The API 550b is a four-band analog EQ re-issuing the 1967 API 550 with an added band. It offers seven switchable frequency centres per band, ±12 dB boost/cut, shelf/peak switching on bands 1 and 4, Proportional Q, reciprocal and repeatable filtering, and a +30 dBu clipping level. It uses API’s 2520 op amp and is built to original blueprints.
A faithful expansion of a 1967 design—not a reinterpretation.
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Switches, not sliders
Seven fixed frequencies per band. ±12 dB. No faders—only switches.
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Where it shapes—and where it locks
Shelf/peak only on bands 1 and 4. Proportional Q tightens at extremes.
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Repeatable. Unclipping.
Reciprocal filtering means cut and boost mirror each other. +30 dBu headroom prevents clipping.
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Worth your time?
Yes. Use the whole thing.
4.5/ 5
What works
delivers consistent, repeatable equalisation across multiple units
Proportional Q gives tighter control at extreme settings
+30 dBu clipping level handles hot signals without distortion
What does not
offer continuous frequency selection
allow independent Q control
provide notch or band-pass modes
extend shelf/peak switching beyond bands 1 and 4
Use it if
engineers tracking and mixing in analog or hybrid studios
those who value channel-to-channel consistency and high-headroom EQ
Skip it if
producers relying on real-time parameter automation
those needing granular frequency control
Who should use it, and who should skipHide who it is for
The written brief1 min read
What it is and what it was built for
A re-issue of the 1967 API 550 EQ, expanded to four bands. Built for studio mixing and mastering where precise, reliable tonal shaping is required.
How it works, in terms a player would use
Four bands. Each has seven fixed frequency centres. Each gives ±12 dB boost or cut. Bands 1 and 4 switch between shelf and peak. Proportional Q narrows the filter at extreme settings. Filtering is reciprocal and repeatable.
What it does better than anything else
It delivers consistent, repeatable equalisation across multiple units. Its Proportional Q gives tighter control at extremes. Its +30 dBu clipping level handles hot signals without distortion.
What it does badly
It does not offer continuous frequency selection. It does not allow independent Q control. It does not provide notch or band-pass modes. Shelf/peak switching is limited to bands 1 and 4.
What people made with it
The sources do not state what people made with it.
Who should use it, and who should not
Engineers who track and mix in analog or hybrid studios. Those who value channel-to-channel consistency and high-headroom EQ. Not for producers relying on real-time parameter automation or granular frequency control.
Is it worth your time
Yes—if you need aggressive, surgical EQ with high headroom and consistent behaviour across channels. No—if you need smooth sweeps, variable Q, or more than four bands.
