The Professional Monitor Company Ltd., aka PMC, was founded in the UK in 1991 by Peter Thomas, of the British Broadcasting Corporation (BBC), and Adrian Loader, of audio distributor FWO Bauch. Their first product, the BB5-A active minimonitor, helped PMC become known for what would become a long line of monitors designed for use in recording studios. Since then PMC has ventured into consumer audio, and now offers many passive speakers in various model lines aimed at audiophiles. However, the subject of this review is not a PMC speaker, but the only consumer-electronics component PMC makes: the Cor integrated amplifier ($6000 USD), which was created to celebrate their 25th anniversary.
For the Cor, PMC decided to put to good use the experience they’d gained over the last 20 years of co-engineering, with other companies, analog power amplifiers and crossovers, and design a component of uncompromised transparency that could act as the soul of a high-quality music system -- as indicated in the name, cor, the Latin word for heart.
At 17”W x 3.4”H x 15.8”D and 26.5 pounds, the Cor looks and feels substantial. Its front and side panels are thick extrusions of bead-blasted, matte-finish aluminum, each with a pattern of four thick, horizontal strips alternating with deep channels milled out by a three-axis CNC machine. (See a bit later for what’s in those channels.) All three panels act as heatsinks. In the black of my review sample (silver is available), the Cor’s look was one not of audio jewelry but of something more rugged and substantial, and inspired confidence. If the Empire of the Star Wars films were ever to build an integrated amp, it might look like this. I really liked the look -- it worked well in my listening room.
The faceplate is an exercise in utilitarian simplicity: clean, each control intuitively laid out. The only bit of fancy is the touch-sensitive standby switch hidden behind the PMC logo at bottom left. The logo glows red in standby, green when the Cor is fully powered up. Directly above this are six small input pushbuttons, each above its tiny LED; these are for CD, Radio, AV, Aux, Balanced 1, and Direct. The Direct input bypasses the Cor’s preamp section to feed only the power amp section, for those using an external preamp.
The right half of the faceplate is occupied by three sliding switches, or faders, one each for adjusting, from top to bottom, the Balance, Treble, and Bass. (These functions are also available on the supplied remote control.) You seldom see tone controls on audiophile preamps, let alone faders, the latter obviously a nod to PMC’s professional roots. Audiophiles are used to seeing a motorized volume potentiometer rotating seemingly by itself at the touch of a remote’s button, but how many of you have sat in your listening chairs and watched motorized faders moving in discrete steps as they obey your commands? I found this mesmerizing.
At the center of each fader’s travel is a small LED. When the fader itself is in its centered position, the LED glows white; otherwise, it’s red. The Bass and Treble controls offer ±10dB of gain/cut; the Bass control’s operating bandwidth is 20-300Hz, the Treble 1-20kHz. Below the Bass fader is a headphone jack, and to the right of the faders is a column of three pushbuttons; from top to bottom, these are Mono, Mute, and Bypass. The Bypass button switches the faders out of circuit, for a purer signal path. At far right is the very large volume knob, its setting indicated by a small built-in LED -- volume can also be adjusted with the remote.
On the rear panel are four pairs of gold-plated left/right connectors (RCA) for the four single-ended inputs, and one pair of balanced input sockets (XLR), all five inputs labeled to match the buttons on the front. There are also pairs of Pre Out and Direct In jacks (RCA), for using the Cor as only, respectively, a preamp or power amp. To the right of all of these are two sets of high-quality five-way speaker binding posts, an IEC power inlet and fuse bay, and, at farthest right, the main power rocker.
PMC’s design goal for this model was pure analog sonic transparency -- inside the Cor are no ADCs, DACs, or DSP circuits. In fact, PMC doesn’t even use the digitally controlled analog circuits that are now ubiquitous in high-end components. And for the Cor’s volume control, instead of a resistor-ladder IC that, while operating entirely in the analog domain, relies on digital control of its solid-state switches, PMC uses a very-high-quality potentiometer.
In pursuit of transparent sound, PMC uses balanced signal routing in the Cor’s preamp section. Although the Cor has only one balanced input and no balanced pre-outs, all incoming single-ended signals are converted to balanced (i.e., the original signal is preserved and an inverted copy is created), and remain balanced when fed to the power-amp section. The preamp section uses very high-quality op-amps, which PMC prefers to discrete amplifier stages for the former’s greater rejection of common-mode distortion, and the resulting lower parts count and shorter signal path. The control circuits have independent power supplies to isolate the audio signal from the electrical noise generated by the motors.
