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wiring cab switchable between 2 and 8 ohms???? DPDT?

Discussion in 'Amps and Cabs [BG]' started by Chuck78, Feb 17, 2008.

  1. Chuck78


    Feb 16, 2008
    columbus, oh
    I started thinking that it would be fantastic for flexibility, if it were possible to somehow wire a DPDT switch into my Acoustic 408's speaker wiring so that with the flip of a switch (located on side of cab in center section, behind grille), to be able to select 2 ohm or 8 ohm operation... Any idea if this is do-able? Our crate guitar cab has a jack panel switch (has a small PCB on in place of wiring) which has options for 4 ohm 4X12, two separate 8 ohm 2X12's, or one 16 ohm 4x12. Wondered if it was possible to do the series/parallel switchover with a simple DPDT switch, and if anyone could enlighten me on how it would be wired?

    FYI, this cab is a monster 4x15", with two drivers in a center section of the cab that face opposing each other, up and down. See picture. I suppose both the top and bottom speaker pairs would both be wired in parallel at 4 ohms, and then the switch would have to be able to make each set either in parallel or series with each other. Is this possible with a DPDT?

    This way if I want to play my 408 by itself with my Acoustic 320 or 370, I can run it at 2 ohms (these awesome beasts can handle down to 1.6 ohm loads). Also if I got my Acoustic model 400 power amp repaired, I could run two cabs, one on each channel, at 2 ohms with my 360 preamp head.
    If I want to run my incredibly powerful Acoustic AC2200 750W@ 4 ohms min. amp with my 360 preamp and two cabs, it can't handle the 408 cab's 2 ohms. This would be very beneficial for the flexibility of my setup to be able to switch this to 8 ohms, so that I could run two cabinets through my most powerful 2 channel power amp. Then I'd be pumping at max 480 watts into the 408 @ 8 ohms, but ideally I won't have to crank the AC2200 past 4 or 6 volume-wise, so around 400 unclipped watts RMS. As you can see, this would be an ideal amp situation using the almighty Acoustic 360.
    Yes, I like the big vintage cabs and 15" speakers, for a monster vintage sound that moves a ton of air. Not so much into the modern, hi-tech stuff, although my Acoustic bi-amp-able BP-10 preamp and the AC2200 power amp will rival any modern amp in terms of flexibility of sound, and options...



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  2. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    interesting idea. make sure the switch can handle the wattage,voltage, current so you don't short out and start a fire or break something...
  3. Chuck78


    Feb 16, 2008
    columbus, oh
    I think I figured it out. Will a switch rated at 20A/120V do it? How many volts do most amps put out? I remember seeing somewhere something like 50 volts? Amp rating for a switch would be Watts power divided by volts, correct? I think, figuring in 800W for clipping peaks, that a 16A is the minimum switch rating I could use. Found a 20A toggle at Mouser that would do nicely.

    Got the wiring figured out, sketched it out which helped me a lot. Here is my lengthy post on the Acoustic forum about how to wire this:


    This setup could make any 2, 4, or 8 speaker cabinet that's 4 ohms or 16 ohms converted to be switchable 4 or 16 ohms.

    I need to have this able to be 2 ohms to take advantage of the monster power available from my Acoustic 320 and 370 heads and model 400 power amp, which can all be run down to 2 ohms.
  4. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    I think AC voltage and power calculations might be more complicated. talk to some of the do it yourself guys. search DIY .
  5. Espidog


    May 19, 2006
    The published rating of the toggle switch will be quoting for AC voltage, because the manufacturer will be assuming it's going to be used for AC mains. 20 Amps at 120 Volts = 2,400 Watts, so in theory its contacts are more than able to handle anything your amplifiers can chuck out. The weakest point in the chain will be where you solder the wiring onto the switch tags. Make sure those solder joints are good!

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