“The main difference between a parallel single-ended Class A amp versus a Class A/B amp comes down to how hot the tubes are running. Basically, in a Class A amp, the tube is running at its maximum output the whole time,” Simon explains, “so it’s running hot. In Class A/B, because you split the output tubes into pairs or single units – one to amplify the positive side of the waveform, one to amplify the negative side of the waveform – then, in theory, when the positive side is working, the negative side is turned off and is cooling down. When you turn the negative side on, when it gets up to temperature you have an increase in a thing called crossover distortion, which as a guitar player you hear as mids, so you hear more pick attack. But if you think about a Class A amp… It’s like a singer, when the singer is about to hit a note, they take a breath and then they release the note.