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Great River 32EQ and PWM-501: 500 Series Processors With a Learning Curve

Great River is known for its high quality, solidly built products, the flagship being the MP-2NV 2-channel microphone preamp. It offers the personality of classic British preamps without the issues that come with 40-year-old electronics.

Great River is known for its high quality, solidly built products, the flagship being the MP-2NV 2-channel microphone preamp. It offers the personality of classic British preamps without the issues that come with 40-year-old electronics. For this review, Dan Kennedy, founder of Great River, sent a GR MP-2NV stereo preamp, two 32EQs and two PWM-501 compressors. The 32EQs and PWM-501s were rackmounted in an API six-slot 500 Series rack while the MP-2NV is a standard 19-inch rack. While this review concentrates only on the 500 Series units, it was a plus to have the MP-2NV as a reference.


The 32EQ is a faithful reproduction of the Harrison 32 console’s EQ section. Great River created the unit in collaboration with the original designer, assuring that the original circuit was accurately reproduced. Each of the four EQ bands comes with boost/cut and sweepable frequency-selecting controls. The peaking style Low-Mid and Hi-Mid controls overlap, but each treats the selected range differently. The High and Low controls are both independently selectable between peak and shelf. There are also excellent sweepable highpass and lowpass filters with on/off controls.

My signal flow in and out of Magix Sequoia was through Mytek D/As, through the 32EQ and back into the Sequoia using Apogee A/D conversion. Monitoring was done on Neumann KH Series monitors at Eclectica Studios in Austin, Texas. My first impression was that the 32EQ is a very smooth-sounding equalizer for shaping rather than a surgical, tight equalizer.

Using the 32EQ on drums really helped me learn the way this unit reacts to different settings. There is a big difference between Peak and Shelf on the Low control. The Shelf settings offer a gentle slope from the chosen frequency dropping to the shelf an octave or so lower. I found that the frequency markings on the front of the unit are merely a suggestion—in Peak mode, the frequency on the faceplate reads 80 Hz but yielded sounds more like 120 Hz.

That said, the 32EQ is very responsive. I was able to dial in a perfect rock ’n’ roll style kick drum EQ quickly by boosting the Low end and cutting the Low-Mids. The toms were also sweetened quickly, faster than using my favorite plug-in EQ. The snare drum sounded better when I boosted using the Low-Mid band as opposed to dialing in the same frequency on the Low band. When I finished, the snare had punch, air and pop. Overhead tracks became smooth and airy once I used the HP filter to clean up the bottom, then boosted the highs in a way that only a wonderfully designed hardware EQ can do.

The 32EQ gave me good results on various bass guitar tracks, again with the learning curve coming into play. For example, boosting 400 Hz on the Low-Mid band created the expected boxy tones, but when boosting the same frequency using the Hi-Mid, the boost extended into the frequency range, with 2k sounding enhanced. This was slight but noticeable. The lesson? Depending on which band/control you choose, the same frequency may give you different results.

The sweepable pass filters are my new favorites. From utility to special effect, the sound is magical. The HP filter ranges from 25 Hz to 2.75 kHz, while the LP filter sweeps from 20 kHz down to 160 Hz. These are listed as 12 dB/octave but there is definitely something else going on, as they sound steeper and have incredible creaminess coming from them.

I had good sonic results when using the 32EQ. But I wish the units were doublewide—my fingers did not fit well on the crowded knobs. I also wish the EQ Boost/Cut controls had center detents to recall the zero point. Wishes aside, I really like the 32EQ; everything I tried it on benefitted from it. If you are also into pass filters, you really need to hear the 32EQ. The filters are worth the price of admission alone.


The PWM-501 is designed using Pulse Width Modulation for level control—the first 500 Series compressor to use this technique. It gives the PWM-501 a beautiful, unique musical sound, and a bit of a learning curve, too.

The controls are straightforward and include Makeup Gain, Threshold, Attack, Release and Ratio. There is also a sweepable HP filter for the sidechain and a hard Bypass switch to completely remove the compressor from the signal path. The Attack control ranges from about 10 ms up to 700 ms, while Release is from a quick 10 ms to a long 5 seconds.

The PWM-501 also has a single, continuously variable rotary control to choose between a FeedBack (FB) and FeedForward (FF) detection circuit. The metering is wonderful—you can quickly set input and output gains by pressing the meter button to display the different modes. The colors are green/yellow/red with the yellow range indicating you are above 0 dB running at a +4 dBu. In gain reduction mode, each LED shows 1dB of reduction. You will need to spend some time with this compressor to really grasp how it reacts to various sound sources. Threshold is affected by the Ratio and Attack setting, and Ratio is affected by the Threshold and Attack controls in a way that I am not used to or have ever seen.

Acoustic guitar sounded wonderful with a 2:1 ratio and only a few dB of gain reduction. A higher ratio and amount of compression tended to clamp down on the sound quickly. Engaging the HP filter helped some, but still felt aggressive even with only a few dB of reduction. Tracking lead vocals through the PWM-501 with relatively slower settings worked well to tame and center the track. Setting the rotary control toward FB (clockwise) was smooth and musical, while moving it to the left (FF), brought a more aggressively compressed sound. Without much effort, the PWM-501 will jump from a few dB of reduction to 12 dB or more. Care is advised.

Drums really liked the PWM-501, making the sculpting of transients fast and easy. Both FF and FB modes worked, each in their own way. Kick, snare and overheads, all with unique FF/FB settings, quickly came to life. Next I went for an 1176-style slam on bass guitar with a high ratio and very fast attack/release setting. But the unit literally flipped upside down and gated the track off in a sort of over-modulation. I spoke with Dan Kennedy and he confirmed that this is normal in a Pulse Width Modulation style of compression. So the PWM-501 couldn’t give me the intermodulation distortion and “hair” I wanted on bass, but I still got a good aggressive rock bass sound.

Next I used the PWM-501 for smoothing out a very dynamic B3 organ track. The B3’s held chords, screaming highs and swells can be a challenge to control. I set the ratio at 4:1 with a slow attack and moderately fast release. This gave me a few dB of reduction on the chords, and 5 to 10 dB of reduction during the loud parts—a more usable sound in the track. I used 50-50 FF/FB settings for this and was very happy with the results.

Despite the learning curve, the PWM-501 offered a wide range of flavors, many of which were smooth and musical when used in small doses. It has a high learning curve, but its uniqueness in function and tone makes it worth taking for a test drive.

Tim Dolbear is an audio engineer and producer at Eclectica Studios in Austin, Texas. Contact him at

Product Summary

COMPANY: Great River


PRICE: $775

PROS: Smooth and responsive. Great-sounding HP/LP filters.

CONS: Very tight layout on this single-space unit. No output volume.

Try This

An Internal jumper provides a selection between a “vintage” FeedBack design (factory default) and a non-FeedBack option. Try both with a bass guitar running through the unit. Listen closely to the differences while adjusting the lows and low-midrange for clarity.

Product Summary

COMPANY: Great River

PRODUCT: PWM-501 Compressor

PRICE: $835

PROS: Great River sound and build quality. Variable detector control. FF/FB. Metering.

CONS: Moderate learning curve. Care needed when adjusting FF settings.

Try This

The FeedForward function analyzes audio as it enters the unit while FeedBack detects audio as it leaves the unit. Try using FeedForward on drums, bass and other instruments to get a faster, more aggressively compressed sound. Then try various FeedBack settings on vocals or even your mix bus for smoother and more musical compression.