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Leslie 722 Guitar Modification

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  • Leslie 722 Guitar Modification

    Hey folks,
    I won't bore you with my life story, but my dad recently passed away and he left me all of his music gear, which included a C3, PR40 and a Leslie 722.The C3 and PR40 both work great, but the 722 is essentially useless in the setup, so I was going to see if I could modify it to function as a guitar amp. My dad played organ for most of his life, going back to the mid 60s, so he knew what all the pinout diagrams meant. But since I didn't grow up with Hammonds and Leslies and since I'm just a lowly guitar player ;-) , I'm not sure what to make of the schematics that I've found for the 722. Basically, I'm just trying to find a diagram to make an interface or even just a description of what the pins are as far as how they would apply to modern wiring. I usually only ever have to deal with line-level and speaker-level connections and, unless they just used different terminology in the late 70s, I'm guessing it's not necessarily just a quick connection thing.
    Anyway, I've searched around and looked on Youtube with no success, so if anyone knows of any resources that might come in handy, I'd appreciate the info.

  • #2
    The 722 is a rather complex solid-state Leslie with two input channels: stationary and rotary and four power amplifier modules.

    "Wiring" has not changed, but a Leslie interface for something like guitar has to do two things: It has to boost the guitar signal to a sufficient amplitude to drive the input of the Leslie, and it has to have provisions for switching the Leslie's rotors Slow/Fast/Stop.

    If you are using the 722 with a single channel instrument, like a guitar, you'd need to provide that signal to both input channels, unless you didn't want to use the stationary speakers.

    There is no way to plug a guitar directly into an HL722 cabinet, even with an interface, without some active electronics between the guitar and the Leslie. The Leslie circuits do not have nearly enough gain for the raw output from a guitar.

    There are some commercial Leslie interfaces out there you can buy. I don't know that anyone is simply giving away a circuit so anyone can build it. That's not a very good business model, if you know what I mean.

    The 722 uses Leslie's "11-pin" hookup standard, one that's been around since the 1970s. The 11-pin interface is very well-documented if you know the right search terms.
    I'm David. 'Dave' is someone else's name.


    • #3
      Thanks for the reply. Yeah, I figured I'd need a preamp of some sort, but I didn't know what level the Leslie was looking for at the input.And getting two channels into it wouldn't be a problem. I have seen cases where folks have used the preamp output from a guitar head to a Leslie, although they were all 147s, I believe.

      I wasn't sure if the motor controls were simply an open loop that closes the circuit to whichever motor you want to engage, or how that works.

      Either way, I guess I'll just have to tinker and see what I can make happen.
      In my head, I envisioned a pedal box with switches for the motor controls and a channel selector.

      Thanks again.


      • #4
        There are Leslie 11-pin preamps, the chrome wedge style with footswitches. They are made for single-channel Leslies, but could be adapted for two-channel.

        Look for a Combo Preamp III schematic.
        I'm David. 'Dave' is someone else's name.


        • #5
          Great. I'll look around. Thanks!