Impedence question

Discussion in 'Amps and Cabs [BG]' started by Warwickthumb, Sep 2, 2003.

  1. Ok I thought I understood this stuff but I guess I dont. I have an old bass head that ive been runing through my new cab till I get a bass amp for it. On the back of the amp for speaker output im pretty sure it says 2 8 ohm speakers or 1 4 ohm speaker. And there is a jack for an extension speaker at 8 ohms. My cab is an 400 watt 8ohm cab. So does this mean when I have to buy an amp that is rated at 8 ohms? And this is what confuses me. Ive been searching around and some amps say like 400 watts at 4 ohms, and 200 watts at 8ohms. I think this threw me off the most. Well again any help from people more knowledebale them me is always greatly appreciated.
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    There is probably a FAQ about this somewhere...

    However, if you have a tube amp, you need to try to match the amp's output impedance (in Ohms) to the cabinet's input impedance (also in Ohms).

    If you have a solid state amp, the amp's rating is its minimum output impedance rating (usually 4 ohms, sometimes 2 ohms, occassionally 8 ohms)

    With solid state amplifiers you should never go below the minimum impedance. If your amp has a published power rating at 4 ohms, you can safely use two (2) 8 ohm cabinets with it (assuming that they're connected in parallel and amplifer speaker jacks are almost always connected in parallel).

    So to answer your question, it is safe and normal to use an 8 ohm cabinet with an amp with a minimum load impedance of 4 ohms. You won't get as much power out of it at 8 ohms, but it will work just fine and won't damage the amp. As a benefit, the amp will probably run cooler.

    Have fun!!!!