From: http://www.mackie.com/technology/perkinseq.html
"The goal of Perkins EQ was to bring the classic EQ sound of British mixing consoles of the '60s and '70s and put it into a small-format mixer, for the first time ever. So Cal started with the Wien Bridge circuit topology--a very musical design made popular by mixing consoles from the hallowed 'British Invasion.'"
"To get past the tradeoffs of the Wien Bridge, he wrote 20 pages of equations describing the seemingly simple Wein Bridge circuit in complete detail. After solving the equations with calculus, Cal was able to specify capacitor and resistor values that would give Onyx mixers an extra 6dB of control (±15 dB) without excessively narrowing the "Q" or bandwidth of the filters. Next, Cal employed combining filters for minimum phase shift, making the entire EQ section as musical as possible.
Well here it is - looks like a bog standard wien-bridge implementation to me.
"The goal of Perkins EQ was to bring the classic EQ sound of British mixing consoles of the '60s and '70s and put it into a small-format mixer, for the first time ever. So Cal started with the Wien Bridge circuit topology--a very musical design made popular by mixing consoles from the hallowed 'British Invasion.'"
"To get past the tradeoffs of the Wien Bridge, he wrote 20 pages of equations describing the seemingly simple Wein Bridge circuit in complete detail. After solving the equations with calculus, Cal was able to specify capacitor and resistor values that would give Onyx mixers an extra 6dB of control (±15 dB) without excessively narrowing the "Q" or bandwidth of the filters. Next, Cal employed combining filters for minimum phase shift, making the entire EQ section as musical as possible.
Well here it is - looks like a bog standard wien-bridge implementation to me.