Making A Better, MIDI Controlled Leslie Stompbox


Way back before the advent of commercial DSP, musicians had really cool looking gear. One of these devices to change the sound of organs, guitars, and other electronic instruments was a Leslie speaker – a speaker cabinet with rotating horns that gives that wonderful warm warble heard on so many classic recordings. [Nigel] doesn’t have an original Leslie, but he does have a much less expensive and lighter digital effect that emulates the original Leslie sound very well. The only problem, though, is the requirement for a proprietary footswitch. No problem, then, because a transistor, a resistor, and a mint tin can take care of that.

[Nigel]’s Leslie simulator – a Neo Instruments Ventilator – has a foot switch to control the speed of the emulated rotary speakers. There are three possible states for the speakers, fast, slow, and brake, all controlled with a TRS phono connector. Possibly in an attempt to price gouge consumers on a proprietary footswitch, Neo Instruments decided they would use the ring and tip of the phono connector to control the speed. They did so in a way that made it impossible for a single relay or switch to change the speed, however.

No problem for [Nigel], then, because with a very simple circuit consisting of just a transistor and resistor he can use any footswitch he wants with his Leslie simulator. The build doesn’t support the brake function, but he doesn’t use that anyway. Not bad for less than a dollar in parts, and a buck fifty in mint tins.

7 thoughts on “Making A Better, MIDI Controlled Leslie Stompbox

  1. “Before the advent of commercial DSP…” sounds noble but then ya go on to describe a DSP project. I like the compact build. Always thought Leslies to be nice but a bit overhyped by the music industry and the guy with 20 hammonds in his barn on CL lol. Back in the day with commercial DSP I had a Peavey Delta Stomp which had an amazing leslie simulator, but as usual nothing I wasn’t able to get with the LFO and VCA with my synth with a bit of work. It was stolen by some gutter punk that my roomie shacked up with one night along with my roomie’s gear. There is a good bit more to the story but it is kinda violent and ends up with me only getting my Turbo Rat back.

    As per the article I do like the way the guy figures out the shortcomings of the pedal input and offers a fixed state of how it shoulda been done :)

    1. “overhyped”? (Now I have to clean coffee off my screen). Despite all the electronics imitators, some quite good, I’ve yet to hear anything that puts the hair up on your neck like the real thing. My experience as a long-time Lesley infatuate who has built sundry imitators is that it isn’t the “industry” but key players, even guitarists, who wet themselves over this sound. But each to his own I guess.

      And of course +1 to [Nigel] for avoiding the gouge.

    1. I am also confused about the MIDI part.

      From the write up it seems like he really isn’t using MIDI itself to control this, but a special midi translator(relay) board that changes from MIDI notes and CCs to voltage or resistance on a TRS 1/4″ plug.

      I have a nice board from Hale Micro which lets me use MIDI to control and receive from input/output pins, but that uses USB not traditional DIN-5 MIDI.

  2. This is a good hack, well thought out and implemented with minimal components in an old school analog way (no arduino) that being said, i don’t even think you read the article you link to; this thing has nothing to do with midi control, nor is it a stompbox. This is a clever adapter to defeat a manufacturer’s attempt to force him to buy a proprietary accessory (again admirable) the midi part is a separate commercial product being used as intended (nothing wrong with that, he gives good reasons why he choose to go this way) it seems obvious to me that you either didn’t read his article (which is well written thoroughly documented) or that you deliberately misled readers with your title in order to pull in as many people as possible so they can look at the ads on your page. I think it’s sad to see a project such as this which stands on it’s own merit used in this way; i can think of a plethora of uses for a circuit such as this, but all you’re doing is tricking the midi and stompbox people into looking at your ads and setting them up for disappointment when they see it isn’t as advertised. Though the guy who actually did the work and kindly wrote it up made no such salacious claims and in my opinion he deserves better then this.

  3. It’s as if some telegraph key makers like to use inverted logic to sell a better key.
    The pedal sustain of all keyboard makers follows both ways of doing this elementary function. So aftermarket pedals have a switch to work in both worlds, NO and NC. This problem gets worse with a pot pedal varying a voltage to control something. This is common on guitar and synth units. The only thing I haven’t seen is the ground terminal being made hot or sense. I just rewire the gear and or pedal to tip-hot, ring-sense.

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