Head/cab ?s, Techies Please Respond!!

Discussion in 'Amps and Cabs [BG]' started by MarkMcCombs, Jan 9, 2001.

  1. I have a 4-ohm cabinet with 2 input jacks, 1/4", it's a Bag End 2x10. Can I run 2 amps into this? If so, what impedance do the amps (individually) need to be at?


  2. No. Don't do it. You'll fry one or both of the amps.
  3. pkr2


    Apr 28, 2000
    coastal N.C.
    I know that I wouldn't try it. My guess is that you will destroy something. It seems that you would ,in effect, be feeding the output of one amp into the output of the other amp. Never tried that. Don't have that much curiosity. :)

    I can't help but wonder why you would want to do this. What are you trying to accomplish?

  4. Pkr,

    Here's the set-up.... the cab handles 400w program. I have a 100w tube head, and I understand tube amps need to have a load on them. Would like more power, so I'd like to run the line-out of that into another power amp, and send both to the only cab I have. I guess I'm unclear as to what "parallel inputs" means. If it's not possible (and that's why I'm askin' first!), then I guess I need 2 cabs, right? Certainly, I will contact the manufacturer of the cab before I do anything.

    See, THIS is the reason I'm a musician and not an amp tech. Maybe more of us should just stick with combo amps.

    Thanks for your advice....

  5. MikeyD


    Sep 9, 2000
    I'm not familiar with that particular cabinet, but usually when a cabinet has two jacks ("in parallel"), it is meant for connecting a second, extension cabinet: you would feed the output of your amp into one jack of that cabinet, then connect a second speaker to the other jack. In effect, the two cabinets would be wired in parallel. They are NOT meant to have you feed two separate amplifiers into the speaker (unless specifically stated on the jack panel). An exception would be a "stereo" or "bi-amp" cabinet, such as the SWR Megoliath, wherein half the cabinet's speakers may be powered by one amp and the other half by another amp.

    One option you could consider, depending on your situation, is to rewire the jacks so that each jack feeds only one of the 10" speakers. Do label your jack panel, though, and make sure the polarity is correct to avoid cancellation. If you did so, then you could get a second amp and feed each driver with a separate amp.

    If you instead go buy a second 4-ohm cabinet to connect in parallel, you need to first ensure that your amp is capable of driving a 2-ohm load.

    - Mike
  6. pkr2


    Apr 28, 2000
    coastal N.C.
    Mark, I'll try to explain the difference between parallel and series. All electrical loads such as speakers and bulbs have two terminals. One terminal is the input to the load. Lets call that terminal + or positive. The other terminal is the ground side of the load. We will call that one the - or negative terminal.

    Lets start with two loads (spkrs, bulbs or whatever).

    First, a series circuit. A series circuit will feed the voltage(or current) into the + terminal of the first device,thru the device and out the negative terminal to the 2nd devices positive terminal. The negative terminal of the second device is the return to ground or common of the source of current. The characteristics of a series circuit are:

    #1 All of the current will pass through each device.Xmas tree lights are generally series connected. If one bulb burns out, they all quit burning.

    #2 The total resistance or impedence of the circuit will be higher than the resistance of the highest resistance in the circuit. two eight ohm resistors will = 16 ohms.

    A paralell cicuit will have the positve terminals of the loads connectd together and go to the output of the source. The negative terminals of the loads will be connected together and will connect to ground or common of the source. If the loads are equal in resistance the current will divide equally between the two loads.

    The characteristics of a paralel circuit are:

    #1 The current will divide and each load will carry 1/2 of the total current in the circuit if the resistances are equal. The lights in your home are wired in paralel. If one bulb burns out the rest of the bulbs in the circuit will continue to burn.

    #2 The total resistance of a paralel circuit will be less than the resistance of either load. Two 8 ohm resistors in paralel = 4 ohms.

    Ohms law states that I=E/R. I= current, E= voltage and R= resistance.

    Electronics is a fascinating subject. There are a number of sites on the web that offer basic electricity tutorials that explain things much clearly than I can.

    If anyone sees any errors in my explanation, please feel free to correct me.


  7. Thanks, pkr,

    (you're gonna be so proud of me)....

    So, my 4-ohm cabinet with 2 drivers, the drivers are probably 8-ohms each, huh?!

    I'm sending away for my kit on how to earn your electronics degree at home and make millions! Screw music.

  8. pkr2


    Apr 28, 2000
    coastal N.C.

    :) :) :)Right on, mark. Yes they are 8 ohm spkrs wired in paralell.

    I am proud of you! I just reread my post and if you understood what I said, please explain it to me.:)

    Good idea on the degree but don't give up music to get it.:)
  9. My 4 ohm cabinet is split into two 8 ohm sections to run sterio but there is not much change in loudness, 100 watts into an effecient speaker is more than enough loudness to permanatly damage your hearing. Getting through the mix with a tube amp shouldnt be that difficult with good EQ settings.