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Help with power amp connections

Discussion in 'Amps and Cabs [BG]' started by Sleepwalker42, Feb 14, 2016.


  1. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    Can a good soul give some advices? :)
    I'm new to these connections, here's the problem I'm experiencing: I just got a Crown XLS 1002 power amp and I'm trying to connect it to my cab (which has a 4Ω impedance) and preamp. It doesn't have the power that a 1000 W in bridge mode should have, feels like 100/200 Watts. By comparison I also have a 400W SWR Amplite so I'm misjudging power.
    I tried a couple different ways: connected banana plugs (in the middle 2 red connectors) to cabinet input female, and a regular guitar cable going from amp to preamp (tried also a 12 gauge type just for trying, same result). Is the little bridge that connects the 2 banana jacks on top a factor?
    Then I tried a Speakon, with ¼ jack on other end, from channel 1 amp to cab, same power. Where am I going wrong? Is there something wrong with the amp?

    IMG_1742.JPG

    Thanks
    Enzo
     
  2. First Never ever use a power amp in bridge mode into a 1/4” phone plug. The risk of damage to the amp is too great. It’s also dangerous to you personally.

    Using Banana connectors the load will be connected to the + connectors of both channels. There should be a switch somewhere on the back panel to put the amp into bridge mode. If not, you’ll need to read your amplifier’s user manual to find out what is required.
     
    mbelue likes this.
  3. Here is the manual page 7 explains bridged mode. You have to set the amp for "Bridged mode" on the front panel. To use a speakon cable for your speaker you need to move the wire from the 1- connector position (negative to speaker) to the 2+ position in the amp end connector only, so lable that one amp only on your speaker cable.
     
    Last edited: Feb 14, 2016
    DavC and bassmeknik like this.
  4. If you didn't take these steps the red binding post connection would be no louder than the speakon connection (with or without rewiring).

    1. Hold the MENU/SEL button for 1 second until the LCD screen displays the MAIN MENU. 2. Highlight AMP MODE and press the MENU/SEL button to enter the AMP MODE menu. 3. Press the NEXT button until BRIDGE is highlighted. 4. Press the MENU/SEL button to select BRIDGE mode. 5. Now the LCD screen displays the MAIN MENU. You may continue to the CROSSOVER menu status screen which will now show that the amplifier is in BRIDGE mode.
     
  5. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    The power amp is set in bridge mode from the front display controls, there are no physical switches in the back.
    Why is dangerous using ¼ plugs? It's a speaker cable, shouldn't it be made for that?

    Yes I set it up in bridge mode from the front controls, in facts when I turn it on it says "Crown" "Bridge".
    The speakon has 2 poles only, I should buy a 4 poles connector then and wire it like you mentioned then.
    But why it doesn't work with banana cables?
     
  6. Using the center (red) should work and be "louder" than just the speakon (you need to get a 4 pole speakon connector to use the bridged speakon even though you will only have two conductors). You may need to change the "input sensitivity" in the menu to high if you are not able to drive the power amp to full output.

    Also a word of warning; Clean undistorted power never sounds "as loud" as a distorted signal until you try to talk over it. It could be much louder than you think (to others not in the same room), try running some distortion when comparing volume with only your ears.
     
    Last edited: Feb 14, 2016
  7. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    Thank you for your time.
    I thought about the input sensitivity function that this amp offers but I don't understand why it shouldn't work in 'Normal' mode. Other power amps don't offer that extra feature. Not working with banana plugs makes me think there's something wrong with the amp. I will buy a 4 poles speakon and do the last attempt.
     
  8. It all depends on what the normal output voltage is of your preamp. This feature is to make "gain matching" easier. If your preamp outputs at 0.775v and you have the amp set to "Normal" (needs 1.4v) you can't get full power from the power amp. You could only get roughly half power from it.
     
    mbelue likes this.
  9. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    Will check that out, preamp is the Mike Pope MPP1 but I can try with 2 other different preamps I have. I'll review the manuals to find some answer.
    If you have other ideas later on please let me know.
    Thanks again!
     
