One of the overlooked advantages of quilter amps is that their tone is not dependent on the mains voltage because they use a regulated switch-mode power supply. The beauty and the bain of tube amps is that they use prehistoric unregulated power supplies, which means that the B+ voltage fed to the power tubes is dependent on the mains voltage, which can vary wildly from venue to venue. That is why a tube amp can sound different from venue to venue (i.e., it is not always acoustics). The voltage at the wall is dependent on how far the venue is from the transformer that steps down the distribution voltage to residential/light commercial secondary voltage, usually from 7,200VAC to 240VAC split-phase in the U.S., as well as the total load on all of the branch circuits. The step-down transformer only produces 240VAC on the secondary if the primary voltage is in spec, which anyone who has ever experienced a town or community-wide brown-out knows is not a given. I challenge anyone to stick the probes from a multimeter in an outlet of your basic restaurant-size club and measure exactly 120VAC. Some venues have amazingly crappy power. I have seen voltages as low as the low 90s VAC and as high as the low 130s VAC. Trust me, the average fixed-bias amp is going to sound different than it did if it was biased at 120VAC because the B+ fed to the power tubes is going to be lower or higher and so is bias voltage. Quilter amps do not suffer from that problem because the power supply can take darn near any residential/light commercial mains voltage and turn it into the proper regulated DC voltage. That is the advantage of using a regulated switch-mode power supply.
Quilters can approach the sound and feel of tube amps due to patented wizardry that transforms the constant voltage/highly-damped output of a solid-state output to a constant current/lowly-damped output. Impedance is not a synonym for residentance. Impedance has a reactive component that is frequency dependant, which means that the impedance of a speaker changes with respect to frequency. Damping prevents these fluctuations from interacting with the power amp. That is why the average solid-state amp feels and sounds lifeless compared to a tube amp. What is happening is that the speaker is not only producing sound as the magnetic circuit is causing cone movement. It is also producing a current as the voice coil in a speaker cuts magnetic lines of force. In an amp with a low damping factor back electromotive force interacts with the signal being produced by the amp coloring it and adding what is known as "push back," which is a flaw in sound reproduction, but a phenomenon that guitarists have larned to exploit with tube amps in music production. In essence, back EMF is the key to tube amp feel. Pat figured out how to do a very good approximation of this tube technology flaw using solid-state devices and a bit of interesting circuitry.
Anyway, I am on my second Quilter amp. I own several tube amps, but they rarely get played. At this point, most of my playing is home practicing and a guitarist will get thrown out of most venues here using any tube amp larger than a Princeton Reverb turned up to its sweet spot. FoH wants to have control of the mix.
