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Complete moron seeks help with QSC RMX 1450 and Acme B4 cabinet

Discussion in 'Amps and Cabs [BG]' started by Justyn, Oct 3, 2002.


  1. Justyn

    Justyn Supporting Member

    Jun 24, 2002
    Richmond, VA
    Hi everyone.

    The complete moron in question would, of course, be me.

    So for a while I've been running my Eden WT-300 as a preamp into a QSC RMX 1450 set for parallel stereo into an Eden 210XLT and 212XLT. Nice setup, but occasionally I thought it might be nice to see if there was something a little smaller (say, a good 4x10) that would have comparable volume. The concern, of course, is that I play a 5-string fretless almost exclusively (in a rock band, no less...I'm just soooo avant garde) and I wanted something that would give me the low-end frequency response to handle that low-B without massive dropoff in db.

    Enter, stage left, a used Acme Low B4. 4ohms, no less.
    "Briliant," says I, "I can bridge my QSC into one massive 1400w 4ohm mono load and I'll have headroom to spare, even for the notoriously power hungry Acme cab."

    Except...when I set it all up, all I got was a lot of clipping at relatively low volume. I actually got more volume running it out of one channel of the amp (450w) at 4ohm then bridged.

    Curious, no?

    At first I thought maybe it was just that I was pushing the amp too hard, as,, after all, a 4ohm bridged load means both channels are runnign at 2ohms (which they're rated for, but I'm never sure how realistic that is)

    Then, figuring I had just missed some crucial piece of information (being, as I've mentioned, a moron), I checked the manual and lo and behold, I think I've got it. Because my QSC only has Speakon and binding post outputs I'd been using Speakon-to-1/4" adapters when running it with my Eden cabinets, so when I set up for the Acme I just used the same Speakon adapter into a 1/4" speaker cable into the 1/4" input on the Acme.

    I suspect this might have been a really dumb move. The manual stipulates using either a speakon connector or both red binding posts, so I think using the adaptor to get the Speakon to 1/4" plug might have done something unspeakable bad to my amp/cabinet combo.

    So...I'll be heading home today with a cable that'll let me use both binding posts into a 1/4" plug and see how that goes.

    Anyone have any thoughts or similar experiences?

    J.

    PS A word about Acme cabinets. Unbelievable tone. Un-be-lieve-able. Imagine the low end response of an 18 with the punch of 10s. And the midrange driver and tweeter yield a really smooth transition all the way up the frequency spectrum. The Edens were all mids by comparison. If you've got the power to drive 'em, by all means, check 'em out.
     
  2. submelodic

    submelodic

    Feb 7, 2002
    Seattle, WA
    I think the problems with the Speakon output of the amp arose from your using an NA4LJ ADAPTER, which allows a cable with 1/4 jacks at both ends to be used with the Speakon output. This adapter is configured to be +1/-1

    If you were to use the NL4FC CONNECTER, which can be configured different ways, then you can change the polarity for use with bridge mono mode to +1/+2.

    I personally find it convinient to have separate cables so I can switch between bridge mono with 1 cab or stereo mode with 2 cabs.

    You're not a moron - I suspect many Speakon users have encountered this problem. RTFM!
     
  3. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Justyn, pull the Speakon connector apart and have a look. It should be easy to move the wire that's currently connected to the 1- terminal to the 2+. Don't spend any money on cables until you've tried this!

    RMXs and Acmes are a great match. I love my RMX 1850HD and my pair of Low B-2s. What I love best is that I can drive both the Acmes off one channel of the RMX and add another cab or two!
     
  4. 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
    Justyn,

    What Chucko said. ;)

    There are four pins in the Speakon connector. On the upper one, 1+ and 1- are Channel 1's outputs and 2+ and 2- are Channel 2's.

    The + and - pins are connected electrically to the red and black binding posts, respectively. Just as you'd connect the speaker cable to the red post of both Channel 1 and 2 in bridged mono, if you use the Speakon connector, you have to use pins 1+ and 2+. It's documented fairly thoroughly in the manual.
     
  5. 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
    Good point, Sub. That would do it, sure. Thanks for pointing that out! :)
     
  6. I'm asking the same questions on my thead QCS2402 setting today. I have the Bergantino HT212 and it's speakons are wired +1 -1 so I am assuming that the speakon that goes in the amp must be changed to +1 +2 and the speaker speakon will stay as is. Just have to remember which end goes were. And only use for Bridged.
    RIGHT??????
     
