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API 550 EQ

..anyone know the difference between API 550 EQ and the 550A ?I know the 550B has 4 bands, whereas the first 2 have 3, but what else ?


Jon Atack Fri, 11/09/2001 - 15:57
Here's your answer. Hop over and visit me at my Tracking and Mixing forum here at Recording.Org!



Hi Jon,

Here are the versions...

The API 550:

Proportional Q, 3 bands on the top, 3 on the bottom and 5 in the middle, 2 transistor buffer amp X 4, a different (than the A) 2 pole filter for the high/low pass switch, a strange way of switching the EQ out (all filters tied together, then to gnd through a switch), 2 2520s and long frequency knobs.

The API 550A:

Proportional Q, 5 bands on the top, 5 on the bottom and 5 in the middle, 3 transistor buffer amp X 4, 1X-10X high and low pass filters-same frequencies as the 550 (50 HZ to 15KHz band pass), each band went through it's own in/out switch, 2 2520s and short frequency knobs.

The API 550A-1:

Basically the 560 graphic circuit with the same frequency settings as an A. Constant Q, though. That's why it sounds so different. IC input and filter stages, 2520 output. Not a bad EQ, just not a 550A. Built to be made cheaper. Datatronix inherited them and I discovered the difference when I worked there. API never checked the Q other than full up at 12 dB, so they never knew that they were different. They actually did not realize that the original 550 was proportional Q, as all EQs were that way then. By that time 2500 were sold and everyone was flipping out.

The Datatronix 550A:

After pressure from everyone, Sunset Sound stepped up to the plate and paid for the design of the 550A to be remade with removable switches and a removable trans buffer board at Datatronix. They got the rights to the first 500 and then Datatronix could sell them. They sold them and used them in the new Sunset Custom console in Studio 1.

The "Paul" 550A:

I built about 250 of the redesigned 550As, shit-canned the 550A-1 (thank me later). I then designed the 5502 rack mount 4 band version, made 85 of them and then Henry Sanicola of O'Henry Studios asked me to build 75 4 band versions that would fit in a regular slot.

The "Paul" 550B:

When we released the original 550B, Allen Sides got ahold of the prototype and did not like it. It turned out that it was oscillating and sounded bad. He to this day still thinks they all sound that way, but every one else likes them. I never discontinued the 550A, and after the release of the 550B, up until this day, have only sold 7 550A's and over 3000 550B's. Everyone bitches at me about them, but didn't buy the new 550As. Go figure. The Experts like Brent [Averill] feed the industry about how bad the new stuff is so they can sell old ones and support their uninspired lives.

So there you have it.

Wait until you hear the 2500 compressor. We put one in the new 80 channel API Legacy Plus installed at the Sound Kitchen as a Bus Compressor and people are booking the room just to hear it. But of course, It will suck like all the rest of the stuff I design.


Note: Proportional Q is a relationship between the energy, boost/cut and the frequency. At any level other than 0, the width and the boost/cut were a constant. That means WIDER at 2dB and NARROWER at 12dB. Wider is better.

hollywood_steve Mon, 11/12/2001 - 16:19
Hey Adam, congratualtions. I've got a pair of very early 550's myself and I wouldn't trade them for anything. There's not that much that can/will go bad on these things, but you might want to have them checked out by someone like Brent Averill, or even API themselves. Other than a few capacitors, mine are just as they left the factory 32 or 33 years ago.