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Question about wiring preamp to power amp and a DI with balanced cables

Discussion in 'Amps [BG]' started by thumbstruck, Apr 13, 2014.


  1. thumbstruck

    thumbstruck

    Joined:
    Sep 28, 2010
    I've been running an Avalon 737 into a Crest CA6 with a JDI passing Thru between the two, so I can give the sound man my preamp tone. I was using regular TS patch cables, but recently noticed that the output on the Avalon is balanced, as is the input on the CA6...

    So two things, I assume I should be connecting the pre/power with a balanced TRS, and with the JDI passing Thru to the CA6, is that messing with that balanced signal? Also, should I notice a difference in tone/noise once I switch to balanced cabling? Thanks guys.
     
  2. walterw

    walterw Supportive Fender Gold Supporting Member

    Joined:
    Feb 20, 2009
    with a balanced out from the preamp you don't need a DI box at all!

    a splitter cable with TRS to two XLR male ends, one for the amp and the other to go into a mic cable and right to the snake, would be all you need.

    alternately, most power amps have their 1/4" and XLR inputs paralleled right together; that means you can use a TRS cable right from preamp to amp, then get an XLR turnaround adapter or little cable with males on both ends, plug that into the XLR input on the amp, and plug the mic cable to the PA into the other end.
     
  3. bongomania

    bongomania Gold Supporting Member

    Joined:
    Oct 17, 2005
    Location:
    PDX, OR
    Disclosures:
    owner, OVNIFX and OVNILabs
    All correct, just two additional points--

    The output of the Avalon will be line level, so the soundmen will need to be alerted to the very high signal level coming in, so they can patch you to a channel with no mic pre, or engage a pad, etc., to avoid clipping their system.

    You can't run a balanced connection path through the Thru of the JDI. Thru is unbalanced only, no matter what cable you use.
     
  4. thumbstruck

    thumbstruck

    Joined:
    Sep 28, 2010
    I'm really embarrassed here, guys. I had posted about this a year ago, and it totally slipped my mind when I was re-racking my rig this weekend. Bongomania was even a big contributor to that thread! I must be overworking myself. Thanks for the replies though.

    I do have a NEW and quick follow up question though- The Crest has a low .75V input sensitivity, and some amps I was looking at as a lighter alternative measured around 1.5V. I can't find any information about the output of the Avalon, except "+30dB balanced 600 ohms". DBU or DBV would've been nice of them to provide. Any ideas?
     
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  6. Passinwind

    Passinwind Charlie Escher Supporting Member

    Joined:
    Dec 3, 2003
    Location:
    Columbia River Gorge, WA.
    Assume the worst case, that the spec means dBu. 30dBu = 27.78dbV = 24.49 volts RMS
     
  7. thumbstruck

    thumbstruck

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    Sep 28, 2010
    Yikes. When would anyone need that much output when nominal line is +4?
     
  8. Passinwind

    Passinwind Charlie Escher Supporting Member

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    Dec 3, 2003
    Location:
    Columbia River Gorge, WA.
    IME, for some applications you want at least 16dB of headroom over what you actually need. My DIY bass amp has a power amp section input sensitivity of around +8dBu, and I budgeted at least 12dB of headroom over that for my basses and how I play them, for example.
     
  9. thumbstruck

    thumbstruck

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    Sep 28, 2010
  10. Passinwind

    Passinwind Charlie Escher Supporting Member

    Joined:
    Dec 3, 2003
    Location:
    Columbia River Gorge, WA.
    No need, the input and/or output sections can just be turned down.
     
  11. thumbstruck

    thumbstruck

    Joined:
    Sep 28, 2010
    I see. So it's just a matter of being mindful of how much output I'm sending toward the power amp?
     
  12. walterw

    walterw Supportive Fender Gold Supporting Member

    Joined:
    Feb 20, 2009
    power amps have level knobs for just this reason; back them down if it's too hot, no big deal.

    (and i thought this situation sounded familiar...)
     
  13. bongomania

    bongomania Gold Supporting Member

    Joined:
    Oct 17, 2005
    Location:
    PDX, OR
    Disclosures:
    owner, OVNIFX and OVNILabs
    Well, except the level knobs are post the input buffer, so they don't help with clipping at the input.
     
  14. thumbstruck

    thumbstruck

    Joined:
    Sep 28, 2010
    All else considered a good match (imepdance, etc..), with adjustments to the output level on the pre, I'd be ok? I read your article "preamps explained". Very helpful, thank you for taking the time to write that. Unfortunately, I couldn't find any info online about the Avalon's line out except that it's labeled +30db (assumedly DBU), which tells me that I'd have more than enough juice to drive the power amp properly, as long as I don't push it into clipping.
     
  15. bongomania

    bongomania Gold Supporting Member

    Joined:
    Oct 17, 2005
    Location:
    PDX, OR
    Disclosures:
    owner, OVNIFX and OVNILabs
    Oh yeah, everything is fine, your system is all in great shape, just watch the levels as noted. All good.
     
  16. thumbstruck

    thumbstruck

    Joined:
    Sep 28, 2010
    Great. Thanks for the thoughts, everyone. And thanks for the article, Bongomania.
     

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