  7. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    Yeah........if your going to go back and forth between bridged and parallel/ stereo it would be a good idea to have two different speakons clearly marked bridged or stereo. You cannot use one for the other.....that much of the manual I did read:D
    Really Big String.......you probably only need the 700 watts from one side to run the Bergie,
    and you always have the option to run another speaker on the other side if needed.
     
  8. Thanks once again Jerry.
    I think I'm going with your set up. Limiters on, 30hz filters and parallel. I just might have to xerox you all the way and get a Berg ht112 to down the road if I can sell my "other" 400+.

    One more question :rolleyes:
    How far up do you run your gains on the 2402?
    I'm thinking maybe all the way up and adjust accordingly on the Dem. I know if I bridge it would not go over half way.

    I don't play a five much, but I do use a drop D tuner quite a bit. 30hz sound good on the filter. I said that didn't I.
     
  9. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    I use the volume all the way up on the 2402, the Demeter doesn't have a master volume...so I keep that low. I sometimes back one channel off a little when I throw the 1/12 Bergie on top...they go great together:D
     
  10. Justyn

    Justyn Supporting Member

    Jun 24, 2002
    Richmond, VA
    Finally got back to my computer and got to read all the replies. I went home today and tried running the QSC in bridged mono with a cable that was a 1/4" plug at one end (into the Acme) and bare wires at the other (into the bridge mono red binding posts). Seemed to work pretty well. I also talked with Andy Lewis of Acme and he recommended between 800 and 1000w for the B4 cabinet, so now I'm thinking I might sell my current 4ohm B4 and buy a brand spanky new one in an 8ohm version, which would pull 900w at 8ohms in bridge mono from my power amp. I'm just worried about running too much power into things like the midrange driver with an overzealous twist of the volume knob. I also heard from a local bass guy that runnning the 1400w of my bridged power amp into a 1/4" plug is a Really Bad Idea...can anyone verify this?

    Then again, I might sell everything I own and buy an Ampeg SVT-4Pro with a BXT 410 and BXT115. I played the 410 today and it had exactly the sound I wanted. Of course, that's a whole lotta dollars, but still...it's nice to have goals, eh?

    You know what truly amazes me?

    I mean, aside from claymation, that is.

    What amazes me is that my two guitarists can get by with barely 100w between them and I can't seem to find a proper amp/cabinet conversation that gives me the tone and volume I want to be heard over them and my drummer. Again, my first thought is that I'm simply a moron and doing something wrong, but even I, Mr. Self-Deprecation, am a little reluctant to believe that. It's driving me bonkers though...surely the right rig is out there somewhere...

    ah well...think I'll go play my B4 again and see if I can find the right spot to run my preamp so the power amp doesn't clip.

    When I come back in my next life as a bass amp builder I'm going to design a powered 1x10 that can fill 1000 seat halls and has one knob that says 'More.'

    J.
     
  11. Justie, I like your MORE knob.
    I also agree, why does it seem so easy for everybody to get were there going with bass. I played geetar for over 25 years and used a 15 watt tube amp most of the time. :rolleyes:

    Thanks to Jerry again and all the rest of you for putting up with my redundant questions. I feel funny turning volume/gain controls ALL THE WAY UP. It seems weird to me. I just have to get used to "real" amplifiers and how they operate.

    Bridging this baby seems to breed caution too, but as I said before, the manual sort of demonstates that set up for one speaker and so did the manufacturer of my cab recommend that set up. But too many real end users have said that 700watts is plenty so I'm going to try that first.
    Thanks again.
     
  12. 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
    If you want to optimize your signal-to-noise ratio, don't turn the amp's gain controls all the way up. Turn the preamp up instead (just don't clip it), and turn the amp down.

    Shoot for settings where you have the sound you want, but also a decent resolution of adjustment. What I mean by that is this: at the low end of their rotational range, most gain and volume knobs have a much greater rate of change than in the middle or upper part. A little bit of adjustment, like a half dB or so, is easy to do in the middle and upper part, but when the knob's turned almost all the way down, you find that just a little turn makes maybe 2 or 3 dB or more of change, and so it's harder to dial in the right level.

    Have fun, and enjoy the amp.
     
  13. Justyn

    Justyn Supporting Member

    Jun 24, 2002
    Richmond, VA
    Hi Bob,

    I've read many of your other posts with great interest and appreciate the time you take to explain all the intricacies of this wacky, crazy thing we call sound reinforcement.

