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Questions: Bass Amp wattage and volume settings vs. electrical draw?

Discussion in 'Amps and Cabs [BG]' started by JacoNOT, Jul 20, 2012.

  1. JacoNOT


    Mar 7, 2012
    Before anybody jumps on me, I looked at the thread titles in the stickie and I tried reading the Amps FAQ by Joris but the related section was full of non-displaying text characters and techno speak that made my head spin. :eek:

    I don't want to use a lot of electricity when I practice alone. I've employed round numbers to keep my question easy-to-understand and discuss:

    - Assume I buy a 100 watt amp.
    - Assume I set the volume knob to 1 (max setting of 10).
    - Next, assume I set the volume knob to 10 (max setting of 10)
    Does the '10' volume setting use 10 times as much electricity a the '1' volume setting?

    - Assume I replace the 100 watt amp with a 500 watt amp.
    Does a volume setting of '1' on the 500 watt amp use 5 times the electricity that's used by the 100 watt amp at the same setting of '1'?
  2. Not all volume pots are created equal, and many aren't linear.
    I'll leave the more in depth answers for others with more knowledge.
  3. Knob position means absolutely NOTHING. Most amps hit their clean output potential WAY before the knob hits "10"

    Maxing out an amps knobs usually means you into distortion area, and could be putting out TWICE the amps rated power.
  4. Sort of, but not exactly.
    In almost all cases, increasing loudness does increase power draw. But it's not a one-to-one thing(knob position) as you suggest. And a larger amp will PROBABLY draw more power at a given volume than a smaller one would, but PROBABLY not much more. Depends on the design of the particular amp. Some amps in the HiFi world draw maximum power all the time, even when not producing sound. But this is rare to see in the musical instrument world.

    Good news is, unless you are cranking a large amp, the draw is minimal.
  5. BbbyBld


    Oct 13, 2005
    Meridian, MS


    If you really want to know how much power you are using, you can buy a meter plug device at Home Depot or Lowes that plugs in line with pretty much anything. It has a LCD readout that will tell you with good accuracy how much power you are using. This would allow you to see how changes in volume and/or tone affect power consumption. I think you may be surprised how little an amp actually requires when operating playing music...unless it's a tube amp.
  6. will33


    May 22, 2006

    (as if I really need to +1 an engineer.:smug:)

    I don't even notice a difference in my monthly electric bill whether we rehearse every week or not at all. And that always includes at least one tube amp, sometimes 2, as well as PA and nothing is smps or class D. It's really not that big a deal, especially compared to a/c or heat.
  7. JacoNOT


    Mar 7, 2012
    Thanks for all answers.

    I've been thinking about buying a Kill-A-Watt tester for a while now. It'd tell me lots of things I want to know about power consumption, BUT...I want to sort this question out before I purchase a practice amp.

    From your comments, it appears that a basic 'electronic' amp (basic, nothing exotic) will generally draw considerably less power than will a comparable tube amp.

    If I've got that right, can you guys recommend a decent budget amp product line or maybe even a particular model in the 25-to-100watt range that's known to be particularly energy efficient?

    I'm not a greener. Just want to keep the utility bills as low as possible. :D

  8. will33


    May 22, 2006
    The newer smps (Switch Mode Power Supply) and class D amps are very efficient. Meaning they don't need to draw much more from the wall than they're putting out, very little power is wasted or burned off as heat.

    The 200 watt GK combos are small amps, but have the "oomph" to handle a gig down at the small local corner bar when you get that far.

    I haven't done all the load calcs. in a long time, but, I'd say just get an amp you like the sound of and is loud enough to do what you want to do. Seriously, TV's, microwaves, refridgerators, water heaters, most anything in your house is going to suck more power than a smallish amp anyway. It's not that big a deal.

    Besides, "green" is a fraud. They don't care about being green, they care about money, and if your usage drops too low, they'll just raise your rates anyway 'cause they'd like more of your greenbacks.:p
  9. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    He's not green...he's cheap ;)

    Ya, turn off your air conditioner for a half hour, and that should give you all the extra power to run an amp for the next year.
  10. teemuk


    Mar 1, 2011
    I'm not even going to start throwing any estimations. They would vary way too much. They would not be nowhere near universal conclusions and the thing is extremely difficult to calculate.

    Efficiency isn't a linear parameter. You can google search class A, AB, H/G, and class D efficiency curves to get a ballpark idea how efficiently amplifiers work at different output power levels, relative to maximum %.

    Additionally, perceived loudness vs. output power is not a linear parameter but logarithmic. For example, twofold increase in loudness requires a 10dB power increase and that's 10 times more power. Essentially power difference between whisper level and roaring level might easily mean a 1000x difference in output power level.

