The 500 Series: Portable Racks, Enclosures, Lunchboxes


If you want to learn about 500 Series, you need to start with API. API first started producing recording equipment in the late 1960s and has been on the cutting edge of recording technology throughout the ’70s and ’80s. The company’s large-frame consoles have gone on to become highly sought after and are comparable in quality to SSL and Neve, while providing a unique and sought-after sound all their own. The one thing that separated API from most other large-frame recording console manufacturers was the modular design, where different types of preamps, EQs, and compressors could be swapped out and reconfigured. This also led to the advent of the API Lunchbox and the current explosion of the 500-Series format. The Lunchbox officially began in 1985 and allowed engineers to carry API components from studio to studio. This also opened the market for project studios, who couldn’t afford an entire console, but allowed them to incorporate the technology in an affordable way.

Today, the 500 Series market has grown and most major high-end audio manufacturers are offering their products in this affordable format. In this series of articles, we will look at the best ways to get into the 500 Series format, with each article focusing on microphone preamps, equalizers, compressors, and effects.

Before purchasing a 500 Series module, you will need a chassis or enclosure to house and power it. 500 Series Rack/Chassis come in a variety of configurations, from two to ten slots. Some enclosures are designed to fit into a standard 19" rack, while others are offered in more portable tabletop design and include handles for ease in transport. The enclosures not only hold the modules, but also supply power to each module. This is one of the reasons the 500 Series format is so cost effective, since a manufacturer doesn’t have to include a dedicated power supply for its product and can pass the savings on to the consumer. One would think that all racks are the same, but there are significant differences in power supplies, as well as additional features that might make each manufacturer’s offering even more useful, such as the inclusion of a built-in summing mixer and the ability to pass signal from one module to another without the need for additional cabling. Make no mistake, however—how well a rack is powered is the most significant consideration one can make when selecting one.

Radial Engineering Workhorse Powerhouse 500 Series Power-Rack

The original API specification requires +/-16V of power with 250mA dedicated to each module. API Audio’s VPR Alliance program provides a standardization for manufacturers producing products that are to be used in API’s lunchbox and 500V enclosures. Other manufacturers, such as Radial Engineering, have developed their own specification guidelines for use of modules in their products and often exceed the specifications of API’s. It’s interesting to see products that exceed the build specs for API, but can’t join the company’s VPR Alliance. While being in the VPR Alliance may assure a certain level of quality, it should be noted that there are many top-of-the-line manufacturers making 500 Series gear who have not bothered to join in this alliance. Let’s distill some of this information down to help you figure out what’s right for your rig.

Portable / Desktop

API has trademarked the term “Lunchbox,” because each enclosure is easily transported and often comes with a handle. The Heritage Audio OST-4 can house four 500-series modules in its heavy-gauge steel enclosure. The unit is designed for desktop use and takes up very little space. One outstanding feature of the OST-4 is the company's "On Slot Technology," which leverages the latest generation of power electronics to provide a supply of power on a "per slot" basis. Each slot has its own power supply linear regulation stage, which makes each module isolated from the rest. This helps address some of the issues encountered when modules of different kinds share one common power supply. The power capability of the unit is 400mA per rail per slot maximum and the total available phantom power is 80mA.

Heritage Audio OST-4 Enclosure for 500 Series Modules

The Lindell Audio 506 Power can accommodate up to six modules in an aluminum chassis. The desktop enclosure doesn’t offer a handle, but does include a neoprene gig bag for protection while on the go. The external 2.4A power supply mitigates any noise issues and offers 400mA of power per module. There is also overload and short-circuit protection to safeguard your investment. The Radial Engineering Workhorse Six Pack and Workhorse Cube use 14-gauge steel enclosures with integrated handles. Each unit utilizes an external power supply to mitigate noise and improve signal-to-noise performance. The Cube can accommodate three modules and offers 500mA of current plus a separate +48V phantom tap to deliver a full 10mA of current for microphone preamps. The Six Pack offers six slots and features 1600mA of power, which exceeds the average with more than 265mA per slot to ensure power-hungry modules stay satiated. The Cube and Six Pack offers XLR and ¼" I/O for added flexibility, while the Six Pack adds DB25 connectors and includes two XLR inputs for channels 1 and 4, which facilitate two three-slot channel strips for stereo operation. Both units include a feed switch that patches one module into the next, a link switch to combine stereo-ready modules, and Omniport, a ¼" TRS jack that adds extra functionality to Radial Engineering’s vast collection of modules.

