Dismiss Notice

Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Need help from Ohm/wiring expert for very small rig!!!!!

Discussion in 'Amps and Cabs [BG]' started by Gintaras, Dec 24, 2004.


  1. Gintaras

    Gintaras Supporting Member

    Dec 11, 2004
    Kent Island, Md.
    Some opinions for a small setup that I am working on. I have a Peavey microbass that I love and want to expand it just slightly. I have in my possession a 12” scorpion bass speaker and a new cabinet to put it in. I also read on a forum, that a microbass user replaced his speaker with a pyramid 8” woofer and got a great increase in sound quality. Now here is the issue. Plugging in the external speaker disables the built in speaker. Both speakers are 8 ohms. If I read correctly, (2) 8 ohm speakers can be wired for 4 ohms giving me a greater output from the amp. If theoretically I am correct then how do I set up the wiring that the external output does not disable the internal and also by using the external speaker, I get a total of 4 ohms. At the same time I believe that not using the external would revert me to the factory setup of 8 ohms. I hope that this is clear and any input would be appreciated from this midlife newbie.

    I presently have a Carvin L75M 5 string and also looking for an acoustic electric.
    :help:
     
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    the ist thing to find out is if the microbass can safley power a 4 ohm load. My guess is, since using the external jack disables the internal speaker, it can't. There are ways to have both speakers connected, but it's likley that using the resultant 4 ohm load would fry you amp.
     
  3. Gintaras

    Gintaras Supporting Member

    Dec 11, 2004
    Kent Island, Md.
    I just went back and did a RTFM. (read the ______ manual) It states that the minimum speaker impedance for the external is 4 Ohms. Does that make my project doable? :ninja:
     
  4. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    yes. as long as the internal speaker is an 8 ohm one. I'm not sure how accessible the guts of the microbass are, but disengaging the bypass function of the external speaker jack should be simple. However, I'd reccomend havign a competent tech do it for you. Or you can wait here to see if one of our resident amp techs knows more about that particular amp.
     
  5. Hollow Man

    Hollow Man Supporting Member

    Apr 28, 2003
    Springfield, VA
    First, find out what the impedance of the internal speaker is. If its 4 ohms, you're sunk. If it's 8, then bypassing the internal speaker cutoff should be as easy as clipping some wires and running a lead between them. Then, all you have to do is wire your two 8-ohm speakers in parallel to get the final 4-ohm output.
     
  6. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    I don't recall Peavey making a 12" Scorpion Bass speaker; I know they made a "Scorpion Plus" 12" guitar speaker; big magnet, designed to be like a loud Celestion. It probably will do just fine with the power your amp can make as they were 100w speakers I think, but you might want to research that with Peavey's Parts Department; there should be a model number on the frame.
     
  7. Gintaras

    Gintaras Supporting Member

    Dec 11, 2004
    Kent Island, Md.
  8. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    I think the microbass is going to have a lot of problems driving that speaker. 20W into a 200W low efficiency speaker is a clipping problem waiting to happen. I would leave the microbass as is for practice and get a better head to drive the speaker.
     
  9. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho