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Discussion in 'Effects [BG]' started by Onofre, Apr 2, 2015.
what does it mean?
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.
Sorry Jimmy, but while you're here; Ive noticed a lot of od pedals have a 'sag' knob. Is this synonymous then with gain?
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.
And this supply drop does what to the sound?
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...
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.
Thank you both, that was very enlightening. Sorry for the thread hijack OP
What does a 60 year woman have between her knees that a 20 year old doesn't? Oh, wrong thread, same answer...
I suppose it was only a matter of time!!
Yeah, admittedly I'm not all that strong with the tech talk I've just always associated sag with onset of overdrive.
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.
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".
AWESOME thread, thanks for the info, everyone!
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.
lol that made me throw up my coffee!!!
Every time I see a kid with those baggy pants I'm going to bust out laughing man that is too funny.
I love the sound of my VOX amplug when the battery starts to die. Same kind of thing with the voltage drop.