I elected to build a John Smith Topsy Organ because I had gained valuable organ building experience on smaller organs and wanted to progress to bigger things. The Topsy organ is a MIDI based machine that stores its music on a micro chip, thus saving the need to carry loads of paper roll or book music. It contains 12V solenoids in the form of pallet valves, a small computer board, and a card reader to carry and read the micro chip music, all of course, powered by a 12V battery. I used a battery from a mobility scooter.
First, plan what you want your organ to look like. I wanted to get away from the conventional square box construction and try and add a new dimension by making the ends and the front curved. Plus having my front pipes following that curve. I planned the layout of the pipes leaving just enough room to get my American made organ pallet valves into the wind chest. It’s so easy to build an oversize organ, but remember you still have to lift and move it when it’s finished. Keep it compact.