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For sale is a rare vintage 500 series API Automated Processes Inc. Audio 550A 3-band equalizer with 1 Huntington N.Y. 2520 opamp and 1 Datatronix opamp (which is the same as a Huntington opamp, just different sticker label, when Datatronix took over Huntington facility they used up the remaining available parts). You can see there are two opamps when you remove the Datatronix board on top. This is of equal quality and sound to other vintage 550A, and this is not a 550A-1. It's fully functional and sounds excellent. Amazing analog warm tone. Serial number 651. Don't pass this up!
