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Pre-Amp output ATTN: Heavy Duty and Bob from QSC please.

Discussion in 'Amps and Cabs [BG]' started by Josh Ryan, Jan 21, 2002.


  1. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    I am thinking about getting a tech21 RBI really soon now, but I wanted to know what the output was from the XLR. H.D., I know you have one, did it give specs for output range? Bob from QSC, I had seen a post you made mentioning your various successes (and lack of) running pre-amps into power amps, I was hoping you might be able to list some high output pre-amps. If anybody else has some data, thanks as well!
     
  2. HeavyDuty

    HeavyDuty Supporting Curmudgeon Staff Member Gold Supporting Member

    Jun 26, 2000
    Suburban Chicago, IL
    Per the RBI manual, the XLR output level is in the 0dB range "due to the wide availablility of digital recorders, which are unforgiving to excessive input levels".
     
  3. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    OK thanks!
     
  4. 0dB what? dBu, dbv, dBm? Do they give the reference? 0 dBu is not the same as 0 dBv. 0 dBu = +4 dBv (please correct me if I'm wrong), so it depends on what the reference is. Either of those as nominal levels should be able to drive most power amps without much problem. 0dBu corresponds to about 1.4 volts. Most amps can be driven to full power with an input of 0.775-1.0 volts, with some at 1.4, so you should be fine.
     
  5. The SWR IOD has the same nebulous crap: "+24dB maximum output." Whatever that means. Fortunately, either dBu or dBV, it is still a boatload of voltage (12 ~ 15) and more than enough to drive hell out of my QSC. Mine requires 1.0 Vrms for maximum output.

    Blisshead is on the right track, asking those questions BEFORE investing the cash. No sense in doing it, if it won't drive a standard power amp properly.
     
  6. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Thanks everybody. Bgavin, that's exactly it. -I bought a power amp (Mackie1400) before I asked enough questions, and though not disastrous, I am trying to be a little more careful for the pre-amp!
    Spacegoat, I was told I need 1.4 volts to drive the Mackie to full power. I'm using a Sans Amp BDDI now with no problem. The more I read about the IOD the more interesting it sounds though. I keep finding bits about it in different threads. Thanks again.
     
  7. HeavyDuty

    HeavyDuty Supporting Curmudgeon Staff Member Gold Supporting Member

    Jun 26, 2000
    Suburban Chicago, IL
    Sorry for the delay in getting back. No reference is given in the manual, but the tech I spoke to at Tech 21 a few weeks ago implied the RBI output was hotter than the SABDDI.
     
  8. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Cool, that would be a plus. I emailed them and got a reply saying they were all at NAMM. I'm 99.9% sure I'm going to get the RBI, as I already know and love that sound. Post when you try it with the Carvin.
     
  9. HeavyDuty

    HeavyDuty Supporting Curmudgeon Staff Member Gold Supporting Member

    Jun 26, 2000
    Suburban Chicago, IL
    Maybe today, just not mounted in the rack...
     
  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
    Hi Blisshead,

    Over the past few years I've tried to get maximum output voltage information from various preamp manufacturers but with mixed success. Typically I'd get responses like "-10 dBV" or "1 volt," and so I'd ask for clarification: is that nominal or maximum? Nominal. Okay, then, what's the maximum output voltage? And around it goes again. (Note: -10 dBV = 0.316 volt.)

    Sometimes you can tell something from a schematic. At least if the preamp's output is an op amp stage with a ±15 volt power supply, you can figure it can put out up to at least ±12 volts peak, or about 8 volts RMS.
     
  11. 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
    0 dBu = 0.775 volt RMS (the dBu reference is derived from the Bell System's "dBm," which was a reference to milliwatts in a 600-ohm load)

    0 dBV = 1 volt RMS = +2.2 dBu
     
  12. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Thanks Bob, do you have any specifics for preamps that are really good (or not!) to drive a power amp? I don't know if you can list something like that, if not no problem. I'll apply the conversion you gave in reply to Spacegoat and check them all out as my emails get answered. thanks everybody.
     
  13. HeavyDuty

    HeavyDuty Supporting Curmudgeon Staff Member Gold Supporting Member

    Jun 26, 2000
    Suburban Chicago, IL
    Today, I finally had a chance to rig up the new Carvin DCM1000 and the RBI. No prob with the amount of drive out of the RBI - I could light up the clip light at will!

    And, damn - what a difference in tone! I suspect a lot of it is the jump from 125W to 700W - major headroom.

    One thing that sucks: having to start from scratch on how to dial in "my" tone. Everything changed!

    Another thing that sucks - the metal venetian blinds in the practice room have to go! :D
     
  14. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Sounds like a problem we'd all like to have. :cool:
     
  15. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Congrats!! earth shaking power is fun.
     
  16. HeavyDuty

    HeavyDuty Supporting Curmudgeon Staff Member Gold Supporting Member

    Jun 26, 2000
    Suburban Chicago, IL
    Total weight of the rack, DCM1000, RBI and Korg rack tuner: 38 pounds! Not bad for 1000W of audio terror...
     
  17. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    That's very cool, my Mackie weighs in at 38lbs. by itself.
     
  18. My MX-3000a weighs 69 pounds...

    yuck
     
  19. Josh Ryan

    Josh Ryan - that dog won't hunt, Monsignor. Staff Member Supporting Member

    Mar 24, 2001
    Wow, it should come with a roadie! -although care of said roadie might make that tough;)
     
  20. Roadies are the most underpaid, overworked guys in the business. I suppose the drugs and babes make up for it

    :D

    My rack is so gawdawful heavy, I am going to split it into 2 sections so I can manage it.