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Silly question of the day...

Discussion in 'Amps and Cabs [BG]' started by JACink, Oct 11, 2018 at 5:25 PM.


  1. JACink

    JACink

    Mar 9, 2011
    Spain
    Just a curiosity here...

    If you have a combo amp, with an extension output, this extension output is almost always wired in parallel to the speaker in the cab.

    If you then had an extension cab, which also has a "through" connection to daisy chain to another cab, this is also (almost) wired in parallel.

    Connecting the extension cab to the combo, whilst powering the cab from the combo, the extension cab also has an output that would connect another cab in parallel to the other two.

    If the amp in the combo was to die, would connecting another amplifier to the extension port of the extension cab basically run both cabs, or would having a dead amp (obviously unplugged from power) on the other end cause issues?
     
    saabfender likes this.
  2. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    The issue is that ganging multiple cabinets together would probably create such a low impedance condition that the amp would be hurt
     
    saabfender and five7 like this.
  3. mmbongo

    mmbongo Dilly Dilly! Supporting Member

    Aug 5, 2009
    Carolinas
    Yes you would most likely fry your new amp as well since you'd have another amplifier still connected in the chain.

    If you rewire the dead combo so the amp is no longer in the picture you could maybe do what you're saying.
     
  4. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    Never connect outputs from two amps together, regardless of status. If I understand your question, you'l have two dead amps ;)
     
    saabfender and JACink like this.
  5. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    My minimally informed guess is that I think it would depend on exactly how that dead amp was built and how it had failed. If there was a dead short across the output, for instance, it might make for a rather bad day.
     
  6. Even if not a “dead” short the output of the one amp, dead or alive, turned on or not is very low by design and would probably be enough to harm the other amp even without any speakers involved.
     
  7. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Ooops
    Missed the second amp issu
    You have the opportunity to possibly kill two amps; if the combo amp was disconnected, you would get to kill the working amp.
    If you gave us info on amps and the impedance of all cabinets involved we could better advise you.
    Ideally a sketch as to the hook up plan too.
    I have big money that says if you create less than a 4ohm load, and your amp isn't designed for that low of an impedance, you will let the magic smoke out
     
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Never connect one amp's output to another's, there is no way to know how the connected circuitry will interact but almost always one or both amps suffer catastrophic failure. If one amp's already failed, then obviously the other working amp would be the most likely amp to suffer.
     
    HolmeBass likes this.
  9. Everything you connect on any daisy chain is then connected to everything else, all in parallel. Don't do it.
     
  10. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Best that you don’t ask a general question. Be specific about the amp’s make and model.
     
  11. JACink

    JACink

    Mar 9, 2011
    Spain
    I asked it as a general question because I was curious. I have no plan on doing this, at all, ever. I learned the "do not connect amp output to amp output" a long time ago (when a friend invented his own way of bridging amps :facepalm:).

    I had just never thought about the result of having a dead amp on the other end or the circuit.

    Again, just a curiosity, not a real life situation.
     
    beans-on-toast likes this.
  12. JACink

    JACink

    Mar 9, 2011
    Spain
    Oh, and thank you all for the input!
     
  13. Jim Carr

    Jim Carr Dr. Jim Gold Supporting Member

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    I've always been disappointed in combo manufacturers for omitting any way of accessing the ampifier's output alone, and the speaker's input alone.

    I realize they assume the vast majority of users would just get themselves in trouble with such features, but Fender mainline guitar combo's have had this feature for at least 65 years, and nobody seems to have been harmed.

    Since I nearly always have a spare amp head at a gig, there have been two occasions where guitarist's amps died. One was a Fender 112 (Deluxe?) and the other a 212 Musicman. In each case, I swapped in my spare head by disconnecting the amp out->speaker jack and hooking in my spare amp.

    Tears of joy always ensued, as guitarists tend to equate amp death on a gig with something akin to erectile disfunction.
     
    Joedog likes this.
  14. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I’ve owned only one amp, a Univox, that had a wire running from the chassis to the speaker. All the others have had jacks.

    I prefer the jacks on the back of the chassis. Some combos have the jack on the bottom so you have to contort and look underneath to find it. Reverb pan connections are fine this way but I don’t care for speaker connections like this. They usually do this when there’s no room on the back of the chassis but not always.

    The same goes for IEC power connections. They should be on the back of the chassis. Having them on the bottom where they can fall out is an accident waiting to happen. Marshall has done this.
     
  15. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    I'd not assume that they're wired in parallel. Many combo amps with extension jacks are actually series...
     
  16. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    No questions are silly. If we all knew everything, we wouldn't need this forum, or anyone else's.
     
    Downunderwonder likes this.
  17. tjh

    tjh Supporting Member

    Mar 22, 2006
    Minnesota
    … no wonder my wife doesn't do the forum thing …

    ;)
     
    Joedog and JACink like this.
  18. yodedude2

    yodedude2 Supporting Member

    edit: oh hey, I just remembered. I have an old 70s guitar combo that was modified. it has some sort of 'disconnect' jack on the back. when you plug into this jack, it disconnects the combo's amp head from the speaker. i'm not quite sure how it works, but it does work. I've used it before. perhaps it was called an 'interrupt' switching jack?
     
    Last edited: Oct 12, 2018 at 3:00 PM

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