The power-amp section was also designed for transparency -- all signal-path capacitors are bipolar, the signal path is shielded from electromagnetic interference, and there are two large independent power supplies, each with 20,000µF of filter capacitance and built around a single 360VA toroidal transformer. The output devices are biased into class-AB, with a topology based on Sidney Darlington’s work at Bell Labs. Key features of Darlington’s designs include very short signal paths, extremely low thermal-lag distortion, and internal thermal and current monitoring for each transistor -- which, per PMC, yield faster, more accurate feedback.
PMC’s specifications for the preamp section include a maximum gain of 15dB and total harmonic distortion (THD) of 0.001% at 1kHz. The amp section has 28.9dB of gain and is claimed to produce 95Wpc into 8 ohms or 140Wpc into 4 ohms. Other specs include a signal/noise ratio of 101dB (A-weighted), an input impedance of 23.5k ohms, THD of 0.001% at 1kHz, and a damping factor of more than 160 into 8 ohms, 20Hz-20kHz. No specs were provided for the headphone amp, but I measured 9.4dB of gain with no load. The specified frequency responses for both sections are 20Hz-20kHz, +0/-0.2dB, and 5Hz-80kHz, +0/-1dB.
The Cor came well packed in a double box, protected inside by thick chunks of foam. PMC includes a pair of white gloves for handling, a detailed manual, a remote control, a detachable power cord, and a comprehensive performance certificate detailing 22 pass/fail criteria, to prove that your unit has passed its final quality-control check. This document, signed by the builder and the tester, includes the unit’s build date and serial number.
The Cor’s sturdy, functional remote control is made of metal, but it was a pain to install its batteries (included). Here was the dark side of PMC’s pro-audio roots: To install the batteries, I had to dismantle the remote with a tiny hex wrench (included) -- a lot more work than the typical user of consumer electronics is used to. Thankfully, this atypical user found the exercise somewhat amusing.
My dedicated listening space is a 15’L x 12’W x 8’H basement room, its concrete-slab floor carpeted from wall to wall. There are broadband absorption panels at the first-reflection points on both sidewalls and on the long front wall between the speakers, and bass traps in each of the front corners. My reference system comprises: two SVS SB-4000 subwoofers, their low-pass filters set to 130Hz (24dB/octave); a pair of Bowers & Wilkins 705 S2 minimonitors on stands, crossed over to the subs at 120Hz by a passive, line-level, balanced Marchand Electronics XM446XLR-A high-pass filter. The speakers, toed in 18°, describe a 9’ equilateral triangle with my high-backed recliner. The subs are linked to a McIntosh Laboratory C47 preamplifier via balanced interconnects, and the subs’ balanced outputs feed the Marchand filter, its outputs in turn feeding a McIntosh MC302 power amp specified to produce 300Wpc into 8, 4, or 2 ohms.
Inserted between the digital sources and the DAC built into the Mac C47 is a miniDSP DDRC-22D room-correction processor running Dirac Live 2.0. Source components are a laptop computer running Windows 10 and Roon, and a Bluesound Node streamer serving as a Roon endpoint and controlled with a Samsung Galaxy Tab S smartphone. I play music from Tidal and a library of CD-quality files stored on a Western Digital NAS device. For headphone listening, I use a pair of Sennheiser HD 800s with Anaxilus modification, with custom EQ implemented through Roon. The EQ settings and modifications are explained on Inner Fidelity by Tyll Hertsens.
When I review an electronics component, I try to test every input and configuration, performing level-matched, time-synchronized (to the best of my ability) comparisons of its sound with that of my reference or another comparable product. I compared the Cor’s headphone amp and preamp sections with my C47 preamp ($4500), and the Cor’s power-amp section with my MC302 ($7000). For the preamp and headphone comparisons I used my references: B&W 705 S2 speakers, SVS SB-4000 subs, and Sennheiser HD 800 ’phones. For my tests of the Cor when used as a power amp or as an integrated amp, I used a speaker that presents a bigger challenge than the B&W -- DALI’s Opticon 8, a pair of which I had on hand for review. This large floorstander has five drivers, including two 8” woofers, and has a specified sensitivity of 88dB and a nominal impedance of 4 ohms.
