based on Jim Patchell's Control Voltage Splitter.
here's a stripboard design by vladosh:
and a PCB design PHOBoS made for perfboard but you can etch it too of course.
original thread here and an improved version (2.0/2.1) can be found here