Adding extention cabinet to Ampeg BA115.

Discussion in 'Amps and Cabs [BG]' started by pricey, Jul 2, 2008.

  1. pricey


    Jun 6, 2008
    I have an Ampeg BA115 100W combo amp which is fitted with an internal 15" 150W 4 ohm speaker and a piezo tweeter. I am interested in adding a 4x10 extention cab to this amp in the future and have a few questions relating to this.

    1) The amp doesn't have an external speaker jack, to add one myself would it just be a simple matter of adding a TS jack in paralell to the wires already connecting the internal speaker? I want the cab to run simultaniously with the 15" internal speaker, not to cut it out.

    2) I understand that incorrect amount of ohms can damage the power amp, the internal speaker is 4 ohms so what impedence of cab would I need to buy to avoid damaging the power amp? What effect on the output power of the amp would this have, I assume that it will reduce my wattage, because it will be driving more speakers, but by how much? I am willing to sacrifice some power for a bit of articulation to my tone. Most gigs I play are with PA back up with the amp miced where possible so It only really gets used as a monitor anyway.

    3) In the future I'd hope to upgrade and get myself a proper Ampeg SVT head, so I want the cab I choose to be able to accomodate this upgrade and not limit me. Any advice?

    I know thats a lot to ask, I hope someone will be able to help out in some way!
  2. lug

    lug Supporting Member

    Feb 11, 2005
    League City, Tx
    4 ohm is probably the minimum impedance the amp can handle. You would have to bypass the internal speaker or wire the new output in series with the existing speaker. Neither way is really optimal.
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    Not possible with that amp. That's why it has no ext spkr output. Better off going with another amp altogether, even another combo with the required output. Most combos that DO have ext spkr outputs will actually go up in power output with an ext spkr.
  4. pricey


    Jun 6, 2008
    Ah, okay.
    Thanks for the help.

    The one 15" will do me for now, I guess it would just be nice having the clarity of the 10s, but I'll wait till I need a whole bigger amp.

    Thanks again!
  5. jamzcl


    Jul 21, 2004
    Des Moines, IA USA
  6. anderbass


    Dec 20, 2005
    Phoenix. Az.
    Actually... You could.

    If you were to simply cut your combos speaker wires and install male/female 1/4" jacks "in-line", similar to mine here:

    (female jack to amp / male 1/4" to speaker)

    And then connected the combo's new speaker plug and the plug running from your secondary 4 ohm cab together through a series adaptor Y-cable like this home made one:


    Your two 4 ohm cabs (connected in series) would then become a combined speaker load of 8 ohms...

    The series Y-cord is wired:

    The male 1/4" positive (tip), to the first female jacks positive.

    Then just loop the first females negative over to the second female jacks positive post.

    The second female jacks negative then connects to the male 1/4" ground. (sleeve)

    Just make sure you use quality speaker grade plugs/jacks and also that you keep your combos positive and negative speaker wires connected the same way (proper-phase) through the new plugs.
  7. loncoaudio


    Oct 2, 2012
    so if u do this to the combo can u still use it the same as if there was no extension cab? i want to do this to my tc electronics combo so i can use my 8 ohm extension cab... this would be awesome! thanks so much
  8. loncoaudio


    Oct 2, 2012
    also my combo is 4 ohms tc electronics bg250 it has a 4 ohm speaker and horn already running the amp down to its max 4 ohm load... i want to add my 8 ohm extension cab... any thoughts without changing the internal speaker to 8 ohms... i dont want to do that..and i know parallel would run me down to 2.6 ohms i think which is too much... if i series that will put me at 12 ohms and cut my power down quite a bit right??
  9. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    Yeah, series-wiring just gets you twice the speakers getting half the power, so not much point there.