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500 Series: Yesterday, Today & Tomorrow

Toys or tools? Compromised facsimiles or innovative diminutive hardware? Is the 500 Series analog processor format hamstrung by its original specs or can it be pushed to new heights by clever designers?

Toys or tools? Compromised facsimiles or innovative diminutive hardware? Is the 500 Series analog processor format hamstrung by its original specs or can it be pushed to new heights by clever designers?

Photo credit: Lynn Fuston at Vintage King Nashville

From Whence It Came

Beginning in 1966, Saul Walker designed audio components for his start-up company, Automated Processes Inc. (API). These components were modular building blocks like preamps and equalizers that fit into uniformly sized “slots” in the consoles API produced. Due to the overwhelming popularity of the consoles, some engineers in the mid-1970s started making home-made racks to house their personal API modules, perhaps inspired by other companies making similar but incompatible modular rack systems, like Allison Research, Valley Audio and dbx.

In 1978, Datatronix (producing API products at the time as API was out of business) made a 10-slot rack. Marvin Caesar of Aphex also decided to build a 500 Series rack that would fit his Aphex CX1 Comp-Gate and the EQF-2 Equalizer. The rack and pin configuration was similar enough that API modules would work in it. About the same time, Art Kelm (Ground One) originated the name “Lunchbox” while using an Aphex rack to create a modular channel strip featuring a preamp, EQ and compressor for customers (including Steve Perry of Journey, for example) so they could have their own consistent sound.

In 1985, Aphex decided to discontinue their 500 Series rack about the same time that Paul Wolff—then a Datatronix employee—became the new owner of API. Wolff (today with Paul Wolff Designs) received approval from Caesar to make 500 Series racks under the API brand name. API produced the Lunchbox as well as 2- and 10-slot versions from that time until the present.

In 2006, partly as a result of the explosive growth of third-party 500 Series racks and modules, API’s new owner, Larry Droppa, launched the VPR Alliance, an open-source free initiative designed to implement uniform standards and approve manufacturers of 500 Series components. According to Droppa, VPR certification involves submitting a production version of the unit to API, which then tests it to make sure it conforms to size standards, fits in the slot and draws under 130 mA. There is no fee for this certification process. The VPR certification has helped with regards to uniformity (instead of having modules that don’t quite fit) yet there are still manufacturers (quite a few, actually) that do not seek certification.

Growing Up

Looking forward from the year 2000, I doubt anyone could have foreseen the impact that the 500 Series format would have, either on product designs or sales. Like many technologies—conceived for one purpose and adapted for others—the format has far exceeded its original intent and has now taken on a life of its own, but not without some growing pains.

I believe the format is similar to two other historical audio precedents. First was the Compact Cassette, a pocket-sized tape transport case that was intended as a portable equivalent of a reel-to-reel recorder. With a tape speed of 1 7/8 ips and originally designed for dictation, no one could have imagined that the Cassette would become a dominant force and high quality option for music recording and distribution. Gradual improvements like advanced tape formulations and Dolby B encoding allowed the Cassette to become a very capable recording medium.

Another analogy is audio plug-ins for DAWs. In the early days, they were pale imitations of their hardware counterparts—workable but not great. Today, nearly 20 years after their introduction, plug-ins have improved and are accepted as standard workhorses in our industry. Some emulations/creations offer more features and are even preferred over their hardware counterparts. So, in much the same way, the humble 1.5- x 5.25-inch 500 Series slot has become a very powerful option for designers and engineers.

The Spec

Over the years there has been some criticism of certain parts of the 500 Series’ technical specs, specifically the voltage and current standards. According to official VPR Alliance specifications (dated 8/28/06), voltage is +/- 16V and +48V for phantom and current is 130 mA per slot. For designers accustomed to working with power rails up to 24V or higher, this voltage spec seemed challenging at first, while others still feel that the current spec is insufficient. Keep in mind that the spec was originally designed to power one thing—API modules—and was never envisioned as an open platform to accommodate all manner of audio hardware. Only through the vision and problem-solving abilities of talented designers/manufacturers have we seen the exponential growth of possibilities in this tiny space.

How significant is the rack itself, the true backbone of the 500 Series format? In a word: very. While some older custom racks did not meet the original API spec (pre-VPR), most do today. The upside of having a stock powered rack is that it allows manufacturers to forego UL, CSA and CE certification so they can spend their time and energies primarily on audio functions instead of power supply design and certification.

With so many 500 Series rack options available (over ten manufacturers by my count), there are still reports of underpowered racks. Those in question work with a few modules but suffer sonically when filled or will not even power up multiple current-hungry modules. Some newer racks offer beefier power supplies with capabilities exceeding the 130 mA per slot spec, even up to 400+ mA. Anyone planning to spend thousands of dollars on modules should carefully research the options when choosing a rack.

How Do They Sound?

Today there are still those who don’t see 500 Series modules as audibly serious contenders—definitely not up to the standards of their full-sized, rack-mounted brethren. True or false?

After eight years of research, here’s my take. Making a 500 Series equivalent of a standard rack unit is not without its perils and some attempts are indeed sonically compromised. But some 500 modules definitely hit the mark. The very first time I ever encountered a rack unit that was morphed into a 500 Series module and sounded “identical” to the rack unit was the Great River MP500NV, sibling to the full-sized MP2NV that I had been using on every session for over 10 years. I did side-by-side testing between the two and was unable to discern any difference at all. How was that accomplished? According to Great River’s Dan Kennedy, “by not changing any components or the transformers.”

