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API was founded in 1969 by the great Saul Walker. Known for their bright, open, punchy sound, API products have been used on countless hit records over the last 50 years.

One of their most coveted products is the 550 Series EQ. In this article, we’ll break down some of the most popular API 550 EQ emulations to help you determine which one is right for you.

API 550 A/B

Initially released in 1971, the 550A EQ utilizes API’s legendary custom 2520 op-amp to achieve a very musical sound.

The 550A features three bands of EQ, with 21 selectable frequencies. Each band can cut or boost up to 12 dB in two dB increments.

The 550A EQ does not feature Q controls. Instead, it utilizes proportional Q technology, which increases the Q value as the gain is increased, creating a narrower band and a more aggressive sound.

Each band is broken into the overlapping ranges, allowing for extreme equalization:

• Low: 50, 100, 200, 300, 400 Hz
  
• Mid: .4, .8, 1.5, 3, 5 kHz
  
• High: 5, 7, 10, 12.5, 15 kHz
  

The high and low bands can be used as traditional bell shapes or converted to shelves using two dedicated switches. The API 550 also features a dedicated band-pass filter set to 50 Hz and 15 kHz, which can be toggled on or off.

API 550B EQ

Decades after the release of the original 550A EQ, API redesigned this classic with an additional band, broken into the following selectable frequencies:

• Low: 30, 40, 50, 100, 200, 300, 400 Hz
  
• Low Mid: 75, 150, 180, 240, 500, 700, 1000 Hz
  
• Hi Mid: 0.8, 1.5, 3, 5, 8, 10, 12.5 kHz
  
• High: 2.5, 5, 7, 10, 12.5, 16, 20 kHz

The high and low bands on the API 550B can still be used as traditional bell shapes and converted to shelves, however, the filter was removed to make room for the additional components. 

Now that you’re familiar with the original API 550 EQs, let’s take a look at some of the most popular emulations available today. 

About the Audio Files

We put some of our favorite API 550-style EQ plugins to the test on drums, bass and guitars with the following settings:

Drums

• +6 dB at 50 Hz
• -4dB at 240 Hz
• -2 dB at 800 Hz
• +2 dB shelf at 5 kHz 
• Filter on

Bass

• +6 dB shelf at 50 Hz
• -4 dB at 240 Hz
• -6 dB at 800 Hz
• +4 dB at 2.5 kHZ
• Filter on

Guitar

• -4 dB at 200 Hz
• +6 dB at 700 Hz
• +4 dB at 10 kHz
• Filter on

Here are unprocessed versions of the three audio files …

Drums

Bass

Guitar

Acustica Audio Pink2 

Acustica Audio’s Pink2 is the ultimate channel strip for fans of API. It features four bands of EQ with fully variable frequency and gain controls. Each band features a button to toggle proportional Q on or off. The high and low bands feature buttons to toggle between bell and shelf shapes. 

Each band also lets you choose between three different circuit models, emulated after the API 550A, the 550B and a hot-rodded version of the 550B. The standalone EQ plugin even features a fourth option!

The Pink2 channel strip plugin also lets you choose between high-pass, low-pass and bandpass filters.

In addition to highly-accurate modeled API EQs, Pink2 also delivers emulations of four different preamp models and an API 2500 compressor with all of the bells and whistles — including three modes of operation!

Acustica Audio Pink2 – Drums

Acustica Audio Pink2 – Bass

Acustica Audio Pink2 – Guitar

Acustica Audio Pink2 Demo – [American Channel Strip Plugin]

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Softube American Class A

Softube’s American Class A plugin is much more than a simple API 550 EQ clone. American Class A features four bands with stepped gain controls, with switchable increments including 1x, .5x, and .25x for fine details. 

In addition to being used as bells or shelves, the high and low bands can also be set to filter shapes. American Class A also features fully variable high-pass and low-pass filters.

American Class A also includes a built-in transient shaper, compressor and saturation controls. Best of all, American Class A is entirely compatible with the Console 1 controller, giving you total access to every parameter right at your fingertips.

