Great River PWM-501 Compressor

Great River PWM-501 Compressor

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Great River PWM-501 — 500-Series Single-Chanel Compressor

500-series compressor with ultra fast pulse-width modulation gain element, selectable feedback/feed-forward operation, and unique threshold control

The PWM-501 is a 500-series compressor module from Great River that owes its sonic agility to a PWM (pulse width modulator) control element and variable feedback/feed-forward operation. Rather than simply switch between feedback and feed-forward operation, the Great River PWM-501 allows you to blend the two functions for varying tonal color. Another unique design feature of the PWM-501 is its threshold control, which operates as more of a “baseline clipper” as Great River’s Dan Kennedy puts it, ignoring most frequencies below the line. And speaking of lower frequencies, the PWM-501 has variable high-pass filter that lets you filter out bass signals that might cause the PWM-501 to act sooner than musically useful. Extremely versatile, the Great River PWM-501 not only works effectively on any single sound source, its stereo link capability lets you set two PWM-501s to do anything from parallel bus compression or shave tiny peaks off your 2-bus mix.

Great River PWM-501 unique features:

  • Pulse width modulated compressor/limiter
  • Feedback/Feed-forward blend control
  • High-pass frequency control

Great River PWM-501 key features:

  • Output level, threshold, ratio, attack, and release settings
  • Stereo linkable with 2 units
  • Designed and built in the USA

Don’t forget to check out RSPE’s Rack Revolution, a virtual 500-series rack builder that lets you custom-configure the perfect 500-series lunchbox for your studio, DAW, or mobile recording rig. RSPE carries every 500-series module imaginable, including mic preamps, compressor-limiters, equalizers, and 500 power racks.

INSIDE THE BOX — Great River PWM-501

By using a pulse width modulated gain control element, the PWM-501 gain control circuit design allows the use of modern high-speed components that can switch on and off in less than a nanosecond. The result is much greater accuracy than older FET and VCA designs, plus the elimination of unwanted audio artifacts.

Another unique feature of the Great River PWM-501 compressor is its variable feedback/feed-forward design. Most compressor/limiters use feedback to generate the sidechain signal. The control signal is always being modified by the action of the unit because of the previous signal. Feed-forward operation uses the input audio to generate the sidechain signal; any previous operations do not have any influence on the operation of later signals. Very generally, feed-forward is a faster, more aggressive operating mode, but it is easy to get too aggressive, especially with hot signals. Typically it is best to start working with a signal in the feedback mode, and then rotate the blend towards feed-forward while readjusting the various sidechain controls to suit. Everything is interactive, and will need attention, but it is worth it because of the versatility it imparts to the PWM-501.

And finally, to sum up the unique features of the PWM-501, there’s its threshold control. At low levels (0-50) the unit looks at all or most of the signal and acts as a compressor, at higher levels (50-100) it looks at peaks and the PWM-501 functions more as a limiter. The signal the threshold circuit is fed comes from the Feed-forward/feedback control.

While not necessarily a “unique” feature, the stereo link feature of the PWM-501 also operates somewhat differently than other stereo linkable 500-series compressors. Any PWM-501’s connected via the link system will “or” their control voltages. One unit can be used to control all, or each can contribute. To defeat a unit’s contribution to the bus, turn the local Threshold and Attack all of the way up, and the Ratio all the way down. This control voltage is unique to the PWM-501 and is not compatible with other manufacturers systems, so the bus must be broken up if other units are using it in the same rack. The bus used is Pin 6 of the backplane connector.

OUTSIDE THE BOX — Great River PWM-501

On the front panel of the Great River PWM-501 are the following controls and their functions:

  • Output level control: This control sets the amount of make-up gain in the output amplifier. Use it to adjust the output signal level.
  • Threshold control: This control determines the portion of the signal that the rest of the sidechain will use to control the operation of the PWM-501.
  • Ratio control: This control sets the percentage of the control signal sent to the PWM attenuator. Fully counterclockwise divides the signal the most, giving the lowest ratio. The actual ratio is approximate, as it is dependent on the variables of the threshold, attack, and release times, as well as the setting of the feed-forward/feedback control.
  • Attack time control: This control sets the initial charging speed of the time-constant capacitor. The circuit feeding this capacitor is an absolute value peak detector, so it can be very fast. It can also generate unpleasant distortion if it is too fast for the signal content. Faster attack times are in the counterclockwise direction of the control.
  • Link switch: This switch will link the control voltage between PWM-501 units installed in a rack with the correct interconnections on the backplane bus.
  • Release time control: This control sets the discharge speed of the time-constant capacitor. Faster release times are in the counterclockwise direction of the control.
  • Bypass switch: This is a hard-wired bypass of the entire PWM-501 when depressed. The unit is also in bypass mode when the rack is unpowered.
  • High-pass frequency control: This is a second order (12dB/octave) variable high pass filter that is inserted in the sidechain immediately after the feed-forward/feedback blend circuit. When engaged it can filter out bass signals that might otherwise influence the action of the PWM-501.
  • High-pass engage switch: The high pass filter circuit is engaged when this button is pressed.
  • Feed-forward/feedback blend control: This control determines the source(s) and the blend of the sidechain signal. In the fully counterclockwise position the source of the sidechain signal is entirely the input audio, in the clockwise position the source is entirely the output signal.
  • Meter function, switch, and display LEDs: This switch determines the signal to the peak reading meter circuit. In the GR mode, the meter indicates 1dB of gain reduction for every LED lit. It indicates in a downward direction. In either the In or Out mode, the meter indicates the signal level at the respective signal point. All green LED’s lit indicates a signal level of +4dBu at the XLR.

Who’s using Great River

I am, and have been the drummer for the band Cinderella for 22 years and am now also a composer for TV and Film. I just wanted to let you know that I just picked up a 500NV and it is without a doubt, incredible. I called Troy at RSPE (where I bought it) and told him 10 thumbs up!!!! I started by plugging into the DI and just turned it up. Holy cow, that was all I needed to convince me. I A/B'ed with a couple of other top shelf pres in my lunchbox and there was no comparison. Vocals through it are ridiculous! I can't wait to track my 26" kick through it. Absolutely awesome piece of gear!

– Fred Coury

When shooting out various mic pre's to match with a pair of vintage U67's to record Jerry Douglas' dobro on the album, Glide, it was Great River mic pre's that WON!

– Bil VornDick (Alison Krauss, Ralph Stanley, Marty Robbins, Bela Fleck, Jerry Douglas, Mark O'Connor, Charlie Hade, Jesse Winchester)

Even though the combination of an MP-2NV with an EQ-2NV provides you with almost unlimited choices for sound shaping, each one is an amazing sound tool in itself. The MP-2NV is my go-to mic pre when I'm not sure which direction I want to go with a certain mic. It provides such a wide spectrum, that I can always count on it to get the best out of any mic. The EQ-2NV is simply one of THE most musical EQ's I have heard and is used on every session at my studio.

– Michael Wagener (Mötley Crüe, Overkill, Accept, Great White, Poison, Alice Cooper, Extreme, Megadeth, Janet Jackson, Ozzy Osbourne, Dokken, Metallica, White Lion, Skid Row)

About Great River Electronics

Located on the banks of the Upper Mississippi River, Great River Electronics designs and builds handcrafted quality audio recording tools. All products undergo extensive research, development, and fine-tuning to meet and exceed the needs of audio professionals. Years of concurrent experience as an OEM manufacturer of industrial measurement and control systems for industries where safety, reliability, and quality control are critical are what give the Great River design-build team an edge. Carefully designed analog signal paths, many with digital controls, are the foundation of Great River audio recording designs.

Using a wide range of classically proven circuit styles, Great River continues to create a product line of audio recording tools that deliver a diverse tonal spectrum and solid sonic performance. From tracking to mastering, dual transformer-based preamps, sweet sounding EQs, and a hybrid-style summing system, all make consistent, concrete contributions to any recording studio.

A unique design from Great River, the PWM-501 500-series compressor opens up a world of possibilities for dynamic control of voice, instruments, and stereo bus. For more information, call or chat with an RSPE representative today.

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ManufacturerGreat River
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