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Adjust volume on preamp or power amp???

Discussion in 'Amps and Cabs [BG]' started by afroman, Jan 25, 2005.


  1. afroman

    afroman

    Aug 31, 2000
    Brooklyn, NY
    Which way is the "correct" way to do it?
    I have a preamp/poweramp setup and I've read some people that adjust their volumes with the power amp's gain knob. Others have the power amp's gain/volume knob all the way and adjust the overall volume in the preamp volume knobs.

    Are both ways correct or is one better than the other??
    I always ran my power amp on full and adjusted my volume with the preamp. I'd just like to make sure that this is the best way.

    Thanks...
     
  2. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    IMO you should keep your poweramp full on for the extra headroom and use your preamp for volume control.
     
  3. 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
    That doesn't give you "extra headroom."

    The correct answer is do whatever works. But you get better signal-to noise ratio and headroom by turning the amp down and putting a hotter preamp signal into it, as long as you don't clip anything, including the preamp.
     
  4. jvbjr

    jvbjr

    Jan 8, 2005
    I prefer the pre-amp master at full blast normally, as the hotter the signal the power amp sees, the less it has to work. Also, you tend to have a better signal to noise ratio when your power amp is doing less work.

    If you have effects in line between the pre and power amps, they will determine what is possible.
     
  5. Larry Kaye

    Larry Kaye Retailer: Schroeder Cabinets

    Mar 23, 2000
    Cleveland, OH
    I always try to set the pramp so that it just slightly clips when I really dig into the B or E string. Then I'll set the master volume to get what I want. I'll end up with the preamp set to around 2.5 to 2.75 and the master around 2.5 to 3 when using my passive basses and have found that by using the pad on the preamp input, I can essentially leave these settings be for my active bass.

    If I set the preamp any higher, it clips and the speakers will fart out, even at low volume levels. If I can keep the preamp from clipping, I can literally run my volume as high as I want to without distortion....of course being "realistic" that I won't want to be so loud that I bury the rest of the band.
     
  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
    The only "work" the power amp has to do is drive the loudspeakers, so it doesn't work "less" with a hot input signal.
     
  7. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    So, if I were to have my poweramp at say, less than halfway...I'd still get full power out of it?
     
  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 could. It would just take a hotter signal to hit full power than at full gain.
     
  9. RAM

    RAM

    May 10, 2000
    Chicago, IL
    That's interesting...I'm gonna have to try that myself.

    Jack Read told me I'm better off turning my Stewart World 2.1 up to at least halfway and adjusting the volume on my preamp.
     
  10. Quality

    Quality

    May 7, 2003
    Long Beach, CA
    I agree completely with larry and in my opinion (for what it's worth) this is the only way to to it. If you overdrive the pre-amp to a clip condition you will go be replacing speakers at regular intervals.
    Of course the pre-amp setting is completely dependent on how hot the bass's input signal to the preamp is.
     
  11. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    "as long as you don't clip anything" is a good point, things may not be as they seem...

    I might mention that the poweramp volume control is usually AFTER a balanced receiver stage.

    Depending on how the amp is set up, that stage may or may not have some gain. If it does, and you turn up the preamp and back off the poweramp volume too far, you may clip the balanced receive stage at or before the clip point of the amp itself. In that case, you could indeed get "extra headroom" from running the power amp volume higher, vs lower.

    That seems to be more of a problem with the import and off-brand units than with mainstream manufacturers like QSC etc. But it's worth remembering all the same.

    The typical power amp has about 10 dB less total gain with the volume turned to half. If you can afford to throw away that much gain, and the receive stage is OK, fine.

    But, I wouldn't, as some (not you, Bob) have suggested, make it a 'rule" to turn down the power amp some specific amount. That has been the main issue with things like the SVP-CL which have lower gain/output.

    The potentially increased signal to noise from turning down is really only applicable if the preamp has uncontrolled gain stages after the last volume control. Or, if the signal path to the power amp is noisy, due to pickup in the cable, etc. In those cases you turn down the noise, and increase the signal to compensate.

    But if the master volume of the preamp is after the last gain stage in the preamp, you really just have two volume controls in series. In that case you can generally use either one without a significant noise problem, preamp volume or power amp volume, just as you please. The only active noise source is the input stage of the power amp.
     
  12. Sundogue

    Sundogue

    Apr 26, 2001
    Wausau, WI
    Then what is the purpose of a gain control on a poweramp if it can just hit full power despite it's setting?
     
  13. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    How do you know if you're clipping the preamp?

    If I turn up the volume on my Alembic F-2B high enough it will start to get gritty, but I thought that this was just overdriving the tube. Is this the same as clipping, and should I avoid it, or is clipping something else? I know what clipping a solid state pre sounds like, but that's a lot different than the distortion I get when I crank the F-2B. Do I need to avoid clipping the F-2B (if that's even possible), and how do I know when it's clipping?
    Educate me, please..
     
  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
    Its purpose is to set the gain. What do you want it to do?
     
  15. ivanthetrble

    ivanthetrble

    Sep 9, 2002
    Orygun
    I'm pretty sure you can drive your pre-amp into clipping without causing damage. Clipping is what causing the nice distortion that some folks favor. If you take a slightly distorted pre-amp siginal and send it thru a power amp that is putting out nice clear power then you get that nice grindy tone. It is only when the power amp is putting out clipped waveforms that bad stuff starts to happen.
     
  16. afroman

    afroman

    Aug 31, 2000
    Brooklyn, NY
    I see there's a lot of different opinions. But I think that leaving the power amp on full and controlling volume on the preamp gives you more headroom. But I think one has to really keep an eye on pwer amp clipping, cause I just blew two speakers on my GS410 and I think it's due to clipping th epower amp.

    Keeps helping and thanks...
     
  17. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    There's others more knowledgable on this than I, but to keep it simple, solid-state (or probably even some hybrid) preamps can generate signal clipping.
    Tube preamps tend to 'squish' the signal instead of sharply clipping off the tops of the signal waveforms.
    Summary generalization: it's easier to generate signals that might potentially be harmful to your speaker system with solid-state (rather than tube) amplification if it's overdriven into clipping/distortion.
     
  18. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    We've (as a forum) disscused this before, clipping doesn't kill speakers, excess power (which is frequency dependant, being worst at resonance as pointed out by Ampeg Insider) and over excursion (which is also frequency dependant being worst below tuning) kills speakers.
     
  19. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    With my current setup, when I am in a live band setting, I tend to run my preamp at a level that is just below a certain hiss threshold (maybe, I just have a noisy preamp). In a venue that requires plenty of volume, I usually run my poweramp all the way open, otherwise, I set the overall volume level with the poweramp level control.

    For practice, I set the preamp volume at about 50% and set the poweramp level at whatever the family (or neighbors) will put up with.
     
  20. ivanthetrble

    ivanthetrble

    Sep 9, 2002
    Orygun
    Then what is the purpose of having all these clipping lights on amps?