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Forgive my ignorance, but...how does a preamp work?

Discussion in 'Amps and Cabs [BG]' started by FuzzyDustmite, Sep 10, 2003.

  1. FuzzyDustmite


    Sep 2, 2003
    never had to use one, but just wondering how a preamp affects your main amp. Does it boost the power output of your main amp to the watts of the main amp plus the preamp?

    Say, for example, I have an amp that puts out 350w, and I hook up a 350w preamp to it. Does that make the output now a total of 700w (assuming all the ohmage is correct)?

    Also, can you use another regular bass amp as a preamp? Say I have an Ampeg head, could I run a GK as a preamp, combining the tone and power of both amps?

    Maybe I have it all wrong, so please correct me if I do, but how do you know how much power you can push through your main head with a preamp without running the risk of blowing up your head?

    Sorry if I sound ignorant, just trying to get a handle on the whole thing.

  2. Eric Moesle

    Eric Moesle

    Sep 21, 2001
    Columbus OH
    What is commonly referred to as a "bass amp" is typically a combination of a preamp and a power amp, all within one convenient casing. When you see "preamp" mentioned here, its usually referring to a preamp which is separate from a dedicated power amp which itself has no tone shaping capabilities, just a raw power machince. The preamp provides the tone, the power amp provides only the power.

    Overly simplistic, but I think this answers it.
  3. makohund


    Dec 12, 2002
    Yeah, that's pretty much it. Let me break it down a little more.

    Preamp: Brings the signal of your pickups/etc up to a workable level. Usually provides tone-shaping tools. Beyond the bass itself (and external processors) this is what gives any particular rig its "sound".

    Power Amp: Takes a relatively low-level signal fed to it (in our case by a preamp) and amplifies it. Perhaps to 100 watts, or to 2000 watts. This is the machine that drives your speakers.

    Head: Basically a preamp and poweramp together in the same unit. I'm assuming the Ampeg and GK you are referring to fall in this category.

    Some heads will have inputs/outputs that allow you to access either the preamp or poweramp portion of it separately. For example, letting you go from the preamp output on your GK to the poweramp input on your Ampeg.

    The end result is using a GK preamp through an Ampeg power amp. There is no sound shaping by the Ampeg preamp, and you aren't getting any power from the GK poweramp. Both have been bypassed.

    You won't get "combined tone and power". You will get the tone of one with the power of the other. (It might give you a slightly different sound, though.)

    If you really wanted to (and were really careful about levels), you could try going from the preamp out on the GK to the preamp in (where your bass normally goes) on the Ampeg. That would sortof give a combined tone of both, with the power of the Ampeg. Or it might just make a hell of a lot of noise. Personally, I wouldn't do it.

    Is that clear as mud? :)

    And lastly... DO NOT attempt to go from any poweramp (speaker) outputs to any inputs on anything. The only thing that might increase is the amount of smoke in the room. And the amount of money you'll need to replace everything. Things will instantly become fried and ruined, or might even catch fire. Never connect those to anything but speakers.
  4. BruceWane


    Oct 31, 2002
    Houston, TX

    Nope. A preamp, essentially, has no "wattage". Power amps have wattage. There is no such thing as a 350 watt preamp. A preamp serves to boost the signal generated by your bass up to a level that a power amp can use, and it also provides the ability to adjust and manipulate your tone via eq and effects.

    It depends. Many heads have jacks that will allow you to do this, some do not. The head will have a jack labeled "preamp out" and/or "power amp in". It's not usually a good idea to run one preamp into another preamp. It can be done, but you'd have to be very careful of the levels.

    If you want to try a different preamp with your current head, the head needs to have a "power amp in" jack. You'd connect the output of your preamp to this jack. You'll be bypassing the preamp that is built into the head.

    As far as "power", like I said, a preamp doesn't really have any (it does, but were talking less than 1 watt). If your preamp level is too high, you'll get plenty of distortion to warn you before anything is damaged.
  5. B String

    B String Supporting Member

    Apr 11, 2002
    Los Angeles
    Well said!