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Acme Low B problems. HELP!

Discussion in 'Amps and Cabs [BG]' started by gatekeeper, Mar 24, 2005.

  1. gatekeeper


    Mar 24, 2005
    okay. I know some peeps here are using a similar setup to mine it is:

    Yamaha PB1 preamp >
    QSC PLX 2402 > using one side of the amp (750 watts @ 4ohm) > speakon out >
    1st Low B2 series II 8ohm (speakon input) > 1/4" cable >
    2nd Low B2 series II 8ohm (1/4" input)

    So I'm just using 1 side of the amp, limiter on. chaining 2 lowBs together.

    The problem is: I've blown 1 cabinet to (melted the coils on both 10's) from this setup. I could tell it was loading back and making the amp clip when I tried to play loud. This makes me think its an OHM thing. Has anybody tried wiring the 2 low B's together in series?? This would make it a 16ohm load...

    Just wondering if anybody has had similar issues. I play funky rocknroll, not THAT loud, But I feel I've never really has these babies setup right with my rig. They sound good, but I can't get the volume without clipping the amp. Any help would be appreciated.

  2. In my opinion, you should be running that amp bridged into both cabs. I don't think 750 watts is enough power for 2 B2's.
  3. Kindness


    Oct 1, 2003
    I would personally use both sides of the amp to give 425 watts to each cab. If there isn't enough volume with that setup you might have the wrong cabs for your playing style.
  4. gatekeeper


    Mar 24, 2005
    Yeah, they just might not be right for me...I've tried really hard to make them work...

    I'm gonna replace the drivers, then try it stereo- 1 cab on each side. then I'll try Bridged and chained. I'm also gonna try running them in series. I'll post the results in a few days.

    thanks guys,

  5. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    750W just isn't enough power if you want to get serious volume out of two B2s. Bridge the amp for a hefty 2400W and watch all the clipping problems disappear. Keep the low cut filters engaged.

    Most blown speakers in Acme cabs (or any bass cabs) are due to over-excursion not voice coil melting. The problem you've had is that the cabs haven't been able to deliver high enough peak loudness (due to a lack of power) and so in attempting to raise the volume level you've pushed the amp into clipping/limiting which has increased the average power beyond the voice coils' ability to dissipate it. With more peak power you'll be able to cut through and hear yourself without putting such saturated average power into the cabs.

    And you'll be able to hear when the cabs are pushed too hard and start to over-excurse, it's pretty obvious if you take any notice of how your bass sounds.

    FWIW I'm giving my B2s 900W each and they're very happy with it, and go louder, with more bass weight, than they did with 425W each. And I don't blow the mid/high protection bulbs anymore, since my amp rarely hits the limiters.

  6. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    I used to run a couple of B-2s with my Crest V900 (450 watts each). I play in a three-piece blues/rock/funk band and it just wasn't loud enough. The Crest was clipping all the time and I blew several drivers. I eventually gave up on the Acmes and sold them (after replacing all the drivers :crying: ). Now my 900 watts is plenty with a couple of 4x10s. As has been posted many times on this site the acmes are very inefficient but have killer low end. They produce a lot of sound below 80 hz which is not a good way to cut through. So you're moving lots of air but maybe not hearing yourself. If you were standing in the back of the room it might be different but standing next to the drummer you need some midrange. I found that a Peavey 2x10 and Avatar 2x12 gave much better sound on stage with my 900 watts. I'm not knocking the Acme's. For ultra-low frequencies they are hard to beat. But for efficiency and cutting through on stage you might prefer cabinets where the main drivers are producing the frequencies that enable you to hear yourself.
  7. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    My primary rig is an SWR Grand Prix driving a PLX 2402 into a pair of 4 ohm Low B-2s, one per channel. I get plenty of sound, and have had no problems blowing up drivers yet. I also don't drive it into clipping.

    Heck, I recently started playing at rehearsal with a single Low B-2 driven by a bridged RMX 1850HD! It'll keep up with a loud drummer, and I haven't blown anything up... yet.

    I suspect the problem might be the PB-1 pre. It is strong on bass but a bit weak in the mids. I find the Acmes lack definition in the mids as well. So to get any definition at all, you're turning up... and the boosted lows are overdriving the Low Bs.

