When looking into hardware equipment for an audio studio, perusers will likely come across 500 series equipment. From microphone preamplifiers and DI boxes to equalizers, compressors and other effects, 500 series gear is readily available.
What is 500 Series Audio Gear? The 500 Series is a modular format for audio equipment developed by API in the 1970s. 500 Series modules are 5.25″ (3U) tall, and each slot is 1.5″ wide (modules can take up multiple slots). Modules fit into 500 Series power racks or, in some cases, directly into mixing consoles.
In this article, we’ll discuss 500 Series audio equipment in greater detail and consider whether investing in 500 series gear is worth it for your studio/work environment.
Related article: Top 11 Best Audio Brands For 500 Series Modules/Equipment
Table Of Contents
- What Is 500 Series Equipment?
- The 500 Series Module (With Examples)
- The 500 Series Chassis/Rack (With Examples)
- How To Set Up A 500 Series Rack
- What Is The VPR Alliance?
- Benefits Of The 500 Series Format
- Is Investing In 500 Series Equipment Worth It?
- Related Questions
What Is 500 Series Equipment?
As previously mentioned, 500 series is a modular format for audio equipment defined largely by its form factor. The format is comprised of two main types of gear:
- Modules: these are the audio processors/effects and include microphone preamplifiers, compressors, equalizers, effects and other processors.
- Racks: these are units that host/store the modules and provide them with power. They also provide the inputs and output for each of the modules they host.
It’s also worth noting that some audio mixing consoles, such as API’s The Box 2 (link to check the price at Sweetwater), also have slots for 500 series modules. In the case of The Box 2, there is one slot for each of its 8 input channels for a total of 8 500 Series slots.
Compared to rack-mounted gear, the 500 series is compact, which, along with lower cost, is arguably its main benefit. Let’s consider the difference in the following chart:
|500 Series||Standard Rack-Mount|
|Height||5.25" (3U)||1U (1.75")
|Depth||5.938” ± .02”|
+ .125" Front Panel
|No Set Standard|
|Power||Supplied By Rack/Chassis||Individual PSU Per Module|
Many 500 series modules are simply more compact versions of larger 19-inch rack gear. They often maintain the same operating specs but comes a fraction of the cost, size and weight.
Of course, there are original designs as well. Some 500 Series modules are even based on more vintage designs and ofter additional functionality.
Before we get into discussions on 500 Series modules and racks, let’s briefly run through the history of the format.
The 500 Series first began in the late 1960s under Saul Walker and his team at Automated Processes Inc. (API) and has since become one of the most sought-after audio equipment formats.
Founded in 1968 (though design and manufacturing started before), API quickly became a go-to producer of high-quality recording/mixing consoles. At the time, modularity was a big deal in the audio world, and API capitalized on this fact with the API 550A 3-Band Equalizer: the first 500 Series module that would easily integrate into API’s consoles via a channel slot.
API is featured in the following My New Microphone articles:
• Top Best Microphone Preamplifier Brands In The World
• Top Best Studio Recording/Mixing Console Brands
• Top Best Audio Compressor Brands In The World
• Top Best Audio Equalizer Brands In The World
• Top Best Audio Brands For 500 Series Modules/Equipment
By the mid-1970s, portability (in addition to modularity) was in demand on the market.
It was only in 1985 that API produced its very first standalone rack, known as the Lunchbox. Since then, the 500 Series has become more about modular portable racks than console customization.
Today, API offers several Lunchboxes (link to check the price of the 10-slot Lunchbox at Sweetwater), and many other manufacturers offer their own racks. More on this later.
From the mid-’80s until now, many other manufacturers have jumped on board to produce their own modules according to the 500 Series specification. These “third-party” designers have come together to make the 500 Series the popular format it is today.
For compatibility’s sake, API began the VPR Alliance to set standards for the format. More on this in the section titled What Is The VPR Alliance?
Let’s recap with a few bullet points:
- 500 Series equipment (modules and racks) is relatively compact, lightweight, portable and affordable.
- API invented the 500 Series in the late 1960s as a way to customize their mixing consoles.
- API produced the first commercially available 500 Series rack, called the “Lunchbox,” in 1985 to accommodate the industry movement toward portability and modularization.
- Today, plenty of manufacturers partake in designing and manufacturing 500 Series equipment.
