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Preamp to Poweramp Connection Question

Discussion in 'Amps and Cabs [BG]' started by jswingchun, Sep 1, 2008.


  1. I just bought a Crown XTI 1000 power amp to use with my Ashdown preamp. The full range output on the Ashdown pre is a 1/4" phone jack. The input on the Crown is XLR.

    First I tried using a 1/4"-1/4" instrument cable with an impedence matching transformer adapter to convert to XLR. It worked, but my output level was really low.

    Next I tried a 1/4"-XLR shielded patch cable. It has the stereo-like plug with the extra ring on the 1/4" phone plug. It buzzed and the level was really low. I tried two of them, both brand new.

    As a test, I plugged my bass into my mixer and ran an XLR-XLR cable from the mixer to the Crown. No buzz and it was crushing loud.

    What am I missing here? Seems like the level coming off the Ashdown preamp isn't right. Is there some other cable I need?
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Does the Ashdown have a -10dB/+4dB switch? Or a pre/post switch? Does the manual for the Ashdown state whether the 1/4" output is balanced or unbalanced (yes I saw you used an external adapter, but it might make a difference anyway) or what the nominal output level rating is for that jack?

    What is the input sensitivity rating for the Crown?
     
  3. bakeronbass

    bakeronbass

    Apr 3, 2007
    Humboldt Ca
    Endorsing Artist; Schroeder Cabinets
    I guess there is not a balanced or xlr out? Seems like there should be. Line out XLR.
     
  4. The Ashdown has an XLR output for DI, with a pre/post eq switch. I just tried it and the level was still almost nothing. The manual says this for the DI out:

    600 ohms balanced, -20dBu nominal.

    The manual says this for the full range 1/4 inch output:

    Impedance 1K Ohms, level switched 0/+4dBU.

    I tried the level switch in both positions. It is a tiny bit louder with the switch at +4.

    Here are all the specs from the Crown that mention input:

    Input Impedance (nominal) 20 kilohms balanced, 10 kilohms unbalanced

    Maximum Input Signal +22 dBu typical

    When I play with the preamp nearly cranked, I am lighting up the "signal" input led on the Crown, I can't get the -20 led to light up. When I tested with the mixer, I could light up the clipping led.

    Any ideas?
     
  5. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    That is bizarre. According to the Crown specs it will accept an unbalanced signal. Is there a 1/4" input on the Crown? If not, I have to imagine they mean you can short one leg of the XLR; I think the other end of the cable in that case would have to be TS (mono) rather than TRS (stereo), but it depends on the output jack of the Ashdown. E.g. if both tip and ring of a TRS plug are contacted by the contact tab inside a TS 1/4" jack, then I think the signal would at least partially cancel itself out at the amp end. I could be wrong about that though.

    At this stage I would bring the Ashdown to a friend's house or a music store to try it with a different power amp. That output on the Ashdown may be faulty.
     
  6. I just found a diagram in the Crown manual showing an XLR plug with an unbalanced connection. It shows the + wire to pin two of the XLR and the shield to pins one and three.

    So, I take it the XLR/1/4" cable I bought is balanced and does not work with the Ashdown's unbalanced out.

    I'm guessing having that cable that may be the answer.

    Sound right? I would imagine I cannot buy that cable at Guitar Center.

    The Ashdown 1/4" output works fine with an older power amp I have that has a 1/4" input.

    Addition:
    There is no 1/4" input on the Crown.
     
  7. Your answer is in the specs: Ashdown +4dBu, Crown up to +22dBu. I think that you have insufficient output from the Ashdown to drive the Crown.

    Paul
     
  8. I don't think so. The Crown's +22dBu is level before clipping. Sensitivity is what we should be worried about. From Crown's specs, sensitivity for max output is 1.4 V. This is roughly 5.1 dBu. It sounds to me like something isn't working properly.
     
  9. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Correct. Your best bet would be to take an instrument cable and chop one end off. Then buy an XLR plug of the appropriate gender, and connect it as per the diagram.
     
  10. I had to go to Guitar Center anyway, so I looked around and they had an unbalanced 1/4"-XLR cable. I picked one up and everything is working as it should now. I am going to do as you suggested and make a shorter one though too.

    Thanks for the responses, you steered me in the right direction!
     

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