Pre/Power Amplifiers

One of the annoyances of modern life is noise. Outside, our ears might be assaulted by traffic roar, construction clamour or roadworks cacophony, plus buzzing leaf blowers and lawn mowers. Indoors, however, it’s rather more subtle. The prevalence of wireless communications around the house, plus the switched-mode power supplies that run pretty much everything, mean the noise is electrical in nature – and more insidious. Enter the £21,900 T100SPA power amplifier from the aptly-named Quiescent, which aims not only to delight your ears, but also ensure this ever-present noise doesn’t get in the way of the music.

This stereo model, plus the £23,100 T100MPA mono amplifier, are the latest items in the UK brand’s T-Series of audio components, alongside the T500VA Balanced Mains Power Supply, for an equally heady £16,300. Quiescent also offers mains and loudspeaker cabling, plus interconnects, and all have a focus on noise reduction. The company’s history stretches past its formation in 2017, being an evolution of noise and vibration control specialist Vertex AQ [see boxout], with co-founder John Cheadle still onboard.

Inside story

As can be seen from the lid-off picture, Quiescent’s T100SPA looks chock-full of compartments and cables, although only a small portion of this is the dual-mono amplification stage itself. Rated at 130W/8ohm and 200W/4ohm [see PM's Lab Report], this amp module is based on a design by Sonny Andersen of Danish manufacturer Phison Audio. Interestingly, these compact amp circuits are the only items here not treated to the company’s noise abatement scheme, short of an ‘RF-absorbent material’ loaded into a cut-out under the PCBs. Quiescent says it is currently working on a matching preamplifier model that will have more extensive vibration control applied directly to its components.

Box clever

Apart from this, the mysterious ‘black boxes’ inside the T100SPA comprise the inline mains filter, bridge rectifier, reservoir capacitors and separate grounding modules for the centre tap of the toroidal transformer’s primary and secondary windings. These incorporate Quiescent’s ‘QPower noise-suppression’ system, claimed to deal with mechanical vibration, and everything from DC to higher frequency noise emanating from the PSU. There is also an input signal module to eliminate ground loops, and two speaker output modules designed to sink any vibrations coming back down from your loudspeaker cable… Quiescent says the T100SPA is a more powerful update of its earlier T50SPA, and is based around two high-power MOSFETs per channel in a conventional (current feedback) Class A/B circuit. All components, apart from the transistors, are surface-mount types to minimise unwanted coupling while keeping the PCB footprint as small as possible.

The PSU’s smoothing capacitors are Audio Note Kaisei electrolytics, totalling 40,000µF per channel, with non-polarised types as bypass caps. Quiescent makes no claim for a dedicated, fast-acting speaker protection circuit, but the output was safely muted during PM’s low impedance power tests [green trace, Graph 1, p79]. Both balanced and unbalanced inputs are provided, selected via a toggle switch on the T100SPA’s rear panel, while a second switch disables the front-panel power status LED, for further claimed sonic improvement. Speaker outputs are through chunky WBT Nextgen silver binding posts.

Above: Atop the toroidal transformer, the ‘Q power’ is a passive ‘acoustic/EMI/RF’ absorption solution. The linear PSU (rectification, reservoir caps and regulation) are all sub-divided into separate enclosures while the MOSFET amp itself is on two small PCBs [bottom left/right]

You’re grounded

The amplifier’s custom-designed, machined aluminium casework, available in either silver or black finish, measures 440x140x400mm (whd) and integrates side-mounted heatsinks with an asymmetrical angled fascia. Again, the chassis has been treated with ‘proprietary techniques’ to minimise vibration and noise – in addition to the isolation afforded by the sheer mass of the enclosure itself. The unit sits on three robust feet. Finally, an additional phono socket on the T100SPA’s rear accepts a special grounding lead provided by Quiescent. This is to be used when the power amplifier’s RCA line inputs are fed from a preamplifier that’s already grounded, otherwise, and with the balanced XLR connections, it may not always be a necessary fixture.

