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Tech Question - Wattage relations with Gain

Discussion in 'Amps and Cabs [BG]' started by BrandonS, Jun 19, 2001.


  1. BrandonS

    BrandonS

    Nov 15, 2000
    I have been wondering about this subject for several years but have never had an answer for it:

    Theoretical Setup - Bass, Preamp, Amplifer (1000 Watts)

    If my amplifier's level control is @ 50% then my amplifier should be pushing roughly 500 Watts irrespective of my preamp and bass volume settings?

    How does the gain settings on the preamp and the volume control on the bass affect the actual wattage being sent to the speaker cabs. If I have them maxed out, does the cab actually see more wattage (i.e. potential damage) due to the increased signal levels

    I am assuming that the speaker cab sees 500 watts @ a nominal gain level.

    Thanks,

    Brandon
     
  2. I think of it this way-

    Your amp is a multiplier, and the settings of all those gain and volume knobs determine what the amplification or multiplication value is. Don't worry about power just yet. The volume knob on your bass controls the signal level coming out of the bass which is then getting multiplied by the preamp and amp:

    bass signal = ~100mV, the preamp multiplies it by say 10, so it comes out of the preamp as 1V, then the power amp multiplies it again, this time adding power to the signal, then sends it on to the speaker. So the settings of your knobs control how much the multiplication is at different points. There is not a direct relation between the knob on your power amp and the power going to the speaker, it depends on the signal size coming in, dig? If you are putting out 2V out of your preamp, and the power amp is set at 50% gain and it is designed to be driven to full power with a 1V signal, then you'll get full power out even though the input signal is twice what it should be, and the gain is set at half. So it's not so much about "if my knob is at 5, am I putting out 500 Watts?" Nobody knows until every other signal is measured, and that's pretty much pointless.

    Just to muddy it up even more, the power is not steady, it varies a lot. You may think your amp is louder than a Harley Davidson, and if you were to measure the power at the speaker, it might only be putting out 100 Watts out of the 1000 Watts it has available. That's what headroom is, you need that reserve of power capability for the thumps and the bumps that cause big spikes of power to go to the speaker. When your note is just ringing out, the power is very low in comparison.

    Want even more mud? Human hearing is not linear, so our ears hear a sound of 1 Watt, then to sound twice as loud, they have to hear 10Watts, then to double the volume again it will take 100Watts, then to double it again will take 1000 Watts! Logarithms, baby. Power of 10. If you just double the power, you'll just barely notice the increase in volume. Crazy, but that's what lets us hear crickets at night and also listen to 1000 Watt bass amps without falling to the floor and crying. Think of it as an automatic gain control in your ear. If the noise is loud, the gain is cut down, if it is very quiet, then the gain turns up so you can heat it.

    Confused even more now?

    Chris
     
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