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2 ohm amp for 2 4 ohm cabs, or 2 8 ohm cabs for 4 ohm amp?

Discussion in 'Amps and Cabs [BG]' started by Azzie Li, Sep 29, 2004.


  1. Azzie Li

    Azzie Li

    Dec 26, 2003
    my dilemma...$$$ vs power.
    I currently have an iamp 600, and a 4 ohms Avatar B212 (1000 watts) that I will keep for smaller/medium shows. I was thinking of getting another Avatar 4 ohms and a 2 ohms amp with higher wattage for the bigger shows I will be playing soon. I'm more into the idea of stacking for versatility and lugging...I don't want a fridge. Would it be better overall to just buy 2 8 ohms and power them thru a higher wattage amp as a 4ohms load? Because I'd hate to have to spend more money on buying 2 cabs and an amp instead of just one additional cab+amp. I also have a Sansamp RBI to use as a preamp and am wondering how most of you use a preamp with a head...run through effects loop...or using the input, (if featured on your amp) bypassing the exsisting preamp? I am very inexperienced with the whole bigger rig, preamp/poweramp thing. I wouldn't even know when a compressor would need to come into the picture. Any reqs...including specific gear? I just don't hear too much about people using 2 ohms amps.

    Thanks!
     
  2. You "COULD" get a QSC RMX850 power amp and an Avatar 8 ohm cab for about $650. That setup would produce 600watts bridged mono. Run that from the preamp output of your current rig and presto! 1200watt 4x12 rig. You would be able to keep your current gear for the smaller shows
     
  3. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    power amps like the stewart 2.1 and the QSC PLX series will let you run as low as 2 ohms per side or 4 ohms bridged (same thing actually)
    if your current amp has a line out or if all of the eq is in the signal path before the effects send you can use your head as a preamp for one of these poweramps
    the advantage to having one of these is you can run your 4 ohm cabinet on one side and then use whatever cabinet you want on the other side regardless of impedance
     
  4. the dude

    the dude Supporting Member

    Sep 19, 2004
    Indy
    So the RMX850 will do 2 ohms bridged?

    The Ampeg SVTCL has a 2/4 ohm switch, so I use that currently for 2 4 ohm Ampeg cabs.

    If you want to use a pre/power amp setup, are there any (1600+ watt) SS power amps that will do 2 ohms bridged?
     
  5. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    if you want to spend about 10k on a 10 thousand watt power amp there are some that can do 2 ohms bridged

    otherwise no
    in order for an amp to do 2 ohms bridged it has to be able to run at 1 ohm on each side - most power amps only go down to 4 ohms per side, some will go down to 2 ohms per side

    for more info click here

    ohms info
     
  6. No, the RMX850 will do 600watts @ 8ohms bridged and 850 watts @ 4 ohms bridged.

    My original suggestion was to run the original cab to the original head and "slave" the signal to a new cab and power amp. Two separate rigs chained together.
     
  7. Azzie Li

    Azzie Li

    Dec 26, 2003

    so when it says that the 2.1 runs 650w into each channel@ 4 ohms each...does this mean i'll get a total of 1300w between the 2 cabs or is 650w the top? and would doing it this way lessen headroom as opposed to the rated 2100w @ 4 ohms bridged if i daisy-chain them? Also, if it's true that running in stereo means the amp is receiving the total load as 4 ohms...is this better than bridging and working the amp @ 2ohms?
    thanks for your input btw!
     
  8. Azzie Li

    Azzie Li

    Dec 26, 2003

    i didn't know you could combine 2 rigs like that. i imagined daisy-chaining the 2 cabs @ 4 ohms bridged...would that be all wrong?
    thanks for your suggestions...while i'm at it!
     
  9. Azzie Li

    Azzie Li

    Dec 26, 2003

    so if i were to use my iamp as a pre...where would i add the rbi to add the growl? would i run it through the effects loop or input after the pre section of the iamp...or into the qsc...does it matter? how do you like your avatar b115/b212 combo? my set-up would be similar. i play a j bass as well...but want the growl too.
     
  10. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    if you "daisy chain" the two cabinets it becomes a 2 ohm load
    i would probably put the rbi in the effects loop of the amplifier
     
  11. I would also run the rbi into the effects loop of the iamp.

    I really like the bottom end of of the B115/b212 setup but it is a little lacking in the upper mids for my "current" tastes. That's where the growl is. I plan on getting a b210 to cover that area.

    I would just get another b212 if I didn't already have the B115.
     
  12. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    Yep. 650 + 650 = 1300.

    Well, first of all the difference in headroom between 1300 watts and 2100 watts is something like 2 dB. You'd have to be playing a hell of a loud gig for that to make a difference. Secondly, it's just not an option. You *can't* daisy-chain a pair of 4-ohm cabs with an amp that's rated at 4 ohms - you'd be presenting a 2 ohm load, and as others have said, it's very rare to find an amp that can do 2 ohms bridged. To get 2100 watts out of that amp you'd need to run it bridged into either a 4-ohm cab or a pair of 8-ohm cabs.

    That amp can't do 2 ohms bridged. You'd probably kill it.
     
  13. Azzie Li

    Azzie Li

    Dec 26, 2003
    First of all, thanks for your input!
    I was informed that this amp does handle a 2ohms load...it says so on their website...so i figured running 2 4 ohms cabs thru one channel was the equivalent of 2 ohms. my only concern is spending the money on an amp to carry this minimum without over-working it..so i was worried about headroom, not volume-wise, but stress-wise. i think i'm only leary because 4 ohms amps have been the standard minimum load for a long time, and there are tried and true models out there that would be less of a risk to invest in. i was hoping to find folks that have been using setups (for a while) that push 2 ohms so that they could recommend a solid 2 ohms amp.
     
  14. When I read the specs on the amps I'm researching it seems that the THD increases dramatically when running 2 ohms. This would lead me to believe that most amps that are rated to safely run a 2 ohms are not running very efficiently there.
     
  15. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    FWIW i've run my stewart bridged into a 4 ohm load and at 2 ohms a side in stereo mode for hours - no problems