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Poweramp attenuator settings

Discussion in 'Live Sound [BG]' started by Snowglo, Oct 22, 2015.


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  1. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    Probably been discussed many times, but I must not be searching properly. I recently began running a stereo rig using preamps & a power amp and am wondering if the power amp attenuators should always maxed or set as needed? Based on preference?

    I've been running the attenuators at ~ 12:00-2:00 and utilizing the preamp's level control as the volume control. Only been in pretty low volume rehearsal situations, but we go live & loud Saturday.

    If it matters, the preamps are a B7k for the treble and a DHA VT1-EQ-Bass-Drive for the bass to a Crest Pro 2.0. Both drive the amp decently (at least in my world of zero experience). The VT1 has a bit of a hiss. I'm assuming it's because of the tube.

    Suggestions?
     
  2. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    I may have found the answer; "A power amp will go to full power regardless of where you set the input pad. It depends on the level of the input."

    Why have attenuators then?

    I'm a confused, lost soul :sorry:
     
  3. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    which amp? Solid state?
    Basically, you want to gain stage your rig...
    The attenuators (they are NOT volume controls) are to allow control of when an amp reaches full power, relative to the speakers being driven.
    Yes, when at minimum, an amp can reach full output if driven hard enough (high input level). When wide open, they will reach full output with a LOWER input level. finding the balance is the challenge.
    In other words, you need to gain stage (google it) your system.
    For a SOLID-STATE amp...
    1. power off, then disconnect the speakers.
    2. power on and turn attenuators wide open.
    3. turn up your input level until the amp clips.
    4. back off attenuator controls a bit.
    Your amp should now not clip at that input level... it will still be able to reach full power, but that's why you match impedance and wattage of the speaker.
     
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  4. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    Perfect instructions @s0c9

    My new TB hero :thumbsup:
     
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  5. Because different signal sources have different output signal levels. For instance, the output levels of a mixing console will probably be a lot different than what your bass pre amp has.

    As an example, if your pre amp – or the aforementioned mixer – has a really hot output and you have the amps gains set for max, you’d have the problem of your system level going from nothing to ear-splitting with say, only 1/4 of the pre amp’s volume control’s travel. Ratcheting down the amp’s gains would allow you a wider sweep of the volume control. Make sense?

    Regards,
    Wayne A. Pflughaupt


    Administrator, Pedulla Club #45
    Administrator, Tobias Club #133
    Fretless Club #943
    Big Cabs Club #23
    My Rig: Stage and FOH Friendly
    My Basses


     
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  6. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    Thanks Wayne!

    I read something today which stated something like attenuators are not volume/output controls, they are input controls. Makes complete sense now. I did not realize the amp is still capable of full power with the attenuator(s) set very low.
     
  7. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    It's actually easier to set attenuator levels when dealing with a known line-level device like a mixer. The procedure listed above is pretty dang close and about the best you can do with regards to gain structure. Bottom line: when you crank up the preamp volume, you want a quasi-linear response from the power amp with no clipping and an optimal signal / noise ratio. No two power amps are alike: my DriveCores require little if any attenuation, my old QSC RMX units had to be cranked down to 37% (...that's a real value as defined by dbx!).

    Riis
     
  8. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    Thanks Riis. Have a live show tonight and plan on following the gain staging steps s0c9 listed prior to sound check.

    Question for any of you savvy sound guys, what if the amp never clips when gain staging? The preamp's level is maxed. Is there a "don't do that" factor? I'm assuming the stage volume would be too loud anyway. Just curious.
     

  9. Keep in mind that the pre amp may not – actually, probably doesn’t – deliver a clean signal at its maximum setting. It can start clipping as much as 30% below max.

    That said, to answering your question: If the amp never clips even with the pre amp at max, it means the pre amp doesn’t deliver a strong enough signal to drive the amp to its maximum output.

    Regards,
    Wayne A. Pflughaupt


    Administrator, Pedulla Club #45
    Administrator, Tobias Club #133
    Fretless Club #943
    Big Cabs Club #23
    My Rig: Stage and FOH Friendly
    My Basses


     
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  10. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    If the amp never clips during gain staging then you can run it "wide open" using that input signal source level.
    I have QSC, Crown and Yammy amps, and they all "clip" at some level when driven by my A&H consoles.
    But remember, it can be a trade-off between output levels and induced noise.
    Meaning that just because you can run them wide open doesn't mean you should.. if it's all whisper quiet, then fine.
    Me.. in that scenario... I'd back off both the attenuator and the input levels just a bit. You lower the potential noise floor and optimize your ouptut levels.. If it's too loud, turn down the input level , NOT the amp attenuator.
     