Radial Engineering Workhorse Cube 3-Space Desktop Power Rack for 500 Series Modules

Rupert Neve Designs R6 holds six modules in a solid steel chassis that’s double shielded to avoid magnetic induction, and includes a collapsible handle for portability. The power supply provides 150% of the required current for a six-unit enclosure. The headroom in available current helps prevent the power rails from falling under a higher than expected load. Comprehensive metering on the front panel indicates how much power is being used. The rear of the rack includes DB-25, XLR, and ¼" connectors. Additionally, the unit includes link jumpers for channels 1-2, 3-4, and 5-6 for quick stereo integration. The channel 7-8 thru connections can be used to convert your signal quickly and easily from/to DB-25, XLR, and TRS connectors.

Rupert Neve Designs R6 Six Space 500 Series Rack

Rackmount Enclosures

Rackmount enclosures come in two sizes; a 1U rack, which offers two or three module inputs, and the larger 3U, which accommodates eight to ten modules. There are even some kits for converting six-module cases into rackmount-compatible formats. Radial Engineering offers three Workhorse models. The WR-8 offers room for 8 modules and features the same overbuilt power supply as the Six Pack and Cube. Each case includes the same assortment of DB-25, XLR, and ¼" I/O and includes the Omniport and Feed Switch features for stereo operation. The Workhorse 8-Modlue Rack with Summing Mixer is offered in the same frame as the WR-8, but includes an eight-channel summing mixer with volume controls, left-right pan, on/off buttons, and LED indicators for each channel, as well as two headphone outputs and controls for main and auxiliary outputs. The rear panel includes XLR and ¼" outputs with ¼" inserts for the main and aux busses. The Workhorse Powerhouse offers ten slots and boasts a 1600mA power supply, which can deliver 300mA to two tube preamps and still have more than 1000mA left in the pool.

Radial Engineering 500 Series WR-8 Workhorse 8-Slot Power Rack

It is also equipped with extra safety features to ensure safe use when mixing and matching various brands. The Heritage Audio OST-10 enclosure is built to the same specs as the OST-4, but accommodates ten modules. It utilizes the same isolated "On Slot Technology" to deliver 400mA per rail per slot. The Heritage Audio MCM-8 Mixer Enclosure offers eight slots for modules with the same “OST” power design. The summing mixer offers pan and fader controls per slot on dual concentric potentiometers. Pan pots have a center detent for precise center positioning. Each channel features an “on” switch to assign the channel to the mix bus. The mix bus follows a passive, voltage summing topology, like that found in the 80 Series consoles from the1970s. The gain loss is restored by the same Class A, 2n3055-driven, transformer-based output stage used in the 1073 by which the company is known.

Heritage Audio MCM-8 Mixer Enclosure for 500 Series Modules

The Black Lion Audio PBR-8 utilizes On-Slot technology, which isolates each module and avoids power sharing. rear of the chassis offers XLR and DB25 connectors, while the front provides a dedicated TT patchbay, allowing it to integrate easily into professional studio environments. Additionally, the unit sports two 3-point TT mults, which allow for signal duplication without splitter cables.

Black Lion Audio PBR-8 Enclosure and Patchbay for 500 Series Modules

There are additional 500 Series enclosures from a variety of manufacturers that are well worth investigating. Check out models from Rupert Neve Designs, BAE, dbx, Empirical Labs, and Trident Audio. Hopefully, this article has demystified some of the mystique, and you’re on your way to building the perfect 500 Series setup. For a complete overview of what the 500 Series format offers, check out our other articles on microphone preamps, equalizers, and effects.