API 550b

Modular 4-band Equalizer, 500 Series, With 7 API-selected Frequency Centers, 12dB of Boost/Cut Per Band, and Proportional Q Control
API 550b image 1
API 550b image 1
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API 550b
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This EQ Has Royal API Blood Lines!

Incorporating API's legendary circuitry, the API 550b 4-band equalizer exudes that royal API blood line in every ounce of its sonic character. Artfully blending the past with the present, the API 550b carries the torch from the now-classic API 550EQ — delivering just the right amount of controls to solve problems and sweeten the sound. On each of the API 550b's bands, there are seven carefully selected, switchable filter frequencies. It's packed with surprisingly surgical capabilities — but it's all about musicality — you'll find out why top engineers depend on the API 550b everyday.

API 550b 500 Series Modular 4-band Equalizer at a Glance:
  • A modern relative of a music-history favorite
  • API's "Proportional-Q" Control
  • Excellent at affecting or reversing tonal modifications
  • API's 500 Series: Long-term flexibility, lasting value

A modern relative of a music-history favorite
The API 550 EQ played a major part in the history of music recording in the USA during the 60s and 70s. Originally conceived for use in API's consoles, this latest 550"B" version, the API 550b, is a continuation of the original 1967 550 through the 550A with one additional filter band and several new frequencies. Incorporating API's exclusive circuitry and proprietary components (such as the legendary API 2520 op-amp), the 550b blends the past with the present. So many hit records still depend on the unique 550 sound — and you'll find that the 550b will be an invaluable tool you'll turn to again and again.

API's "Proportional-Q" Control
Making use of "API Proportional-Q", a design introduced by API in the 60s, the 550b intuitively widens the filter bandwidth at minimal settings and narrows it at higher settings — without the need for additional bandwidth controls. This feature minimizes the "phase-shift" sound found in many equalizers.

Excellent at affecting or reversing tonal modifications
You'll be surprised by the possibilities the API 550b 4-band equalizer opens up. One of the 550b's most compelling features is its ability to affect or reverse tonal modifications. If major tonal restructuring is required, the extraordinary headroom made possible with API's 2520 op-amp offers predictable and gentle "analog" performance under duress. You've got a surprisingly wide range of tonal variations, just a few knobs away.

API's 500 Series: Long-term flexibility, lasting value
The beauty of the entire API 500 Series is its long-term flexibility and lasting value — especially when you consider that needs change over time. With a range of mounting frame options, the API 550b will be a valuable asset to your ever-changing studio rigs. It's also ruggedly designed with sound you just won't outgrow — crafted to be your sonic partner for year after year.

API 550b 500 Series Modular 4-band Equalizer Features:
  • 4 bands of their famous-sounding equalization
  • Each band offers 7 API-selected frequency centers
  • Reciprocal and repeatable filtering
  • 12dB of boost/cut per band
  • EQ Band 1 and 4 offer shelf/peak switching
  • "Proportional Q" narrows filter Q at extremes
  • Traditional API fully discrete circuit design
  • High-headroom +30dB clip level
  • Reissue of 1967 API 550 EQ with an extra band
API 550B 500 Series Modular 4-band Equalizer Specifications:
  • Modular 4-band Equalizer
  • Filter Type:"Low" and "High" bands are Peak/Shelf switchable. Low-Mid and Mid-High are peaking type
  • Low Filter Frequency Center: 30, 40, 50, 100, 200, 300, 400Hz
  • Low-Mid Filter Frequency Center: 75, 150, 180, 240, 500, 700, 1Khz
  • Mid-High Filter Frequency Center: 800, 1.5K, 3K, 5K, 8K, 10K, 12.5K
  • High Filter Frequency Center: 2.5K, 5K, 7K, 10K, 12.5K, 15K, 20K
  • Filter Boost/Cut: +/- 12dB
  • Filter Slope: 12dB per Octave
  • Input Impedance: 18.5 K +4 in, 7.5 K -2 in
  • Output Impedance:Less than 75 Ohms
  • Nominal Levels: -15 to +15 dBu
  • Clipping Level: +30 dBu at +/-16 V
  • Frequency Response:+0, -.3, 30 to 20 kHz
  • Noise:Actual, unw noise, <-98 dBu, 20-20 kHz
  • Distortion:.07% max, at +18 dBu Output
  • Connectors:15 position .156sp edge connector
  • Size: 1.5" X 5.25" X 6" Deep
  • Weight: 2.5 lbs
The API 550b 4-band equalizer artfully blends classic API sound with modern features!

Additional Media

500 Series Buying Guide

Tech Specs

Number of Channels 1
Number of Bands 4-band
High Pass Filter Yes
Low Pass Filter Yes
Q Type Proportional Q
Boost/Cut Range ±12dB
Frequency Response 30Hz-20kHz
Freq Range High 2.5kHz-20kHz
Freq Range Hi-Mid 830Hz-12.5kHz
Freq Range Mid 75Hz-1kHz
Freq Range Low 30Hz-400Hz
Height 5.25"
Depth 7.5"
Width 1.5"
Weight 2.02 lbs.
Manufacturer Part Number 550B

Customer Reviews

Based on 3 reviews
Write your review

This is the one

Been using these at studios for years and always wanted one for my own. Sounds great, easy to use, repeatable settings. Just get it, you'll use it on everything.

Better than Awesome?

I really didn't want to spend this much money on an eq when there are so many eq's out there. I heard it was great so finally just got it any way, thinking by the best and don't look back. I won't! This is the most musical eq I've ever used. It it is so detailed and instead of just boosting frequencies you like, it is like musical surgery getting rid of the nasties in your track. Used in conjunction with a good preamp (I chose the 512c) you can get your microphones dialed in and sounding so wonderful with just the details you want. This unit give me the control on the way into my DAW so that I don't have to do much if any eq'ing in software. I've used it with different mics, and it brings out the greatness in all of them. I will never sell this eq, it's just that good.
Music background: Singer/ songwriter/ Frontman

you get what you pay for

Let's face it people, API has been the "go to" people for great professional sound since before I started giging. I'm happy that other companies are producing 500 series products with success, but it's not API. I've been playing off api products since the early 90's in studios and have had great success with these units. I have two of these beauties in my lunchbox that I use for my bass stack (you read it right) for live sound. Don't be intimidated by the looks or price. These units are very easy to set, they sound so wonderful and once you play off this you will be chasing this sound untill you buy a pair! I know because I did. I chased this sound to no avail. As far as price goes my bass stack sounds like God and I know it. I do not need to improve my sound anymore or look for other products that claim they do just as good if not better. When you get a bassist that loves thier sound as much as I do it's just the right thing to do at any price. I will play through these for the rest of my life and will never have any regretts.
Music background: Bassist

Sweetwater Advice

Tim Holsinger

What amazes me the most about the API 550b is that it never fails to make any track better than I think it can get! The Proportional-Q is a great feature that really sweetens up a mix, but still allows me the room to really sculpt my sound in the studio.

Daniel Vranic

The API 550b is the staple sound of my studio. This EQ has a no-nonsence attitude that makes it a joy to use. There's no fumbling around to find frequencies — operation is very cut and dry — and the 550b packs serious punch. There's a reason this EQ is an absolute classic!
See also: API, API 500 Series EQ