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G-K MB150 and a 4ohm cab?

Discussion in 'Amps, Mics & Pickups [DB]' started by tony-moore, Apr 1, 2005.


  1. I use a little G-K MB150 cab as a stage monitor for myself when needed. But I need a little more power for a small club gig. I have access to a 4ohm cab. I've always thought I could only use an 8ohm cab with the G-K, but thought I'd ask with hopes of getting lucky :)

    Thanks,

    Tony

    PS - I'm not looking to get into a "tone" debate. I completely understand and agree about the little G-K's limitations. I'm looking to upgrade but want to see what options I have with the gear I already have :)
     
  2. You could use the 4-Ohm cab by itself (with the GK-150 internal speaker switched off). The GK-150 will put about 150-Watts into a 4-Ohm load (normally 2 x 8-Ohm speakers in parallel).

    - Wil
     
  3. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    Tony,

    If you connect the MB150 to a load less than 4 ohms, it will run very hot, which is not a good thing. 4 ohms is pretty much an absolute minimum load with that amp. If you connect the external 4 ohm cab with the internal speaker switched off, as Wil suggested, you should be OK. If your GK gets a lot warmer than usual, however, take heed, since it's telling you something.

    -bob
     
  4. Aleph5

    Aleph5

    Feb 24, 2004
    Tennessee
    I have done that with my GK by putting a 4 ohm dummy load wired in series w/ the 4 ohm speaker. I used this.

    However, remember this needs to be wired IN SERIES, so needs to be built into a special cable; you can't just put this across the terminals or you'll be going in the wrong direction. And it will eat up a little of the power, but you won't notice that. It will give you a total nominal Z of 4 ohms w/ both speakers, however.

    I would echo, too, that the little GK shouldn't be overstressed. They're not the most bullet-proof amps in the world.
     
  5. Thanks guys! It's exactly as I thought :-(

    Tony
     
  6. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Wiring a resistor in series with a speaker will change the tone characteristic. This is like using a power amplifier with a damping factor of 2.
     
  7. gkintn

    gkintn

    Mar 6, 2005
    I know this won't give you more power. However I added a Peerless dome tweeter to my MB150 and it totally opened up the amps tone and made a big difference in definition. It makes the amp much more clear sounding, which might make it easier to hear as a monitor even without doing anything to address the low end or power.

    The stock 12" is very muddy sounding, and to me sounds like it probably rolls off at 3 or 4k. You might check my other post as the mod only cost about $50 to do, and it's all internal to the existing box.

    http://www.talkbass.com/forum/showthread.php?t=171253&highlight=peerless+tweeter
     
  8. Aleph5

    Aleph5

    Feb 24, 2004
    Tennessee
    Wiring a resistor in series with a speaker will change the tone characteristic.

    Sorry, maybe I wasn't clear. The 4 ohm res goes in series w/ the 4 ohm speaker, and this combination (now 8 ohms) will be in parallel w/ the 8 ohm internal speaker to make a total of 4 ohms seen by the amp. No, a 4 ohm resistor is not the same as another 4 ohm speaker sharing the load, but it will keep the impedance in the proper range and work just fine. Just a hassle to wire in and mount the resistor somewhere.

    Re the added tweeter, this sounds interesting but not enough for me to want to do it to mine. I just don't hear anything wrong with my highs. Not to be closed minded or anything, but it doesn't seem in the category of a quick easy mod that I can try first.
     
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    aleph5, all I am saying is that a speaker driven through a 4-ohm resistor will have a different tone characteristic than the same speaker driven directly by the amplifier.
     
  10. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    If you run a 200 watt amp through a 4 ohm speaker and a 4 ohm resistor in series, you'd better make that resistor a 150-200 watt non-inductive type and supply some cooling air to be safe... might be simpler and cheaper to just add another speaker ;-)
     
  11. Aleph5

    Aleph5

    Feb 24, 2004
    Tennessee
    The resistor I used (see Parts Express link above) was all of those things. Yet it never got warm. Average power tends to be very low (high crest factor). I have switched to an 8 ohm auxiliary speaker for different reasons, however, so I haven't been using that setup of late.