The API-originated '500-series' is an ever growing universe of modules for all sorts of tracking and mixing applications, and as equalizers are at the heart of this craft it comes as no surprise that there are many superb options for the so-called “lunchbox” format. Here are ten of Gearspace favourites - in alphabetical order:

API Audio 550A

It’s hard to think of any piece of gear more associated with the 500-series format than the API 550 - in both its 'A' and 'B' variants. Featured here is the 'A' variant, which is a proportional-Q design that has won countless accolades since its introduction in the late 1960s - and was recently brought back to production by API. This highly flexible single-slot EQ offers three bands of EQ with fifteen frequency points, shelf or peak options for the extreme bands, LP/HP filters, classic '2520' op-amp and up to 15dB of boost or cut on five points for meaningful tone tweaking and easy recall. Need an extra band and can do without the filters? Then the 550B is the solid alternative!

API Audio 560

If the 550s are synonymous with 500-series parametric equalization, the same can be said about the API 560 as a graphic EQ. An iconic piece on its own, the 560 is arguably the most popular graphic EQ in recording studios worldwide, widely praised for its vast tonal-changing capabilities on ten select equalization bands that covers the entire spectrum with up to 12dB of boost/cut on each band. It also packs API’s acclaimed 2520 op-amp and custom output transformer to deliver the classic "American" console sound and transform sounds without breaking a sweat.

BAE Audio B15

The B15 is an interesting offering from BAE Audio that takes design cues from EQs such as the classic 1073 but also seizes the opportunity to add a few twists of its own. This single-slot module packs three EQ bands with five frequency settings on each band, shelf (with peak option) for the low and high band, up to 16dB of boost or cut and some premium components, including Avedis 1122 op-amps, Jensen transformers and Elma Gold plated rotary switches. A crafty EQ that not only evokes great memories of the hardware it's inspired by but also the game further.

Chandler Limited Little Devil Equalizer

Chandler’s quality is second to none and the Little Devil Equalizer demonstrates this in spades. This exquisite inductor-based equalizer offers four bands, comprising of two flexible hi-mid/low-mid bands with two bandwidth settings (hi/low Q), Baxandall shelves for treble/bass bands and switchable high-pass filter at 47, 82 or 150Hz. All bands can deliver up to 6dB of boost or cut, which makes it a great EQ to give recordings a nudge towards that final polish. Rest assured, this little red demon is on the side of good, rather than evil!

Electrodyne 511

Electrodyne is a pioneer in our industry and many recordings from the 1960’s and 70’s - the “golden age” of music for some - passed through their transistor-based consoles. The 511 is based on equalizers from that era, offering two powerful bands for adjusting lows and highs on a rather unique (and large) concentric knob design, with each band capable of acting as a peak/bell or as a shelf with four frequency choices per band and up to 12dB of boosts or cuts on stepped stages. This EQ is known for its smooth and transparent sound along with great use and it’s a classy choice to take recordings to the next level.

elysia xfilter 500

The elysia xfilter 500 was such a hit that elysia had to take it outside of the 500-series frame and rack it as a 19" unit. This flexible stereo EQ takes two slots for its flexibility: it packs low/high shelf bands that can be switched to resonant filters, high-mid and low-mid peaking bands with wide/narrow Q options, “passive massage” high frequency shelf for extra air, stepped controllers and a super transparent sound all the way through. The xfilter 500 also comes with a rather friendly price tag, which makes it a budget-conscious choice with virtually no compromises.

Kush Audio Clariphonic 500

If the xfilter made the journey from 500-series to regular 19" racks, Kush Audio’s Clariphonic went the other way around, and even further - from the 19” slot to the lunchbox and also to our DAWs as a plug-in. Unlike its stereo rack sibling, the 500-series edition of the Clariphonic is a mono single-slot module but the signal path and distinctive EQ curves are identical, presenting the “clarity” and “focus” bands on all their iterations. As with other Kush products this is a unique and thought-provoking design, but ultimately it sounds great, which is always the main reason to buy.

Lindell Audio PEX-500

Lindell Audio makes one of the most coveted equalizers in history more accessible than ever with the highly affordable PEX-500, a single-slot module based on the glorious Pultec EQP-1A. The core feature that made this passive EQ such an iconic piece of gear is the unique “push-pull” technique that so many crave, with its unique combination of lifts and cuts. The PEX-500 provides three frequency options on each band and can deliver up to 10 dBs of boost or attenuation. Although it’s not a 1:1 clone of the EQP-1A it’s a pretty close approximation, especially considering its size and very keen price. Also available as a plug-in for your DAW!

Mäag Audio EQ4

The EQ4’s eye-catching blue faceplate, filled with colorful knobs can be easily spotted in many studios across the globe, but it was definitely its exquisite sound that made it famous. Mäag Audio opted for a rather intriguing approach to this EQ, with five carefully selected EQ points with up to 5dB of boosts or cuts ranging from the subs to the bold high-shelf starting at 2.5 kHz. The icing on this cake is the trademark “Air” band that can go up to 40 kHz for super smooth high end boosts. Definitely a wise choice if you’re a bit bored of the “vintage” stuff and want something fresh yet still sonically superb.

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A few notes:

* It's an interesting mix of stuff, with classic designs interspersed with entirely new ideas and many stops in between.

* Although all the EQs on our list are 100% analog, the rise of modules that are bringing digital tech to integrate with DAWs. The Bettermaker 502P and Wes Audio Hyperion come to mind.

* There’s no shortage of excellent EQs for the 500-series format, so honourable mentions go to the IGS Rubber Bands, Purple Audio LilPEQr and Louder Than Liftoff Chop Shop.

* Need some preamps for your growing lunchbox? We have those covered too: Ten of the best 500-series Mic Preamps