API 5500 Dual Equalizer

Dual 550 EQs with selectable boost/cut steps
MFR# 5500
API 5500 Dual Equalizer
API 5500 Dual Equalizer API 5500 Dual Equalizer


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The lineage of the API 5500 circuit can be traced back to the original 550 equalizer designed by Saul Walker, the founder of Automated Processes Inc.  The 550 was designed as a console equalizer which, due to the architecture of the recording console, uses an unbalanced input.  Because the ergonomics of a console dictate that the controls take up little space, sometimes the number of included functions can be limited.  The 5500 is specifically designed to address these limitations.  It has a balanced input, a true straight-wire bypass, an integrated power supply with noiseless muting and a range control that expands it versatility to mastering applications.

Like all API products, the 5500 contains no integrated circuits in its signal path.  The gain comes from two hand-built 2520 operational amplifiers in each channel. The balanced input is handled by a 2510 discrete operational amplifier, which is similar to the 2520, but without the high current output stage.  Besides being a key component of the API sound, the 2520 coupled with the API 2503 output transformer is capable of delivering +30dBm before clipping.  With this much headroom, it is unlikely that the 5500 can be driven to distortion unless perhaps another API unit is driving the input!

A new feature in the 5500 is the range control.  The range of the amplitude controls can be reduced to 1/2 or 1/4 of their stated scale, providing a means of adjusting the tonal balance with finer resolution in an even gentler manner.  This should be especially useful for complex program material as contained in stems or submixes, and is ideally suited for mastering purposes.

Also new on the 5500 is a true hard-wire bypass.  In this mode the output connector is wired directly to the input.  Shortly after the power is first applied, or immediately after it is lost, a special circuit enables bypass mode so signal is never lost and power thumps are never heard.

The input XLR is connected to an active balanced circuit.  The output XLR is driven from a transformer coupled output and can drive any load from 600 ohms or greater to full output capability.  The polarity is such that there is no change from input to output, so it is suitable in studios using either pin 2 or pin 3 as the "hot" connection.  In addition, there is a 1/4" input connector that interrupts any signal that is present on the input XLR.  It is balanced and can be driven from either balanced or unbalanced sources.  A positive signal on the tip will deliver a positive signal on pin 2 of the output XLR.  Using the 1/4" input does not bypass any internal circuitry and does not change gain or operating level.



  • Classic 550B equalizer design
  • two range switches individually alter gain steps
  • Useable as a 550B, 550D or 550M
  • Peak/shelf switch on hi & lo bands
  • True hardwire bypass
  • Balanced in and out on XLR
  • Unbalanced Input on 1/4"
  • EQ in/out switch

Additional Information

Condition New
Channels Dual-Channel
Chassis 19-in Rackmount
Rack Spaces 1u
Digital I/O No
EQ Type Parametric

This EQ can be aggressive or surgical. I love it on the MixBus!!!

By Tony C on January 29, 2019

An API EQ has always been my favorite. They're so easy to use, every band on every instrument seems to work in one way or another. They've been a key element to my drum and guitar tones throughout my entire career. Lately I've been experimenting with compression and EQ on the stereo bus, I noticed that a lot of today's top mixing engineers start the mix with them already set. I was using plug-ins for a bit, but wanted to move into using hardware on the mix bus. In the box I landed on using an API 2500 as the compressor followed by a stereo 550B EQ, might not be the ideal choice for everyone but I was familiar with both of units so it felt at home for me. I was going to order a lunch box with two 550Bs, but my sales guy at vintage king turned me onto the 5500. I had no idea they made it, ended up being a perfect fit in the rack right below the 2500 and it still has the same sound, controls and feel I'm used to on the 550b. My mixes have never sounded better, having these on from the start makes a world of difference, the entire mix has more depth in the low end, open top and appears closer and wider in the speakers. Saves a lot of time with surgical EQ. Game changer for my studio, these days I can't imagine mixing without the 5500.

By Scott H on December 18, 2017

Heard about the 5500 from a friend who uses it extensively on the buss and for tracking. Tried it out on a session with him and was so impressed I had to grab one. Love the flexablity of selectable volume increments. 1/2 DB volume switched steps for mixing subtleness and larger increments for tracking. The volume switch pots are great for accurate recall. API punch all the way with nice clarity and a musical feel I was looking for.

By TheBigGuy on May 11, 2017

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