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Only one gyrator stage is shown: all 7 gyrators are the identical circuit, best the capacitors change, as proven in the chart. I even have shown three of the seven faders to level out where they go. 

A gyrator is a circuit the utilization of active tools and transistors to simulate an inductor. In this case the gyrator is the transistor appearing with R1, R3 and C2. It may just as simply be a cohesion acquire op-amp. 

The circuit embraces three formulae: one which offers f, the the centre frequency of the band. The 2nd shows how the Q is related to the capacitor ratio. The third presentations the impedance offered with the help of the circuit. Note that this embraces 3 time periods, the primary merely resistive, the 2d is the capacitative contribution from C1 and the 0.33 is an inductive term from the gyrator. 

If anyone wants the distinct mathematical working out of these formulae, I could be triggered to submit it (donations accepted!). The arithmetic for energetic filters shouldn't be as tough as most tutors tend to make it and I in point of fact didnt take into account it correctly until I labored it out for myself and found that it wasnt complicated, I simply hadnt been taught how you can take into account it! 

If you do the arithmetics for this you'll in finding the actual frequencies are if truth be told a little completely different from the target frequencies proven within the diagram: thats what comes from the utilization of standard values. Audibly they're masses close enough. 

The rest of the circuit is simply an op-amp. If you imagine a tuned circuit (the gyrator) striking from the pot slider, it's being linked either to the certain input or the poor to a variable extent. One will elevate the response at the turned frequency and the opposite will decrease it. 

You must after all selected a excellent, low noise op-amp: once we manufactured these we used 741s but we chosen low noise ones. The transistors also need to be low noise, however you might easily exchange a noisy transistor in the adventure you to find you will have one. 

And thats about it. A very straightforward, effective circuit. The most tough bit is going to be sourcing the parts - specifically appropriate fader pots!.