Equalizers were first used in the movie industry in the USA to solve a serious problem; microphone placement was difficult and the dialogue sounds achieved varied significantly, so they needed to design electronic circuits that would equalize the sounds from different microphones so that they all sounded the same. The name has stuck and now we have complex digital equalizers that engineers use for effect. The original purpose was to sweeten the sound.
 
The equalizer circuits were originally designed by Peter J Baxandall in the 1950’s as part of a competition where he won a wrist watch. Variations of his designs have been used by nearly all broadcasters and HiFi manufacturers ever since. Ted Fletchers variations incorporate the original class A circuitry and modifications to the curve have been shaped specifically for sweetening of final masters.
 
Technical Specification
Frequency response: 20Hz to 20KHz
Line input: 10KHz current-mode transformer balanced
Gain: Unity
EQ – high: +/- 12dB with shelving at 10kHz
EQ – mids: +/- 12dB with shelving at 1600Hz
EQ – lows: +/- 12dB with shelving at 100Hz
Relative input noise: better than -90dB
Harmonic distortion: <0.05%
Crosstalk: better than -50dB
Maximum output: +21dBu