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Crest power amp help .... Please

Discussion in 'Amps and Cabs [BG]' started by Picker, Nov 20, 2003.


  1. Picker

    Picker

    Nov 10, 2003
    Howdy y'all

    As some of you know I just got my rig
    Tech 21 RBI Sansamp
    Crest CA-9 power amp
    Avatar 4ohm 2x12

    I initially had some difficulty hooking up. Initially I thought one of the inputs on the Avatar wasn't working, but I have since tested and found both work normally. I have since discoverd how to get sound, but I'm not sure of the Why or if I'm doing things correctly. The problem was with my hookup to the power amp.

    Sorry, I couldn't find a pic online of the back of the amp, but here's what we got:

    There is a selector switch offering
    1. Stereo
    2. Parallel
    3. Bridged Mono

    There are three output jacks labeled.
    1. A
    2. B
    3. AB (bridged mono)

    The power amp is rated at 900 watts @ 4ohms and the speakers supposedly can handle 1000 @ 4ohms. I was going to use one channel from the power amp to power the cab.

    Initially (when it didn't work) I had selected Stereo from the switch and had plugged the output into channel A. I had assumed that I could use the gain knob from channel A to control output and leave channel B empty, but no sound. Tried this same configuration using the Parallel option on the selector with the same result.

    Actully by accident when attempting to switch channels I plugged into the AB output jack and Bingo.... we have sound.

    Now... what disturbed me was that this said Bridged mono and I wasn't running in Bridged mono.

    My suspicion is that if you have a speaker plugged into channel A, the amp expects there to be something in channel B also. If you don't have something plugged into both then it will not send power. If you want only one speaker you must plug into the AB jack.

    My second assumption is that even thought the AB output jack is labeled "AB Bridged Mono", the amp is not running in Bridged Mono unless you also have the selector swich set to that. If it is set to Stereo and you are plugged into the AB jack you are only sending the power from one channel as intended. What if you also turn up the gain on channel B?

    Am I correct in my thinking? What am I missing here??

    By the way, I already RTFM and it didn't say anything about it.

    Thanks
     
  2. 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
    There would be signal at the bridged output, even if the amp is running in stereo. The only thing is that one side of the output would be channel B's output instead of ground. How about in stereo on channel B--does that work?

    If you can't work it out, call Lenny Tedesco at Crest at (201) 909-8700. Tell him I said hi!
     
  3. Picker

    Picker

    Nov 10, 2003
    No... if I had it in Stereo or Parallel neither channel A nor channel B would work. Either setting does work if I am useing the AB channel to the speaker. That's when I came up with the theory that the amp would not allow it unless you were plugged into both channels.
     
  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
    The amp doesn't switch signals to the output jacks.

    Assuming the AB jack is wired channel A on 1+ and 1-, and channel B on 2+ and 2-, the A jack is wired to 1+ and 1-, and the B jack is also wired 1+ and 1-, the next step I would recommend is opening up the Speakon plug on your cable and see how it's wired. From your description, it seems like it may be wired 1+ and 2+; you want it to be 1+ and 1-.

    So open up the Speakon plug. If it is wired to 1+ and 2+, use a suitable screwdriver or Allen (hex) wrench to loosen the setscrew on 2+, remove the wire, insert it into 1-, and then tighten the setscrew on 1-. Then re-assemble the Speakon plug.
     
  5. Picker

    Picker

    Nov 10, 2003
    Thanks Bob...

    I have discovered that I do have an incorrect cable. The cable was designed for Bridged Mono and is wired differently. I will be returning it to GC offering a few choice words to the salesman that sold it to me.

    I'm really relieved that it was just the cable. I was worried there was something wrong with the amp.

    Thanks again:bassist:
     
  6. 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, I'm glad the problem was something small. Have you tried changing the wiring of the Speakon plug yourself?
     
  7. Picker

    Picker

    Nov 10, 2003
    Someone else suggested that to me... If it's easy to do I might give it a try... I've never even looked at the inside of a SpeakOn/Neutrik connector before...

    Know where I can get a good deal on a soldering station? ;)
     
  8. 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
    You don't need to solder with a Speakon. My post above tells you what to do.

    Have a look at http://www.neutrik.com/images/ock/downloads/Media_293225003.pdf to see how the plug disassembles. You unscrew the bushing that the cable goes through (you might need a 3/4" wrench if it's too tight to do by hand).

    Then you'll need either a Phillips screwdriver or a 1.5 mm Allen or hex wrench (depending on what kind of setscrews it uses--I think all the newer ones use Phillips screws) to do the setscrews.

    Follow my instructions in the post above.

    When you're done, just tighten the bushing onto the housing again, and you're set.

    It takes only a couple minutes, and probably less if you've done it before.
     
  9. Picker

    Picker

    Nov 10, 2003
    So I only need to adjust the SpeakOn side of the cable then? Nothing needs to be done to the 1/4" side?
     
  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
    No, unless your speaker cabinet doesn't have a 1/4" jack. If it doesn't, but instead has a Speakon, then you'll need to take the 1/4" plug off the cable and install a Speakon plug. If that's the case, then it might be easier just to return the cable for something appropriate.
     
  11. Picker

    Picker

    Nov 10, 2003
    No... the amp has SpeakOn and the cab has 1/4"

    Ok... I'll open up the connector tonight and see if I can figure out which connector is which. Hopefully, it will be labeled clearly and I can just switch from the 2+ terminal to the 1- terminal. I will leave the 1/4" side as it is.

    Thanks once again.
     
  12. BOB LEE ROCKS!!!!!
    :bassist: :bassist: :bassist:
    Seriously, I wanted let you know how much I appreciate your participation in this forum. Taking your time to help get a competitor's amp up and running is just another example of your excellant contributions.
     
  13. Picker

    Picker

    Nov 10, 2003
    Take a bow Bob :D:D:D
     
  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
    Thanks, but I just share what I've learned over the years. With customers and non-customers alike. ;)

    I think most people would do the same. It's like when you see someone who needs help, and you can easily give that help, why not? Sometime I'll need help, too.

    Have a good weekend.