Before doing any critical listening, I tried all of the Cor’s inputs to ensure that everything worked, including its balanced inputs (thanks, trusty old Rotel RC-991 CD player!). Everything worked. I experimented briefly with the tone controls, which worked as expected, providing the typical broadband bass and treble cuts and boosts all audio enthusiasts were once used to. Although most audiophiles are nowadays quick to condemn tone controls, they can be useful when used judiciously with problematic recordings -- e.g., those that are too bright or dull in the treble, or thin or bloated in the bass. I also compared the Cor’s sound with its tone controls bypassed and engaged, all faders at their central, “0” positions. Although I heard no obvious differences between the Cor’s sound with its tone controls engaged and Bass and Treble at “0,” and its sound with the tone controls bypassed, for all subsequent listening I switched the tone controls out of circuit. With no signal playing and its volume control set to max, the Cor produced very little hiss and hum, even with my ear next to a tweeter. This is a very quiet integrated.
With the DALI Opticon 8s connected to the Cor’s speaker outputs, and the C47’s fixed line-level unbalanced outputs (which bypass the C47’s volume control and gain stage, effectively turning the C47 into a DAC) connected to the Cor’s CD input, I sat down to listen critically. “This will be an easy section to write,” I kept thinking -- track after track, I heard nothing out of the ordinary. My system sounded exactly the same as it had the day or the week before, when I drove the DALIs with my Mac C47 and MC302. The Cor seemed to be fulfilling PMC’s design goal of transparency -- it sounded like nothing at all.
For example, from the opening notes of the title track of Colin James’s National Steel (16-bit/44.1kHz FLAC, Rhino), I heard every bluesy chord from the gritty-sounding guitar at left of center, as well as the very subtle echo of the recording studio’s walls and the leading-edge sparkle of the second guitar to right of center. When James’s voice entered it was palpably present, floating dead center above the tops of the speakers and just behind the plane described by their frontmost edges -- I could hear all of his subtle intonations as he sang, and as his voice shifted effortlessly from a throaty rasp to a smooth, full-bodied sound. The Cor hid nothing. I realized that if I was going to hear any differences between the PMC and my McIntosh separates, it would be in quick, level-matched comparisons.
Power-amp comparison: PMC Cor vs. McIntosh MC302
I connected the balanced outputs of the Mac C47 to the balanced inputs of the Mac MC302, and the C47’s single-ended outputs to the Cor’s Direct input, bypassing its preamp section. I matched the levels to within 0.01dB.
Up first was “Run-Around,” from Blues Traveler’s Four (16/44.1 FLAC, A&M). I focused on the extension and slam of the lows; the shimmer and extension in the highs; the detail and smoothness of voices; differences in soundstage width, height, and depth; layering and details of instruments; and pace, rhythm, and dynamic contrast. After swapping back and forth a half-dozen times, I gave up -- the two amps sounded exactly the same in every regard. Both drove the DALIs with aplomb, letting me hear the quick, rhythmic bass that underpins this track, the texture of John Popper’s harmonica and lead singer Jono Manson’s voice at center stage, and all the detail in the quickly strummed guitars panned hard left and right.
Then came “Beloved Wife,” from Natalie Merchant’s Paradise Is There: The New Tigerlily Recordings (24/48 FLAC unfolded to 24/96 MQA, Nonesuch/Tidal). It begins with slow, melodic piano to right of center stage, and a string arrangement to left of center. Neither amp did anything to color the sounds of these instruments. The standout aspect of this track is Merchant’s haunting singing, well recorded at dead center with superb presence and detail. Driving the DALIs alternately with the two amps yielded the same experience -- the feeling that Merchant was in my listening room, performing for me. Her every delicate inflection, inhalation, and exhalation was re-created with palpable realism. I heard no differences between the amps.
I figured that if I was going to hear any differences between them, subtle or otherwise, I’d have to play some bass-heavy electronic music at LOUD volumes into these 4-ohm loads. “She Will,” from Lil Wayne’s Tha Carter IV (16/44.1 FLAC, Cash Money), has a strong foundation of pulsing ultra-low bass notes complemented by rhythmic thumping in the lower midbass. I listened at volumes high enough that I could feel the pulsing low-frequency notes in my chair and the bass thump in my chest. I estimate that the needles on my MC302’s power meters were peaking in 100W land! In terms of dynamic punch, that feeling of pressure in the chest, the amps performed the same, controlling each DALI’s two 8” woofers with authority, and the sensation of bass slam was powerful and taut -- in a word, impressive. With respect to the low-frequency extension -- the rumbling pulsing I felt in the lower half of my body -- I thought those lowest notes sustained just a bit longer through the MC302. But even this difference was tiny. Kudos to the Cor’s power-amp stage for holding its own against the far more powerful MC302 at these high volumes.
