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The New Vintage

It's rare to find a truly outstanding solid-state channel strip that can deliver a vintage vibe reminiscent of classic high-end products, yet employs a thoroughly modern design. To find one that you can buy without heavily depleting your bank account is even more rare.

But there is one channel strip that delivers the goods without the big tab: the PreSonus® RC 500.

The Gentleman Magician

Once upon a time, in the historic city of Baton Rouge, Louisiana, a white-haired gentleman quietly pored over a chassis filled with circuits. He was clearly designing an analog preamp and processor, which wasn't unusual for him.

But this wasn't just any fellow puttering around, and his project wasn't just another preamp and processor. This was Robert Creel, the engineering mastermind behind many of PreSonus’ best analog circuits, including the ever-popular XMAX™ preamp, and his project was the ADL 700 tube channel strip, which turned out to be a terrific "boutique"-style, high-end channel strip.

At least, the PreSonus team thought his project was the ADL 700. As it turns out, he was doing something more.

In the process of developing the ADL 700, which uses the same high-voltage tube preamp found in the award-winning ADL 600 (codeveloped by PreSonus and Anthony DeMaria), Creel came up with a new design for a very special solid-state preamp that uses a Class A hybrid input stage with discrete transistors and the latest-generation, low-distortion operational amplifiers. Everyone at PreSonus who heard his prototype was so blown away by its transparent, detailed, clear sound that the new preamp immediately became an in-house legend. By popular demand, Creel’s superb preamp became the heart of the new RC 500, named "RC" in Robert Creel's honor.

The RC 500 combines the custom-designed FET compressor and semi-parametric EQ circuits that Creel developed for PreSonus’ highly lauded ADL 700 tube channel strip with his new ultra-low-distortion, high-gain, solid-state Class A preamplifier design, which delivers consistent, repeatable, transparent, detailed audio. A balanced analog insert sends the source signal out of your RC 500 before the compressor, EQ, and Master Gain stages and returns the signal directly to the compressor stage, allowing you to add external processors.  

The result is a top-of-the-line — yet very affordable — channel strip for recording engineers and recording musicians, with a sound that is reminiscent of classic, vintage solid-state preamps.

"The sound of the new RC 500 preamp is clean, solid, and has a positively huge low-end presence," notes Paul Vnuk, Jr. (Recording, December 2013). "Its full thick tone and simple classic-console feel allow it to hold its own with vintage units, rather than simply trying to sound like them."

The RC 500 solid-state microphone preamp features a Class A hybrid input stage with discrete transistors and the latest-generation, low-distortion operational amplifiers. The design maintains the sonic qualities of Class A and benefits from the repeatability in performance of the operational amplifier.

Power amplifiers are classified primarily by the design of the output stage and are designated Class A, B, AB, D, G, or H. In a Class A preamp, the output circuits are always on for the entire cycle of signal swing or the bias current flows at all times. As a result, Class A preamps have the most linear design, with no crossover distortion, and they deliver purer, clearer, and more musical results than the Class AB designs that are found in many preamps.

Compared to a tube preamp, the RC 500’s solid-state preamp offers better definition at the edges of its frequency response range. High frequencies are crisper and low frequencies are tighter, producing a transparent, musical signal that retains the “airiness” of a room and provides a more three-dimensional result than a tube mic preamp can deliver. Paul Vnuk, Jr. (Recording, December 2013) writes, "Compared to the ADL 600/700 tube pre, which I found bold with an opulent top end, the preamp in the RC 500 is thicker and punchier with a more focused top."

The Compressor: Fun with FETs

‚ÄčThe RC 500’s FET (Field-Effect Transistor) compressor includes fully variable attack, release, and threshold controls, as well as bypass controls. The compression ratio is fixed at 3:1. This combination provides lots of flexibility without giving you enough rope to hang yourself!

"Although 3:1 is a much subtler ratio than we typically find on fixed-ratio comps," writes Paul Vnuk, Jr. (Recording, December 2013), "here it works well, especially with the soft knee to produce a smooth, even grab that is very well suited to vocals, bass and electric guitar.... I would call it a musical and controlled comp rather than the slam-it-and-smash-it kind."

User tip: The input-gain stage can be driven harder with a lower threshold to emulate higher compression ratios. You can make the RC 500 compressor pump if you want to.

As noted earlier, this compressor design is also found in the ADL 700 and has drawn rave reviews. For example, Hugh Rabjohns (Sound on Sound, August 2013) remarked, "The compressor is accurate and responsive, and very good for managing the normal dynamic excursions of most vocal performers, subtly but firmly." 

FET-based compressors such as the one in the RC 500 use transistors to emulate a triode tube’s operation and sound. This type of compressor generally provides a faster attack time and better repeatability than the optical compressors that are more commonly found in channel strips in this price class.

Broadly speaking, there are four types of analog compressor designs: those that use opto-isolators (optical); Field-Effect Transistors (FETs), as found in the RC 500 and ADL 700; voltage-controlled amplifiers (VCAs; an example is the PreSonus Studio Channel compressor); and variable-gain compressors. Each has its uses, but we’re going to focus on the two types you’re most likely to find on today’s high-end channel strips: optical and FET.

The majority of today’s high-end channel strips utilize optical compressor circuits. In general, the response time of the optical circuits in these compressors tend to soften the attack and release, which can smooth out uneven volume fluctuations. They often have a distinctive sonic signature, so they can be as much an effect as a gain-control device.

FET compressors use a special transistor to vary gain, emulating a triode-tube sound. Inherently high-impedance devices, FET compressors tend be very clean and reliable and provide a faster attack time than most optical compressors.

To some extent, which you prefer is a matter of taste. You might want the sound of an optical compressor for one application but prefer a FET-based compressor for another application.

