Just to add my twopence worth ... I believe that tone controls were originally included primarily to compensate for differences in recordings. The reason that they were taken out was because certain amplifier manufacturers made a big marketing point about 'spending the money' on better components and circuitry instead. Pretty soon, amplifiers without tone controls became trendy and eventually tone controls became a symbol for low quality amps. However, there's no reason why tone controls shouldn't be included in addition to high quality circuitry and components and, provided there's a cancel/bypass switch (àla Quad), there shouldn't be any degradation whatsoever. Except of course that compensating for differences in recordings is rarely worthwhile or even a good idea. However, if I was designing the perfect preamplifier I would compensate for room resonances at the bass end and I would allow for compensation for speaker voicing at the top end. Speaker designers choose differing treble roll-off characteristics which 'place' you closer or further away from the band. I would therefore include parametric or digital equalization for the bass and a fairly conventional old-fashioned treble control for the treble. All with a bypass/cancellation switch of course.