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Crown & Sansamp - clipping?

Discussion in 'Amps and Cabs [BG]' started by subexpression, Mar 5, 2013.


  1. subexpression

    subexpression

    Oct 9, 2010
    Iowa
    Heya folks - I have to push my volume to about 1 o'clock, to about 2 o'clock in order to get decent volume for my metal and prog rock band. If the input on my comp pedal is turned up too high, the gain on the RPM, turning up the CH1 volume knob on the Crown pushes it to clip (the red light flashes occasionally). Fortunately, I'm using the built-in limiter, but I was hoping that having 2400W would give me more headroom for only 1500W of speakers.

    My rig consists of Sansamp RPM pre & Crown XLS 2500 running into Hartke HyDrive 410 (1000W@8ohms) and HyDrive 115 (500W@8ohms). It affords me 2400W @ 4 ohms bridge-mono...and the speakers are daisy-chained with 1/4" speaker cable. In front, I have a modded CS-3 (Monte Allums).

    What could I be doing differently to extract more power from my rig?
     
  2. Have you fallowed the instructions:
    Bridge-Mono Mode
    Bridge-Mono Mode delivers the power of both amp channels into a single 8 or
    4 ohm load.
    Before you get started ensure that you:
    1. Connect signal source to Channel 1 only using either the XLR, ┬╝ Inch, or
    RCA connectors.
    2. Connect the speaker as shown.
    a. If using the binding post outputs, connect the positive terminal of the
    speaker to the positive terminal of Channel 1 and the negative terminal of
    the speaker to the positive terminal of Channel 2.
    b. If using a Speakon® connector, connect the positive terminal of the speaker to 1+ and the negative terminal to 2+.(Note: This requires you to rewire your speakon cable)
    Plug the connector into the Channel 1 output only.
    Follow these quick steps to confi gure the amplifi er for “Bridge Mode”:
    1. Hold the &#8220;Mode/Menu&#8221; button down for 3 sec until the LCD screen displays &#8220;Amp Mode <More>&#8221;.
    2. Press the &#8220;Mode/Menu&#8221; button to begin con&#64257; guring the Amp Mode.
    3. Press the &#8220;Next&#8221; button until the LCD screen reads &#8220;Mode: Bridge&#8221;.
    4. Press the &#8220;Mode/Menu&#8221; button to con&#64257; rm your selection.
    5. Now press the &#8220;Next&#8221; button until the LCD screen displays &#8220;Bypass&#8221;. Press the &#8220;Mode/Menu&#8221; button to con&#64257; rm your selection. The LCD screen should now read
    &#8220;Bridge Bypass&#8221;.

    Found here: http://www.crownaudio.com/media/storagebk/pdf/amps/142169-1_XLS3_MultilingualManual_032410.pdf

    Where is the attenuator set? Careful with both cab especially the 115 as you will blow/burn them very easy with that much power, worse in bridged mode!
     
  3. subexpression

    subexpression

    Oct 9, 2010
    Iowa
    I have the amp set so the LCD screen reads: "Bridge Bypass", meaning, it is running in bridge-mono (4 ohms, 2400W), and bypassing the filters. I also have the limiter set for CH1 so nothing is getting damaged with the clipping, but just knowing the light flashes once in a while bothers me.

    The attenuators: 410 rocker switch is in the middle...which means 0db boost for tweet; 115 is set to "OFF" so the tweet is not being used.

    I have run the rig in 8ohm stereo, but it lacks the punch I get from 4ohms.

    I'm using the XLR out on the RPM into the Crown CH1. Perhaps my XLR output knob on the RPM is up too high...it's dimed.

    I'm still thinking that I should be able to have tons of headroom with that much power, but I end up turning CH1 up beyond 12 o'clock to play with drums and a guitarist running a 150W head & 412 cab. This rig should slam and I'm not sure what could be the hangup.
     
  4. Mike in Chicago

    Mike in Chicago Supporting Member

    Apr 3, 2011
    Chicago
    That's a LOT of power. How loud are you guys? I have a xls1000 run it in bridge bypass and it will peel the paint off the walls w 2 500w 410 (when needed). Go out the 1/4 "sansamp" to the 1/4 in on channel 1...use the binding posts...not the speakon, you need 4 connector speakon (I think thats what they're called) the binders are way less complicated, and you can just convert that end of the cable. then daisy to cab 2 with regular 2 connector speakon.

    Thats what I do, I have a RBI.

    Easy sleazy
     
  5. Have you re-wired the speakon cable? Turn the power amps attenuator up full and use the RPM's output control as your "master volume".

    Attenuators on PA amps are not master volume controls.
     
  6. subexpression

    subexpression

    Oct 9, 2010
    Iowa
    Mike in Chicago, I'm using a Speakon out on the amp and a female 1/4" adapter on the end....and plug in my 1/4" speaker cables to daisy chain. I will invest in the right Speakons and try the binding posts again. I have been using the Binding posts on occasion, but no difference. Perhaps it's because they're not 4-connector Speakons.

    B-string, I will do that, thanks :)
     
  7. bumperbass

    bumperbass Supporting Member

    Jun 19, 2012
    This ^^
     
  8. dincz

    dincz

    Sep 25, 2010
    Czech Republic
    If you're not using a 4 pole Speakon connector, then your amp is not bridged. As was mentioned before, you need to connect 1+ and 2+ to your cab.
     
