In 1996, Douglas Self published a design for what became known as the Precision Preamplifier, which included a treble/bass tone control with variable turnover frequencies. Starting with the idea to revisit the design with the benefit of years-long experience and newer parts, the design developed into much more than just' a tone control preamp. The necessary additional stage to correct the phase reversal of the tone control stage was called up for a Baxandall-type active volume control duty. Then, reminding himself that we don't all use symmetrical listening spaces, Douglas realized that a vernier' balance control would be very useful but of course without interfering with either the tone or the volume controls. Add to that the need to maintain very low noise and distortion levels, and you have a article that is more like a tutorial on preamplifier design.
A low-noise preamplifier with variable-frequency tone controls