Preamplifier and headphone amplifier comparisons: PMC Cor vs. McIntosh C47
I compared the Cor’s preamp section with my Mac C47 preamp, whose tone controls were also bypassed for this test; levels were matched to within 0.02dB. I got the same results as with most of the power-amp comparisons: no audible differences between Cor and Mac. Both sounded dead neutral and dead quiet. Although this spoke well for the Cor, I must add that while the C47 costs a lot, it has some key features the Cor lacks; e.g., a full-featured DAC with a plethora of digital-input types, a moving-magnet/moving-coil phono stage, and a second pair of balanced inputs. The Cor’s preamp stage is sparse by comparison, even with the fancy faders. Also, it would have been nice had PMC included balanced preamp outputs, not just single-endeds, if only to increase the Cor’s flexibility -- its sound quality was that impressive.
To compare headphone amps, I was able to match the levels to within about 0.01dB. I heard no noise from the Cor, which was dead quiet at maximum volume level with no signal playing. Inspired by my recent viewing of the Elton John biopic Rocket Man, I listened to John’s own recording of that track, from his greatest-hits compilation Diamonds: Deluxe Edition (16/44.1 FLAC, Island/Tidal). The Cor’s headphone amp got out of the music’s way, letting the Sennheiser HD 800s reproduce every sound with all the realism and detail I’m accustomed to: John’s acoustic piano spread across the soundstage, his voice dead center, Davey Johnstone’s guitar plucks hard right, Nigel Olsson’s crisp cymbal work in the crescendos -- all was reproduced with tonal accuracy, detail, and smoothness. Between the headphone amps in the Cor and my C47, I heard no differences.
For those curious about the Cor’s ability to drive high-impedance cans such as the HD 800s, I believe that the Cor will be up to the challenge in most cases. The 9.4dB of gain I measured at the Cor’s headphone output at full volume should be plenty for most applications, but it’s not the output of what I consider a high-gain headphone amp. Listening through the HD 800s to a cut from Bryan Adams’s Cuts Like a Knife, an album with high dynamic range and very low average volume (16/44.1 FLAC, A&M), I could turn the volume all the way up; it was loud, but not deafening -- still listenable. The Mac C47’s headphone amp offers 16dB of gain, though with a high output impedance of 47 ohms. As the proportion of output impedance to load impedance increases, less voltage is dropped across the load-reducing output -- for example, with 300-ohm headphones such as the Sennheiser HD 800s and the 47-ohm output impedance of the C47, 1.3dB is lost across the output of the headphone amp.
$6000 is a good chunk of change, particularly for an integrated amplifier -- at that price, we’re flirting with high-end audio’s boutique category. However, a glance at PMC’s Cor lets you know that “boutique” audio is not what they’ve gone for here. The Cor’s utilitarian look, which I like, states firmly, in a businesslike tone, “I’m not messing around -- get out of my way and let me do my job.” That job is to effortlessly drive almost any pair of speakers with uncompromised transparency.
The Cor gets that job done, and well. It essentially matched the sound quality of my McIntosh Laboratory separates, which together cost almost 50% more: $11,500. And what features the minimalist Cor has worked flawlessly. If you’re in the market for a powerful, no-nonsense, all-analog integrated amplifier that doesn’t only rival pricier separates but equals them, look no further -- PMC’s Cor is easy to recommend.
. . . Diego Estan
- Speakers -- Bowers & Wilkins 705 S2, DALI Opticon 8
- Subwoofers -- SVS SB-4000s (2)
- Headphones -- Sennheiser HD 800 with Anaxilus Modification
- Integrated amplifier -- NAD C 316BEE
- Power amplifier -- McIntosh Laboratory MC302
- Crossover -- Marchand Electronics XM446XLR-A (between preamp and amp)
- Preamplifier-DAC -- McIntosh Laboratory C47
- Room-correction EQ -- miniDSP DDRC-22D with Dirac Live 2.0 (between digital sources and DAC)
- Digital Sources -- Rotel RCD-991 CD player, Bluesound Node streamer as Roon endpoint, laptop computer running Windows 10, Roon
- Analog source -- Pro-Ject Debut Carbon Esprit turntable with Ortofon 2M Red cartridge
- Speaker cables -- 12AWG oxygen-free copper (generic) (locking banana plugs)
- Analog interconnects -- AmazonBasics unbalanced (RCA), Monoprice Premier balanced (XLR)
- Digital link -- AmazonBasics optical (TosLink)
PMC Cor Integrated Amplifier
Price: $6000 USD.
Warranty: Five years parts and labor with registration.
The Professional Monitor Company Ltd.
Holme Court, Biggleswade
Bedfordshire SG18 9ST
Phone: +44 (0)1767-686300