API 5500 Equalizer (2-Channel Rack-Mount)

The beginnings of the 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 uses an unbalanced input due to the architecture of the recording console. 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 its versatility to mastering applications.

Typical of 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. A key component of the API sound, the 2520 coupled with the API 2503 output transformer, is capable of delivering +30dBm before clipping.

An extremely useful 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 to adjust the tonal balance with finer resolution in an even gentler manner. This is especially useful for complex program material as contained in stems or submixes and is ideally suited for mastering purposes.

API's 5500 also features a true hard-wire bypass which wires the output connector directly to the input. Shortly after the power is first applied, or immediately after it is lost, a special circuit enables "bypass mode" so that power thumps are never heard.

The 5500's input XLR is connected to an active balanced circuit. The unit's output XLR is driven from a transformer coupled output and can drive any load from 600 ohms or more to full output capability. There is no change from input to output in the unit's polarity, so it is suitable in studios using either pin 2 or pin 3 as the "hot" connection. Additionally, the 5500 has a 1/4 inch input connector that interrupts any present signal 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 inch input does not bypass any internal circuitry and does not change the gain or operating levels. The 5500 features API's industry exclusive five-year parts warranty and exhibits the reliability and long life characteristic of all API products.

• Classic 550b Equalizer design
• Two range switches to individually alter gain steps
• Usable as a 550b, 550D or 550M
• Peak/shelf switch on Hi and Lo bands
• True hardwire bypass
• Balanced In and Out on XLR
• Balanced input on 1/4"
• EQ In/Out switch

Specifications

Pro Audio Review || "Everybody sing! "550, glorious 550 .. " The 550B modules paired within the 5500 can indeed sing, and they do it extremely well, thank you very much. Theyalso whisper, growl, purr and soar - in short, it's unlike any other beast out there. Truth be known, despite my long-term and deeply rewarding relationship with AP! preamps, I have never owned, and have barely used, API equalizers. So it was with great anticipation that I waited for the 5500 to move in with me for a month.

"Let's face it; except for mastering facilities, high-end equalizers qualify as luxury items in most studios. Even the typical world-class studio will have a limited number of outboard, high-end equalizers in their racks, and the number diminishes at every stop below. High-end EQs have historically faced stiff competition from console EQs and resources that gravitate towards more pressing equipment needs. With the ubiquity of DAW plug-in EQs of every flavor (including several modeled high-end hardware EQs) that competition has expanded exponentially.

"Then along comes the AP! 5500 - with its enduring all-discrete analog component design and eminently useful new features - to remind you what a truly great EQ can achieve and at the same time put so many plug-ins and digital console EQs to shame. AP! deserves credit for its adept addressing of the obstacles a high-end EQ faces in the market. The 5500 is endowed with top-notch audio quality and innovative features, making it versatile enough to use in any application, from the gentlest coloring of an input signal all the way up to world-class mastering applications." - Stephen Murphy