However, aside from having a distinctive sound, optical compressors have drawbacks. Most notably, when the components in an optical compressor heat up or cool down, the resulting attack and release times can change considerably. That means you might not get consistent results—even on, say, multiple snare hits in the same song.

Unlike optical compressors, FET compressors such as the one in the RC 500 are not susceptible to temperature fluctuations, so they provide consistent, repeatable results.

There’s also an environmental issue with optical compressors. Optical circuits contain a small amount of cadmium, a metal that is banned in new electronic equipment under the European Restrictions of Hazardous Substance (RoHS) Directive. Unlike optical compressors and certain professional athletes, the FET compressor in the ADL 700 uses no banned substances. We’re just sayin’….

The compressor has a “soft knee” compression curve and can be hard-bypassed.

The term “knee” refers to the way the compression curve bends at the threshold point when represented graphically.

With hard-knee compression, the gain reduction applied to the signal occurs as soon as the signal exceeds the level set by the threshold.

With soft-knee compression, the onset of gain reduction occurs gradually after the signal has exceeded the threshold, producing a more musical response (to some folks).

The RC 500 compressor and EQ can be independently “hard” bypassed, meaning that the processor is completely removed from the circuit when bypassed. Some processors have a “soft” bypass where the processor is still in the circuit when bypassed but the parameters are set “flat.” However, since the signal is still going through the processor, the sound can still be slightly altered. A “hard” bypass eliminates this problem.

A Smooth, Refined, Musical EQ

The RC 500’s 3-band semi-parametric EQ was designed by Robert Creel to match the preamp and compressor. It combines isolated filters and optimized, per-band Q to provide subtle signal-shaping without harsh artifacts.

Paul Vnuk, Jr. (Recording, December 2013) opines, "The EQ… is of the bold-stroke variety where little knob tweaks go a long way. You can push and pull your sound like taffy with this EQ and there is nothing surgical about it."

This EQ employs the same circuitry as the 4-band semi-parametric EQ in the ADL 700, which has received rave reviews.  “The EQ was designed with musicality in mind,” comments Chris Grainger (Mix, January 2013). Resolution magazine's George Shilling (March 2013 issue) found that, "The EQ is smooth and refined.... [It] is more than powerful enough for general use but is pretty forgiving, and the low end can be huge (without wooliness) in Peak mode."

All three bands have Gain (±16 dB) and Frequency controls and fixed Q (0.5), and the mid and high bands have overlapping frequency ranges. The low and high bands are switchable between shelving and peak. The EQ can also be hard-bypassed.

The RC 500 offers Gain controls that range from -16 to +16 dB.

The center-frequency range for the low band goes from 20 to 400 Hz; the mid band ranges from 400 Hz to 5 kHz; and the high band ranges from 2 to 20 kHz. Note that the mid and high bands overlap.

The mid band is a peak band. A peak equalizer boosts or cuts a band of frequencies around a center frequency (selected by the Frequency control). The width of the band is variable in a fully parametric EQ, typically using either a bandwidth control or, more often, a Q control. (Q is defined as the ratio of the center frequency to the bandwidth; a lower Q results in a wider frequency band.) A good example is the parametric EQ in the StudioLive 32.4.2AI and 24.4.2AI digital mixers.

In a semi-parametric EQ, the Q (and the bandwidth) is fixed. The Q on the RC 500 is fixed at 0.5, a low value that provides a fairly wide frequency band.

To summarize: In the RC 500 peak EQ bands, you can boost or cut a wide (Q=0.5) band of frequencies by ±16 dB at a selectable center frequency.

The high and low EQ bands can be switched between peak and shelving operation. When used as peak bands, they behave the same way as the mid band except for their center-frequency ranges.

A shelving EQ attenuates or boosts frequencies above or below a specified cutoff point. In this mode, the band’s Frequency control sets the cutoff frequency rather than the center frequency.

In shelving mode, the RC 500’s high band becomes a low-pass filter, passing all frequencies below the cutoff frequency, while attenuating all frequencies above the cutoff. The low band becomes a high-pass shelving filter, passing all frequencies above the cutoff frequency, while attenuating everything below. In both bands, the frequencies beyond the cutoff are rolled off, following a predetermined curve—not cut off sharply.

Yes, of Course It Has That!

Of course, you get +48V phantom power, polarity inversion, and a 20 dB pad! Those features are a given with PreSonus preamps and channel strips. And there’s more!

In addition to all of the aforementioned features, the RC 500 provides a -12 dB/octave highpass filter with a frequency threshold set at 80 Hz. Use this filter, instead of the equalizer, to remove unwanted low frequencies from your source signal. For example, the 80 Hz filter can be used to reduce the “boominess” or “muddiness” of a vocal and to improve the overall clarity of the signal.

A large, backlit, dual-mode analog VU metering enables monitoring of output and gain-reduction levels. A master level control adjusts the overall output from -80 to +10 dB.

It's easy to make connections with the RC 500, too. Rear-panel XLR mic and line inputs and a front-panel ¼” instrument input accept a variety of sound sources, managed by a handy Input Select switch. You get balanced outputs on XLR and ¼” TRS connectors as well as a balanced analog insert to patch in your favorite boutique processor to get a different sonic flavor.

Paul Vnuk, Jr. (Recording, December 2013) sums it up nicely: "The magic of the RC 500 lies in how well the pre, compressor, and EQ work together. I have reviewed a number of channel strips over the years, and often they are either too simple with elements that are more gimmick than useful, or they are overcomplicated with too many features. By contrast, the RC 500 is just right! Each section is really well integrated and complements the others well."

Visit your PreSonus dealer and check it out!

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