Now let’s consider the 500 series module and the 500 series rack (chassis).
The 500 Series Module (With Examples)
A 500 Series module is the actual unit that processes audio. These modules are much like the larger rack-mounted hardware gear in their performance, only more compact.
Examples are invaluable when learning about anything, so in this section, we’ll consider a few examples of 500 Series gear. More specifically, we’ll look at the following:
- 500 Series microphone preamplifiers
- 500 Series compressors
- 500 Series equalizers
- 500 Series effects units
- 500 Series specialty modules
500 Series Microphone Preamplifiers
What is a microphone preamplifier, and why does a mic need one? A mic preamp is a type of amplifier with the purpose of bringing mic level signals up to line level for use with professional equipment. Microphones output mic level signals and need preamps if they are to be used with mixing consoles, recording devices or digital audio workstations.
Like many 500 Series preamps (and unlike the 500 Series effects, including compression and EQ), the 512c has inputs on its front face. More specifically, it has an XLR mic input and a 1/4″ high-impedance instrument/line input. Note that these inputs can also be accessed via the back panel of the given rack if that rack happens to have both XLR and 1/4″ inputs.
As for gain, the 512c utilizes the traditional API fully discrete circuit design with 2520 Op Amp. It offers 65 dB of gain in the mic preamp and 45 dB of gain in the line/instrument preamp.
The Neve 1073LB (link to check the price at Sweetwater) is a Class A microphone preamplifier in the 500 Series format.
This preamplifier has a front-panel combo jack to accept both mic (via XLR) and line level (via 1/4″) signals. The front panel also has polarity swap, impedance (high or low) and Front Input selector switches.
The coarse gain knob gives the mic preamp a gain range between -80 dB to -20 dB in 5 dB steps, and the line preamp a gain range between -20 dB to -10 dB in 5 dB steps. The trim control with an integrated phantom power switch allows for fine-tuning of the gain between -20 and +5 dB.
AMS Neve is featured in the following My New Microphone articles:
• Top Best Microphone Preamplifier Brands In The World
• Top Best Studio Recording/Mixing Console Brands
To learn more about microphone preamplifiers, check out my article What Is A Microphone Preamplifier & Why Does A Mic Need One?
500 Series Compressors
What is dynamic range compression? Dynamic range compression is the process of reducing the dynamic range of an audio signal (the difference in amplitude between the highest and lowest points). Compression does so by attenuating the signal amplitude above a set threshold point.
Atlas Pro Audio Leviathan 500
The Atlas Pro Audio Leviathan 500 (link to check it out at Reverb) is a 500-series optical compressor inspired by the Universal Audio LA-2A and LA-3A that marries vintage and modern technology together.
APA’s Leviathan 500 is a class-A opto compressor with a fully discrete design. It features a Vintage Mode whereby the attack falls between that of the LA-2A and LA-3A.
Modern features include variable attack (2 to 40 ms) and release (100 ms to 2 s) times along with variable ratio (2:1 to 20:1). There’s also a low-frequency roll-off (high-pass filter) sidechain option called “Punch” for keeping the low-end well-represented.
In addition to these controls, the Leviathan 500 offers gain and peak reduction (threshold) controls and LED metering. These units can easily be bypassed, and two units can be linked together in a stereo pair for bus and master compression applications.
For more information on optical compressors, check out my article What Is An Optical Compressor & How Does It Work?
Shadow Hills Dual Vandergraph
The Shadow Hills Dual Vandergraph (link to check the price at Sweetwater) is a 2-channel (stereo) class-A VCA compressor in the 500-series format.
Whether you choose to use the Dual Vandergraph on a single channel or two, the signal path/paths will be affected by the same superb compressor circuits.
This VCA comp offers 4 different ratios selectable via a 5-position lever switch (off, 2:1, 2.5:1, 4:1 and 8:1). Each of the four ratio presets engages its own predetermined attack and release times as well. These time constants are as follows:
- Ratio: 2:1
- Attack time: 30 ms
- Release time: 100 ms
- Ratio: 2.5:1
- Attack time: 30 ms
- Release time: 500 ms
- Ratio: 4:1
- Attack time: 10 ms
- Release time: 500 ms
- Ratio: 8:1
- Attack time: 0.5 ms
- Release time: 250 ms
Another 5-position lever switch engages filters to act upon the sidechain. These positions of the switch are as follows:
The amount of gain reduction is shown on the Dual Vandergraph’s VU meter.
