Anthem STR Pre/Power Amplifiers: The science of the music

A brand new stereo pre-amplifier and power amplifier combination from Canadian audio marque Anthem links innovation to loads of tech – but thankfully doesn’t lose sight of the music in the process

Anthem is arguably best known for its home theatre products – and specifically for its AV receivers and AV processors. The brand has created a unique niche for itself in an overcrowded AVR market, thanks to a combination of robust build quality and exceptional performance.

That performance is augmented, to a significant extent, on the company’s proprietary calibration system that allows highly accurate measurement of speaker response in the end user’s acoustic environment, and then calculates room correction based on those measurements.

While the notion of room correction is nothing new – all AVRs offer some form of correction and digital signal processing – the Anthem system is based on a high-quality microphone, an accurate measurement system, and sophisticated software.

The downside is that it takes a bit of time and effort to complete the calibration process. But the results ensure a level of optimisation that is virtually unrivalled outside professional calibration systems.

The arrival of Anthem’s new STR stereo amplifier products, comprising an integrated amplifier, pre-amplifier and power amplifier, also marks the application of the Anthem Room Correction (ARC) system in a stereo context.

This latest version of ARC addresses the ease-of-use issue by offering two more user-friendly, mobile app-based alternatives. One uses the device’s own microphone, and the other requires the use of a better, purpose-designed USB microphone, supplied with the STR pre-amp.

To be fair, the latter comes close to the Windows-based system, and will probably suffice in most cases. But when you’re setting up a system once, it’s worth making the most of it, and there’s no doubt the Windows-based system remains the best.

The question is whether ARC’s impact on overall sound performance will be as marked as in its multichannel application – and to what extent the Anthem reputation for components that punch above their weight is applicable here.

AT FACE VALUE

We’ve come to expect solid, no-nonsense build quality from Anthem, and the new STR pre/power combination is no different. But the innovation that’s aslo part of the marque’s mantra is even more obvious here.

The STR power amp is a big and heavy beast, confirming that this is no lightweight Class D design. Cleverly, Anthem has located the heatsinking internally, so that there are no sharp edges, and the result is a clean, contemporary execution.

Almost 50 percent of the front fascia is taken up by a large colour display that acts as a bright, clearly legible watt meter. The display mimics two large analogue VU meters, one for each channel, on an arced, vertically arranged scale.

Those with a preference for minimalism might find the concept a little garish or gimmicky, but it adds to the amp’s high-tech appearance, and as the likes of McIntosh, Technics and Accuphase already know, many users actually like them.

The display can also be set to show internal temperature (a useful feature – in our listening room, the temps stabilised at between 32 and 34 degrees C), and the meters can be set to show watts into 4 ohms or 8 ohms.

Too bright or too distracting? The display is dimmable, and can also be switched off completely.

The metal fascia to the right of the display is subtly curved, creating further visual interest. It’s home to just three small buttons: a power switch, and two buttons marked Dim and View.

The former adjusts brightness, while pressing the latter brings up a detailed status and information screen. Using the View and Dim buttons together allows access to a set-up menu.

The menu allows the display parameters to be adjusted, including the brightness, the information shown, the impedance used by the display to express output, and the temperature units.

The rear panel offers few surprises, with a choice of single-ended RCA and balanced XLR inputs, a single pair of gold-plated binding posts for each channel, and an IEC power socket. Toggle switches allow the amp to be powered up by 12V triggers, or by auto-detecting an incoming audio signal from the pre-amp.

The matching STR pre-amp follows the same clean, contemporary styling direction as the power amp. Again, the left half of the fascia is occupied by a large, high-res display that shows volume level in large numerals by default. This display can also be dimmed or switched off completely.

The right-hand side of the faceplate hosts a large rotary controller, and buttons for mute and power on/off. The remaining four buttons are used to access and navigate the pre-amp’s setup menu, in conjunction with the rotary controller. More about those options later.

By comparison, the rear panel is densely populated, providing an initial indication of the STR pre-amp’s comprehensive feature and function list.

Both balanced XLR and single-ended RCA connections are catered for in analogue stereo input and output terms, but the STR also offers digital inputs in AES/EBU, coaxial, Toslink optical, and asynchronous USB flavours.

Its talent set extends to an integrated phono stage with separate moving coil and moving magnet inputs, although gain and load cannot be adjusted, which limits this feature’s usefulness, especially for moving coil cartridge fans.

