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Discussion in 'Amps and Cabs [BG]' started by matt_dutyfree, Jun 21, 2004.

  1. This is something I don't really understand and it seems to only be availible on the top end heads... If i'm aiming at a 1*15 and a 4*10 then i guess this is gonna be a big benefit???

    It is something thats really needed if i go for this speaker config??

    also is running a 2*10 and 4*10 a back idea of equally powered outputs?!?
  2. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    I don't have tons of experience on the subject (I recently bought my first stereo instrument amp) I think that any time you hook up two different cabs there will be the potential of volume/sensitivity differences. some is caused by speaker sizes like running 110 with a 115, some depends on speaker sensitivity rating (aguilar gs210 has a sensitivity of 102db @ 1w1m and the gs410 is 104db @ 1w1m) if one speaker has a higher sensitivity rating that speaker will appear to sound louder than the lower rated speaker.

    this is a problem if you are running two cabs off a mono amp. even if you have only one stereo amp, unfortunately, the bridged (mono) mode will yield much higher output, but in stereo mode (on some amps you can fine tune the output of each channel to balance volumes) the amp will yield much less power, usually less power than you'd like to run into one cab. for example I have two aguilar gs112 cabs (300w 8ohm) I run in bridged mode for max power per speaker (600w). but lets say I had the speakers mentioned above. with my stewart 1.2 it can only put out 200w perchannel stereo into 8ohms. so it could put 200w max into the 700w gs410 and 200w into the 350w gs210 at 8ohms each. so I'd be "underpowering" the cabs yielding a unpunchy compressed sound, maybe not even as loud as I need for a gig. buying a powerfull enough stereo amp like the QSC PLX3402 will cost you around $1000 and weigh in at about 40 LBS

    Possible solutions: buy two cabs with similar sensitivities and run a mono amp or bridgeable amp.


    buy another power amp and split your preamp output to each higher power amp.

    in my situation if I bought more cabs or had some different sensitivity cabs I'd probably buy another stewart just to be safe so I can run 700w 8ohm into one cab or 1200 into two similar cabs per amp (stewarts gain control works in stereo or bridge modes)
  3. right... thanks. that might take a few goes to fully understand it but i reakon you explained that pretty damn well!!

    a couple more questions (i'm thinking about a possible pre power setup)

    Is the sans amp RBI definatly a good enough pre amp and will I get the full wattage using it along side a power amp???

    Is anyone using or has used a behringer bass v-amp??? what are they like etc... and roughly waht sized power amp am I gonna need for these kinda setups! All help will be greatly appreciated!

    are these kind of systems gonna sound and perform much better than say a yorkville XS400H
  4. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    I've been very happy with my RBI. it is a very flexible (tone wise and connections). It will provide adequate preamp voltage to your power amp, unlike the BDDI which has a lower output. I'm very eager to get my hands on the tech21 RPM which is very similar to the RBI except that it has a sweepable mids control and some different tonal characteristics. other useful features include user controled wet and dry (not user controlled) xlr output to go to mixer, effects loop, overdrive, blend of gtr/sansamp circuit.
  5. jondog


    Mar 14, 2002
    NYC metro area
    Mcrelly is describing a Stereo (or technically Dual Mono) setup, not a true Biamp setup. For a Biamp rig, you need a device called a crossover, which comes built-in on some high end heads. This crossover will split your signal, sending the high frequencies to one cab and the low frequencies to the other. This setup is not as popular as it once was because cabs are getting better at handling a wide frequency range. I like biamping because it lets you pick cabs for what they are good at and you don't have to ask them to do what they're not good at. Yes, my BE s15xd is technically a full range cab that could be used alone, but when I only give it frequencies over 100hz it is even better at its trademark midrange punch because it is not even trying to cover fundamentals on the B and E strings.
  6. do some power amps come with frequency control on each channel

    I've found a couple of power amps on ebay... i live in england and the range isn't too good! i also pay rough what you do in dollars in pounds!