For more information on VCA compressors, check out my article What Is A VCA Compressor & How Does It Work?
500 Series Equalizers
What is audio equalization? EQ is the process of adjusting the balance between frequencies within an audio signal. This process increases or decreases the relative amplitudes of some frequency bands compared to other bands with filters, boosts and cuts. EQ is used in mixing, tone shaping, crossovers, feedback control and more.
The IGS iQ505 (link to check the price at Front End Audio) is a fully parametric analog equalizer designed into a 500-series module. It has 5 parametric overlapping bands, each with ±12 dB cut/boost.
The IGS iQ505 offers a notably wide EQ range spanning from 10 Hz (infrasound) all the way up to 24 kHz (ultrasound). The lowest and highest bands each have the option of a bell curve filter or a shelving filter. Each band has a Q knob which is responsible for the quality factor of each filter.
For more information on parametric EQ, check out my article The Complete Guide To Parametric Equalization/EQ.
TK Audio TK-lizer 500
The TK Audio TK-lizer 500 (link to check the price on Amazon) is a 500-series 3-band Baxandall-style EQ (with an included high-pass filter) with mid-side capabilities.
This powerful yet simple unit can be used in stereo (L/R) or mid-side mode (M-S). The M/S toggle switch will toggle between the two modes.
Each of the bands has ±8 dB of boosting/cutting in 41-step controls. The low and high bands can be switched between peak filter and shelving filter modes. The 12 dB/octave high-pass filter can be set at 25, 30, 35, 40, 45 or 100 Hz.
For more information on stereo and mid-side EQ, check out the following My New Microphone articles:
• What Is Stereo Equalization/EQ In Audio & How Does It Work?
• What Is Mid-Side Equalization/EQ (Audio) & How Does It Work?
500 Series Effects Units
What is an audio effect? An audio effect is any process that intentionally alters an audio signal for a desired (or undesired) effect. In other words, an audio effect is a device (analog or digital) or plugin that affects the sound of a signal.
Audio effects include the aforementioned compression (a dynamic effect) and equalization (a spectral effect) but also include time-based (reverb, delay), modulation (chorus, flanger, etc.), and other processes that manipulate the sound in one way or another.
In this section, we’ll focus on the non-dynamic and non-spectral effects.
Meris Mercury 7 500
The Meris Mercury7 500 Series Reverb (link to check the price at Sweetwater) is the world’s first 500 Series algorithmic DSP (digital signal processing) reverb.
This powerful module features the following controls (read the manual for more detail):
- Space Decay knob: sets the decay time of the reverb effect
- Predelay (Alt): sets the amount of predelay before the onset of the reverb effect.
- Mix knob: adjusts the mix of the wet and dry signal.
- Pitch Vector Mix (Alt): adjusts the mix between intra-tank pitch-shifted signals & normal reflections.
- Pitch Vector knob: sets the intra-tank pitch vector interval to octave down, slight pitch up, slight pitch down, 5th up, or octave up.
- Attack Time (Alt): sets the attack for the swell envelope.
- Modulate knob: sets the modulation depth of the reverb effect.
- Mod Speed (Alt): sets the speed of modulation of the reverb effect.
- Lo Freq knob: alters how low frequencies react to the reverb effect (to alter the perceived size of the effect).
- Density (Alt): sets the amount of initial build-up of echoes before the reverb tank.
- High Freq knob: alters how low frequencies react to the reverb effect (to alter the perceived size of the effect).
- Vibrato Depth (Alt): adds vibrato to the reverb input.
- Algorithm Select switch: selects between Ultraplate (inspiring & lush plate w/ a fast build) and Cathedra (massive & ethereal algorithm w/ a slow build). Hold the button down to access Alt functions.
- Swell switch: engages/disengages auto swell function.
Meris is featured in the following My New Microphone articles:
• Top Best Boutique Guitar/Bass Pedal Brands To Know & Use
• Top Best Audio Brands For 500 Series Modules/Equipment
TB Audio TBDD Stereo Chorus
The TB Audio TBDD Stereo Chorus (link to check for prices at Reverb) is a “modern” version of Roland’s classic Dimension D rack-mount chorus from the 1970s.
