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another silly ohms question...

Discussion in 'Amps and Cabs [BG]' started by ::::BASSIST::::, Jun 3, 2005.


  1. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    I am about to get a 4ohm schroeder mini 12+ (yay!) I am also about to acquire a Stewart World 1.2.

    Since i will be running one 4ohm speaker would i plug into the stereo configuration for 350watts (but as its only one speaker would it be stereo?). I also want to clarify that i can run two 4ohm cabs and i will get 700w stereo. I really dont see how i would need more than that. I guess i shouldnt run it bridged at all since thats 1200w into one 500w driver. Or maybe that would sound really good with all that power if i am careful not to turn it up too loud. Sorry if this doesnt makes sense. Its passed my bed time.

    Specifications

    FTC Power Rating
    <0.1% THD
    20Hz-20kHz
    both channels driven


    200W x 2 @ 8 Ohms




    350W x 2 @ 4 Ohms

    FTC Power Rating
    bridged mono


    700W x 1 @ 8 Ohms




    1200W x 1 @ 4 Ohms
     
  2. rabass6

    rabass6 Commercial User

    Jun 3, 2004
    Italy
    Owner, Groovemania.it
    I think that if you'll be careful with your volume level, you can use the Stewart bridged mono ino the Mini 12 without fear of burning something.
    Or, you can use one side of the power amp with the Mini, and you'll have access to 350W, and yes, you can use both sides to power 2 cabs, supposing they're both 4ohm you can use 350+350W.
    If the power amp has separate volumes for either channel, you should lower at minimum the unused one, to prevent damage, even if Solid state amps are much less susceptibles from no load issues, I think...
    I'm sure you'll love the Mini 12, if it has the same kind of performance the 1210 has, you'll be amazed!!!
     
  3. +1 on the bridged amp. You will only be using that 1200 watts if you are peaking out everything. Bad. And extremely loud. The extra power is known as headroom, and for transients it makes a true difference. It's like the difference between an 9v and 18v on board preamp in a bass.

    Go for the bridged operation.
     
  4. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    thanks for your replies.

    is it safe to run 2 4ohm speakers in bridged mode?

    this would be running the amp at 2ohms. I would rarely do this but i wonder if i should even attempt it.
     
  5. rabass6

    rabass6 Commercial User

    Jun 3, 2004
    Italy
    Owner, Groovemania.it
    If you like to play with smoke and fire surrounding you, that could work (for some second...)
    Otherwise, if you want to use a second 4 ohm cab, use them in parallel mono, or stereo.
    What you'll loose in pure power, you'll gain in dispersion due to the greater surface moving the air.
     
  6. Don't do it. If they showed someone doing that on TV, it would require a disclaimer at the bottom of the screen.

    Do not attempt. Professional fireman. Closed course.

    Randy
     
  7. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    yeah, okay.. the 2ohms thing wont be done.

    if i got another less efficient cab (perhaps the ampeg pb 1-12 93db) and plugged into one of stereo channels and the sch mini 100db in the other stereo channel would be the result? i know that one would be louder than the other but as there running from seperate channels i should still get decent volume from the ampeg pb 1-12 right?
     
  8. rabass6

    rabass6 Commercial User

    Jun 3, 2004
    Italy
    Owner, Groovemania.it
    That only depends by your definition of "decent volume"...
    I'm using my Schroeder 1210 with an Acoustic Image Focus, 600W@ 4 ohm, and the volume I can use is much more than the one I actually need, but one of my students choose the 1212 for the fact that Jorg said that it has a little more output, and he's very satisfied now.
    But, even given the low efficiency of the Ampeg cab, if the pow.amp can put out lots of clear, undistorted output, this setup, paried ith the Mini 12, should be more than necessary, if you don't play really loud
     
  9. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    well looks like the sale for the 1.2 fell through. now i am considering a stewart professional reference 1000

    The ohms specs look different, but are similar:

    PR Series Printable Spec Sheet

    Specifications
    FTC Power Rating
    <0.1% THD
    20Hz-20kHz
    both channels driven 200W x 2 @ 8 Ohms
    350W x 2 @ 4 Ohms
    FTC Power Rating
    bridged mono 400W x 1 @ 16 Ohms
    725W x 1 @ 8 Ohms
    Frequency Response
    +0, -.5dB, 1W 20Hz - 20kHz
    Full Power Bandwidth
    +0, -3dB 15Hz - 45kHz
    THD+N >108dB
    Damping Factor >500
    Slew Rate 30V/microsecond
    Input Sensitivity 1V (0dbV)
    Standard Voltage Gain 40X (32dB)
    Input Impedence
    balanced/unbalanced 20k Ohms/10k Ohms
    Class A B

