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Mesa M9/M6 - 2 ohm / 4 ohm switch

Discussion in 'Amps and Cabs [BG]' started by babebambi, Apr 14, 2010.

  1. babebambi


    Jan 7, 2008
    What does the switch actually do?

    The Mesa literature says that it reduce the current at 2 ohm to protect the amp from over-heating, while still generating full power of 900 watt.

    But how is that accomplished? Does anybody know? I supposed it's totally different from (tube) amps with an output transformer and different tap, right?

    Would I get reduced power when switch to 2 ohm, but run a 4 ohm load?

    I tried running the M9 with a 4 ohm load, in both 2 ohm and 4 ohm switch position, but it does not seems to affect the volume level at all. Any ill effect if I just leave the switch in 2 ohm position all the time

    I wonder why there isn't more amps operating the same way to provide 2 ohm capability.
  2. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    It IS a tap. If you're running it with a 4 ohm load, no need to have it set to 2 ohms.
  3. babebambi


    Jan 7, 2008
    So how do they tap it with out an output transformer? The Carbine don't have OT, right?
  4. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    I believe they use a tapped toroidal transformer in the power section, not the output section.
  5. A SS power amp will try to output double the wattage into half the load. IE If the amp puts out 200W into 4Ω it will try to give 400W into 2. If the output stage and power supply can handle this all is good. If not the output stage will fail. To get around this some amps have a minimum of 4Ω. A 2Ω load would blow them. However if you reduce the voltage feeding the output stage you reduce the power dissipated by the transistors and 2Ω operation becomes safe. You will, however, no longer be able to get 200W into a 4Ω load. When it comes to "loudness" you need ten times the power to get twice the volume. The difference between the outputs with the switch in either setting will not be that significant.

    Hope that helps...
  6. KramerBassFan


    Jan 3, 2009
    Transistors can supply the impedance down to a certain level, no "tap switch" needed.

    Just plug in 2 ohms worth of a speaker load - and the amp will supply the speakers with however many "watts" the amp puts out at 2 ohms.

    Transistor amps do not have "taps" such as a tube amp with a output transformer does. HOWEVER some older transistor amps - DO have Output transformers.

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