Volume control between Audio Amp and Speaker

Discussion in 'The Projects Forum' started by maverik007, Mar 5, 2009.

  1. maverik007

    Thread Starter Member

    Feb 6, 2009
    Hi everyone!

    I have to install a volume control between an audio amplifier (8ohms) stage and a speaker (50W rms, 100W max, 8ohms). I am clueless about what calculations need to be done to figure out the correct type of potentiometer to be installed.

    Any tips or suggestions will be appreciated!

  2. KL7AJ

    Senior Member

    Nov 4, 2008
    The practice of putting a pad in line with a speaker is falling into disuse in recent years, though the practice was very common in the heyday of Hi-Fi, back in the 60s. You really burn up a lot of power in speaker pads, and if there's any alternative, it's probably a bit better.

    However.....if you go this route....you don't really want a potentiometer, you want a PAD. Generally, these consited of THREE ganged rheostats, or sometimes switched resistors.

    Here's a good site with calculatons for various pads.


  3. Externet

    AAC Fanatic!

    Nov 29, 2005
    Try a wirewound rheostat of 50 to 100 ohm. Its wattage dissipation will depend on the amplifier power; not the speaker rating.
    The rheostat power depends on the 'usual' attenuation level it will mostly run; but you may get away with not less than around 10 watt.

    Better calculations would need the maximum power the amplifier will put out.

  4. KL7AJ

    Senior Member

    Nov 4, 2008

    This is certainly the simplest way. If you wire it as a true rheostat (two terminals) you won't be able to turn the speaker down to nothing...which may or may not be a problem. If you wire three terminals "potentiometer-wired" rheostat, you will be able to turn the level down to nothing...but with a bit more loss in the rheostat.
  5. beenthere

    Retired Moderator

    Apr 20, 2004
  6. Audioguru

    New Member

    Dec 20, 2007
    a resistor in series with a speaker ruins the damping of speaker resonances by the extremely low output impedance of the amplifier.
    In stadiums and in homes, a switched transformer is used instead of a huge and hot rheostat.
  7. maverik007

    Thread Starter Member

    Feb 6, 2009
    thanks everyone for your comments and suggestions :) i really appreciate the information you have provided! I bought a 100Watt, 8 0hm L-pad variable potentiometer from Orange County Speaker in California. It works for my application! I'll post more questions if I have any issues!