It could be done as separate controls instead of concentric but they would probably still be customs. On a 550b, the frequency select is a 3 deck switch and the cut/boost is a 4 deck switch.
Here are a few pics of a 550a-1 just for the heck of it. Remember, this one is different as the Q is constant not proportional. And of course the presence of IC's and only one 2520. The switches are not as complicated but still not exactly a stroll thru the park. Even with all the negative talk over the years, this is still a damn, fine sounding equalizer.
A lonely 2520...
And those slightly less but still bastard rotary switches...
Best, Jeff
Here are a few pics of a 550a-1 just for the heck of it. Remember, this one is different as the Q is constant not proportional. And of course the presence of IC's and only one 2520. The switches are not as complicated but still not exactly a stroll thru the park. Even with all the negative talk over the years, this is still a damn, fine sounding equalizer.
A lonely 2520...
And those slightly less but still bastard rotary switches...
Best, Jeff