Musical Fidelity A3.5 Amplifier - Knob Feel Review Due to popular demand, here we have a lovely piece of Musical Fidelity kit. The A3.5 amplifier is as expected, an all round fantastic Knob Feel. So rather than gush about how awesome the feel is, I’ll just highlight the VERY minor flaws. The rim is a little on the sharp side, but nowhere near skin penetration. And at the extremities of the rotation, there is a little extra movement, as if the whole Knob mechanism is almost a little loose on it’s mountings. But, this is an unbelievable all rounder. True attention to quality.