output power vs gain-volume settings

Discussion in 'Amps and Cabs [BG]' started by Crockettnj, Nov 10, 2005.

  1. Crockettnj


    Sep 2, 2005
    North NJ

    is there a linear relationship between the output power of a typical bass amp and the settings on your amp? Furthermore, if 0 is zero watts output, is 10 the max of your amp, or does it peak prior to that?

    For example,
    identicle eden wt-300's, played with identicle fender p-bass with passive pickups, with identicle cables, into identicle 4 ohm speakers...
    Lets say a steady, picked note with no changes or runs... a low E for Arguments sake. All Eq's set flat.

    WT "A" is set at 6 oclock on the pre and 6 oclock on teh post gain.
    WT "B" is set at 6oclock pre, 3 oclock post.
    WT "C" is 6 and 12 oclock.

    is A running twice the watts as B? Is C running twice the power as A?

    What wattage is A running at?

    noone i asked has been able to answer this, except with teh obligatory "well, it depends", which i am sure it does but still fails to address the intent of the questions!

    thanks to all who attempt / help.
  2. 0 doesnt = 0 watts

    i know how it works, but its hard to explain

    one thing i think your getting at

    single master volume is just a post gain with a set pre gain

    think of the amplifier in 2 parts

    the pre amp, where the tone shaping happens, and the power amp, where the signal is boosted to drive a speaker cab

    Now, imagine the power amp, it itself is not controllable and is always at its max settings, however, the output of the power amp depends on the strength of the signal it recieves

    the pre gain controls the signal level of the preamp, and the post gain controls the signal level just before it hits the power amp

    hope that helps somehow
  3. BruceWane


    Oct 31, 2002
    Houston, TX
    No, there's not really a "linear" relationship there.

    The lower you set preamp gain levels, the harder it is drive the power amp stage to full output. That doesn't mean that an amp will put out more wattage when the knob is set to 10 versus being set to 8. Let me put it this way....I could set pre- gain at 10 and play softly and have no problems, or I could set it at 8 and dig in hard and it'll clip like a mofo.

    In other words, you've still got the variable of the strength of the incoming signal.

    Now, if you were to use a sine wave generator for the input signal, and the preamp output voltage was precisely matched to the sensitivity of the power amp, and the potentiometers on the preamp were of a linear taper design........then yeah, setting pre- gain to 5 would cause the power amp to generate half the output wattage compared to setting the pre- at 10.

    But there are no pre-amp power amp configurations that are built like this - there's no need to. Preamps and power amps often have clipping indicators, and even if they don't the sonic indicators are pretty obvious.

    Every bass amp I've ever played through will hit peak wattage a long ways before getting the volume knob to "10".
  4. BruceWane


    Oct 31, 2002
    Houston, TX
    Something to understand - potentiometers come in different designs - linear taper and audio taper.

    Linear taper means that at the 20% position, the pot passes 20% of the signal; at the 50% position, the pot passes a 50% level....and so on

    Audio taper means that the relationship between position and output has been adjusted to compensate for the way human ears percieve volume changes. Instead of a straight line like a linear taper, it's a curve.

    So the knob position on an amp can't really be interpreted to represent a certain percentage of output directly, because a knob position of "5" on an audio device does not mean that the potentiometer is passing 50% of the signal.

    Any device dealing with audio will use audio taper pots, otherwise it will seem like it doesn't react the "right" way to adjustments because of the way our ears percive sound and volume.
  5. Crockettnj


    Sep 2, 2005
    North NJ
    ok, i think the difference between the pots , linear vs audio taper, is the root of my question. ("So the knob position on an amp can't really be interpreted to represent a certain percentage of output directly, because a knob position of "5" on an audio device does not mean that the potentiometer is passing 50% of the signal.")

    Something obvious i hadnt thought about is digging in or playing soft... you can really alter the output of the amp without going near a volume or tone knob. its intuitive, but i hadnt considered it.

    So there is no "100 watt" setting on any amp's knob. There cant be, could there? nope, i dont think so.

    furthermore, There isnt really a way for me to know the avg wattage that is necessary for the vast majority of my playing. All i know is that if i use a 300 watt amp, and it is enough, than less than 300 watts is enough. I cant break it down from there and determine if 100 or 150 would have been fine. ( i know i am considering thngs that are, in all practicality, irrelevant. It's just curiosity)

    anyone else want ot interpret this question and toss something in the ring, i'd apprecaite it

    thank you..