Ohm question help ppppplllleeeease!!!!

Discussion in 'Archived Threads 2001-2004' started by Zak Solo, Mar 14, 2002.

  1. Zak Solo

    Zak Solo Agent

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    This is probably the crassest question anyone is going to ask.

    I have a Sony STR DB940 (which I love) and B&W 603 s2's and the CC6 centre. My rears are Celestion. All are 8 ohm rated.

    Now I was just dusting and making sure all my connections were okay on the receiver and saw the 4ohm/8 ohm switch. It was on 4 ohm's. (I hadn't thought anything about ohm's until I saw the selctor switch).

    The question is do I want the switch to be on 4 ohms or 8 ohms. I don't know anything about impedence is 4 hi or low? Does one give more power than the others?

    Thanks
     
  2. jeff cr

    jeff cr Agent

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    if all your speakers are 8 ohms than you will want to have the switch set to 8 ohms to match. a lower impedence will draw more power from the amplifier.
     
  3. Cees Alons

    Cees Alons Moderator
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    Cees Alons
    In fact, setting it to 4 Ohms will make it draw less power. The amp will "think" that 4 Ohms speakers are connected, so it will assume less voltage is needed to produce a certain amount of power - but in fact the speakers are 8 Ohms.

    Setting your amps to 8 Ohms will correct that, but don't expect amazing results. The differences are hardly audible.

    You may wonder if this setting was bad. No, it wasn't. You just didn't get "everything" out of your system. The other way around would have been worse (4 Ohms speakers, amps set to 8 Ohms), but even then, nothing dramatic.

    Be sure to listen carefully to your set up after the switch: you can now steer it further to its limitations, so you may want to put the overall volume just a tad lower.

    Good luck!

    Cees
     
  4. Kerry Hackney

    Kerry Hackney Stunt Coordinator

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    Cees >>> I am curious as to exactly "what" these switches do. I had read that they change the sensitivity of the thermal overload circuit and that was all. Do they somehow alter the power stage of the amp ????
     
  5. Zak Solo

    Zak Solo Agent

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    Thanks for the info, much appreciated
     
  6. Cees Alons

    Cees Alons Moderator
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    Kerry,

    Ideally, yes.

    In the old days, when we had vacuum-tube amps and end-trafo's, it was rather straight-forward: they would switch between different positions on the secondary (output-) coils (or even between different coils). So then they genuinely changed the output impedance and current-times-voltage characteritics.

    In integrated circuits, it's more tricky. Some amps don't do anything at all, leaving it to the feedback circuit to deal with the different loads (and simply generating more watts into lower impedances). When there is a switch, it depends on the quality of the design. Some seem to simply change a series resistance, some really change feedback characteristics (and thus the output impedance).

    There even is a commercial power amp on the market now, featuring an "output impedance sensing circuit". I don't know what it does exactly, and if we would wish for it.

    Cees
     

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