This chorus unit features two identical signal paths for stereo processing. They’re made from the same new old stock analog bucket-brigade device (BBD) delay chips that were used in the original Roland model.
The input can be set to mono or stereo, and the Blend knob mixes the phase-shifted/delayed signal with the direct signal at the output. Levels can be metered with the ten-segment LED meter.
This unit has 4 modes/presets and an off button. There’s not a whole lot of tweaking to do with this chorus unit, but it still sounds great.
For more information on the chorus effect, check out my article Complete Guide To The Chorus Audio Modulation Effect?
500 Series Specialty Modules
500 Series specialty modules are the miscellaneous bunch that are worth mentioning. They’re generally not “effects” or preamplifiers, as we’ve discussed. Rather, they are more involved in signal routing, metering, line level amplification, and other processes.
Purple Audio Cans II
The Purple Audio Cans II (link to check the price at Sweetwater) is a stereo headphone amplifier with a KDJ3 opamp for mono and KDJ5 opamps for output.
In addition to its superb headphone amplifier capabilities, the Cans II also functions as a control room amplifier, offering the control of a console master section in a compact design.
With its push buttons, the Cans II offers the following functionality:
- Swap the phase of the left and right channels.
- Sum the stereo (left and right) channels to mono (useful for checking phase issues).
- Cut the left channel, the right channel or both channels from the output.
For more information on headphone amplifiers, check out my article What Is A Headphone Amplifier & Are Headphone Amps Worth It?
Radial X-Amp 500
The Radial X-Amp 500 (link to check the price at Sweetwater) is a re-amping distribution module in the 500 Series format. This module allows users to take a pre-recorded guitar track and send it back to amplifiers and effects so that you can tailor the sound to suit.
The X-Amp 500 has two Class-A-buffered transformer-isolated outputs to send the signal to two amplifiers at once. Each output has a ground lift option to help combat hum in the signal, and Output 2 even has a polarity switch.
Radial Engineering is featured in My New Microphone’s Top Best Audio Brands For 500 Series Modules/Equipment.
The 500 Series Chassis/Rack (With Examples)
Though 500 Series modules were originally designed for modular mixing consoles, they’ve evolved to become modular portable racks.
To properly store, connect and power 500 Series modules, we need a 500 Series rack/chassis (often referred to as the eponym “Lunchbox”).
A 500 Series rack will effectively power all the modules within it, reducing the hassle and cost of needing individual power supplies for each module. The modules will be screwed in by the flanges of their front plates and connected electrically to the rear of the rack for inputs/output routing and powering.
The input/output connections are commonly either multichannel DB-25 connectors, discrete balanced I/O (XLR or TRS jacks), or a combination thereof.
Racks will come in a variety of sizes, defined largely by the number of available slots. They can be portable tabletop units or even fit within an aforementioned standard 19″ rack-mount rack.
As we’ve discussed, most 500 Series modules will fit within one slot, though there are double-wide or even triple-wide modules that take up 2 or 3 slots, respectively.
The routing within a 500 Series rack can be rather simple or complex, depending on the design. Additional signal routing functionality could include:
- Internal patching (between modules beyond the input/output)
- Stereo linking (having the module of one slot control a second of the same module in another slot)
- Audio summing (combining multiple signals together in a single output)
Once again, let’s improve our understanding with a few examples. More specifically, we’ll look at the following:
Radial Workhorse Cube
The Radial Workhorse Cube (link to check the price at Sweetwater) is a 3-slot portable desktop 500 Series power rack. Its heavy-duty 14-gauge steel construction provides superb durability and even some amount of improved shielding from EMI.
The Cube provides up to 500 mA of shared current between its 3 slots. The convenient front panel power switch makes it easy to turn the power off when swapping modules.
Each of the rear panel slots contains both XLR and TRS I/O. The feed function allows us to connect one module to the next, making it easy to set up channel strips without having to hard patch modules together using cables.
Phantom power may be turned on and sent through each of the mic input.
The omniports in each slot allow for external control of the modules if that external control is possible. Examples include external sidechain signals and control voltages.
Black Lion Audio PBR8
The Black Lion Audio PBR8 (link to check the price at Sweetwater) is an 8-slot 500 Series power rack with a built-in patchbay built to fit nicely within standard 19″ rack-mounts (3U high).
