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.

power amp knob = attenuator?

Discussion in 'Amps and Cabs [BG]' started by jondog, Oct 26, 2004.


  1. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    I'm pretty sure I understand this, but I just want to confirm. My power amp has signal level lights and then a clip light. If I set it to the edge of clipping, so the light only comes on on peaks, then my amp is putting out it's maximum wattage, right? Even if the power amp knob isn't dimed?
     
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    clipping would tend to indicate that. The "volume knob" is actually an input sensitivity adjuster and not a "wattage control".
     
  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
    That's right. The gain control adjusts the overall gain of the channel and does not affect how much power the amp can put out. Even with it turned down from full gain, you can make the amp hit full power by putting in a hotter input signal.
     
  4. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    OK good, thanks. Now how about this question, can I bridge into 8 ohms even though the manual doesn't give me a wattage rating for 8 ohms bridged? If I understand this bit, each side would "see" 16 ohms. The manual doesn't give a rating for 16 ohms either, but higher ohm loads are supposed to be ok, right?
     
  5. 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
    If the amp is rated for 4 ohms per channel, it should be able to do 8 ohms in bridged mono. An 8-ohm load impedance in bridged mono is equivalent to a 4-ohm impedance (not 16) on each channel. Check with the manufacturer to make sure, though. Do you know what brand it is?
     
  6. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Ok, yes I had the per side thing backwards. The amp can do 4 ohms per channel, it's even able to go down to 2 ohms per side. It's a Mackie 1400i. I used it for my bass rig for 3 years (one 8 ohm cab per side) but now I'm going to use it to power the PA subs and I'm trying to figure out how to get the most out of it. My new (used) subs are 8 ohms each, but they are big and heavy so I'd like to only bring one out, so if I bridge into 8 ohms that should be best, right?
     
  7. 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
    Yes, that should work fine. The Mackie should have no trouble with it.