  10. Could not get the info from his web site. That site needs some help it is barely functional. We can only hope your manual has some mention of output voltage as there is nothing online I could find.
     
  11. Using 1/4” plugs in bridge, both the tip and the sleeve, and the barrel for metal plugs, (normally at ground potential) are live with respect to ground. There can be a significant voltage between them presenting a shock hazard. If the sleeve or barrel of the plug touches something grounded, one side of the amp is shorted out.

    When a 1/4” plug is removed from the cabinet, the tip and the sleeve are shorted together momentarily shorting your amps outputs together. That really isn’t good for the amp.

    !/4” plugs and sockets were derived from the connectors used on manual phone switchboards. They were designed to work with a voltage of around 48V DC at a current of a couple of hundred milliamps. Speaker loads far exceed that and an amp in bridge can cause the connectors to burn out. As amps of ever increasing power became available the need for a safer connector led to the Speakon where there is no possibility of a short or a shock.
     
  12. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    Thanks for the heads up, I will definitely pursue the speakon route.
     
    mbelue likes this.
  13. Even more "history". XLR's were used for speaker connections for a while the problem being you can't use big wire sizes. So in high power PA's we used AC twistlock connectors (in reverse gender of AC connections) that still lead to "accidents". 1/4" jacks and plugs were burning with high power levels. The SpeakONs (patented by Neutrik) are a god send to high power audio.
     
    mbelue likes this.
  14. Remus_Redbone

    Remus_Redbone

    Dec 27, 2010
    Western AR
    I'm betting it's input level / sensitivity. I have a Drivecore XLS 1000, which does NOT have selective input sensitivity. I've only used the speakon for bridging, but I experienced the same issue until I got the input level up to clip minus a hair. Then the amp run into an Ampeg SVT 410 HLF will absolutely bring rain.
     
    mbelue, carsbybigd and Sleepwalker42 like this.
  15. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    The input sensitivity lowered at .775 improved the output a little bit but makes the preamp clip go crazy until I lower the gain to 9 o'clock and at that point the volume is low again. I tried with 2 different preamps with same result. My SWR Amplite (400W) still blows the Crown away, which makes me believe something is wrong with amp.
     
  16. Maybe you did get a bad one. You have learned some more about bridging and power amp settings anyway. Call for a replacement, but the input sensitivity on the power amp should not have affected the preamp clip light. It only sets the gain on the power amp.
     
    mbelue and Sleepwalker42 like this.
  17. Remus_Redbone

    Remus_Redbone

    Dec 27, 2010
    Western AR
    Not impossible, but you should be able to determine that by some testing. Set the amp up in stereo and and send a signal in to each side separately with a speaker connected to the same channel you are feeding a signal. If both channels seem to be working properly, it could still be the setup of the amp or your speaker cable connection.

    Good luck.
     
  18. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    Tried in stereo, connected single speakon to Ch1 and Ch2 (changing of course also the preamp to PO cable), they both have same power.
    Pumping up the Vol on amp at max, bass Vol at max too, master Vol on preamp at 2 o'clock, input gain at 12 o'clock I get only 2 green LEDs signal on amp lighting up. The same was in bridged mode. It's like you drive a car with the hand break pulled up hard.
     
  19. Keep pushing up the master on the preamp. You should be able to get 3 green LEDs on the power amp and even the red clip occasionally. A preamp unit is not like a amp head with a master volume, you should get a clean signal from the preamp with the preamp output master full up (it does not go into a power amp inside the preamp box, so no distortion).
     
  20. Sleepwalker42

    Sleepwalker42 Supporting Member

    Dec 30, 2008
    Chicago
    Will try that too.
    But the mystery remains, with the same exact set up, my SWR Amplite, with only 400W makes the walls shake and a the Crown with 1000 bridged feels like half, if not a third of the power.
     

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