  9. GrowlerBox

    GrowlerBox

    Feb 10, 2010
    Nude Zealand
    I recall a thread from many moons ago wherein it was revealed that certain Sansamp pres did not supply sufficient voltage at their outputs to drive many (?most) power amps. May not be the issue here of course, but worth considering.

    If you suddenly do gain sufficient power from the amp, I suspect you'll find that those speakers reveal themselves as a limiting factor, as B-string intimated earlier.
     
  10. odineye

    odineye Supporting Member

    Dec 29, 2011
    Bear DE
    Not to cause a derail here but. Are we sure about this? I only ask because I was a strong proponent of this approach until I read this recently.

    Seeing as the poster is an applications engineer for QSC, I figured I must have been wrong for all those years. Any thoughts or insight?
     
  11. "Regarding gain structure, set your pre to produce a decently strong signal with the input gain, and to deliver a strong signal with the output or master gain. Use as much gain in to the power amp as you need."

    I believe one word would clear that up. The control on a PA amp is not a "gain" control either.
     
  12. bumperbass

    bumperbass Supporting Member

    Jun 19, 2012
    "Use as much gain in the power amp as you need". That's a loaded statement there. As has been the case for all of my career, the input control on a power amp is only an attenuator. It can only REDUCE, not produce, amplification.
    The statement is correct in theory. If "Use as much gain in the power amp as you need" means turning it up all the way, then 'that's how much power you need'.
    As in PA use, the input on the power amp is typically maxed and the sliders on the mixer are used as a gain control. There ARE exceptions, however. If you're running a 1KW amp and your speaker only handles 250W, then you may want to reduce the power amp input to produce a safe level should your preamp accidentally get turned up enough to cause damage.
    Bob Lee's statement is correct in that for gain structure (noise/distortion performance) your preamp input level should be at a decent level to where the rest of its circuitry is not being clipped, yet producing a strong enough signal so that turning the preamp's output control doesn't produce noise. Likewise, he's correct to say the master preamp gain should be set high enough so that you're sending enough voltage to the power amp.
     
  13. Look out, you are going to unleash way more power by bridging.

    I don't know how the amp works with it set to bridge mode while not actually bridged at the output. At a guess you have been 4 ohm mono off one channel only.

    You will have already got 90% of the performance acheiveable with your cabs in 8 ohm stereo. Do not expect a large jump in loudness or headroom, you will only blow up the 15.
     
  14. obimark

    obimark

    Sep 1, 2011
    I played thru another guy's rig at an open mic which was an older sansamp into the Crown QSC- believe 1500 watts model, and it was WEAK. Real weak, without the PA you would not even hear the bass at all. This was into an old 410 Hartke cab- XL series.
    I had the volume on the Crown at 3 oclock, and it had no PUNCH at all. Maybe he didn't have it setup right, but the volume and gain were real high on the Sansamp PRe as well. 1500 watts, No, 800 watts no, sounded like 200 at most. My TC BG250 would slay it, serious, way louder and punchier. Now that I think of it the red clip light was coming on the Crown a TON as well. Probably about to blow the hartke cab, even though it was not loud or punchy at all.
     
  15. Probably set up like that. Samnsamp RBI has a mess of output if you crank it up. OP already said he is driving the amp to clip, get over it.
     
  16. BTW, you don't get 1500W of power handling adding a 500W cab to a 1000W cab on one channel.

    You are limited to the power handling of the 15, which won't be anything like 500W before it farts out with normal bass tone.
     
  17. It would only have the speaker cabs under voltage control for one half of the cycle. It would allow a higher peak when on it's cycle half (push for example), but with no return voltage (pull) for opposite half of the voltage swing (from the zero voltage point) .
     
  18. Mike in Chicago

    Mike in Chicago Supporting Member

    Apr 3, 2011
    Chicago
    If you look at the sansamp recommended settings for say "svt" the level isn't the master volume, it's a setting it seems to me they want you to crank THAT sound w the power amp. I have a older RBI, and I'm in line w sweetwater for the VT rack mount which I feel will be a little hotter
     
  19. kavvmxuh

    kavvmxuh

    Mar 5, 2013
    I have run the rig in 8ohm stereo, but it lacks the punch I get from 4ohms. [​IMG]
     
  20. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    I have the same exact set-up sitting 20' from me...good combination. Couple of recommendations:

    *Don't use the RPM's XLR to drive the Crown, use the 1/4" "SansAmp" output and feed the Crown's "Link" input just to the lower left of Channel 1's XLR. IMO, this is a must, not just a recommendation. The RPM's XLR out is for feeding signal to a mixing board, not driving a power amp.

    *Sounds like you have the Crown configured correctly w/ "Bridge Bypass". The HyDrive has a natural low-end rolloff but you still may want to consider enabling the 50 hz highpass filter. Set the Channel 1 attenuator @ 2-3:00.

    *I use a banana plug > Speakon cable (+1, -1). The banana plug "bridges" the two center red binding posts. You can also configure a Speakon > Speakon cable with the amp-end wired +1, +2.

    Done correctly, this will probably blow the drivers through the grill if not cautious.

    Riis
     

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