Paradoxically, the phono EQ can be adjusted to get the most from older, pre-RIAA records such as 78rpm discs, or even older shellacs. It’s a unique capability that will please collectors of vintage vinyl.

A feature familiar to users of Anthem AV receivers, is the STR’s in-built room calibration system. I haven’t seen Anthem use this in a stereo application before.

Anthem Room Correction (ARC) is a comprehensive room calibration system that uses a pre-calibrated microphone, in conjunction with Windows software, to measure the acoustic properties of a room, and then adjust frequency response accordingly.

As this correction occurs in the digital domain, the STR employs its own 192 kHz/32-bit analogue-to-digital converter to transform analogue input signals into digital streams before applying the room correction curves.

Of course, nothing prevents the STR pre-amp user from not applying ARC, and to use the pre-amp in a conventional, all-analogue role. Each of the STR’s inputs – analogue, digital and phono – can be individually set up to this end.

The STR can also be configured to share the front left/right loudspeakers, as well as up to two subwoofers, for use in both a stereo-only system and a multichannel setup. A home theatre bypass function allows configuration of selected XLR or RCA inputs and outputs for this purpose.

UNDER THE COVERS

One could write an entire article just on the technical aspects of the STR pre-amp and power amp. For those who’d like to delve into all the detail, the product sheets of the two components provide a comprehensive rundown.

They’re available for viewing and downloading here.

However, it’s worth highlighting some of the key aspects. The power amp uses a proprietary input stage with eight bipolar input devices in a cascoded feedback arrangement.

On the output side, 16 bipolar devices per channel operate in a Class AB configuration. Each channel gets its own, low-impedance power supply, allowing the two channels to operate independently and to cope with very low impedance loads.

The output stages are directly coupled to the power supply capacitor bank to keep the impedance low, thus freeing up more power.

The STR power amp continuously monitors temperature, voltage and current to determine actual load, and reacts instantly to overload events in order to protect both the amp and the speakers connected to it.

The STR pre-amp is both an analogue and a digital pre-amp, and either controls and passes on analogue audio signals with minimum intervention and maximum signal integrity, or converts them into192 kHz/32-bit digital signals, after which it is able to apply ARC-derived processing for room correction.

It’s also able to upconvert and reclock lower-resolution digital audio signals to 192 kHz/32-bit resolution. The DAC features thin-film resistors and low-noise op amps, and the DAC stage has been optimised in its entirety, rather than simply relying on the DAC chip itself.

The DAC will decode incoming PCM digital signals up to 192 kHz/24-bit via AES/EBU, coaxial and Toslink optical. The asynchronous USB input will even accept 384 Hz/32-bit PCM, as well as DSD 2,8/5,6 MHz.

The pre-amp offers an extensive array of set-up options. While it has two stereo XLR balanced inputs, four stereo RCA inputs and both MM and MC phono inputs, each of those inputs can be customised.

In fact, up to 30 virtual inputs can be created by saving different settings for the same input (for instance, analogue direct or digital conversion) and naming that input accordingly. You can change the input offset to compensate for source components with different output levels, and associate the input with a different speaker/room correction profile.

Again, there’s a lot more detail to be found in the STR pre-amp datasheet, downloadable from the Anthem website here.

SETTING UP

The STR pre-amp and power amp duo reviewed here were brand now, and were allowed to burn in for a good150 hours. They were partnered with both our regular KEF R500 reference floorstanders, as well as a pair of Paradigm Persona 5Fs submitted for test (review pending) at the time.

Both analogue and digital source signals were delivered by our Lumin D1 network player, allowing a direct comparison between the STR pre-amp’s analogue and digital sections, as well as comparing ARC-calibrated signals with unaltered ones.

The Lumin sourced its material from a Lumin L1 NAS, as well as a Synology NAS – and since the D1 is MQA-capable, I also roped in some of the MQA-encoded material on offer in streaming service Tidal’s Masters catalogue.

The system was calibrated using ARC twice: once while the KEF R500s were in use, and again when they were swapped with the bigger Paradigm Persona 5Fs. In both cases, the different inputs were configured with and without the relevant ARC profile activated.

The calibration procedure requires a minimum of five measurements, using the supplied microphone, and takes about 20 minutes. However, it’s worth spending the time – the results are significant, and will also address system issues such as asymmetrical speaker placement and level imbalances.