The PBR8 is equipped with a fully-balanced TT/Bantam patchbay. Users can easily patch various routing options within the rack and send/receive signals from other rack or outboard gear for virtually unlimited routing possibilities.
This rack utilizes Heritage Audio’s On Slot Technology to ensure clean, isolated power for every module. Its power specification reads 1.8A per rail or 400mA per rail per slot, whatever is reached first.
Each of the 8 slots has an XLR input and output on the rear panel. Two separate 25-DB connectors are also present to handle Inputs 1-8 and Outputs 1-8 separately.
Cranborne Audio 500ADAT
The Cranborne Audio 500ADAT (link to check the price at Sweetwater) is an 8-channel ADAT expander with 8 500 Series slots; a cue mixer; ADAT I/O, high-powered headphone amps, and analog summing. Needless to say, this is a powerful unit!
The 500ADAT is a super option when looking to expand upon the I/O of any ADAT-equipped audio interface and allows for integrating 500 Series hardware and audio interfaces.
This unit offers 250mA per rail and a maximum of 2 amps of current for all 500 Series slots. Each slot has its own XLR input and output and a 1/4″ insert on the rear panel.
To learn more about the 500ADAT, head over to Cranborne Audio’s official website.
How To Set Up A 500 Series Rack
Now that we know about 500 Series modules and racks let’s take a look at setting up a rack. The standardization of the 500 Series makes this as easy as sliding the modules into place and securing them.
First off, all we’ll need a rack (or racks) with enough slots to fit all the modules we want to use.
On top of that, we should ensure that the rack meets or exceeds the combined power requirements of the modules. To do so, add up the current draw from all modules and make sure the number is lower than the total capacity of the rack/chassis.
Note that solid-state modules generally require less power than their vacuum tube-based counterparts.
Not having enough power will lead to poor performance and distortion in the audio signal.
As is the case with all audio equipment, it’s also important to connect the rack to a surge protector to protect the rack and modules within from power surges, brownouts, etc.
When installing 500 Series modules, start by having the rack disconnected from power. Proceed by gently sliding the modules into their respective slots. Line up the pins of the module and rack slot and push the module in firmly until you hear a click. Once electrically connected, secure the module into the rack with screws through the faceplate screw holes.
As an additional note, try to position preamplifiers and other modules intended to boost the signal further away from the rack’s main power supply. This can improve the signal-to-noise ratio by reducing electromagnetic interference.
Once all the modules are connected and secured, cover any unused slots with blank plates to keep dust out of the rack cavity. Make sure the rack has sufficient ventilation; plug it in and turn it on.
Once the 500 Series rack is set up, routing between modules becomes the same as other outboard gear. Turn down the volume of monitors and headphones to prevent loud popping and avoid hot patching microphone signals if phantom power is present.
Set up the resulting channel strip’s signal flow to your liking via the inputs/output at the back of the rack or the internal patching (if available).
Then integrate the 500 Series rack into the audio system before the audio interface, as a hardware insert in a console, with a patch bay, etc.
What Is The VPR Alliance?
The VPR Alliance is a standardization and consistency guidelines developed by API for the 500-series rack format. It provides complete design specifications for manufacturers interested in producing modules that will work specifically with API’s 500 racks/chassis.
Specifications include power requirements and specific size measurements of the modules.
Of course, API is not the only manufacturer of 500 Series racks/chassis, and so the VPR Alliance is not a true industry-wide standard. However, the specifications therein are worth checking out if you’re interested in designing and distributing your own 500 Series modules and want approval from API.
The truth is that most manufacturers do their due diligence to ensure their 500 Series products (whether it’s a rack or a module) will work safely with other 500 Series equipment.
So the VPR provides a useful framework for 500 Series specification, but it is by no means the be-all-end-all industry standard. Virtually all 500 Series modules that make it to the professional marketplace will work with other 500 Series equipment on the marketplace.
That being said, since API created the 500 Series format, it certainly makes sense for them to produce a program of standardization in the VPR Alliance.
Benefits Of The 500 Series Format
We’ve touched on the size and weight benefit of 500 series when compared to standard rack-mounted gear.
