stereo turntables in DD use.

[lordkenmore]

The tone control system that always interested me was a system that NAD used on their higher end equipment in the late 1980s. They called it "semi parametric". There was the usual "Bass" and "Treble" knob. But each knob also had a switch that could select one of three frequency ranges for that knob. This supposedly gave more control, and more chance of having a meaningful fix for a problem, while still staying fairly simple. The tone controls could be bypassed, too. They even gave suggestions of a few fixes. This system has struck me as possibly being an exception to my "tone control systems make things worse or do nothing!" stance.

http://nadelectronics.com/products/hifi-amplifiers/1300-Stereo-Preamplifier

 

[swestoyz]

Sansui had a similar tone control switch for the bass and treble controls on their TOL receivers and pre-amps through the 70's. Both swtiches allow the user to choose a frequency level for bass or treble (mid level is always active), or defeat the individual tone control as needed.

As I've grown more accustomed to the sound of the 990db, I have found that I almost always defeat the bass control. The natural sound from both the recording and the amp section do not need to be fooled with at the preamp stage.

Ben