I also tried the mobile app-based version of ARC, and found that using the app with the supplied microphone yielded very good results, while offering a more intuitive measurement process.

Even with the full Windows-based measurement process, results will obviously vary, depending on the system and the acoustic environment it operates in, but there is no doubt that ARC succinctly and successfully addresses a variety of anomalies.

SOUNDS LIKE …

I started off a succession of listening sessions with the KEF R500s partnering the STR pre/power combination.

Comparing the pure analogue sound of the STR pre-amp with the ARC-managed digital inputs proved interesting: in the AVSA listening room, ARC certainly had the ability to tame and tauten any excessive mid-bass response, allowing a cleaner, more impactful representation.

As a result of the significant improvements in low-frequency definition and control, the overall sound picture was more incisively presented.

The effect of ARC further up the frequency scale was less pronounced in our particular room and with the two speaker pairs employed, but actual results will always depend on speaker set-up and positioning, and actual room acoustics.

The Anthem STR duo delivered a sound that was bold and attention-grabbing, with plenty of pace and an abundance of headroom. They took command of the music, regardless of genre, and always managed to extract the essence and intent of the performance.

Soundstaging was expansive, affording the sound plenty of spatial scope. That sense of wide-open space was further qualified and refined by an ability to believably recreate ambience and dimension, further contributing to a vivid, engrossing sound picture.

There was never any sense of exaggeration or artifice, however: large-scale works were presented with measured majesty and muscle, while more intimate performances retained the delicacy and nuance of the real thing.

The STRs presented their sonic wares with a burnished assurance that believably captured the timbre and texture of the music. Rather than clinically accurate, the sound was a smooth and endearing one.

That doesn’t mean that the trebles were rolled off, nor that the sound was warm in a valve-like, glowing way. There wasn’t any dulling of detail, either.

The tonal range was broad, extending from a deep, sonorous low-frequency foundation to upper trebles lucid enough to capture and project fine strands of detail.

The STR power amp is a muscular beast and never got even close to running out of steam, even at higher listening levels. It always sounded effortless and in control, and never robbed the music of pace or effervescence, while also affording it loads of dynamic scope.

As a result, there was a real sense of flow and momentum to the way the music was delivered, further adding to the appeal of the listening experience.

While the results with our KEF R500s were very favourable indeed, hooking up the STR combo to the unashamedly high-end Paradigm 5Fs allowed the class and capabilities of the pre/power duo to shine through even more vividly.

Of course, it also helps that Anthem and Paradigm are closely aligned, and that the Personas were used during the final development of the STR line-up.

As the larger Personas are able to reach down substantially lower down the tonal ladder than the KEFs, they also benefited more from the ARC’s attentions, and there was never any doubt that the overall delivery with ARC in play was consistently better.

Listening to the Tsuyoshi Yamamoto Trio’s rendition of ‘The Nearness Of You (from Midnight Sugar) was a revelation: the performance was vividly and persuasively portrayed, allowing each instrument to be closely examined while retaining the taut interplay between the musicians.

The Anthem system had no trouble reflecting the dynamics of the production, allowing the percussive impact and the delicate intricacies of Yamamoto’s piano to be portrayed with equal verve.

The rich timbre and eloquent attack of Isoo Fukui’s upright bass were perfectly preserved, while the carefully measured drumming of Tetsujiro Ohara was delivered with impeccable timing and presence.

With ARC, the delivery was tonally linear but never constrained or bland, allowing the low frequencies to be produced with measured power and authority, even at higher listening levels.

The stereo image was completely seamless and generously dimensioned, affording the three performers an almost physical presence on the soundstage. The delivery was so lucid and vivid that the illusion of hearing the actual performance, rather than a mere recording, was consistently and believably maintained.

Dire Straits’ classic, eponymous debut remains one of my favourites, and ‘Lions’ is as good a track as any of the more widely acknowledged hits accumulated by the outfit over the course of their career.

The bass lines on this track can be overbearing on less balanced systems, but here, the perfectly modulated control of the STR power amp and the clarity and detail of the pre-amp made for engaging, foot-tapping listening.

With the bass providing an almost physical foundation, the lead and rhythm guitars maintained a close and entertaining dialogue on either side.

The percussion provided an effervescent backdrop of pace, while Knopfler’s casually delivered vocals were set far back in the sound image. Despite the very apparent placement of the instruments, there was a thrilling cohesion to the mix that really brought the music to life.

