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Leslie Hot Rod

Discussion in 'Electronic Repair' started by Trevor, Jan 27, 2004.

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  1. Trevor

    Trevor Guest

    To whom it may concern,
    I'm trying to biamp my new Leslie Speaker model 122A. My master plan
    is to use the stock 40-watt amp to drive only the horn and a Mackie
    SR1530 for the low-end duties. The Mackie is a solid-state tri-amped
    system. In this scheme, I won't need the services of either the Mackie
    mid or upper drivers. In other words I'll be using the Mackie amp to
    power only its woofer, which now resides in the Leslie cabinet.

    Here is the cut and paste spec sheet for the Mackie SR1530:

    SR1530 Specifications
    Freq. Range (-10 dB)
    40Hz - 20kHz
    Freq. Response (-3dB)
    45Hz - 18kHz
    Horz. Coverage Angle (-6dB)
    Vert. Coverage Angle (-6dB)
    Directivity Factor; DI(Q)
    10.77 (11.95) averaged 2kHz to 10kHz
    Rated Maximum SPL (peak)
    126dB @ 1m
    Crossover Points
    700Hz, 3,000Hz

    15-inch (381mm)
    Power Handling
    300 watts Dynamic Program Power

    6-inch (152mm) diameter
    Power Handling
    100 watts Dynamic Program Power

    High Frequency:
    Exit Throat
    1-inch (25.4mm)
    Power handling
    100 watts Dynamic Program Power

    Low-Frequency Power Amplifier:
    Rated Power
    300 watts @ Low-Frequency Driver Impedance
    Rated THD
    < 0.05%
    Class AB Convection Extrusion

    Mid-frequency amplifier:
    Rated Power
    100 watts @ Mid-Frequency Driver Impedance
    Rated THD
    Class AB Convection Extrusion

    High-frequency amplifier:
    Rated Power
    100 watts @ High-Frequency Driver Impedance
    Rated THD
    Class AB Convection Extrusion

    Being more musician than electrician results in the following
    Shortcomings of knowledge;

    Do I need a load of any kind where the mid and upper drivers were so
    the Mackie amp doesn't suffer any ill effects from only being
    connected to the woofer? (e.g. make amp run to hot, not at peak
    efficiency, shorten its life, etc…)

    If I need to have a dummy load where the mid and upper drivers were,
    what is the best way to go about this. Just wire in the appropriate
    resistor? If so what is the appropriate resistor?

    The Leslie 122A is a 40 watt tube amp. I plan to put a load (16 ohm
    10 watt resistor) on it where the original woofer was after the
    crossover. Is that the best way to do it? The way I understand it
    the woofer, driver and crossover all are 16ohm in the Leslie 122.

    I would like to optimize the power going to the driver w/o alteration
    of the driver's sound. Will running the amp into the crossover then
    into the upper driver with a dummy load where the woofer was complete
    the task? Or am I missing something here?
    The driver is the new Leslie Ferro-fluid 100 watt driver.

    I would be much obliged for any help I can get on this project.
  2. jakdedert

    jakdedert Guest

    I'd keep the Mackie 'as original,' sell it and get a pair of power amps and
    2-way electronic crossover for the Leslie. I've seen several setups like
    that, replacing the original tube amps completely. Is this an older model
    Leslie, or something new? The setups I refer to are the units which came
    with the original B-3's. There are tons of mods out there for those. I'm
    not familiar with the newer models.

    Of course, if you want to keep the tube sound, your options are a bit more
    limited, but you could still sub in a mono solid state amp for the low end,
    and a cheap crossover can be had for $100 or less used. I've even seen
    people drive them with a guitar amplifer head. Just make *very* sure that
    the horn driver only gets high frequencies.

  3. Trevor

    Trevor Guest

    Thanks Jak that helps.
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