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Amp with 2 outs to 2 different cabs

Discussion in 'Amps and Cabs [BG]' started by WG79, Nov 19, 2019.

  1. WG79


    Nov 19, 2019
    Hi all. This may seem like a rookie question but I cant find a good answer anywhere after youtube/forum/google searches.

    I'm hoping to better understand the out puts on the back (mono/vs stereo) of my old Ampeg B4 amp (non R model). I have two 8 ohm cabs that I want to run it through. One is 400 watts (4x10") and the other cab is 250 watts (1x12"). The out puts on the back say 350 watts per channel at 4 ohms stereo, 500 watts per channel at 2 ohms stereo, and 1000 watts at 4 ohms mono bridge (4 ohm min load). Ive been running just the 4x10" cab and it sounds good, but want to bump it up. Specifically my questions are: could I run both these cabs in stereo by plugging one into the A channel and one into the B channel without damaging the head or cabs? Or would it be better to daisy chain the cabs and go into the head in one channel mono? Or is this all together not a good idea because the 1x12" has a lower wattage rating than the amp, or just in general not a good idea because of another reason? Thanks
  2. abarson


    Nov 6, 2003
    Santa Cruz
    Mono: a single source of signal amplified in full range of frequencies.
    Biamp: the signal is divided into low + highs , with each frequency portion being separately amplified.
    Stereo: signals are uniquely assigned spatial placement in reference to a left/right binaural soundscape, with each channel being separately amplified.

    In my opinion, the whole notion of bass in stereo is rather pointless unless you have Rick-O-Sound. All other basses are mono sources of sound.

    I don't know about that amp (Ampeg doesn't even have a users manual for it) but your 112 will be completely lost against the 410. Maybe biamping would work, sending the higher frequencies to the 112, but it's a crapshot. I don't know if the high frequency amp in biamp mode is internally power limited, but there isn't a separate control to judiciously limit the output to the 112. I wouldn't risk it.

    That B4 is an odd beast.
  3. WG79


    Nov 19, 2019
    Thanks for writing back. Here is Ampeg's response to my questions:

    "As the two power amps in the B4 are completely separate, it's completely fine to run 2 different cabinets, one in each power amp. This is the best way to hook up in this type of situation. Daisy-chaining to the Mono output would give you an impedance that is lower than the safe recommended impedance of 4 ohms.
    Since the B4 and B4R are functionally identical (the only difference is cosmetics), you can use the B4R manual for a reference."
  4. The ‘stereo’ position is in actuality parallel mono. The same identical signal appears at both power amp outputs.
  5. WG79


    Nov 19, 2019
    Thanks BassmanPaul. So would I run into issues since the wattage on the amp per channel is 350 and one of my cabs (1x12) is only 250 W? Do I run the risk of blowing that speaker? And if both cabs are plugged into separate channels should the switch on the back for mono/versus stereo be set for mono or stereo? Sorry if these seem like dumb questions- I just don't want to have an oh poopie moment and mess up my gear!! Thanks
  6. Raw N Low

    Raw N Low If I can't hear it, hopefully I'll feel it Supporting Member

    Jul 16, 2009
    Denver, Colorado

    Basically, the B4 (or B4R - dumb naming convention on Ampeg's part), is just a scaled-down Ampeg 4pro in terms of power. Yes, both amps in the amp are completely independent but, each amp only reaches its full potential of 500 watts at 2ohms per side. It can be cumbersome unless you're going to run (2) 4-ohm cabs per side of the amp to reach that kind of power.

    In theory, you could run (2) 212 cabs (usually rated at 4ohms) and the amp would shine with an efficient neo design. The Achilles heel of the SVT-4pro and B4(R?), is that both amps rely on the single onboard preamp to get the balance the shared EQ. In my experience, you lose a good bit of sound dynamics, and this becomes even more apparent with mixed cabs - even from the same manufacturer.

    However - there is good news...kinda...

    The amps have the ability to run separate preamps into each amp input. This means you can have more control over the EQ of what your sending to each cabinet and rely on the amps single input to defeat having to use an ABY pedal or Rick-O-Sound (designs that are really based on pickup dynamics rather than amp flavors) and get much better results. You can do this with pedals, rackmounts, or another amp pre's to achieve this flexibility.

    In case you didn't know - this amp has the ability to run mono-bridge output, so you can dump all 1000 watts into both cabs. Of course, you will need a Neutrik cable that is designed for such, and it's much more efficient. Ampeg doesn't have they are manually listed on their website but, I have found a link that describes the functionality of the amp. Ampeg: B Series - B-4R

    Not that anyone asked but - The 4pro, 5pro, B4(R), SVP-1600, and (to a lesser extent) SVP-1500 shared this feature. The SVT 400T was the only other bi-ample design (ala Peavey Megabass) that was unbridgeable with its dual power sections.

    I hope this helps...
    BasturdBlaster likes this.
  7. Raw N Low

    Raw N Low If I can't hear it, hopefully I'll feel it Supporting Member

    Jul 16, 2009
    Denver, Colorado
    Correction (it's been a long day)

    Yes, the 400T was bridgeable...

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