    is a power amp and a sansamp RBI all i would need then??
  7. Thunderfunk


    Mar 27, 2004
    McHenry, IL

    Right on. A Bi-Amp setup is to split freqs, primarily between a full range cab and a sub-woofer, or a cab and a tweeter. The reason for it is to avoid the power lost in a passive crossover (coils and caps), and to keep a clipped woofer amp from distorting a tweeter. You need two amps to do it, so why not just use two amps to drive two cabs and split the signal at the input? Then use each amp's gain and tone controls to adjust each cab separately for the best tone and volume balance. You'll find that if you have two differently loaded cabs and just plug them in, one will predominate.

    BTW, I used a stereo Ric bass in the '70's into a Showman head. Neck pickup into channel one, and bridge pickup into channel two. Then I eq'd each channel for maximum effect of each pickup. It really opened up the tonal range. Still mono output although it sounded huge (at the time). :p

    Dave Funk
  8. jondog


    Mar 14, 2002
    NYC metro area
    I think some Peavey power amps come w/ a built-in crossover. Nobody needs to biamp, it's just one option among many. What you need is based on the style of music you play, who you play with (wattage on guitar amps? loud drums?), and what size rooms you play in (PA support available?).
  9. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    You haven't even bought your 4x10/1x15 setup and you're asking about biamping?? Seems to me that you're making a false assumption: that biamping is better because some high-priced gear has biamp capability. For those with the proper gear and expertise, biamping can be better... *sometimes*... but most of us here do not biamp.

    FWIW, I've experimented with biamping but have always chosen to run full-range. Yes, it's less efficient in terms of power but it sounds better to my ears. YMMV, of course. However, biamping adds a level of complexity (and cost?) that might not be worth any improvement in tone that might occur.
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    I think biamping a 15 and a 4x10 is not an optimal configuration. The 4x10 is probably going to become quite directional with the higher frequencies, whereas as a single 10 of comparable quality could be more omnidirectional and a better complement to the directionality of the single 15.

    Some power amps have crossovers built in, but they are few and far between. You can also have a set of crossover filters installed in a PLX amp, but it would not be externally adjustable.

    IMHO, in bass amplification, the benefits of biamping are not great.
  11. sorry i understand the whole situation a whole lot better now(i think)... i only ask because it's something i don't understand. I've been reading alot of the pages across TB and i find everything very informative and useful! i'm very new to the bigger rigs (I'm in a band starting to tour the UK so i need to sort myself out quick) and it's something i didn't understand! I didn't think it was an issue until i read a comment from some one saying they wouldn't buy a mono amp.

    thank you for the replies!

    If anyone has any advice for some one looking for a reasonable rig (head rack anything) that is really flexible and has a pretty good standard rock tone, i'm open to as many suggestions as possible!
  12. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    Ah, I see. The common amplifiers are mono (single channel) and stereo (two channel). Stereo amps can be run in mono quite easily, so they are more versatile, and that is why many bassists prefer them. As noted above, stereo (two channel) operation is not the same as "biamp"... even though it sounds the same!

    Most dedicated power amplifiers (that is, with no preamp) are stereo. Most consolidated bass heads (equalizer and power amp combined) are mono.

    Consolidated bass heads are generally easier to use and set up than modular "rack rigs" which contain multiple components. But I really like the SansAmp RBI, and it should work just fine with just about any power amp. Set up should not be difficult.
  13. haha yea i thought it would probly be me being stupid!

    i've managed to find some one selling their sans amp RBI for £200 it turns out they don't sell them over here anymore... same goes for the Bmax... any other pre amps I should look out for?? (£200 is very roughly $280, i think, is this a good price?? bear in mind stuff over here costs a fair bit more new or old)

    also I just found a QSC 850 on ebay... this looks about right for my requirments, everyone seems to recomend them so i'm guessing thatd be worth the investment!
  14. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Is it an RMX 850 or a USA 850? There never was just an 850 model.
  15. sorry i meant to put RMX