{"product_id":"api-550a-1-eq-used","title":"API 550 A-1 EQ (Vintage)","description":"\u003cp\u003eClean used example of this unit. Formerly used in Studio A at Looking  Glass Studio in NYC, where the likes of David Glass, David Bowie and  David Byrne recorded.\u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003eAvedis describes the 550A-1 best: Same features as the 550A but made to  be an economical version in the late 70s. Key differences with the 550A  are:\u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eElectronically balanced input in contrast to the  unbalanced input of previous three band eq's. This alone makes some  prefer using it when experiencing the 6 db drop when interfacing  electronically balanced output to an unbalanced input. \u003c\/li\u003e\n\u003cli\u003eConstant Q instead of the proportional Q of the 550A \u003c\/li\u003e\n\u003cli\u003eUse of integrated circuits (IC) \u003c\/li\u003e\n\u003cli\u003eUses one 2520 opamp in the output stage\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003col\u003e \u003c\/ol\u003e\n\u003cp\u003e \u003c\/p\u003e\n\u003cp\u003eAccording  to Al Davis, a designer at API, it should have been called a 551 but  readily available old stock 550A faceplates were used instead. One way I  can usually identify an A-1, without looking inside, is the rubbery  feel of the rotary switches instead of the snap you feel with a 550A.  550A-1's were sometimes found on ebay and sold as 550A's by sellers who  may or may not have known what it was because often the serial number  sticker said \"550A\" without a mention of A-1, and sometimes there was no  serial number sticker.\u003cbr\u003e\u003cbr\u003eLooking at the inside, there is one 2520  driving the output transformer with a feed-forward design using a NPN  transistor. The other amps are IC's with an LF356 balancing the input  and a TL074CN quad amp powering the bands and filter. The front rotary  switches plugged into the circuit board with connectors.\u003cbr\u003e\u003cbr\u003eContrary  to what internet loudmouths may say, the 550A-1 was not a bad module,  it sounds very similar to a 550A with 2 or 4 db and becomes more  noticeable when pushed to 9 or 12 db, which is probably where most  people would boost or cut if something was wrong. Overall, it was a good  design with good noise performance and had the same headroom as any  550A due to the 2520 and output transformer in the output stage. It is  not exactly a 550A with the Q difference and not quite as full in the  low end, in my own tests, but still better than other eq designs of its  time, as the popularity of using IC throughout in the late 70s became  prevalent and overall quality diminished.\u003c\/p\u003e","brand":"API Audio","offers":[{"title":"Default Title","offer_id":44449447215207,"sku":"4959","price":795.0,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0658\/8848\/5479\/files\/used_api_550a-1_eq_f347ff82-33e7-4cb3-bb03-8e4fdc82dd1c.jpg?v=1787088989","url":"https:\/\/vintageking.mom\/products\/api-550a-1-eq-used","provider":"Vintage King","version":"1.0","type":"link"}