Turning a combo amp into an extension cabinet

Discussion in 'Amps and Cabs [BG]' started by ErikW, Feb 18, 2010.


  1. I would like to use my 15" combo practice amp as an extension cabinet at larger gigs. I am thinking I could put some kind of switch between the amp and speaker and route the speaker to a speakon jack. Any ideas on what kind of switch and how to wire it?
     
  2. Sneakypete

    Sneakypete

    Jul 22, 2009
    How is the combo speaker connected? If it is wired with a standard speaker jack plug that goes into the back of the combo amp I would just make up a special speaker cable for it - a standard male plug on one end to go into your main amp and a cable-mounted, female jack socket on the other end that the combo speaker plug goes into. The cable-mounted socket is easily available here in the UK so i should think somewhere like Radioshack should have them.
     
  3. I believe it is hard wired into the amp. No external cable. I'll have to remove the amp head to gain access to it.
     
  4. LarryO

    LarryO

    Apr 4, 2004
    you can do it by cutting the wires that connect the power amp to the speaker and soldering 1/4" jacks......But, if you are using the combo as an extension, that means you have another amp and cab sooooooooooooowhy not leave it as is and just buy an aby pedal or stereo out pedal and run both the combo and your other rig stereo?
     
  5. sleepytime

    sleepytime

    Nov 10, 2007
    Chicago, IL
    You forgot something. When asking for help, information is really cool. :cool:
     
  6. My mistake, however, don't think it makes much difference. Behringer BXL3000.

    Trying to keep it simple and just throw a switch and plug in a speakon cable from my big amp.
     
  7. MrRumble

    MrRumble

    Aug 8, 2006
    Plymouth, MN
    If your master amp has a headphone out you can run that to the input of the Behringer as a slave amp. Or vice versa.
     
  8. Mikhail1

    Mikhail1

    Apr 8, 2008
    Daisy Chaining?
     
  9. Pilgrim

    Pilgrim Supporting Member

    You can insert a 1/4" plug and jack into the existing wiring between head and cab, but if you do, make sure to phase the jack (female part) the same as the other cab. You don't want the cabs out of phase with each other.

    Then turn off the cab head, unplug, plug in cable and run it to the other amp's output jack. Make SURE that the other amp will tolerate the total impedence achieved by adding the second cab.
     
  10. Thanks Pilgrim. I was thinking I could do that but not sure about back feeding the signal into the combo's amp. I'll probably bi-amp the two cabs. Might try your suggestion. Either that or LarryO's suggestion of just breaking the connection between the amp and speaker and running them to separate jacks.
     
  11. bobcruz

    bobcruz

    Mar 10, 2004
    CA
    It's critical that you totally isolate the combo's amp from the speaker when applying power to the speaker from an outside source, otherwise the combo's amp will fry. A switch like you first proposed would do that but you'd run the risk of mistakenly leaving it in the wrong position, or it could get bumped, or even short itself out while in use, then goodbye combo's amp. The most foolproof way would be to wire the combo's speaker to a jack and connect the combo amp to the speaker through the jack, so it would have to be unplugged in order to plug in the outside power source. (Some combos already have this or something similar--not sure about yours.) But the easiest way, as already suggested, is to run the combo with a Y cable, or use a signal from the other source (headphone output to combo input, or preamp out or effects out to combo's effects return, if any).
     
  12. Quote from bobcruz
    "The most foolproof way would be to wire the combo's speaker to a jack and connect the combo amp to the speaker through the jack, so it would have to be unplugged in order to plug in the outside power source. "

    Yup. That's what I decided to do. Already ordered my speakon connectors and cables. Thanks for your help everyone.
     
  13. ::::BASSIST::::

    ::::BASSIST:::: Progress Not Perfection.

    Sep 2, 2004
    Vancouver, BC Canada
    Hmmm.... interesting idea.

    I could get a small combo like a markbass cmd121p and put it right infront of me with a wedge and using a Y cable (etc), use it as a monitor AND have my main rig behind me... That way I'd always be able to hear myself and I would not mess with how the audience hears my rig.

    Now you got me thinking...
     
  14. I have a Trace Elliot GPS7SM combo amp and the speaker enclosure is entirely separate from the head. A short speaker cable with a 1/4" male jack comes out of the top of the speaker cabinet and is long enough to plug in to the back of the head. I often use just the amp's 15" speaker and combine it with a solid state SVT head. I use a double-female connector (it lets you connect one 1/4" male plug to another 1/4" male plug) and use a standard speakers cable to go from the cabinet to the SVT head.

    I'm with Sneaky Pete here --- if you can't do it yourself, have a qualified technician run a speaker cable with a 1/4" male plug out of the back of the speaker cabinet, and install a 1/4" jack in the back of the amp. It shouldn't cost very much and will get you exactly what you want, plus give you a lot of flexibility in how you use the amp.
     
  15. meshica7

    meshica7

    Mar 7, 2009
    Florida
    Cool thread! I have a Carvin MB12 Micro Bass Amp..it's a 3 way (12",6.5" mid-range, & tweeter) but it died on me a couple of years ago. Carvin no longer sells parts for it or provides any support. I took it to a tech here in Orlando and before he was able to repair it (said the power-amp was fried) he closed up shop..retired. I haven't tried to find another repair guy..so I was thinking about turning it into a stand-alone cab. Looks like from what I am reading on this thread that it will be possible?
     
  16. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    Yeah, a combo is just a speaker cabinet with some electrics stuffed in the top, so you can always pull out the electrics and just use it as a cabinet.

    There are some gotchas though, especially with bass rigs. The main one is physical volume. If the amp was in a completely different compartment to the speakers you can ignore this. Otherwise the air the amp was occupying still needs to be occupied.

    In your case though there's another and potentially bigger one. That rig must have a crossover to split the sound between the three speakers. No crossover = no tweeter in seconds and no mid driver soon after. The crossover might have been on an external separate circuit board, but almost certainly it was built into the main amp board, and the likes of you and I wouldn't be able to separate it out. So either you disconnect the mid and tweeter and just run the woofer, which will probably be unsatisfactory, or else you source a suitable crossover with all the right properties, which will be tricky.

    Bottom line, sadly this unit probably won't make a good external speaker without significant work and expertise.
     
    meshica7 likes this.
  17. meshica7

    meshica7

    Mar 7, 2009
    Florida
    Yeah, I figured. The first thing I thought about was the crossover. I got one more tech to check with in regards to getting it rapaired. We'll see what happens. Thanx for your input!
     
  18. Primary

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    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Oct 20, 2021

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