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.  :D  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
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Thats the cleanest copy of the 550A schematic I've seen!

Funny thing is looking at the schematic and then the pictures it's like where is the missing stuff at...

must be dual sided switches...
Intentionally left blank


I have a question on the 550b.   some of the capacitor networks are duplicates in value:

(see attached pic)

Does this mean that these can be consolidated into a single signal path?   in my noobness, it seems redundant.    I used the schematic from the GroupDIY account, in case anyone is curious where I got this pic from.
www.youtube.com/mulletchuck for all my recordings


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