In addition to the compact form factor, 500 modules are designed to be compatible with other 500 modules and fit within a rack that not only hosts the modules but also powers them. This provides the benefit of not requiring separate power supplies for each unit.
Once mounted with a rack, 500 Series modules become rather portable, allowing users to easily carry their favourite signal chains with them to remote recording sessions and live performances if need be.
Due to the popularity of the format and the variety of different manufacturers, 500 Series equipment also offers plenty of choices. This is a huge benefit for budgeting and for developing a wide range of sonic palettes.
As we’ve discussed, 500 Series modules include mic preamps, compressors, equalizers, effects and other signal processors. With all the options and the inherent modular nature of the format, it’s easy to swap modules in and out of a rack and patch the modules in all sorts of ways.
Let’s recap. The benefits of the 500 Series format, in point form, are:
- Relatively compact size
- Standard size and power requirements
- Relatively low weight
- Plenty of options
- Relatively affordable
Is Investing In 500 Series Equipment Worth It?
Now that we understand 500 Series audio equipment and its benefits, the question remains: is it worth it? Of course, the answer is “it depends.” However, let’s at least discuss the matter in this section.
The two most important factors to consider when deciding whether to purchase 500 Series gear are your budget and the current state of your studio.
Starting with the budget, people have plenty of different beliefs regarding money. That being said, I’m no financial expert, but if the question is paying rent or paying for a new 500 Series module, then you’d be unwise to invest in the module!
If you’ve got money in the bank and are looking for new toys, then a 500 Series rack could be an option for you. As mentioned, the gear is relatively affordable, and it’s fun to mix and match. Just beware of the clever design and know that it’s okay to have an empty slot or two… for now!
As a professional, I would ask myself what the return on investment would be. Do I absolutely need this hardware to complete a job I’m working on? If I bought this gear, would it allow me to take on work that I previously wouldn’t be able to do? How long would it take for me to pay off the 500 Series equipment with paid work that requires it?
These are all consideration I suggest taking into account.
Related article: 52 Ways To Make Money In The Audio Industry
As for the current state of your studio, investing in any outboard gear should come after the basics are covered (computer, DAW, interface, headphones/monitors, microphones, cables, acoustic treatment, etc.). Once you’ve got a functional studio setup, I’d say that 500 Series equipment could be considered but not before then.
Related article: Top 45 Must-Have Tools For Audio Recording/Mixing Studios
Coming from a totally in-the-box setup (where all processing comes in the form of plugins), adding some outboard 500 Series gear can add that extra sonic character. It can even improve the overall enjoyment of the mixing process by adding real knobs and buttons to the workflows (instead of having everything done via mouse click).
That being said, high-quality plugins can definitely achieve professional results and should not be overlooked. Perhaps it’s best to start with plugins (bought legally!) to get an idea of what you like before getting into 500 Series gear. Plugins are inexpensive versus hardware gear.
If you’re coming from a larger successful studio that already has tons of outboard gear, a 500 Series rack can add extra character by providing alternative signal chains (over the channels of the mixing console, let’s say).
So getting in 500 Series gear can be a fun and rewarding experience and can really help get you to your sonic goals. However, determining whether or not to invest in the gear is something you’ll have to figure out for yourself.
What is standard rack mount audio equipment? Rackmount gear is designed to be modular and formatted to fit into a 19″ rack (width). Each rack unit (U) is 1.75″ (height). Rackmount gear has flanges with screw holes which allows for the equipment to be fastened to the frame of the rack. Racks can hold multiple pieces of rackmount gear.
What are all the audio effects and processes? The full list of audio effects and processes for mixing/production is as follows (link to detailed My New Microphone articles):
- Sample Rate Reduction
- Tape Saturation
- Valve Saturation
- Noise Gating
- Noise Reduction
- Transient Shaper
Sound Manipulation Processes
- Time Compression
- Time Expansion
- Pitch Correction
- Pitch Shifting
- Analog (BBD) Delay
- Digital Delay
- Doubling Echo
- Haas Effect
- Ping Pong Delay
- Reverse Delay
- Shimmer Delay
- Slapback Delay
- Tape Delay
- Acoustic Emulation Reverb
- Bloom Reverb
- Convolution Reverb
- Gated Reverb
- Plate Reverb
- Reverse Reverb
- Shimmer Reverb
- Spring Reverb