In 1951, Pultec introduced the first passive program equalizer, the EQP-1. Pultec combined the passive design with a tube gain amp to overcome the typical 16 dB insertion loss of a passive equalizer. So this made the Pultec appear to be “lossless.”
[blockquote type=”left”]The Pultecs are known as magical tools that improve the sound
simply by passing signal through them.[/blockquote]
In the documentation supplied with hardware version of the EQP-1A, it is recommended that both Boost and Attenuation not be applied simultaneously to the low frequencies because in theory, they would cancel each other out. In actual use however, the Boost control has slightly higher gain than the Attenuation has cut, and the frequencies they affect are slightly different. Perhaps the sonic equivalent of a subtle low-midrange scoop, which can add clarity. A great trick for kick drums and bass instruments.
I’ve done extensive research how the Pultec EQP-1A eq curves actually work. These graphs are based on Waves Puigtec using 24bit/96khz sine sweep using Fuzz Measure software. People claiming that by boosting and cutting the same frequency results a dip in that center frequency. Bollocks…. it’s behaviour is quite different.
Red curve +4db boost @ 20 CPS
Green curve +4db boost @ 20 CPS / -4db atten
Red curve +4db boost @ 100 CPS
Green curve +4db boost @ 100 CPS / -4db atten
Red curve +4db boost @ 30 CPS / -4db atten / +4db boost @ 10 KCS broad
Green curve +4db boost @ 60 CPS / -4db atten / +4db boost @ 5 KCS sharp