Discussion in 'Amps and Cabs [BG]' started by Pharmecopia, Aug 20, 2002.

  1. Pharmecopia


    Jul 31, 2002
    what is a power amp? what are the advantages / disadvantages of having one? :confused:
  2. Brendan


    Jun 18, 2000
    Austin, TX
    An amp head is a preamp and poweramp in one. A poweramp is a strictly power amplifier. A preamp is what shapes the tone and sound of an amp.

    Advantage: Preamps are cheaper than a whole head (usually), can swap with little hassle, can have more than one plugged in to the same poweramp at the same time.

    Disadvantage: More parts, more cables, probably need a rack to get away with it, not all that much cheaper, if at all.
  3. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    A power amp takes a small signal, like a few tenths of a volt up to maybe a couple volts (this is called line level), and boosts it, multiplying that voltage by a factor called gain. The output is a larger version of the input voltage; it might be 10, 20, 50 volts or more depending on the amp and the gain.

    The amp also has a lot of current capacity in that output because it drives one or more loudspeakers, which is a low-impedance load. Low impedance means that for a given voltage applied to the load, it'll pass a higher current than a high-impedance load will. Current is the rate of flow of electrons, and speakers require a strong flow of electrons because they are what make the voice coil's magnetic field. The field's reacting with the magnet in the speaker driver is what moves the speaker cone; essentially, it's a linear motor with a big diaphragm to move air molecules back and forth.

    The signal to the power amp comes from the preamp, which takes the small signal voltage (generally around a fraction of a volt; this is called instrument level) from the bass and boosts it up to be able to drive the power amp. The preamp also usually has tone controls and maybe some processing and/or effects.

    The main advantage is versatility; you can get different ranges of tone by trying different preamps, and different ranges of power by trying different power amps, etc. You're more likely to find an effects loop in a separate preamp, which can give you some more versatility in your sound if that's what you want.

    The disadvantage is complexity; you have more gear to interface with each other, and it's not as simple as just plugging into a combo or a head.

    I'd say that the biggest criterion would be what you're comfortable with. It's kind of like with cars, some people are die-hards about manual transmissions, and others want the convenience of an automatic. If you like to mix and match equipment and aren't timid about figuring out how to make several things work together, then you'll probably have a decent shot at success going the pre / amp / cabinet route. If you prefer to plug and play and not mess with connecting a preampp to a power amp, then a combo or head is the way to go. There is no right or wrong answer to the combo/head vs. separate question. It's up to what you want.
  4. Brendan


    Jun 18, 2000
    Austin, TX
  5. Thank you Bob. I just learned a lot.:D
  6. ldiezman


    Jul 11, 2001
    I was just about to say that all of that.. but you beat me too it.. so i see no need to repeat it.. oh well ;)