Power Supply:



The new power supply modeling is a significant improvement over previous versions. The power supply sag is now incredibly realistic and far superior to the "expander/compressor" techniques used in other products. Learning to adjust the pertinent parameters can make a good tone great.



Supply Sag is the most fundamental of the power supply controls. It controls the virtual resistance of the AC input. In a real tube amp the supply sags due to a combination of power transformer resistance and rectifier resistance. Increasing Supply Sag increases this resistance and vice-versa. The higher the resistance the more the supply sags and the more bouncy and spongey the amp will feel. I like to increase Supply Sag a bit and reduce gain. You can monitor the virtual supply on the hardware by selecting the Supply Sag parameter. The gain reduction meter will display the supply voltage in dB relative to idle.



Tube Bias controls the idle current of the virtual power tubes. The models, in general, are biased on the hot side because that's how most people like their amps. Reduce Tube Bias to simulate a colder bias. It is rumored that EVH liked his amps biased cold. When the bias is reduced the amp sags and bounces more and the bass will be a little tighter and the tone edgier.



B+ Time Constant controls the capacitance of the virtual power supply. The more capacitance the "slower" the supply and vice-versa. Most guitar players like a fast supply but too fast will cause excessive AC ripple and create ghost notes (although I think a little ghost note is cool). When the supply is fast it will sag rapidly accentuating the pick attack and compressing after. This parameter works in conjunction with Supply Sag parameter. The time constant remains constant so if you increase Supply Sag the virtual capacitance decreases.



Cathode Bias controls the virtual resistance for "cathode bias" amps, i.e. AC-30. In these amps the grid bias is held at ground (ignoring bias excursion) and a resistor is inserted between the cathode and ground which self-biases the power tubes. These amps are typically marketed as "Class A" but in reality they are not truly Class A but rather a hot Class AB. The cathode biasing keeps the tubes in the safe operating area (SOA). A Cathode Bias value of 50% represents full Class A operation. Both tubes will be on over the full input signal range. Values less than 50% are actually beyond Class A. Why would you want to go beyond full Class A? Bias shifts always push an amp towards Class B operation so if you bias beyond full Class A you will get pushed back into Class A operation when you actually play. Typical "Class A" amps, as stated earlier, aren't really Class A. The default Cathode Bias values reflect this and are usually around 70%. Decreasing Cathode Bias will give a rounder, softer tone. Increasing it will give a bouncier and edgier tone. You can adjust the time constant of the cathode bias network as well, if desired.