    A pre that does better justice to the mids might allow you to turn down the gain a bit.
  8. Folmeister

    Folmeister Knowledge is Good - Emile Faber Supporting Member

    May 7, 2003
    Tomball, Texas
    I think it depends upon what sort of music you are playing too. I would never use my Acme in a situation where volume is the central component. My B-2 is a tone machine. My Mesas are volume machines.
  9. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL

    what this guy said...

    tho i am a bit more conservative, and say 600 SS watts / 400 tube watts per B-2.

    also, i kinda answered your question in the "Acme Users Unite" thread. but again IMHO, i think you need greater Acme firepower. in which case, a pair of B-4's might be more appropriate. with the 2402, you'll have plenty of power.

    oh and btw, if i havent said it 2,342,623 times enough...

  10. Tim__x


    Aug 13, 2002
    Alberta, Canada
    That's functionally equivalent to running one cab per a side which is what he should be doing, if he still needs more power after that he should bridge into both cabs in parallel (assuming 8 ohm Acmes and an amp capable of 2 ohms per a side operation).
  11. BruceWane


    Oct 31, 2002
    Houston, TX
    I'll second this. The PB-1 is a very neutral preamp. If you've got a bass that doesn't have a lot of bite to it's sound, the PB-1 isn't going to add much by itself. It's neutral nature does work well with effects though. I've found that putting just a touch of chorus - so little that you can't really tell it's there, just that it sounds a little different - helps this preamp out a lot.

    Also, if you use either the low-cut filters on the power amp or the parametric eq on the PB-1 to cut lows a little below 40Hz or so you can crank the Acmes about as loud as you can stand it. The Acmes will crank out the low end, but I've found that above a certain volume level all that low end gets beyond "audible" and into more like "my head is being pressurized".
  12. gatekeeper


    Mar 24, 2005
    OK.. Thanks guys for all the good advise.

    Here's what I've done:
    After replacing the 10's in one LowB2, I bridged the plx2402 and used a banana plug from the amp to the 1st cab. Then out 1/4" to the other cab. Also, I placed a dbx compressor/limiter after the Pb1.

    Needless to say, the volume issues are over, and the amp has yet to clip.

    the updated setup is:
    Spector bass (active)> Boss GT6-B > Yamaha Pb1 > dbx 1046 comp/limiter > QSC plx2402 (bridged mono 2400 watts @ 4ohms) > 1st Acme lowB2 series II > 2nd Acme lowB2 series II

    There are some new questions now, and I'm a little wary cuz I haven't played it with the band yet (its always a totally different perspective)

    So, here's a question:

    I now have several places to adjust my volume from (besides the bass & pedals): The volume on the Pb1, the XLR output level on the back of the Pb1, the output gain on the DBX, and the level knob on the QSC. What's the best way to approach this chain?? In the past I've used the Pb1 volume like an "input gain" knob, then the QSC volume like an "output gain"...A friend of mine said the amp should be all the way up and then adjusted from the preamp...I dunno.

    And what's up with the Pb1 not having a gain control??? Can certain basses be too hot for it? I love the way it sounds (for the money) but the lack of that feature makes me uncomfortable.

    thanks for playing.
  13. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL

    your friend is right.

    leave the volume knob on your power amp cranked. best to have as much wattage feeding the cabs.

    then keep the yamaha volume up rather high, so you're feeding the most signal to the compressor. but not too much as to drive the compressor into constant compression or even distortion. then use the output knob on the compressor as an overall "volume" knob.

    also, you should be sending the proper signal to your compressor. if it doesnt mind seeing an unbalanced signal, then send that, and use the balanced XLR DI to the PA. but if it has to see a balanced XLR signal, then best to invest in a nice DI box.
  14. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    Cranking the power amp is not necessarily the way to go. All that matters with the power amp is that it's getting enough signal and that it's not clipping. It doesn't have to be turned all the way up to get the maximum wattage. The controls are input attenuators so it is just another way of controlling how hot the signal is going into the amp. You can attain the same wattage by either increasing the input signal or increasing the output. I use a PB-1 into a crest and have found a sweet spot with the PB-1 volume and the Crest input attenuators both at about 50%. I use a footswitch compressor before the PB-1 and that seems to work fine too. So there are many ways to skin a cat (sorry PITAs).