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Poweramp question

Discussion in 'Amps and Cabs [BG]' started by Sahe_Bassist, Mar 31, 2013.

  1. hello all, been looking into poweramps lately and i had a question.

    most power amps seem to have two channels. when connecting two cabinets, would you use both channels or just one?

    IE- a carvin model poweramp

    1 CHANNEL RMS continuous
    - 8 ohms: 200 watts
    - 4 ohms: 350 watts
    - 2 ohms: 600 watts
    BOTH CH RMS continuous
    - 8 ohms: 160/160 watts
    - 4 ohms: 280/280 watts
    - 2 ohms: 500/500 watts
    BRIDGED RMS continuous
    - 8 ohms bridged: 560 watts
    - 4 ohms bridged: 1000 watts

    if i wanted to run 2 8ohm 400watt cabs - would i run both off of the 1 channel at 4ohm load for a 350w into both cabs OR would i run one cab per channel in 8ohm loads for 160w into each cab OR would it be (basically) the same thing?

    OR i could bridge them and run the two cabs for a 4ohm load for 1000w?

  2. mystic38


    Dec 4, 2012
    Mystic CT
    you have..

    2 cabs of 8 Ohms and 400W each... connected together that is 4 ohms 800W

    So if you use one channel per cab your max power is only 320W so if you want the volume, then bridge the amp and connect both cabs...then you can use the full potential of the cabs.. sick loud..lol
  3. Oobly


    Jun 19, 2008
    You CAN connect them in all the configurations you listed, but the one that moakes the most sense is running the amp bridged with both cabs connected (4 ohm). Lots of headroom and it will go very loud. For smaller gigs, keep it bridged and use just one cab. If you need even less volume (if it's just too loud even with the attenuator really low, for bedroom practice, etc) you can run one cab off one channel.
  4. Right. To run both channels off a single input you set the "parallel" switch in the back, and the amp can make 160W into 8 ohms per side, for a total of 320W; or you can run the two on a single channel for 350W into 4 ohms. The 30W difference is negligible. So those two options are basically the same thing. If you want people two counties away to file noise complaints, that's when you bridge the amp.

    I don't think there are many realistic instrumental uses for the parallel mode in this amp. It can handle 2 ohms, so even if you had two 4-ohm cabinets you could run them on one channel. Maybe I'm overlooking something, but it seems like it's mostly for PA-type applications.

  5. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    And yet that's exactly how I run ALL of my amplifiers. One 4Ω cabinet, and sometimes two, on each channel with the amps run in parallel.

    When you bridge an amp, it's more about getting enough voltage swing into a higher impedance than squeezing every last drop of power the amp is capable of giving. I've been using stereo amps since the late Seventies. I have never felt the need to run any of them bridged.
  6. Why that way, rather than two cabinets on one channel? I understand if you're driving more than two cabinets, or if the power amp can't handle 2 ohms, but is there a reason to prefer separate channels in a case where the amp can handle them on a single channel?

  7. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I have two channels and two cabinets. Running in parallel, my amps are in no way stressed and I'm more than loud enough. My cabinets are rated at 350W each. One per channel they get up to 325W each. I don't need any more than that. If you need to get louder then adding cabinets is the way to go every time.
  8. It's not like this is the most important question in the world, but I think I didn't manage to ask my question right.

    Suppose you were using the Carvin PA described above with those cabs. It seems to me like you have two options:
    (1) one cabinet per side: 280W into 4 ohms, twice over for a total of 560W deliverable to the two cabs.
    (2) two cabinets on one channel: 600W into 2 ohms, split between the cabs.
    As far as I can tell nothing is stressed in either scenario, and essentially the same amount of power is being fed to the same complement of cabs, resulting in the same volume; the only difference is the impedance seen by the PA.

    Looking at those I kind of see a tossup, or strictly speaking a negligible disadvantage for case 1 (very slightly less power available). But you prefer case 1 and I'm not sure why---is it a function of the higher impedance?


  9. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    2Ω operation and 4Ω bridging both push the amplifier harder, creating heat, and also drawing more power out of the wall. good amps can take that with no problem, but it is more stress on them.

    with 2 4Ω cabs, bassmanpaul's setup gets him plenty of power without extra stress on the amp.

    for me it's using an amp big enough to run my two 8Ω cabs off one side and have that be plenty of volume. (my 750/side@4Ω crest is enough here.)

    that leaves me another amp channel to use for other stuff, like monitors.
  10. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    In scenario #1 twice as many output devices share the load, and at half as much current load per power device to boot. There is often twice as much heat sink area at work on top of that. ;)
  11. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    I'd bridge it for 1,000 watts into the two cabs.
  12. Oobly


    Jun 19, 2008
    With the quoted amp and cabs, if you don't bridge the amp you're only pushing 160 or 175W into each 400W cab. That may be fine if you don't need much volume (in which case you may as well just use one cab), but if you want to use the cabs effectively you need to bridge it to push more power into them.

    You'll probably put more strain on the amp if run a single channel, since you'll need to really crank it to get good volume = worst option. Running both channels separately, or running bridged you'll be pushing the amp the same at the same volume level, but you can go louder with bridged (which will push the amp harder, but it is within spec and can handle it).

    Anyway, that's my take on it, I CAN go into the physics if you want.
  13. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I have no interest in getting every last watt of power out of my amplifiers. If the system gets loud enough for everything i need to do that's all I ask. Both Walter and Charlie have ably answered the reasons behind what I do so I'll leave that.

    My main amp in question here is a DCM1000L. It gives me what I specified in my post. It's all I need.

    Although I hate to disagree with Munji, hyper elite as he is :) , I have never felt the need to bridge any of the stereo amps I've used since the late Seventies. Yes I could use one channel for my bass and the other for some other purpose but why? Those are covered by their own systems. In an emergency I will alter my configuration and have done so on occasion.

    Running my equipment conservatively has meant very little trouble occurs at the gig and that's just how I like it. :D
  14. Thanks. I'm an ol' software guy for whom hardware is magic, so I appreciate the education. If I ever need enough power to make my rig (same model as it happens) break a sweat, I'll bear it in mind.

  15. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    You have to remember that the majority of cabinet power ratings are thermal. That's about where they start to melt. A typical driver runs out of excursion at about half that level. So your 400W cabinet will probably only be able to actually use what the parallel configuration is able to give. In such a case the increased power from the bridge connection may well lead to damaged drivers. Once the excursion limit is reached, the cabinet will get no louder no matter how much you increase the power you give it.
  16. if you have 4 ohm cabs run one on each side, if you have 8 ohm cabs run them bridged

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