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Discussion in 'Effects [BG]' started by Onofre, Apr 2, 2015.

  1. Onofre


    Feb 28, 2015
    what does it mean?
  2. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Onset of noticeable distortion. There comes a point in a tube amp where the signal transitions from clean to dirty, and the extra compression when that happens tends to make the notes less sharp edged and focused, and the term people have elected to call it is "sag." I think it's accurate.
    leonard, Gougedeye, Jamvan and 2 others like this.
  3. Onofre


    Feb 28, 2015
    Thanks JimmyM
  4. Sorry Jimmy, but while you're here; Ive noticed a lot of od pedals have a 'sag' knob. Is this synonymous then with gain?
  5. SteveCS


    Nov 19, 2014
    Hampshire, UK
    JimmyM is partly correct. Sag is a type of compression prevalent in tube amps that occurs when the power supply cannot keep up with demand from the output section. As the output demand reaches the limits of the power supply, the supply voltage starts to drop, leading to a limiting of power. The term sag refers to this drop in rail voltage. In some cases it sounds great, but if the DC smoothing capacitors in the power supply are not large enough, it can also introduce 100Hz ripple in the DC supply which may not sound so good as the output volume gets modulated.

    The Sag control found on some pedals reduces the supply voltage to the gain stages in an attempt to emulate the effect of power supply sag without the need to drive the amp to its limits. In some it is a simple rail voltage reduction - in others it is a more sophisticated 'closed-loop' controller. Some people deliberately install carbon batteries in their pedals to achieve the same effect. This works because carbon batteries have a relatively high internal resistance which means they cannot deliver high current. As the current demands of the pedal increase with higher gain settings the supply voltage drops because the battery cannot keep up. This only really works with discrete transistor-based analogue circuits - big muff and the like.
  6. And this supply drop does what to the sound?
  7. SteveCS


    Nov 19, 2014
    Hampshire, UK
    Drop in output power and hence volume. In a full tube amp where the pre and power stages are fed from the same power supply, a saggy power supply can also cause momentary increases in plate starvation at the preamp which adds to the effect. Very nice all round...
    Last edited: Apr 2, 2015
    Bassic Playing likes this.
  8. Dave W

    Dave W

    Mar 1, 2007
    White Plains
    It can be, but it depends on the pedal.

    In the case of the Barbershop, the Sag control reduces the voltage going into the pedal. It basically simulates a dying battery which gives the pedal less headroom and thus the possibility of more gain depending on how it's set.
  9. Thank you both, that was very enlightening. Sorry for the thread hijack OP
  10. jamro217

    jamro217 Supporting Member

    What does a 60 year woman have between her knees that a 20 year old doesn't? Oh, wrong thread, same answer...
  11. SteveCS


    Nov 19, 2014
    Hampshire, UK
    I suppose it was only a matter of time!!
    jamro217, SirMjac28 and nightwulf like this.
  12. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Yeah, admittedly I'm not all that strong with the tech talk ;) I've just always associated sag with onset of overdrive.
  13. friendlybass


    Jul 19, 2012
    I clicked on the thread for the volt starving, stayed for the old lady/man jokes.
    Like mentioned above its when you don't have enough power. In effects it means less headroom, so distortion at lower volumes, less high end response, all that goodness.
  14. edbass


    Nov 8, 2004
    Excellent description IMO, I hope you don't mind if I add an addendum;

    *a situation generally associated with amps using tube rectifiers, "sag" can induce a tonal effect often referred to as "browning".
    Coolhandjjl likes this.
  15. Sixgunn


    Jun 6, 2012
    Colorado Springs
    I don't wait 30 minutes after eating, to go swimming.
  16. nightwulf


    Feb 27, 2011
    Edmonds Wa
    AWESOME thread, thanks for the info, everyone!
  17. Mosfed


    Apr 21, 2013
    Chamonix Mont-Blanc
    Partner - CCP Pedals
    I have mainly seen SAG on overdrive or fuzz pedals or even on the Voodoo Labs power supplies. They limit the voltage going to the pedal and induce different and quicker distortion.

    Trying to simulate how a dying battery can just sound so epic on a fuzz pedal.
    electracoyote likes this.
  18. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion Supporting Member

    Aug 25, 2010
    The Great Midwest
    lol that made me throw up my coffee!!!
    Sixgunn likes this.
  19. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion Supporting Member

    Aug 25, 2010
    The Great Midwest
    Every time I see a kid with those baggy pants I'm going to bust out laughing man that is too funny. :)
  20. Smurf_Byte


    Aug 21, 2011
    I love the sound of my VOX amplug when the battery starts to die. Same kind of thing with the voltage drop.

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