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preamp level vs. power amp level

Discussion in 'Amps and Cabs [BG]' started by Juniorkimbrough, Oct 16, 2006.


  1. Juniorkimbrough

    Juniorkimbrough

    Mar 22, 2005
    Mississippi / Memphis, TN
    Endorsing Artist: Lakland Basses
    for those of you running pre/power amp rigs I have a question...

    Do you think it's better to run the preamp signal as hot as possible without distorting so the power amp will not come close to clipping or making the power amp work as hard.

    For example, on my RBI/QSC rig......when I run the levels on my RBI at around 2-3 o'clock, I only have to run my QSC at around 12 o'clock or less to get the desirable volume and the lights on the power amp don't come anywhere near clipping when i do this.

    Whereas when i run my RBI levels at around 12 o'clock, I usually have to turn my power amp up to 3 o'clock or so and the lights come just under clipping but never clip.

    It seems like the first way would be better, am I correct by thinking this? It just seems like your power amp would run a little cooler since it's not working as hard, or am I completely mistaken by my way of thinking?

    Would love to hear everyone's opinions!
    Thanks!
     
  2. Fuzzbass

    Fuzzbass P5 with overdrive Gold Supporting Member

    When setting my pre/power rigs (one of which features an RBI), my goal is optimum tone, minimal hiss, no unwanted distortion, and enough volume and headroom for the job. Sounds like you have all of these going for you in both examples you cited above.

    So, I don't think it really makes a difference either way. Both examples are cool. The only question I see is, "what to do if you need even more volume?" If your RBI is nearly maxxed, then it'll be better to goose your power amp... and vice versa.
     
  3. Juniorkimbrough

    Juniorkimbrough

    Mar 22, 2005
    Mississippi / Memphis, TN
    Endorsing Artist: Lakland Basses
    the main thing I'm wondering is will turning the preamp level up higher will that in return put less strain on the power amp?
     
  4. Rune Bivrin

    Rune Bivrin Supporting Member

    Oct 2, 2006
    Huddinge, Sweden
    Not really. The power amp doesn't care where the signal gets boosted, it only cares about the level at the speaker output when it comes to strain. (And as a side note, max strain is generally NOT at maximum output, but somewhere at 40%.)

    As a general rule, if you want as clean sound as possible: Turn the power amp up max, and use the preamp volume for volume control.
    That said, this may be impractical for reasons such as hum or hiss, and then you'll have to back down to acceptable levels.

    And there's no accounting for circuits that change the frequency response as you change volume knob position.

    Rune
     
  5. dunamis

    dunamis

    Aug 2, 2004
    Charlotte
    I've always heard that you should turn the preamp up a point just before clipping occurs on the input stage of the power amp, and then adjust the power amp for the upper level of the appropriate volume range. You can then turn the preamp gain down a bit if you're too loud.

    Adding gain early in the chain maximizes the dB difference between the noise floor and the program (the signal you want to hear). Each stage of amplification adds gain to the entire signal (noise + program), so starting with a higher dB difference early in the chain means that the difference between noise and program signals is greater at the end of the chain as well (ie: what you hear from the speaker).
     
  6. dunamis

    dunamis

    Aug 2, 2004
    Charlotte
  7. Rune Bivrin

    Rune Bivrin Supporting Member

    Oct 2, 2006
    Huddinge, Sweden
    That is sound :)smug:) advice in general, and with really low level sources such as dynamic microphones it's definitely essential, but I've yet to come across a bass rig that actually presents a problem as far as noise is concerned. And since I like to stay clear of clipping, I make sure to have as much headroom as possible. Now, having the power amp gain / master volume at max might be a bit over the top, but set it higher than you'll ever need and pre amp gain a little lower than what seems resonable. Then you can safely control volume with the pre amp volume control.

    If you want distorsion, it's a different ball game, of course.

    Rune
     
  8. dunamis

    dunamis

    Aug 2, 2004
    Charlotte
    That's a reasonable suggestion and would seem to allow for a greater range of volume control at the preamp gain knob.

    Thanks!

    Matt
     
  9. RAM

    RAM

    May 10, 2000
    Chicago, IL
    I had this discussion with Jack Read who sold me my Purity and my Stewart World 2.1. My question to him was essentially the same you ask, and his response was interesting: he prefers to turn the power-amp up to at least 5, then adjust the preamp, accordingly. After discussing this with him further, what he told me is it varies from person to person and rig to rig.

    I've found my optimal tone comes from boosting the poweramp to around 6 or greater, then adjusting the preamp, much as Jack recommended.

    I've heard others make claims a different group of settings works better for them.
     
  10. Juniorkimbrough

    Juniorkimbrough

    Mar 22, 2005
    Mississippi / Memphis, TN
    Endorsing Artist: Lakland Basses
    Thanks for all the suggestions!!!



    This is also what I'm finding. It just seems like I have more headroom if I put the power amp on 12 o'clock and adjust the preamp level accordingly.
     
  11. Juniorkimbrough

    Juniorkimbrough

    Mar 22, 2005
    Mississippi / Memphis, TN
    Endorsing Artist: Lakland Basses
    The following reply from Bob @ QSC seems to reassure me of what I am thinking....

    "The general idea in optimizing gain is to have a reasonably hot signal from as early in the signal chain as possible. This allows the use of low to moderate gain in later stages to avoid a big buildup in the noise floor."

    Keep in mind I do use only passive basses, I imagine the more elements you have in the chain with change how you want to set it. I only have passive bass -> preamp -> power amp -> cab.
     
  12. Yep, that basically sums it up nicely. :)
     
  13. dunamis

    dunamis

    Aug 2, 2004
    Charlotte
    ^
    |

    ...and it sounds vaguely familiar...

     
  14. Sorry, didn't read through the thread first....:rollno:

    Kudos to you too!:)
     
  15. Juniorkimbrough

    Juniorkimbrough

    Mar 22, 2005
    Mississippi / Memphis, TN
    Endorsing Artist: Lakland Basses
    Thanks to EVERYONE for your help!!
     

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