Many manufacturers have to use smaller transformers or possibly forego shielding to squeeze the components into a single 500 Series slot. Great River got around that by not fitting into a single slot. “The transformer itself wouldn’t fit in a single slot, so I took two,” explains Kennedy. “Then it was easy.” While some 500 Series buyers may be reluctant to give up two slots for a single device, I personally would rather have it sound right than be half as big. “Also paying careful attention to a power supply circuit that regenerates and regulates the rack’s power to a stable +-24Vdc—just like the rack units—was important.”

One of the things that will make 500 Series believers out of old-school engineers (like me) is integrating features in 500 modules that previously never existed in the rack equivalents. For instance, I’ve used two Millennia 8-channel preamps for years, the original HV-3D and the newer HV-3R. Both are incredible for orchestral recording and I use them for drums, percussion and vocals as well. However, I frequently have to patch in external EQ to accomplish hi-pass filtering for low frequency issues such as AC rumble. Apart from that, I can typically go from preamp to recorder input, which is my preference. Guess which preamp has a hi-pass filter on it? Not the $4,000 Millennia HV-3D or the $5,000 HV-3R, but the $700 single channel HV-35. Add to that a Ribbon Mic mode (+10 dB), pad (allowing down to 1 dB of gain, which is great for when I put an R-122 on kick drum) and the Instrument Input—each not available on the multichannel units—and the HV-35 is a unit I’d actually prefer over full-sized rack gear, especially since they sound just the same to my ear. Checking the specs, the racked HV3 will output +32 dBu vs +28 for the HV35, will take 5 dBu more input level (+23 vs +18 dBu), and the HV3 is 3 dB EIN quieter than the HV35, -133 vs -130 dBu, respectively.

Another revolution was the first 500 Series module that featured a tube stage. Running a tube that requires 250V on a +/- 16V supply might seem impossible, but that is what engineers are for: accomplishing the impossible. It was a challenge, one that father/son team Mark and Scott LaChapell accepted for the LaChapell 583 tube preamp introduced in 2006. I won’t go into technical details but according to Scott, they used “a complex little DC-to-DC converter to step up from 16V to 300V at a very high frequency (280kHz), which makes it very quiet, that allows 250V at the plate and 12V for the filament.” The current limitation of 130 mA per slot was overcome by utilizing two slots, which upped the current allotment to 260 mA. One of the few concessions was not using the tube output stage of the big-brother 992 since two tubes wouldn’t fit; the single full-sized 12AX7 tube is used for the preamp gain stage with transformers in and out (Cinemag/Jensen, respectively). With no room for the transformer DI input, an active stage was successfully substituted. I have used the now-discontinued 583 for many recordings and it’s a very sweet piece of gear that doesn’t sound compromised in any way. Presently there’s a double-slot 583e with EQ and the newest 583s Mk2 that fits in a single slot.

As more manufacturers jump on the 500 Series bandwagon, more R&D money and innovative features are seen first in this format, as with the Millennia HV-35. Moog’s recent 500 Series Analog Delay and Ladder Filter are great examples. The Aphex 500 Series rack with integrated USB is another prime example; I haven’t seen too many racked preamps/EQs with USB. The popularity of the format is encouraging manufacturers to attempt things they haven’t before, like Crane Song’s first tube entry, the Syren tube preamp. A few of my other favorites are Shadow Hills’ Mono Gama (having three transformer options is wonderful), Inward Connections’ Brute optical limiter and, of course, the API 550A EQ. With just those three to work with, I could be a very happy man. Others I am curious about but have yet to hear include the AnaMod AM660 (Fairchild), Chandler’s Little Devil compressor and the Pendulum OCL 500.

What’s Next?

When asked about his hopes for the future, Larry Droppa from API mused, “I hope the format stays viable, that people recognize the positives of that form factor: portability, ease of use, easy to swap modules. It has become—purposely or otherwise—a form for some innovative and interesting pieces of audio gear. It allows an engineer, or even a hobbyist, to manufacture a piece of gear without having to worry about the periphery of power supplies and casing so they can easily put a piece of gear out in the marketplace and see if people like it.”

There are already 500 Series racks that offer summing (Radial Workhorse) or switchable chaining/linking (Mercury G810). Some units overcome I/O pinout limitations on the back rail by adding TRS inputs on the front for link or inserts (Tonelux TX5C). Also available are a digital delay line (Eventide DDL-500); a tape emulator (Rupert Neve Designs 542); mixers with 500 Series slots built-in (API The Box, Pete’s Place MK VIII, and SSL XL Desk, for examples); a modular mixer and output section built into a rack (Malcolm Toft Ocean Audio); and even a limited edition, original-design mic preamp from the custom-built console at Sunset Sound (S1P Tutti).

And what does the future hold for 500 Series pricing? These small, low-cost alternatives are still one thing: small. While there are still units in the “under $500” category, as innovation and features continue to expand so does the impact on one’s wallet. Some units are priced upward of $1,000, like a $2,200 preamp (Heritage Audio 1073), $1,600 EQ (Bettermaker EQ502P) or $2,500 compressor (Dramastic Audio Obsidian). How much will people pay for 500 Series modules? Only time will tell, I guess.

Looking ahead, I would echo the sentiments of Paul Wolff, who was there at the beginning. “It’s funny because it seems the format of the ‘70s has become the format of the new millennium.”

Lynn Fuston is the Technical Editor of Pro Audio Review and a prolific recording engineer based in Nashville.