    As you've no doubt noticed from my earlier posting, I've been having concerns relating to my RMX 1450 into my Acme cabinet. The question has come up of whether it's safe and advisable to be running a cable from the two red binding posts (in bridge mono) which terminate in a quarter inch plug, which is all that my cabinet has. Is this asking for trouble? I heard that above, say 350w a quarter -inch connection can start to be a little sketchy. What exaclty that means I'm not sure and hope to clarify.

    Thanks for your time.

    j.
     
  14. Justyn

    Justyn Supporting Member

    Jun 24, 2002
    Richmond, VA
    After re-reading one of my last posts on this thread I'm realizing that maybe what I need is just a bigger car and not necessarily a smaller amp. For the record, I drive a 4-door Honda Accord. The Eden 210XLT and the 212XLT fit across the back seat (believe it or not), my little rack goes in the truck with my pedalboard and my basses usually ride shotgun in a double gig bag. As I've put some nice gashes in my door upholstery courtesy of unforgiving brand spanky-new stacking corners coming into contact with the vinyl door bits, my approach as of late has been to look for a setup which will yield the most volume in the smallest package, with tone being an important, but not necessarily deal-breaking consideration as I've found I can pretty much approximate my 'sound' with just about any amp I play, give or take a little bit. Thus, I've shyed away from the popular 410+115 stack, or the venerable SVT 810. I'm thinking maybe it's just time to get a damn trailer or look down the road towards a mini-van or something when my current vehicle reaches the end of it's useful life (which, given that it's a Honda, should be in another ten years or so).
    Then again, I think I may be suffering from a near-terminal case of G.A.S. as I've gone through a lot of gear over the past year without, I'm now realizing, spending the proper time to really learn all the little ins and outs of tone and volume. For instance, I'm not even sure what is really responsible for volume. I know it involves wattage and speaker surface area, but how they relate is something I'm still discovering.
    I'm also in that weird middle-ground of band evolution where we're playing some shows where we've got full PA support (i.e. everything goes through the PA and my amp just needs to provide stage volume) and some other shows where it's just vocals through the PA and my amp needs to provide all of my volume, and I'm still trying to find what works for each situation.
    So maybe I don't actually need a bigger car to hold that 410 and 115 I don't actually own. Maybe I just need to figure out how what I've already got works.

    Hmmm...have to think about that.

    Thanks for listening to my blathering everyone. I've been in this nightmarish orgy of amp and cabinet buying and selling for about a year now and every so often I just need to vent online.

    Back to work,
    j.
     
  15. 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
    Frankly, I hate 1/4" plugs. Even on instruments; XLR would be so much better, but that's water under the bridge; 1/4" is the accepted standard. I especially dislike them for high-power, high current use--that is, speaker circuits.

    That said, I have to admit that I haven't yet gotten around to replacing the 1/4" jack on my 8-ohm EV bass cab with a Speakon. I'm running a PLX 1602 in bridged mono; that's 1000 watts, although I've run it up to near full power only a few times in the four years that I've owned it. Most of the time, even when I'm playing loud, it's averaging maybe 10 to 20 watts or less.

    1/4" connectors were originally invented a century or so ago for the telephone industry. In fact, they're also called phone plugs. They're suitable for quick connections and disconnections of small-signal, high-impedance circuits by hand, like telephone operators used to have to do.

    1/4" connectors vary a lot in quality. You've got brands like Switchcraft and Neutrik at one end, whose stuff is fairly robust, and then there are all sorts of no-name connectors. Some fit better than others; that's popped up as an instrument cable topic itself now and then on TalkBass. But the contact area between the tip of the plug and the contact of the jack is not very large, and the sleeve-to-sleeve-contact depends on the spring action of the tip contact to press the plug against the side of the jack. On lower-quality jacks, the tip contacts often bend or lose their springiness, or the contact surfaces tend to oxidize. Also, in 1/4" connectors, the conductors are fairly close together and generally not well insulated from each other. And when you plug in a 1/4" plug, you briefly short both sides together.

    When instrument amps were first starting to be mass produced in the late 40's, all there really was to use were 1/4" connectors, which wasn't too bad because you're talking about mostly 10 to 40-watt amps. Now we have amps that put out hundreds and even thousands of watts, and that legacy of 1/4" plugs has to end somewhere. QSC stopped using 1/4" outputs back in about the early 80's.

    You probably won't have any problems with your 1/4" connection. I haven't had any with mine, but I'm aware that it's a potential weak spot. One day I will change it to Speakon! ;)