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Hammond L-100 pedal issues and working with a Leslie 720

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  • Hammond L-100 pedal issues and working with a Leslie 720

    Hi all, this is my first post here.

    I've been playing piano for 10 years, and have been listening to Dr. Lonnie Smith and Booker T. my whole life. I recently got a Hammond L-101 from Goodwill for $45, and a Leslie 720 for free.

    First question:
    When I turn on the L-101 with the pedal drawbar pulled out, after I let the tubes warm up, a very loud bass humming/buzzing sound comes from the speakers. When I put the pedal drawbar back in, the noise stops. How can I take care of this problem? I've checked the connections around the drawbar and they're all good, so I'm not sure what the problem might be.

    Next question:
    What kind of modifications do I have to make to the L-101 to be able to connect it to the Leslie 720? Do I need to get an 11 pin cable and a Leslie pre-amp? Also, where should I add the line out to my L-101? I've seen suggestions on this forum to add it to the speaker wires, and others that say to add it to the white RCA cable before the main speaker amp.
    What kind of pre-amp should I get for the Leslie 720, and what kind of outputs should I add to the L-101 to be able to connect to the Leslie pre-amp, and where is a good place to get control pedals and stuff for the Leslie?

  • #2
    Re the leslie. Two things.

    1) I think you should buy or build a suitable connector kit. It will take its audio signal straight from the amp. Don't mess around with expensive pre-amps and pedals. Building a kit isn't rocket science and there are plenty of schematics and advice available!

    2) The 720 is a very good, gutsy leslie but it does have an issue when being played from a single channel organ like the L. By default, the audio signal will go to the leslie's rotary channel. As this cannot handle much bass, it's merely filtered off and lost. Other 11 pin cabinets have a crossover that filters off the bass frequencies and sends them to the leslie's stationary channel, which has a 15" woofer. If you want to play pedals, then you'll have to recreate that crossover in some way. It shouldn't be too hard and again advice is available here.

    I'll let others chip in with advice on the pedal drawbar problem, but I will give you one definite instruction. You MUST change the motor capacitor as these are prone to exploding, given the age of the organ. Do this before you do anything else and preferably before you switch the organ on again.
    It's not what you play. It's not how you play. It's the fact that you're playing that counts.

    New website now live - www.andrew-gilbert.com

    Current instruments: Roland Atelier AT900 Platinum Edition, Yamaha PSR-S970, Kawai K1m
    Retired Organs: Lots! Kawai SR6 x 2, Hammond L122, T402, T500 x 2, X5. Conn Martinique and 652. Gulbransen 2102 Pacemaker. Kimball Temptation.
    Retired Leslies, 147, 145 x 2, 760 x 2, 710, 415 x 2.
    Retired synths: Korg 700, Roland SH1000, Jen Superstringer, Kawai S100F, Kawai S100P, Kawai K1

    Comment


    • #3
      Originally posted by andyg View Post
      Re the leslie. Two things.

      1) I think you should buy or build a suitable connector kit. It will take its audio signal straight from the amp. Don't mess around with expensive pre-amps and pedals. Building a kit isn't rocket science and there are plenty of schematics and advice available!

      2) The 720 is a very good, gutsy leslie but it does have an issue when being played from a single channel organ like the L. By default, the audio signal will go to the leslie's rotary channel. As this cannot handle much bass, it's merely filtered off and lost. Other 11 pin cabinets have a crossover that filters off the bass frequencies and sends them to the leslie's stationary channel, which has a 15" woofer. If you want to play pedals, then you'll have to recreate that crossover in some way. It shouldn't be too hard and again advice is available here.

      I'll let others chip in with advice on the pedal drawbar problem, but I will give you one definite instruction. You MUST change the motor capacitor as these are prone to exploding, given the age of the organ. Do this before you do anything else and preferably before you switch the organ on again.
      Thanks for the advice. I'll look around for schematics and stuff for adapters and crossovers. What kind of capacitor does the motor need? I'll get one on digikey or at the surplus store.

      Also, by pedals I meant the pedals that control the rotary speed of the Leslie, that's what I was talking about.

      Comment


      • #4
        Nice find , good to see a fellow New Mexico Hammond player. Trek makes a crossover LCO-1A which converts a roto-sonic 710 or 720 to single channel use. It puts the bass in the 15" where it can be handled and out of the roto-sonic speaker . Check for a loose ground on the bass circuit otherwise check the tube which powers the bass circuit. The cap that needs replacing is call a run-motor capacitor, tall silver can next to the run motor.

        Comment


        • andyg
          andyg commented
          Editing a comment
          The 720 doesn't have a Rotosonic, but a 12" speaker facing into a normal baffle type rotor. As such it's closer to the 'normal' Leslie sound than the 710. Trek's crossover will work fine, but I think with a bit of thought and advice you could build a crossover into a connector kit for pennies.

          Not hard to source a run cap - here's one place: https://www.bborgan.com/products/run...tarting-motors

          Other sources are available! :)

      • #5
        Also nice to see another New Mexican. I'll check out those crossovers you mentioned, and I'll also look at the bass circuit tube. Thankfully I found a full PDF of the manual with all the schematics on archive.org. I also just got my oil in today, so time to get to work!

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