    Stewart World 1.2 Printable Spec Sheet

    Specifications
    FTC Power Rating
    <0.1% THD
    20Hz-20kHz
    both channels driven 200W x 2 @ 8 Ohms
    350W x 2 @ 4 Ohms
    FTC Power Rating
    bridged mono 700W x 1 @ 8 Ohms
    1200W x 1 @ 4 Ohms
    Frequency Response
    +0dB, -.5dB, 1W 20Hz - 20kHz
    Full Power Bandwidth
    +0, -3dB 15Hz - 45kHz
    THD+N >100dB
    Damping Factor >500
    Slew Rate 30V/microsecond
    Input Sensitivity 1V (0dbV)
    Standard Voltage Gain 40X (32dB)
    Input Impedence
    balanced/unbalanced 20k Ohms/10k Ohms
    Class H

    ************
    can someone please breakdown the difference in lamens terms for me?

    Much appreciated :)
     
  10. rabass6

    rabass6 Commercial User

    Jun 3, 2004
    Italy
    Owner, Groovemania.it
    The most obvious difference is that with the Reference 1000 you cannot use it in bridge mono with a 4 ohmm cab.
    This means you can only use it in stereo, with 350W per side.
    350W will be all you can use with a single 4ohm cab.
    Why don't you think about an 8 ohmm Mini 12?
    This way you can use more than 700W in bridge mono, a good option...
     
  11. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    The seller says that Kevin Stone at stewart world emailed him and says that it can run 4ohms bridged. So I guess it can then? why wouldnt they just publish this in the specs then? wouldnt it be to their advantage to do that? sounds kind of wierd.
     
  12. rabass6

    rabass6 Commercial User

    Jun 3, 2004
    Italy
    Owner, Groovemania.it
    Maybe it can do the 4 ohm bridge, but could be not really reliable in this case, with the risk of a protection circuit to shut down the amp during a fast transient like a G string pop.
    Or, they discovered it's stable at 4 ohm after yhey publicized the specs, and they didn't updated them.
    Well, the Reference 1000 is an AB class.
    This means it's not very efficient, and some of the current you put into it doesn't go as sound, but as hot to be removed.
    Hot is usually what destroy power amps.
    The Word 1.2 is instead an H class, a better efficient one.
    So, it can run much cooler even when drived hard at 4 ohm bridged mode, as opposite to the 1000, that could easily run hotter than safely allowed, thus the 8ohm rating in bridge.
    But, under some circumstance, and if not really pushed, it could do the 4 ohm thing, I suppose.
     
  13. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    Thanks so much for your assistance Rabass.

    If i used a small portable fan to blow across the PR 1000 would that keep it significantly cooler or am I just delaying the inevitable shutdown while in 4ohm bridged mode?
     
  14. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    both channels fully driven

    350w x2 @4ohms

    This is in respect to the PR 1000... does this mean i can use one 4 ohm cab per channel and get 350w out of each cab?
     
  15. Yup. And the fan thing isn't a bad idea, figure out which way the internal fan blows air and use the other fan to help it out. Running bridged at 4 ohms runs each channel at 2 ohms, so extra cooling will definitely help keep you out of the thermal protection circuits' area of expertise.

    Randy
     
  16. rabass6

    rabass6 Commercial User

    Jun 3, 2004
    Italy
    Owner, Groovemania.it
    Yes, sure, and you could also try with the fan, but I don't recommend it.
    I think 350W per channel should be sufficient
     
  17. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    the stew can do 4 ohms bridged. but if as you said you were to use TWO 4 ohm cabs and bridge it into this it would be bridged into a 2 ohm load, and each side of the amp would "see" a 1 ohm load.

    not good
     
  18. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    okay now I am confused (not hard is it!?).

    this is copied from the spec sheet

    **************
    FTC Power Rating
    <0.1% THD
    20Hz-20kHz
    both channels driven 200W x 2 @ 8 Ohms
    350W x 2 @ 4 Ohms
    FTC Power Rating
    bridged mono 400W x 1 @ 16 Ohms
    725W x 1 @ 8 Ohms
    ************************

    based on this, my initial question was... can i use two cabs (both are 4ohms) and run them at "350w x 2" which would be stereo as each cab gets its own channel.

    so the total would be 700 stereo watts coming from two 4 ohm cabs (mini schroeders). Correct?

    This isnt bridged right?
     
  19. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Yes, that is correct.


    Yup.


    Nope.

    Why are you confused? You got it!

    Just remember that if you do decide to run bridged-mono you will not be able to use 2 4ohm cabs, only 1 8ohm cab. 2 4ohm cabs would lower your impedence to 2 ohms and would eventually let all the magic smoke out of your amp.

    :D

    Joe.
     
  20. ::::BASSIST::::

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

    Sep 2, 2004
    Vancouver, BC Canada
    Thanks for your replies!

    IvanMike mentioned the bridging thing and that threw me off, but then i re-read his post and realize that if i ran it bridged....

    now if i did run it bridged with one 4 ohm cab would I be in safe territory? It would be nice to have that extra headroom

    so that would be 725w bridged into one 4 ohm cab, correct?

    :cool: