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So what makes a pre-amp a pre-amp?

Discussion in 'Amps and Cabs [BG]' started by Switched, Sep 26, 2003.

  1. These are most likely dumb questions but I'd like to be educated a little in this regard :)

    Just wondering what the characteristics of a pre-amp are that separate them from the world of effects? Why do I need a pre-amp before the power amp?

    From my unenlightened point of view, pre-amps just seem to contain tone shaping circuitry - something that can be provided by the myriad effects out there.
  2. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    You are correct that the pre-amp usually has some tone-shaping circuits, but it also boosts your bass' output level to something that can be used by the power amp. It's also a buffer between the instrument and the amp. Most basses have insufficient voltage output to properly drive a power amp.
  3. GooseYArd

    GooseYArd Guest

    May 15, 2003
    A preamp serves as an interface between an instrument and an amplifier, by providing an input impedance that is suitable for the instrument (a bass, microphone, etc), and serving as a gain stage to drive the amplifier.

    That's all that makes a preamp a preamp, at least in the historical use of the term. A preamp could be a box that sits between an instrument and an amp, a circuit inside a head or combo amp that comes before the power amp section, or on a little printed circuit board inside your instrument. Anything that matches impedances to the power amp and provides gain enough to drive it could be a preamp. The knobs and stuff are just gravy.
  4. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    matching impedence is the key to proper preamps. a pedal or other tone shaping or device with a volume control will "seem" to work with a power amp, but if impedence is not matched properly you will not have optimum tone signal being conveighed to the power amp and then to your ears.

    Some people who have tried just connecting a guitar to a pedal usually complain of not enough volume or headroom provided to the amp and it doesn't sound as loud as it could with the use of a proper preamp.
  5. Aha! Z matching. Thanks folks. I really appreciate that. :)