This API 550b has been fully tested by our expert team and comes with a money back guarantee and lifetime support. We have multiple units from the same production run if you would like a pair.

The API 550b is a four-band 500 Series equalizer descended directly from the original 1967 API 550 — one of the most influential EQ designs in recording history. Built around the legendary 2520 op-amp and taken from API's original archive drawings, it offers four overlapping bands with seven switchable frequency centers per band, each chosen for musical usefulness rather than round numbers. The key to its character is Proportional-Q: bandwidth narrows automatically with larger boosts and cuts for precise, focused shaping, and widens with subtle moves for broad, natural-sounding strokes — all without an extra knob. The result is an EQ that's equally at home solving problems and sweetening a mix, with the punchy, forward tone that has appeared on countless records across every genre.

Welcome to Providence Sound and Vision, where your satisfaction is our top priority!
As an employee-owned company, we deeply appreciate your support. Your trust in us means the world, and we're committed to providing unparalleled service every step of the way. Here's what you can expect with every purchase:
Extended Warranty Enjoy an additional year of warranty on all new items. We're so confident in the quality of our products that we go the extra mile to ensure your peace of mind.
Quality Assurance Our used items undergo rigorous testing and servicing to guarantee their performance. Plus, they come with a money-back guarantee, so you can shop with confidence.
Risk-Free Shopping Not completely satisfied? No worries! We offer a 7-day money-back guarantee on pre-owned items and a 14-day money-back guarantee on new items.
Lifetime Support We're here for you for the long haul. Whether it's warranty support, part replacements, tune-ups, or trade-ins, count on us to assist you for as long as you own the product.
Ready to elevate your sound shopping experience? Explore our store and website for a diverse selection of top-quality items. Your journey to producing amazing sound starts here!
Thank you for choosing Providence Sound and Vision. Let's make music magic together!