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electronic MUSICIAN

Roundup – API 500 Series Chassis

By GINO ROBAIR | October 10, 2013

ONE OF the most exciting hardware categories in pro audio is the 500 Series format. Originally based around a modular system developed for Aphex and API products, the 500 Series has increased in popularity to such a degree that manufacturers are retooling their standard products as modules, as well as developing new ideas for the platform.

Modular systems not only provide a way for you to create a setup that fits your immediate needs, but one that can grow as your projects do. Among the tasks that 500 Series systems excel at are voice and instrument tracking, audio processing, analog summing from a DAW, and live-performance applications. While preamps, EQs, and dynamics processors are among the most common modules, utility modules are also available, such as the spring reverb and guitar-speaker simulator from Radial Engineering, and the dynamic ladder-style filter and analog delay from Moog Music.

At first glance, a modular system may seem expensive, but they are priced in line with other hardware of this quality. Individual modules range in price from a couple hundred bucks to well over $1,000, with the price of a manufacturer’s module reflecting the product in its traditional format. In the modular format, you’re paying for the ability to assemble a custom, portable rig that shares a power supply and chassis, and may have additional features, such as integrated signal routing and mixing.

The heart of a 500 Series system is a powered rack or chassis, which is available in different shapes and configurations that support from one to 11 modules. Some of the chassis can be rackmounted for studio or stage use, while others are designed for desktop use and portability. This roundup will explain the typical features of a 500 Series rack and describe several popular models. (Prices are retail unless otherwise noted.)

Rack ’em Up The 500 Series specs, such as the slot sizes (5.25" x 1.5" for a single panel) and ±16VDC per rail are, for the most part, standardized. Behind each module is a 15-pin card that fits into a slot on the inside backwall of the rack. The pin connections must conform to the standard spec—for example, pin 1 is for chassis ground and pin 15 is for +48 VDC phantom power. However, some manufacturers use redundant pin connections in different ways.

These systems are designed for pro studio use, so they typically feature +4dB output levels using balanced I/O connections—XLR and 1/4" TRS jacks, as well as 25-pin D-sub connectors. However, rack power supplies vary among makes and models, as do the power requirements of the modules themselves, which draw a certain number of milliamps (mA) of current. As you’re shopping for a chassis, be sure the power supply provides enough power for the system of modules you plan to assemble.

Because of the growth in the 500 Series market, API launched the VPR Alliance in order to provide “complete design specifications for manufacturers interested in producing third-party modules that physically fit and electronically conform to API’s rack specifications.” This provides API a means to avoid potential warranty issues. For example, if an unapproved third-party module is used in an API rack and it causes problems or damage due to the module’s design, wiring, or power draw, it essentially voids the warranty of your API chassis. A list of compatible modules can be found at At the time of this writing, no third-party chassis have been VPR approved.

However, inclusion on the list of VPR Alliance-approved products is not a requirement in order for a module or chassis to be well within, or even surpass, the 500 Series spec.

Like all pro audio gear, hearing is believing: While price, style, and brand loyalty all play a role in the products we buy, sound and performance should be among the biggest considerations in the purchase of your modular system. Some resellers offer a try-before- you-buy deal for serious customers, allowing you to spend some time with a system before you make the final purchase. At the very least, the salespeople specializing in this product category should be able to give you expert advice in compatibility between modules and rack chassis.


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