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OT thread for you amp/electronics experts

Discussion in 'Amps and Cabs [BG]' started by secretdonkey, Jul 10, 2004.


  1. secretdonkey

    secretdonkey

    Oct 9, 2002
    Austin, TX
    I tried posting this in OT, and got one good response (thanks, Almighty Bass) that tended to side with me, but I'm being told by a self-described expert that I'm wrong about this, and I could use some expert opinion here. Amp mods hopefully will allow this here since I tried it first in OT...

    Anyway, I recently bought an iPod MP3 player, and also some audiophile earphones (Etymotic ER-4P) that are specially designed with a lower impedance than the company's other phones, so as to maximize the potential of small, portable players as opposed to home hi-fi.

    Anyway, I noticed immediately that my iPod's battery seemed to drain much more quickly using the low impedance phones, as compared to the "stock" phones. Common sense tells me that since my bass rig puts out more watts at lower impedance, and seems to convert more electricity to heat, that it must be drawing more power... and therefore it is reasonable to hypothesize that a lower impedance "speaker" load will drain my iPod's battery more quickly.

    So, am I right or wrong? My "adversary" tells me that the iPod puts out a fixed amount of power and that quicker battery drain must be a coincidence attributable to other factors. Technical explanations one way or the other would be appreciated!

    Thanks!

    :)
     
  2. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    Well, when i run my sub amp in my car at a lower impedance, it does get hotter. Which tells me that more energy is being converted to heat, AND it's pushing out more power, too. Couple those both together, and you are using a considerable amount more energy. So yes, it makes complete sense that your batteries would drain more quickly.

    Let us look at it like this. A plain wire has very low resistance. When connecting this across 2 terminals on a battery, you get heat and drain the battery very fast. (This can also damage batteries, but this is outside the scope of our discussion). The reasoin being is that the electrons have a free flow between the two points, and there is no work being done. Now, when we put a load on it, we still have energy being used and transfered to heat, but there is also usually work going on. Like lighting a bulb, moving a motor, or something. On the other side of the load is a reduced amount of electric flow, but it is still needed to complete the circuit.

    Basically what I am trying to say is that those low impedance ear phones are closer to 0 resistence, thus expending more energy as heat, and drawing more energy in the first place. This uses up more battery power. I hope this helps explains things...
     
  3. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Agreed. That would be generally true for solid state amps. A lower impedance load will result in greater current draw and increased power output. Up to a point. Then the amp will fry. Usually there is a clearly labelled "minimum impedance" for solid state amps, which is typically 4 ohms, and sometimes 2. Never try to run any load below the minimum rated impedance of the amp, otherwise the amp will surely go belly up. Regarding the iPod, there's probably a spec for output impedance listed in the owner's manual.
     
  4. Unless the iPod has an output transformer (which, of course, it doesn't :D) you are right. The output of the amp will follow ohm's law. The amplifier will produce the same output voltage regardless of load (well, pretty much, let's assume ;)). So if you lower the impedance that output voltage is across, more current will flow (I=V/R) and more power will be produced (P =IV). If the amp produces more output power it's definitely going to draw more input power as per conservation of energy. So your so-called expert is wrong.
    Where's that thread btw?
     
  5. secretdonkey

    secretdonkey

    Oct 9, 2002
    Austin, TX
    Awesome! Thanks for the replies - Mark Reccord, that's *exactly* the technical explanation I needed to vindicate my thinking!

    BTW, Mark, this little debate over the iPod isn't on TB... I just turned to TB in hopes of finding an amp expert who could give a qualified thumbs up or thumbs down to my position. The thread I referenced in my earlier post is: http://www.talkbass.com/forum/showthread.php?t=134734 but there is nothing really interesting there except Almighty Bass' reply that pretty much agrees with everything said in this thread.

    Thanks again for all the replies! :hyper: