The 500 Series format is comprised of a whole slew of different signal processing modules in a compact rack unit. Mic preamps, equalizers, compressors, DI boxes, filters, effects... You name it, you can find it in a 500 Series version from a wide variety of manufacturers.

Most of those manufacturers participate in the VPR Alliance, established to set standards for the format to ensure that the end user can rely on consistent specifications with regard to voltage, current draw, size, etc. along with proper compatibility with existing modules. The essence of this idea is to make it simple for the user to mix and match modules from different makers, thus allowing for the broadest range of implementation for their products.

In general, a 500 Series module will have the same operating specs as its larger size brethren from the 19” wide rack world. So in many cases, a 500 Series module will simply be a down-sized version of a regular rack size unit. But in other cases, manufacturers take the opportunity to add extra functionality to their 500 Series units, especially when they’re a modern version of a vintage design. But whether a straight up clone or an enhanced remake, a 500 Series module is designed to be compact, user-friendly, and able to deliver all the performance you’ve come to expect from your full-sized outboard gear.


The History Of 500 Series Format

The roots of the 500 Series begin with Automated Processes Inc. better known as API Audio. Founded in 1968 by the legendary Saul Walker, API came out of the gate with one of his signature designs, the 2520 op amp. Still in production today, the 2520 is one of the keys to the "API sound."

Within a couple years, recording consoles were in production, and another by the signature product was released, the 550A 3-band equalizer. This was designed to be a modular unit, 5.25” x 1.5”, ready to slot into any channel on the console. Modularity was a big selling point at the time, as many consoles were custom-made and difficult to modify after the fact. Being able to swap out an EQ or preamp for something different, or just to replace it in case of failure during a session, was a huge selling point.

It wasn’t long before a full range of modules was available; the 512C mic preamp, 550B 4-band EQ, 525 compressor, and 560 graphic EQ. You’ll notice that all the model numbers begin with a 5, thus they’re referred to as the 500 Series. Engineers and producers loved the API sound, and it’s been used on more hit records than you can name.

By the mid 1980s, portability became an important selling point. Engineers wanted to have a couple of channels for on-the-go recording, and API brought out their famous Lunchbox. Originally it held four modules, so you could have two channels of mic pre and EQ. Later, the rack expanded to the 500-6B, holding 6 modules and giving you the option of a couple channels of compression as well or whatever floats your boat. It naturally extended all the way out to a full 3U 19” rack size, to become the 500VPR (vertical powered rack) holding 10 modules of your choice.

In the next couple of decades, the idea behind the 500 Series had taken root, as manufacturers began coming up with new products (or new versions of existing ones), to fit into the Lunchbox and the 500V racks. When problems with compatibility became apparent, API began the VPR Alliance, a voluntary group of manufacturers to set standards for the format. Members get certified that their gear is interchangeable with other 500 Series modules, so nobody’s warranty gets voided and everyone plays together nicely.

The idea has blossomed over the last decade to the point where you can get a 500 Series module from every major manufacturer of professional audio gear. That means lots of choices, and that translates into putting you in control of your sound.


The Benefits of the 500 Series Format

The primary benefit of the 500 Series is choice. There is an amazing array of modules made in this format, and not just mic pres, EQs and compressors. There are filters, reverbs, DI boxes, re-ampers and the list goes on. They appear in solid-state or tube-based. They proliferate like the proverbial rabbits, and that gives you mega choices.

The next best benefit of the series is cost. A 500 Series module is generally considerably cheaper than its full-rack-sized cousin from the same manufacturer. The form factor plays a role, as there is a physically smaller enclosure to build. Also, there is no need for a power supply, whether internal or external, because the PSU is built into the rack. Once the rack and the first couple modules are invested in, the cost per unit goes down considerably, making the 500 Series an awesome choice for getting lots of colors on your palette, for lots less money.

Another great benefit is modularity. This, after all, is the whole reason for the format in the first place. You can easily swap modules from your rack in minutes. A couple of screws to turn and you’re done. Try doing that with your regular rack gear! Modularity also allows you to have several different flavors in a single rack, so you’re not tied down to just one configuration. But once you’re locked and loaded, another benefit becomes apparent, as you’ve got all your controls aligned in a single rack - easy to see, easy to manipulate.

Last but certainly not least is the portability factor. The Lunchbox got its name because of the size and the fact that it had a handle, so you could carry it anywhere. Nowadays this idea is so ubiquitous that we forget it wasn’t always that easy to carry around a portable set of channel strips. But now it is, and now you can, and now you should!


500 Series Racks

Unless you’re using a console that accepts the format, you will need a 500 Series rack to store and power your modules. Racks come in sizes from 2 slots to 10, and can be portable or designed for a standard 19” rack mount. Most modules take up one slot, but there are 2- and even 3- slot sizes, depending on the function of the module.

Whatever the configuration of modules you choose, the rack provides the power and the In/Out interface, with I/O provided by multi-pin DB-25, balanced XLR of TRS jacks. Depending on the rack, you can also have internal patching, a variety of signal routing, stereo linking or audio summing. There are several manufacturers of 500 racks, so you have plenty of choices to pick from, including our very own custom model from Vintage King.

Suggested 500 Series Racks: Vintage King Rack 500, API 500-8B - 8-Channel 500 Series Lunchbox, Rupert Neve Designs R6 500 Series Rack, API 500VPR 10 Slot Rack w/PSU, API 500-6B - 6-Channel 500 Series Lunchbox, Purple Audio Sweet Ten Rack, BAE 11 Module 500 Series Rack Mount - with PSU

Vintage King Rack 500

Designed by our Tech Shop engineers and built in Detroit, Michigan, the Vintage King Rack 500 is the result of endless testing. We've built these racks to take on nearly any mix of 500 Series units and through this testing, we've yet to find a combo of modules that would result in the system failing.

Types of 500 Series Modules

500 Series Microphone Preamplifiers

The heart of any channel strip is the microphone preamplifier, or mic pre for short. This is the initial interface between the signal from the microphone, and the rest of your processing chain. Because the output level of a microphone is very small, it needs to be brought up to "line level," after which it can be processed with other gear, including being amplified. Thus the initial step is ‘pre-amplification’.

Because this is the first stage in the processing of your electrical signals, it is also the most crucial. What happens here will get amplified and multiplied as you proceed down the chain. Not only is it impossible to add what was never in the signal in the first place, it is also more work to eliminate aspects of the signal that are undesirable, (through equalization or some other means). So you want to match the mic pre with your microphones in the most flattering way possible, to make your sound better and your life easier as you continue processing the signal.

Many mic preamps also have the ability to double as a line and/or Direct Injection (DI) input, thus increasing its importance as the first step of interfacing with the rest of your equipment. As you shop for mic preamps, be aware of what your needs are, and whether paying for extra functionality is necessary. If you want to be able to plug a guitar straight into your rack, or send a line level signal through the preamp, then you’ll need a mic pre with those extra functions. And if you plan on using a ribbon mic, you’ll want a mic pre that has a large amount of gain, (usually at least 60 dB), in order to make the most of your low level ribbon mic output.

Microphone preamps are ideally suited for the 500 Series format, as they only need a few basic functions to be usable, such as 48 volt phantom power (a must), a phase switch, and a gain control. A DI (usually a ¼” jack) and line/mic switch (often an XLR input on either front or back) are extras that increase your routing options. Regardless of the particular options you choose, for recording you will need to have at least one mic pre, and often 2 or 4 total, in your 500 Series rack, depending on what kind of recording and processing you’re doing.

Suggested 500 Series Mic Pre Modules: Neve 1073LB, Rupert Neve Designs Portico 511, API 512v, API 512C, Chandler Limited TG2-500, Shadow Hills Mono GAMA, BAE 1073MPL, Avedis Audio Electronics MA5, Burl Audio B1, Burl Audio B1D, SSL VHD 500 Series, Grace Design m501, Rupert Neve Designs Portico 517, Meris 440, Great River MP-500NV

500 Series Equalizers

After the microphone preamp, the most important module in your 500 Series rack is usually the equalizer. Coming in all kinds of flavors and functionality, the EQ is where a lot of your "color" can be generated. The two basic styles of equalizer are graphic and parametric. Each has their strengths and benefits.

With a graphic EQ, you usually have sliders that increase or attenuate the signal at a given frequency, as well as neighboring frequencies to a greater or lesser degree. The bandwidth of affected frequencies is known as the "Q." this Q is usually fixed on a graphic EQ, but sometimes it is program dependent, where the more you boost or cut the tighter the frequency range becomes. Since you can use the positions of the sliders to visualize the overall look of your waveform, it is known as a graphic style EQ. It literally shows you a picture of the overall frequency output. For example, raising the high and low ends and gradually tapering down to the middle frequencies from both ends results in the infamous "smiley face" EQ.

Parametric equalizers work on an entirely different principle. With a parametric, you choose a specific center frequency along with the width of the neighboring bands to be affected, and then raise or attenuate that portion of the spectrum. This type of EQ gives you much more power over your sound by letting you control all three aspects: the level, the frequency, and the Q.

Typically, the equalizer comes next in the chain after the mic preamp, but you can always experiment to see what works best for you. Equalizers are a great match for the 500 Series format because they can focus on just that aspect of the job within a small footprint. When you have a mic pre/EQ combination, it generally takes up more room and isn’t as suitable for downsizing to the 500 Series. Another benefit, of course, is that you can have a mic pre from one maker and an EQ from another. The 500 Series makes that possible. So mix and match and experiment to find the EQ that best suits your sound and your style.

Suggested Equalizer 500 Series Modules: Trident A-Range, Trident 80B EQ, API 550A, API 550B, API 560, SSL 611EQ 500 Series Equalizer Module, Neve 1073LBEQ, Maag Audio EQ4, Pultec EQP-500X, Kush Audio Electra 500, Rupert Neve Designs 551, BAE 1023L, Spectra 1964 STX500, DBX 530, Buzz Audio Tonic, Inward Connections The Brat, Chandler Limited EMI TG12345 MKIV EQ, Phoenix Audio Gyrator EQ

500 Series Compressors

Compression is one of the key components to the color of your sound and there is a huge variety to choose from. The three main types are VCA, FET and Opto, and each has its benefits and signature sound. In many cases, the compressor will come after the mic pre and EQ in the signal chain, but there is no hard and fast rule about how to use a compressor. Your use will be somewhat determined by the style of compressor you choose, as each of the three types has strengths and weaknesses depending on the material you are working with.

When redesigning vintage models for the 500 Series format, many manufacturers choose to upgrade the model with extra options, such as stereo linkage or side-chain control, so it’s helpful to check the specs and don’t just assume you’re getting a mini version of a vintage comp; you may actually be getting more than you expected. In most cases, the down-sized models will sound very close to their older, larger brethren and give you all the controls and meters that appear in the full rack size.

Besides the venerable models of the past, the field of 500 Series compressors is full of new designs that push the boundaries of what a compressor can sound like, and what it can do. Browse through the different offerings and you’re sure to find something that can be brought into your workflow. Here again, the mix and match approach gives you loads of flexibility when building your ideal 500 Series rack.

Suggested 500 Series Compressor Modules: Rupert Neve Designs 535, Inward Connections The Brute, DBX 560A, Retro Instruments Doublewide, Retro Instruments Doublewide II, Chandler Limited EMI TG Opto Compressor, Neve 2264ALB, API 527, Acme Audio Opticom XLA-500, IGS Audio 576 Blue Stripe, Shadow Hills Mono Optograph 500, Shadow Hills Dual Vandergraph, Serpent Audio Splice SA76-500, Standard Audio Level-Or MK2, SSL Stereo Bus Compressor

Miscellaneous 500 Series Modules

The growth of the 500 Series has seen a slew of new designs from many different manufacturers, including lots of specialty modules that are tailored to very specific tasks. Whether it’s reamping or summing, reverb or DI, distortion or digital delay, there are tons of modules to choose from. Both live sound and traditional recording benefit from the wealth of options available. Whatever your audio needs, there is probably a 500 Series module that can accomplish it. That’s what makes the 500 Series format so great – choosing exactly what you need at a reasonable cost and creating your own individual rack. And when it’s time to switch to something new, it’s quick and easy to swap out modules and change your signal flow.

Suggested Miscellaneous 500 Series Modules: Rupert Neve Designs Portico 542 Tape Emulator, Radial Engineering EXTC, Eventide DDL-500, Meris Mercury7 Reverb, Meris Ottobit, Elysia Karacter 500, Heritage Audio BT-500

Navon WeisbergIf you’re interested in purchasing any of the 500 Series modules or 500 Series racks mentioned in this blog, contact a Vintage King Audio Consultant via email or by phone at 866.644.0160