Up for sale is the legendary API 550A 3-Band Discrete EQ module. First designed in 1971 by Saul Walker, the 550A is an undisputed industry staple for drum tracking, guitars, vocals, and bus processing. I have a dual channel API 5500, which is the only reason why I'm letting them go! I have three for sale, individually or as a package deal.

Equipped with the classic 2520 operational amplifier and API’s proprietary "Proportional Q" circuitry, this EQ intuitively narrows the bandwidth as you apply more boost or cut—keeping everything remarkably musical, punchy, and phase-coherent no matter how hard you push it.

💬 What the Legends Say

"The API 550A is the absolute secret weapon for drum punch and guitar authority. You can throw 6dB of boost on a snare or acoustic guitar and it never sounds harsh—it just sounds like a record."

— Bruce Swedien (Grammy-winning engineer for Michael Jackson, Quincy Jones)

"When I want mid-range character, edge, and immediacy on vocals or guitars, the 550A is the first module I patch into."

— Chris Lord-Alge (Grammy-winning mix engineer for Green Day, Muse, Eric Clapton)

"The API EQs are great for tonal shaping, and you don't have to be shy about cranking the knobs around. Even with crazy boosts and cuts, they still sound natural."

— Brad Madix (FOH Engineer for Rush, Jack White, Shania Twain)

"For hip-hop low end and snare punch, running into an API 550A gives you absolutely amazing low end—it's unstoppable."

— Jaycen Joshua (Grammy-winning mix engineer for Beyoncé, Jay-Z, Rosalía)

"API EQs are an instant pleasure on drums, vocals, guitars, and the stereo bus mix."

— Bob Clearmountain (Legendary mix engineer for Bruce Springsteen, David Bowie, The Rolling Stones)

⚙️ Key Specifications & Features

Format:

- 500-Series Modular Rack (1 Slot)

- Circuitry: All-discrete design featuring the iconic API 2520 Op-Amp & custom output transformer

- EQ Bands: 3 overlapping bands with 7 selectable frequency centers per band:

- Low Band: 50, 100, 200, 300, 400 Hz (Switchable Peak or Shelf)

- Mid Band: 0.4, 0.8, 1.5, 3, 5 kHz

- High Band: 5, 7, 10, 12.5, 15 kHz (Switchable Peak or Shelf)

- Boost / Cut Range: Up to +/- 12 dB across stepped 2, 4, 6, 9, and 12 dB positions per band (reciprocal & repeatable)

- Filter Switch: Independent 50 Hz} to 15 kHz Band-Pass Filter

- Headroom / Clipping: High headroom with a +30 dBm clipping level

- Circuit Technology: Proportional Q (bandwidth automatically scales with gain adjustments)

📌 Condition & Terms

- Condition: Excellent functional and cosmetic condition. Clean, scratch-free pots and switches.

- Tested: Fully tested, low noise floor, and 100% operational in a smoke-free studio environment.

- Price: $1,200CAD for one; $2,300CAD for two, $3,300CAD for three. ($850USD for one; $1615USD for two); $2,315USD for three).

- Location: Local pickup/drop off near Kitchener/Guelph, drop off in the Greater Toronto Area also available; and willing to ship insured at buyer’s expense anywhere in the world if required.