Dismiss Notice

Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Can 4 ohms bridged be more than sum of 2 ohm stereo?

Discussion in 'Amps and Cabs [BG]' started by GreyBeard, Nov 12, 2002.


  1. Yes that's possible, it has to do with the power supply.

    This is what happens, I think:

    Amp power supplies always consist of two almost identical part: one for the positive output swing and one for the negative one, aka as power rails.

    Some power amps have one of their channels "reversed", so the two channels will never draw maximum current from the same rail. The output terminal is also reversed, so the user won't see the difference.

    If you load the power supply with a monaural signal, it has to do only one half of the signal at a time, ever. Each power rail has half a signal cycle to reload it's buffer caps, and thereby it can supply more power the next time it is loaded.

    With a stereo setup, both rails are always supplying power, so there's less time to reload the buffer caps.

    Someone correct me if I'm wrong.
     
  2. 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
    It's possible, but I'll also point out that the stereo/dual channel power specs are stated as 20 Hz–20 kHz, while no frequency range is stated for the bridged power specs. Maybe they're just at 1 kHz? Can't tell one way or the other.

    At any rate, it's not much of a difference.
     
  3. I see what you mean. Since it is rated at 900 watts RMS into 2 ohms stereo 20-20k <1% distortion then one might assume that 1800 Watts into 4 ohms bridged is a more realistic figure? Funny thing is, there is a big difference between a 50 watt amp and a 300 watt amp but little if any difference between 1800 watts and 2100 watts. :D
     
  4. 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
    Since you would only ever hit at or near full power on peaks, neither figure is really unrealistic.