Hans Zimmer’s sweeping sonic vistas and evocative, cinematic melodies have never been portrayed more vividly than on his Live In Prague set. It’s compelling listening, but also a stern test for a system because of its extended tonal range, complex arrangements and expansive, densely populated soundstage.

The STRs were able to portray the ‘Gladiator Medley’ on the set with both bold vigour and compassion, allowing not only the broad strokes and the arresting tempo of the music, but also the fine details and subtle tonal hues to be appreciated.

Again, it was the energy and the attack of the STRs that impressed, allowing the full impact and tempo of the music to be expressed with an almost visceral, emotive intensity.

But this is also music typified by extreme dynamic shifts, and the STRs were able to closely and confidently track those shifts, while also delving deep into the heart and soul of the music. The result engaging and spellbinding.

While the sheer density of the music often threatens to mask individual instruments, the clarity and purpose of the STR duo’s approach allowed exceptional insight, unravelling a sound that can all too easily sound oversaturated. Add a vast and enveloping sound image, and the listening could only be described as immersive.

Finally, if you want to hear acoustic bass that you as much feel and experience as hear, then Brian Bromberg’s aptly titled Wood is not to be missed.

On ‘Freedom Jazz Dance’, the bass is the solo star, without any distracting accompaniment, and the result is a virtuoso demonstration of both Bromberg’s musicianship, and the sheer breadth of sound and power that can be extracted from a acoustic double bass.

The solo instrument filled the room with a richness of tone and a hue that would threaten to become overwhelming in a less poised set-up.

However, the Anthem STRs were not in the least intimidated, easily following the intricacies of Bromberg’s playing and reflecting the full spectrum of the insturment’s tonal range and percussive traits. Bass will never be the same again …

THE BOTTOM LINE

With the STR pre-amp and power amp, Anthem has successfully migrated its innovation, digital signal processing expertise, room correction know-how and commitment to quality into the notoriously difficult high-end stereo environment.

The pre-amp’s versatility and the power amp’s tremendous reserves make for a satisfying partnership, while also delivering as far as musical accessibility and engagement are concerned.

VITAL STATS

Anthem STR pre-amplifier
Frequency response (analogue): 10 Hz – 80 kHz (+0,0, -0,10 dB)
Frequency response (digital 192 kHz): 10 Hz – 50 kHz (+0,0, -0,10 dB)
THD + N: 0,0006% (DSP); 0,0016% (analogue direct)
Signal-to-noise ratio: 113 dB (DSP), 120 dB (analogue direct)
Digital inputs: 1x AES/EBU, 1x asynchronous USB, 2x RCA coaxial, 2x Toslink optical
Analogue inputs: 2x balanced stereo XLR, 4x stereo RCA, MM/MC phono stage
Outputs: 2x XLR (configurable), 3x stere0 RCA (configurable)
Connectivity: 802.11 Wi-Fi, Ethernet, RS232 serial port
Dimensions (WxDxH): 432 x 377 x 100 mm
Weight: 7,6 kg

Anthem STR power amplifier
Power output:
– 400 watts/channel (8 ohms, 20 Hz- 20kHz, – 600 watts/channel (4 ohms, 20 Hz- 20kHz, Frequency response: 20 Hz – 20 kHz (±0,1 dB)
Signal-to-noise ratio: 121 dB
Inputs: 1x stereo RCA, 1x stereo XLR
Outputs: 1x set of five-way binding posts
Dimensions (WxDxH): 432 x 470 x 172 mm
Weight: 27,3 kg

PRICE
STR pre-amp: R71 995
STR power amp: R101 595
SUPPLIED BY
Audio Specialists https://audiospecialists.co.za/

ASSOCIATED EQUIPMENT
Lumin D1 network player
Marantz KI Pearl Lite CD/SACD deck
Primare PRE32/MM30 pre-amp
Parasound Halo A21 power amp
KEF R500 loudspeakers
Paradigm Persona 500F loudspeakers
Isotek and Tice power conditioners
XLO Reference and TelluriumQ cabling and interlinks

SOFTWARE
Tsuyoshi Yamamoto Trio – Midnight Sugar (Sony Music 44/16 AIFF)
Brian Bromberg – Wood (A440 44/16 FLAC)
Dire Straits – Dire Straits (Universal/Mobile Fidelity DSD64)
Hans Zimmer – Live In Prague (Eagle Records 48/24 MQA FLAC via Tidal)