Parametric EQ problems
I'm trying to build a parametric eq outlined near the beginning of this site, but when doing a simulation of the frequency response, I get a weird boost past 100kHz. I chose values for C1 = 0.1uF, C2 = 0.68uF, C3 = 0.015uF, C4 = 0.082uF, replaced the 51k resistor with a 200 ohm resister, and used a 10k pot instead of the 1M pot in the gyrators.
I chose those values because I would like the first band to have fmin = 280Hz, fmax = 2kHz, and the second band to have fmin = 2kHz, fmax = 15kHz. With these values and the calculations outlined on that page, I should get pretty close to the desired frequency response in the simulation(ignoring tolerances, etc.), however, I get a very weird boost as shown:
The first peak occurs at about 280-300Hz(fmin for the first band) just as I calculated, but there should also be a boost at 15kHz(fmax for the second band). Instead I get a weird boost after 100kHz
The commercial parametric equalizers I've seen use state variable filters rather than gyrators. Gyrators are common for graphic. The state variable filters allow Q , gain or frequency changes without affecting the other parameters.
There is also DSP for the more ambitious.
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