Where to set the gain knobs on my amplifier (or powered speaker)?

A work in progress.

Moderators: Bob Lee, Cameron Shoffner, Thanh Nguyen, Christian Cook, Kirk Fyvie, Martin Barbour, Brad Sambrano, Fred Thomke, Tracey Homan, Gary Evans_QSC

  • Basically, know that the "gain" knob is essentially an adjustment for different strengths of the input signal. It does NOT affect the amp's ability to send out full power to the speakers! Even if you turn down the knob almost all the way, it is still possible to drive the inputs hard enough so the amp's full rail voltage gets to its output speaker terminals. Turning up the knob (full clockwise) merely allows a weaker signal to now drive the amp to full output. Either way, you can ALWAYS drive the amp to full output! And keeping the amp in a turned-up-all-the-way state COULD potentially lead to blown drivers if the amp inputs get any sort of spike or huge input signal, since a smaller spike could be amplified into a very large spike. Heck, that's what amps do!

    What this means is: my recommendation is to turn up the amps LAST, and only loud enough to provide full volume in the room or environment for the loudest parts of the program. Start with some sort of hot (loud) music source, such as a CD player with dynamic music playing. Adjust your input gains at the mixer console, your mixer channel sliders up, output sliders up, so you are sending the "loudest, cleanest, non-clipping" signal you can get from the mixer. Do the same for any intermediate processing gear (EQs, crossovers, delays, etc.). The goal is a hot signal but not quite clipping. Finally, turn up the knobs SLOWLY, until it is loud enough for the room. Usually you will find that about 1/2-3/4 way is where you will end up with the knob, more or less. You will find that you now have a quieter system (less "hiss") because you are not amplifying noise as much, and the mixer sliders will be MUCH more responsive, allowing you full stroke of those sliders. If you DO end up having to turn up the amp knobs all the way, and it's STILL not loud enough, then you need more amp and/or more loudspeakers for the room.

    All of this explanation is a VERY simplified, generalized approach. There are lots of better described explanations of this process; just Google "audio system gain structure" and you will get dozens of discussions, tutorial videos, and white papers.
    Fred Thomke
    NO PRIVATE MESSAGES, PLEASE (use email address)
    Application Engineering Team
    Systems Support - Senior
    QSC Audio Products, LLC
    +1-800-QSC-AUDIO Tech Support
    +1-800-854-4079 Sales

    User avatar
    Fred Thomke
    QSC Audio Products
    Posts: 136
    Joined: Thu Jun 19, 2003 1:01 am
    Location: Costa Mesa, CA

Return to Amplifier FAQ

  • Users browsing this forum: No registered users and 1 guest