This is something I've been after for a while now as a DIY project and no one has done it. Where I think half of what it does would be relatively easy... There are bits that I suspect might be more than a little challenging.
The easy bit I suspect could be achieved by two vibratos. The ROG Tri-Vibe for example can get a sufficiently rotary sounding effect on one of it's settings. One would be needed to cover the high frequencies and the other the low (as they need to be able to run out of sync and at different speeds). To be like a leslie, you need to be able to stomp between a fast setting and a slow. Again not to much of a problem... I would have thought were it not for the need for the speeds to ramp up and ramp down, and for them to do it at different rates (as the low frequency rotary speaker spins up and down slower than the high frequency horns do).
Things you could drop are stereo and the overdrive that a lot of these pedals have. In an attempt to simplify and keep the parts down.
This is a good demo of the DLS RotoSim that does pretty much everything and is less complicated than the likes of the Ventilator or Lex:
This is a real Leslie so you can see what it's emulating (ignoring the sales blurb):
I love the Tri-Vibe -- and the phase, amplitude, and pitch modulation really does give a convincing Doppler effect. At high speeds and the right depth, its pretty much as good as anything you'll find built into a keyboard, so pretty mcuh good enough for live gigging.
It uses an LM13700 used in place of matched FETs, so it's pretty easy to build (well, don't try modding the perf layout on the fly to fit it in a smaller box and it's easy!), and it sounds great. We're basically talking about a modified four-stage phaser here. So you need a knob that would fool the circuit into thinking that one of the FETs isn't perfectly matched.
To do a fast/slow switch, you can just stick a second speed pot on a momentary switch. Then you can control how much it speeds up by.
Whoops, just bought a RotoSIM on eBay...
hahahahaha that didn't take long.
My buddy has one and I love that thing. Almost bought one a couple times.
The "whoops" cracks me up :D Sounds like what I would say to my wife ;D
Oh it was a dilemma. He'd listed it fairly badly with an insanely low starting price and a very reasonable Buy It Now price (£100 less than I've ever seen one go for). It was do I chance it with the low starting price and potential grab an utter bargain. But the risk there is that someone like me finds it and we end up in a bidding war which would easily go over the BIN... I pondered this for at least 3 minutes before hitting the BIN button.
I am weak.
Well, the RotoSIM arrived and it's a) bloody amazing and b) rather more complicated than I expected!
(http://www.juansolo.demon.co.uk/misc/rotoguts.jpg)
So that's 5 Vactrols, 10+ trimmers, the painted out IC I suspect is something along the lines of the Spin chip in the Rainbow Machine and the socketed one next to it might be a eprom. Maybe.
Holy bejesus !! I am not ready to tackle that one.
Whatever Scott... looks a walk in the park!
Jacob
I bet half of those parts aren't even connected to anything ;D
I love the lone gigantor cap in there. 1000uF for 25V.
Jacob