Softube American Class A – Drums

Softube American Class A – Bass

Softube American Class A – Guitar

American Class A Demo – Softube

PSP preQursor2

The PSP preQursor2 is probably the most unique plugin on this list. While it features four bands like the API 550B, the selectable frequencies don’t match either of the original models. Not only do they not overlap each other; they don’t even cover the entire frequency spectrum. 

While it does offer improved variable gain controls and a selectable high-pass filter, it’s missing key features such as high and low shelves.

Despite these setbacks, the preQursor2 sounds impressive. It features push-button controls for analog circuit modeling and saturation for adding grit. It’s also the most affordable entry on the list, coming in at just $69!

*I had to use two preQursor2 EQs to achieve the same EQ curve as the API 550B emulations since the bands don’t overlap.

PSP preQursor2 – Drums

PSP preQursor2 – Bass

PSP preQursor2 – Guitar

PSP preQursor2 a specialized EQ plug-in.

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Overloud Gem EQ550

Although Overloud may not be entirely as well known as some of the other plugin manufacturers on the list, this Italian company has some fantastic products at affordable prices — and their Gem EQ550 is a prime example. 

Featuring four fully variable frequency bands and gain bands, the Gem EQ550 offers even more versatility than the original. However, instead of modeling the four bands on the 550B EQ, the Gem EQ550 models the three original bands from the API 550A EQ and includes an additional midband with the same frequency settings.

Gem EQ550 features push-button controls for high and low shelves and a dedicated switch that toggles the filter from off to high-pass to band-pass.

Gem EQ550 also features a Cue button, which allows you to hear the part of the frequency spectrum that you’re working on, giving you a clear view of how you’re affecting the sound.

*I had to use two Gem EQ550s to achieve the same EQ curve as the API 550B emulations since the bands don’t overlap.

Overloud Gem EQ550 – Drums

Overloud Gem EQ550 – Bass

Overloud Gem EQ550 – Guitar

Overloud Gem EQ550 Proportional Q equalizer

IK Multimedia EQ PA/PB

IK Multimedia offers two separate plugins modeled after the API 550A and 550B; the EQ PA and EQ PB. 

Both models provide accurate recreations of each model, including shelf switches, and a band-pass filter. They also feature a few new upgrades such as fine-tuned decibel controls, with a 1 dB resolution up to 6 dB and a 1.5 dB resolution up to 12 dB.

EQ PA and PB also feature a dedicated preamp button, which can be driven using the gain knob to introduce classic American saturation. 

*The EQ PA Series has a slightly different sound than the original API 550B, with much more low end.

IK Multimedia EQ PA/PB – Drums

IK Multimedia EQ PA/PB – Bass

IK Multimedia EQ PA/PB – Guitar

Honorable Mentions

In addition to the options listed above, there are many API 550 EQ emulations available. 

Many engineers will remember the Waves API 550 EQ plugin as one of the first available. While it doesn’t offer much in the way of extra features, it still sounds great! 

The UAD API 500 Series EQ Collection also includes an emulation of the API 560 Graphic EQ — both of which offer highly accurate recreations of the original devices.

Slate Digital recently released the FG-A, a lightweight version of the API 550B that seamlessly integrates with your Virtual Channel Strip.

The URS A Series EQ is a bundle of two plugins: a highly-accurate recreation of the API 550B with fully variable frequency and gain controls, as well as the hot-rodded URS A MIX EQ, which features five fully variable bands and two fully variable high and low-pass filters for added versatility.

Antelope Audio offers the VEQ-55A and VEQ-55B as part of their FPGA FX series, which model the 550A and 550B respectively.

And that’s just the beginning! What are some of your favorite API 550 EQ emulation plugins?

Brad Pack

Brad Pack is an award-winning audio engineer and writer based in Chicago, IL. He currently owns and operates Punchy Kick, a professional mixing and mastering studio that specializes in pop punk, emo, punk, grunge, and alternative music. He has been helping artists connect with fans through emotionally resonant mixes, cohesive masters, and insightful guidance for over 10 years. Check out his website PunchyKick.com or say hi on Instagram @PunchyKick