    Volume controls can be logarithmic or linear.

    The power supply of an amplifier will store energy to x amount of capacitance that will be used as reservoir during power draw. The amount of capacitance has an effect on overall power draw from mains.

    If you use a generic bass guitar input signal its amplitude level will vary tremendously between transients during note attacks and overall amplitude level during note sustain. It's a variable that's damn hard to estimate.
  11. If you want to draw even less current get yourself a cheap micro mixer and a pair of headphones. No amp to power that way!
  12. JacoNOT


    Mar 7, 2012
    I DIG. Thanks for these replies. I get useful insight from both "the basics" answers and "the technicalities" answers.

    I won't be buying anything exotic, so will probably choose from the efficient "newer amps (Switch Mode Power Supply) and class D amps" mentioned by will33.

    All your comments have helped me to form the following questions, which should provide exactly the answer I seek:
    Assume two modern Switch Mode Power Supply / Class D amps side-by-side. A 50-watt model and a 100-watt model, both from the same manufacturer. The volume level is set to middle '5' on both (max is 10), and all other controls are set identically.

    Q1. Under these specific conditions, can I expect the 50-watt amp to draw less electrical power (amperage?) than the 100-watt model?

    Q2. Under these specific conditions, is it likely that the 50-watt model will draw approximately half the amperage that the 100-watt model draws?

    I appreciate and understand (in layman's terms) that many variables affect this, but in this scenario, the two amps are from the same mfr and are probably identical except for their power ratings...

    (and I'm not cheap. I'm not working at present, ergo the focus on keeping costs down ;)
  13. John D

    John D Guest

    Dec 27, 2009
  14. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    You're talking pennies a month difference, bro, if that.
  15. John D

    John D Guest

    Dec 27, 2009
    Good point. I had not seen those before. I may get one for myself.
  16. MarkoYYZ

    MarkoYYZ Commercial User

    Jan 31, 2012
    Hammersmith Music
    JacoNOT - put it this way...

    You're probably paying somewhere around 0.10 per kW/h. That means if you use 1000 Watts for an hour, it will cost you ten cents.

    So, imagine you own a 200W amp, but when practicing at home at lower volumes, you're really only using about 50W (actual draw from the wall), at any given time. Suppose you practice 2 hours a day, 5 days a week, that works out to about 40 hours a month.

    40 hours x 50W = 2000W... or 2 kW/h... or 0.20 total electrical cost. Give or take.

    Keep in mind that a 100W amp used at 10 0'clock could use just as much power as a 200W amp used at the same level. They are not created equal and benchmarking the power consumption of one model/brand/size against another is a fool's errand.

    If you want to be environmentally conscious, then use a Class D power supply. These are more efficient in terms of watts used that are turned into sound, but also have a very high power factor rating. A lot of people don't realize that PF is far more important than actual watts measured when trying to figure out what the environmental impact would be.

    For example (in the simplest terms, rather then get all technical)...

    100W at PF of 85% requires the hydro company to deliver 117.6W worth of power to your outlet. You will pay for the 100W used while the 17.6W of transmission power is wasted. It still needs to be created by the power plant (whichever kind it is).

    100W at a PF of 50% means that the power company has to generate and transmit 200W for you to get the 100W you need. Your bill will reflect the 100W used, but the extra 100W of created and wasted energy is still your fault.

    So... using a very efficient 200W amp can actually use less power than an inefficient 60W amp. Some amps are both inefficient AND have a low PF%. It might be rated at 100W output, consume up to 200W from the wall, and that 200W may be at PF% of 65.

    Confused yet?
  17. And this is why, as Jimmy so eloquently explained ( :D), your quest for efficiency is really rather pointless.
    But you didn't know that. Now you do. There's no amp on earth that would cost you more than, oh, a dollar or so a month to run.
    But if you must nit-pick, go class D- they are the most efficient.
  18. The answer is - no. This is what you need to know ~

    Watts divided by voltage = current. For example, a 600w amp draws 5 amps (600w/120v = 5 amps).
  19. will33


    May 22, 2006
    As an example, the Ampeg 3pro draws a max of 1000 watts from the wall to make it's 450 watt max output. (Class a/b, conventional power supply leadsled).

    The GK mb500 draws a max of 580 watts to make it's 500 watt max output. (Class D, smps).

    Those are just examples, not favoring, or picking on those particular amps.

    The newer micro stuff is more efficient, but remember, that's when you're cranking it to full power.

    Some little 30 watt combo, even if it's inefficient, won't pull more than 60-70 watts out of the wall. If you're not cranking it, it's basically less than turning on one more light bulb.

    And yes, pretty much ignore the number settings on volume knobs. Depending on your input gain, you may be running the amp to full power in the first half of the dial.

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