  11. mbelue

    mbelue

    Dec 11, 2010
    When setting your input level on your poweramp you were playing right?
    Your preamp needs an input to preamplify right?
    Just turning up the preamp won't send the poweramp anything if you aren't plugged in and providing the preamp signal.
     
  12. MJ_Sotti

    MJ_Sotti formerly "Mike in Chicago"

    Apr 3, 2011
    Chicago
    for soc9...that's for class D too?
     
  13. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    As far as I know....ALL SS (solid state, meaning it's not a "TUBE" amp).
    If you crank up a tube amp with no load/impedance (speakers) attached, be prepared to "let the smoke out" and prep for a LARGE repair bill.

    Meaning DO NOT use my directions above on a TUBE amp!!
     
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  14. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Given the preamps, I would be inclined to find the maximal operating band for them and then establish the power amp input attenuation level.

    I had a Vha-1 ...or was it a vht-1. Years ago and I forget. Loved it tonally but the noise floor made it unsuitable for me. If I had really needed it, I might have invested some time in figuring that aspect out. It was so close to cool...

    How are you sending your signal to the FOH? Seems like you'll need 2 lines or mics. If I understand what you're doing which is not a given...

    So what cab's are you driving with this beast ? Is there a crossover ? Depending on the cab's I wonder if something like the SfX microMix would be an addition. Let you funk with the preamps and combine before the power amp to drive a backline cab sort of thing...

    I did something like that using an Alembic F2-B years ago. At the time it ws the best way I could find to gain balance my effect chain and dry signal before the amp. The f2b has a mono summed output as well as the A& B outputs....
     
  15. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Oh cool, you're in Oregon. Where about ?
     
  16. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    I agree, the VT1 is noisy at moderate to high gain levels. I've been meaning to ask the smart folks here if there is a way to filter it.

    Both signals are run to FOH. One from the B7k, one from the VT1. Cabinets are a fEARful 12/6 and a Dr. bass 12/6. Hopefully soon I can build a matching fEARful and ditch the Dr. Bass cab. Not a bad cabinet by any means. It's very Ampegish in tone, but I prefer the GB cabs.



    Dallas. A small town 20 miles west of Salem.
     
  17. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Ah. I've ridden my bike through there. Eola Hills bike tour. Nice country down there. I'm across from Hood River on the WA side. Funny on the GB thing. I run an f12.6 and if I need more, add an f12.sub. I just don't need more than the single 6 for my ear.

    I have an extra 12.sub cab of you want to try that out some time. When I got the GB bug, I did 2 subs and 2 12.6's I ran that setup exactly once ... Wt 800 slaved with a plx 2402... I could barely crack the volume ;-) looked nifty though...
     
  18. Snowglo

    Snowglo Pro Aris et Focis Supporting Member

    Nov 15, 2013
    Orygun
    U.S. Military endorsement since 1984
    Oh man, two 12/6 stacks with subs! Now that would be fun. If I remember correctly, you were selling a sub awhile back. Wanted to grab it, but I'm not sure if adding a sub is for me. IDK???

    If I decide to stay with a stereo rig, another 12/6 would be perfect.

    My band played our last show Saturday and it was the first time I ran a stereo rig live. I really liked it, but didn't have enough time to set the FOH properly. It needed more of the bass pup dialed in. Our sound guy is a good friend of the band and basically monitors the mixer to ensure nothing gets out of hand. Honestly, I can get my tone easily with a mono rig, so a sub may be the way to go.

    Does adding a sub really increase the volume that much? Volume being a very subjective term.
     
  19. s0c9

    s0c9 Supporting Member

    Jan 9, 2014
    Ft.Worth/Dallas
    1964 Audio artist, Fractal Audio Beta Tester
    Subs are about FOH control, not volume (tho' they can add that).
    They are about giving the sound guy control over the house mix.. so YOU don't need to blast everyone out of the room to be heard from the stage!
    Needing them depends on music style and room size. Probably not really necessary for a folk group in a wine bar tho'! :rolleyes:
    I used to run a couple of Yorkville LS100P's (1500w ea) for subs, but cut back to one since TWO was overkill for most clubs/bars/venues my old rock band used to play.
    Current band runs a 15" sub each side now.. and one venue we play (house PA) has SIX dual-18" subs UNDER the stage.. lotsa bass!! :bassist::hyper:
     
  20. mbelue

    mbelue

    Dec 11, 2010
    I believe he is referring to a fEARful 12/sub. Which can be used as a FOH sub but in his case is used to reinforce backline bass amps.
     
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  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Mar 1, 2021

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