Simon Fraser-Clark of Laney explains the tonal difference­s between Class A amps and the more common Class A/B designs


“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. That’s the thing about a Class A amp: because it’s running hot, it will compress naturally more than a Class A/B amp. So as you strike the string, the amplifier, for want of a better word, takes a breath and then sings. In Class A/B because it is a little more efficient and because the tube is starting from cold, it doesn’t take as much of a breath, it’s more instant, and because of this crossover distortion, there’s more meat to it and it sounds a little brighter, too. But Class A has some very nice characteri­stics from a player’s point of view. It just sings.”

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