The bias control affects where the idling state of the tube is "located" if it's hot or cold. Proportion changes depending on the idling state of a power tube. The Bias control affects the balance between distortion between power tube saturation and distortion from power tube cutoff. However, most cathode biased amps are running the tubes hotter than most fixed bias amps. This parameter is highly reactive with the Drive and Master settings.īias on cathode biased amps Many people have an association that cathode biased = class A. Bias X is a bit like Sag, except it controls change in a tube’s operating point due to change in the tube bias when the amp is driven hard. Lower or “cold" bias will make the sound less sweet, but will tighten it up and make it more dynamic.ĭetermines how the power amp tubes' voicing reacts when pushed hard, controlling how much the bias changes when the amp is driven hard. Higher or “hot" bias will increase the warmth, reduce headroom, distort earlier or at a lower Master setting, and (in a tube amp) decrease the tube life. At maximum, the amp is operating in Class A.
Lower values achieve a "colder" Class AB biasing. Also generally left at 0 unless you are looking for a specific effect.Ĭhanges the Bias of the power tubes. This is similar to hum but is on the plate of the tube instead of the heater and has a different shape.Īt higher settings, things get freaky. If the amp is driven hard, these capacitors can’t provide sufficient filtering and some AC ripple is introduced into the signal. The power supply of a tube amp is filtered with large capacitors. Generally left at 0 unless you are looking for a specific effect.Ĭontrols how much AC ripple in the power supply interacts with your tone. Higher levels cause some intermodulation distortion as the heater hum mixes with the signal. Tube amplifiers generally used low voltage AC in the tube heaters, and sometimes this could add some hum into the signal.Īt higher settings, things get freaky. But the amp will appear somewhat less responsive especially at the low end and can get muddy.Ĭontrols how much heater hum interacts with your tone. Large sag gives more compression, better sustain, and can accentuate pick attack. Unlike compressors before the amp, sag compression occurs even when the amp is already very distorted. When the power sags, the amp output drops and then recovers, creating a unique compression effect with some additional, but temporary distortion when you pick hard. Sag is caused by the amplifiers power supply being unable to meet the demand when the map is pushed hard with high Master. Sag doesn’t exist in class A amplifiers since the average plate current doesn’t change. High Bias (closer to class A) reduces the effect of the Sag control. Lower Sag values offer a "tighter" responsiveness for metal and djent playing higher values provide more touch dynamics & sustain for blues and classic rock riffs. Low Master and high Drive gives smother preamp distortion while high Master lower Drive gives more power amp, symmetric and more aggressive distortion.Ĭontrols power amp sag or compression 0% tight, 50% normal, 100% more touch for dynamic sustain. This parameter is highly interactive with all other power amp parameters-the lower the Master is set, the less effect the other controls will have. Consider using lower values, or the minimum distortion required to fit the song. Note that 50% may not be normal as the amps may have been modeled with the Master set too high. MESA/Boogie Bass 400+ Cali 400 (channels 1, 2)Īdjusts the amount of power amp distortion: 0% clean 50% normal, 100% driven.Ampeg SVT SV Beast (normal, bright channels).Vox AC-30 A-30 Fawn (normal, bright channels).
Matchless DC30 Matchstick (channels 1, 2, jumped) (added in 1.06.0).Marshall Super Lead 100 Brit Plexi (normal, bright, jumped channels).Marshall JTM-45 Brit J-45 (normal, bright channels).Fender Twin Reverb US Double (normal, vibrato channels)]].Fender Deluxe Reverb US Deluxe (normal, vibrato channels)]].Fender Bassman Tweed Blues (normal, bright channels)]].
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