Poweramp & wiring questions

Discussion in 'Amps and Cabs [BG]' started by Transverz, Jul 16, 2004.

  1. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    Hey TB,

    I got a few questions that I'm sure other under-experienced guys like me will have:

    1) Does a poweramp strain more or less when in mono-bridge mode or when driving the same load/wattage with both channels separately?

    2) Is there a major advantage to bridging my amp and daisy chaining my two cabs over just running them on their own channels? It's either going to be 800watts bridged or 300watts per channel. Pros? Cons? (this is also going to help me decide if I should go with two 8 ohm cabs for bridging or two 4 ohm cabs for one cab per channel)

    3) What is the proper SpeakOn-to-SpeakOn cable to get if I go from a QSC RMX 850 to my Avatar B410? I don't know the polarities (1+, 1-?) of either amp nor cab. And I can't seem to find them either.

    :help: I'd appreciate any of it! Thanks!

  2. page 11 of the RMX series manual explains how to bridge your amplifier: use the 1+ and 2+ terminals of a speakon connector in the top (channel 1) speakon jack.

    most cabinets are 1+ 1-; i would be surprised if your avatar is any different.

  3. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    thanks rcz, page 11 does have the information. I just didn't quite know what I was looking at until you told me what it was. Then it became clear :D thanks!

    Know anything about my first 2 questions? T'would help...thanks yet again!

  4. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    There is a potential slight advantage in bridge mode. The power is drawn symmetrically, some from each supply on each "half cycle" of the signal.

    In parallel mono mode, twice as much current is drawn from each supply. But each supply only is loaded on alternate half cycles.

    The symmetric loading leads to lower peak currents in the power supply, less "ripple current" and probably is "less strain" in that sense.

    The output devices don't see any particular difference.

    You could parallel two higher impedance speakers, just use one speaker of the right impedance for bridge mode, or you could do two lower impedance speakers in series.

    Two ways to do series.....

    One, you can just hook them up in series, if you have a way to wire so as to put them in series instead of parallel. It would probably take a special jack set up.

    Or, if you can flip phase for the wire to one speaker (like reversing a banana plug on the speaker wire) , just connect them both up normally (like stereo mode) but flip one phase and set the amp to bridge. That way, the speakers need not even be identical, they will still share the output, because each is connected between its output terminal and the "ground return" wire (center ground). Effectively they have each got their own channel, but they are still controlled by one control, and act just like a speaker in bridge mode.

    If you put two non-identical speakers in series without a center ground, you really have no idea how well they will share. it depends on their "relative impedance change over frequency". One may end up getting extra power much of the time, or they may interact in other undesirable ways.
  5. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    Wow, that is some heavy reading! I must have read it 10 times before it started soaking in. Thanks!

    Gotcha. So bridge mode should give less strain (at least theoretically, if not actually) on the poweramp.

    With bridged mode now explained better to me, series cabbing it is. ("cabbing"? wow. that's a new one!)

    Fortunately, the future cabs I am planning on getting have dual 1/4" in/out jacks. So if the lowest ohmage for the amp is 4 ohms, two 8 ohm cabs then, right? :eyebrow: Or would two 4 ohm cabs be a more flexible option? ACK. :confused:

    Anyway, thanks Ampeg Insider. I'm going to buy an Ampeg preamp but not quite sure which one. Right now I'm using a B5R head. Pretty cool. Just not enough power for me. Naturally I thought the SVP-BSP but now I'm wondering if I could get the same sounds plus more versatility out of the SVP-CL or the SVP-PRO, eh? Your thoughts? I play rock, btw, for your reference. I don't use brutal distortion on the B5R. Just enough to get slightly overdriven and warm things up a bit more than usual.

    But thanks for the info on half cycles and ripple currents. Amazing! :hyper:

  6. you might be happy with the SVP-CL (though it's probably different), but the SVP-Pro does not sound in any way like the B5R/SVP-BSP. i used to own a BSP that i loved (listen to mine at basstasters.com!), and i used a B5R in stores when i was trying different cabinets without my rig. search for the BSP here and read my comments about it.

  7. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    Thanks rcz,

    Yeah, I'm trying to find a used SVP-CL out there but not much luck. I realize that this and the SVP-PRO are pretty different from the B5R/BSP, but can you get into warmly overdriven territory with the CL and PRO like the B5R/BSP can? Is it just the increase in gain and some EQ manipulation that does this? Sorry, I have no experience in tone shaping with EQs or a stand alone preamp in general.

    Any other same or lower price point preamp suggestions? (Go as low your imagination can take you and my wallet would appreciate it) This is for my trusty backup rig in case my main amp goes temporarily kaput. I've been interested in seeing what these preamps sound like:

    -Peavey Alpha Tube Preamp
    -Peavey Bassist Preamp
    -BBE Bmax (non tube, lack $!)
    -Older BBE bass preamps
    -Sansamp Bass Driver DI / RBI (used)
    -Any other ideas?

  8. DougP


    Sep 4, 2001
    i have an SVP-CL and it will barely start to break up when the gain is maxed out. might not be enough for what you are looking for. but your bass may be capable of putting out hotter signals than mine. i have Bartolini PUs and a 9V active preamp in mine. probably with the BDDI in front of it, i could get a hot enough signal to get the over drive, but thats not really what i was looking for.

    The CLs are still a little hard to find in some areas. you could always do the musicians friend 30 day paid trial. :)

    check out www.basstasters.com for samples of the preamps.