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What does the "presence" knob do, usually?

Discussion in 'Amps and Cabs [BG]' started by KingRazor, Jan 14, 2012.


  1. My bass amp has a "presence" knob. What does that normally do on an amp?

    Before you ask, I don't have the manual and couldn't find it online. The brand is RMS and the model is RMSB20.
     
  2. Doug Parent

    Doug Parent Supporting Member

    May 31, 2004
    San Diego, Ca.
    Dealer Nordstrand Pickups.
    probably boosts around 4khz or higher.
     
  3. rh2music

    rh2music Supporting Member

    Feb 18, 2009
    Bellevue, NE
    Most presence knobs on guitar amps are very high frequency, like a super treble. So, I'm guessing the same on a bass amp, I just don't know what frequency it would be. Hope that helps.
     
  4. smadder

    smadder

    Nov 13, 2004
    On a bass amp, the presence knob (also goes by the name "enhance") usually boosts the highs and lows while decreasing the mids the more you turn it clockwise. Counter-clockwise does the opposite or just flattens it out. Essentially it's a variable mid-cut/scoop knob.

    HOWEVER!!!! It's important to note that it's called different things by different manufacturers and will affect different frequencies as well from amp to amp. It all depends who made your amp. But speaking generally, this is what the enhance/presence knob functions as on amps that have it.
     
  5. Ok, thanks for the info. I keep it fully counter-clockwise, lol. It sounds awful when I turn it up past 5. But, this is a very cheap amp.
     
  6. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    It marks you present.
     
  7. It gives me presents? :hyper:
     
  8. testing1two

    testing1two Gold Supporting Member

    Feb 25, 2009
    Southern California
    On tube amps the presence control works differently than on a solid state amp. On a solid state amp a presence control is just another band of eq with a higher frequency than the treble eq. Tube amps function quite differently and the magic happens in the power amp, not the preamp thanks to a circuit called a negative feedback loop. What's that you ask? I am borrowing this excellent synopsis from a TGP friend:

    "So you know that two audio waves that are "out of phase" will cancel each other out, right?

    Negative feedback exploits this. Tube amps are hardly "linear" or "flat" when it comes to frequency response. Specifically, there is usually a 'bump' in the midrange. In many hi-fi circuits (and guitar amps starting with the fender brownface amps, since Leo was always looking for a more 'hi fi' sound) there will be a small amount of the output signal "fed back" into the audio path at an earlier point with polarity inverted so that it is out of phase with the main signal.

    Since we know that two signals out-of-phase will cancel, this means that a little bit of the audio gets cancelled out. This works to "flatten" the frequency response, since the frequencies that are loudest in the fed-back signal get attenuated most in the overall output. The loudest bits of the fed-back signal are doing "the most cancelling," to put it another way.

    Now, if we add tone controls (like a simple capacitor treble-bleed off tone control as on your guitar) to the negative feedback circuit, we can control how much treble gets fed back and "cancelled out." By turning the presence "up" we are actually 'darkening' the signal in the negative feedback loop, making it so that the treble frequencies are "less cancelled." This gives not just a brightness, but an overall liveliness in the top end that cannot be accomplished with a simple treble boost."
     
  9. BBQV

    BBQV

    Feb 13, 2010
    Uppsala, Sweden
    On the SansAmp BassDriver DI the presence knob gives you an instant vintage sound when you turn it off. It controls the amount of high frequency sheen. And string noise...

    Sounds like your knob is doing that too. Better leave it off! ;)
     
  10. Very interesting.
     
  11. Duke21

    Duke21

    Nov 14, 2010
    Narvik, Norway
    It gives you vintage tone also if you turn the presence on. Some vintage tube amps have the presence knob, and the knob on the BDDI emulate a vintage tube head. At least it is what Tech21 says.
     
  12. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Actually, while you're right that it varies from one manufacturer to the next, "presence" is usually NOT used with the same meaning as "enhance" or all the other euphemisms that are used for "mid scoop". Presence is, as the others indicated, either a high treble boost, or an adjustment of the circuit to keep highs from being cut.

    Nearly all other weird undefinable knob label words are typically a mid scoop. :)
     
  13. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    Thanks for that explanation!

    All I know about the OP is that on a Sansamp RBI, the Presence knob is a boost only super-treble control. Boost only meaning Full CCW is "flat", and noon is 50% boost. How that relates to the amp in question, I have no idea :D
     
  14. smadder

    smadder

    Nov 13, 2004
    I know, and believe it or not I've encountered some bass amps that had the mid-cut function on a knob( or button or switch) and had it labeled as "presence." I should have done a better job explaining this in my previous post so I apologize. The fact is, as you point out, there will always be gimmicky euphemisms tossed out just for the sake of having another toy/feature to help sell the amp (sometimes useful, sometimes not). The lesson is always read up and experiment as much as possible (hopefully BEFORE you buy your amp) to make sure you're getting a function you want and that you know for certain what it does and how it does it... whatever "it" may be. I remember a certain manufacturer at one point had their mid-cut button labeled "funk factor." Ugh. A victim of the slaptastic 80s...
     

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