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quad headphone amp

Discussion in 'Electronic Design' started by [email protected], Apr 13, 2006.

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  1. Guest

    Hello all,
    Anyone know of some quad output headphone amp schematics. I've
    searched and found some great single output amplifiers. Which brings me
    to a question. If I build one of these, times four, and connect each
    amplifier to the same input, will it work properly?

    main page for headbanger headphone amp
    http://www.minidisc.org/headbanger.html

    schematic
    http://www.minidisc.org/schem.gif

    another hp amp
    http://headwize.com/projects/showfile.php?file=szeke1_prj.htm

    What I mean is if say I have all of the pots at half value, and then
    bring three (6 in stereo) of them down to zero, will it make the output
    of the remaining channel go through the roof? I know I should be more
    up on my basic electronics (sad because I'm an electronics mechanic,
    but thats the keyword, not a technician) Thanks a bunch!
    Jester
     
  2. No. They'll all be independent of each other.

    The load that this circuit presents to the source is 100k. That's very
    high. Four of them in parallel, 25k, still quite high. And the position of
    the pot does not change the load significantly; so the position of the pot
    will not change the output voltage from the source, which means that the
    other amps will not notice a difference.
     
  3. Ban

    Ban Guest

    Jester, I didn't look at your schematics, but if they are IC based there
    shouldn't be any problems.
    Normal headphones have an impedance between mostly 32 and 600 Ohms(those
    legacy HiFi ones) and require maybe maximal 100mW for a decent loudness.
    Some DJ headphones can go up to 400mW, but small earphones are blown with
    that level. When we calculate the required voltage Vrms= sqrt(P*R) = sqrt
    (32*0.1) =1.8Vrms for those newer ones and 7.5Vrms for the legacy ones. The
    DJ type would need 3.6Vrms.
    Now we can use a resistor of 120ohms with at least 1W rating in series with
    each output to drop the unrequired voltage and connect to a 10Vrms output
    amplifier(25W into 4ohms). Any old stereo amp will do.
    To adjust the level individually, we put a 1W-250 ohms linear
    potentiometer(best is wirewound or Cermet) in front of each headphone. Maybe
    a little box for each person with 2 mono pots (dual ones are hard to find,
    but try PartsExpress), so you can adjust the balance too. You can wire all
    boxes in parallel and connect as many as you need. They do not influence
    each other. To avoid damage to the amp in case someone shorts the incoming
    wires, put two 10R/10W resistors directly on the red speaker outputs and
    your outgoing wires. You only need one black gnd wire, since these are in
    parallel.

    see diagram with fixed font.


    AMP speaker
    red ___ terminals
    L o-|___|--o----o----. mini jack .---|
    10R/10W | L +red | .------| |
    | .-. ___ | .---| L |
    | 250R| |<--|___|----o----' | '---|
    blk | | | 100R .--o----. |
    o---------)+ '-' | o----)--+
    gnd || -blk | | |gnd | |
    |+---o----+----------)--+ | | .---|
    red ___ || gnd | | '--)---| |
    R o-|___|--))+--o----. | | '---| R |
    10R/10W |||R +red | | | '---|
    ||| .-. ___ | |
    ||| 250R| |<--|___|-' |
    ||| | | 100R |
    ||| '-' |
    ||| | |
    ||| '-------------'
    |||
    |||
    |||
    ||| next box
    |||
    ||'--------o R
    |'---------o gnd
    '----------o L
    (created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
     
  4. Guest

    Thank-you everyone!
    Jester
     
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