Written by Kent Learned, 4 December 2018, originally posted to the Wonderland History Facebook group.
The Demon Pipe was one of those fun projects that was harder than it first appeared. At first glance we just thought we’d use a “Colour Organ Kit” from someone like Dick Smiths or Jaycar. The first problem was, they’d all stopped making them. The second problem was to make it in such a way that it didn’t burn the light bulb out all the time, as the grill in front of the pipe was bolted on in a manner that was hard to take off for maintenance.
In an earlier career I had made a circuit that converted AC current (sound) to DC current in a very accurate manner. If you put a very small AC signal (sounds) into it, you got a very small DC signal out of it; conversely, large AC in = large DC out, i.e. very bright eyes.
The simplest circuit to control the lights didn’t treat small currents very well, and we were missing a lot of subtle lighting effects in the Demon’s eyes when we played the sound track. The solution was to borrow a model train throttle control circuit I’d used a few years earlier. As per usual, I tweaked it a little so it would keep the eyes glowing just slightly, instead of going out completely. You could only see this when it was very dark. Doing this was very gentle to the globes. The eyes were two round trailer stop light housings about 100mm in diameter, with two 18 watt stop light globes in each housing. Daryl Smith, the resident painter, painted the nice spooky eye patterns on the lenses. Anyway, once it was up and running and adjusted, it ran pretty much every day for about 3 years. It was turned on and off by a 24 hr / 7 day a week time clock. I also made a little circuit that put the CD player into “repeat mode” every time it was turned on. I had to replace the globes once, the CD player once, and the timer once over about 6 years.
The speaker cabinet had four 200mm diameter speakers in it, and a 250 watt amp powering it. It was shaped so we could get maximum size in the bottom half of the pipe. The soundtrack had the low frequencies boosted some to make it a little more fierce sounding. The original amp and speakers were still working well when I left in mid 1999.
One time the time clock got confused by a nearby lightning strike, and started turning on again around midnight, while the security guards were on their rounds. The first time it happened, it really scared one of the guards. It took several goes to get the time clock working correctly again.
I put together the soundtrack in our recording studio using some animal sound effects, that I changed the frequencies on and slowed it down a bit, added some bat screeches, chain rattles, etc., and evened out the loudest parts of the track. I put several layers of very long reverb and echo on it to help it sound eerie. It certainly scared a lot of guests.