See-thru sonics
Once laced up to my regular Yamaha C-5000 preamp [HFN Aug ’20], the Quiescent T100SPA quickly put a grin on my face. If I was feeling poetic, I’d say the hard work that has gone into the unit’s design is mirrored by the enthusiasm with which it approaches music reproduction. This is a performance of power, weight and transparency. I did need to connect the grounding earth lead to remove a slight hum, but after this the T100SPA was pleasingly quiet. On the other hand, experimenting with the on/off switch for status LED wrought no appreciable difference. If it were up to me, I’d be inclined to re-purpose this switch to provide that grounding link as required. What was in no doubt, however, was the level of information the T100SPA can pull from a recording – if it’s in there, believe me, it will find it! Where it did fall down ever so slightly was presenting all this musical information in an ordered manner. With mediocre-quality recordings, everything was there but I found I sometimes had to concentrate on locating a particular instrument. The T100SPA appears ruthless in this respect and keener to point out the failings of a recording than try to make the best of it.

As a result, the atmospheric keyboard and string accompaniment to Creeper’s ‘Four Years Ago’, from the British goth rock band’s Sex, Death And The Infinite Void album [Roadrunner 0190295283933], did tend to merge in on itself. In contrast, though, the vocal performances of both Will Gould and Hannah Greenwood stood clear of this to fully capture the sombre emotion of the track.

To be frank

Fortunately, when you give the T100SPA something better to work with, its presentation becomes more confident. Buckshot Lefonque’s ‘Another Day’ [Music Evolution; Columbia 484195 2] was a masterclass in instrumental order, with the deliberately muddy electronic percussion providing a fine base layer for the main players on top. Frank McComb’s vocals held court exquisitely centre-stage and the saxophone of Branford Marsalis soared out of my loudspeakers, sounding rich and real. On the album’s title track, the T100SPA grabbed hold of the synth bassline and thundered it out into the room with gusto. This amplifier’s low-end presence is prodigious, and does a superb job of adding solidity and weight to proceedings. This is accompanied by tightly controlled timing, but with an appealing underlying sense of warmth, too.

The double bass backing Diana Krall on ‘I Don’t Know Enough About You’ from her Love Scenes set [Impulse IMP 12342] had a magnificent woody resonance to it, making it feel like an authentic, vivid presence. Slightly further up the frequency range, I have heard the hand movements on the fretboard on this track rendered more distinctly, but the T100SPA definitely captured the instrument’s essential nature and resonance.

In spatiality terms, Quiescent’s amplifier presents a slightly unusual character to the world. Throughout my listening there was a very wide image extending well past the positions of my loudspeakers, but less in the way of front to back depth. This left the soundstage reminding me of one of those curved-screen OLED monitors that are becoming popular in modern offices. The T100SPA could indeed wrap a performance around me, but it seemed slightly shallow rather than deep or truly immersive.

Above: Inputs are on switched single-ended WBT RCAs and balanced XLRs (the former requiring an external earth/signal ground link to be attached). Single sets of WBT speaker terminals are included, and the front panel LED may be switched off...

No sugar, please

Nevertheless, the organisation of the performers within this curved perspective was excellent, assisted by the amplifier’s sheer openness and clarity at the top end. Vocal performances were strong and positive, and percussion was crisp and confident. Once again, the last of these could become too strident if the source material was less than stellar, leaving pieces like the title track from Care/Ian Broudie’s Diamonds And Emeralds compilation album [Camden 74321 500232] a little too ‘jangly’. That said, my ultimate impression was that the T100SPA was simply telling it like it is, without any sugar-coating. It would be churlish to reprimand it for making a thin, edgy 1980s recording sound thin and edgy… Again, feed the T100SPA with something more befitting of its audiophile credentials and it excels. It also welcomes a big push on your preamp’s volume control, as despite not being a ‘powerhouse’ on paper, it goes impressively loud very easily. Quiescent’s amplifier is perfectly at home when the volume rises and retains a superb sense of composure even at ‘anti-social’ listening levels. After lapping up a session with Metallica and the San Francisco Symphony Orchestra, courtesy of ‘The Day That Never Comes’ from S&M2 [Blackened Recordings BLCKND043-1C], I was once again thankful that I have no close neighbours. However, the same track still had a vivid impact and presence at a more sedate volume. All too often amplifiers that are delighted to blast you into next week can seem to lose their eagerness when you ask them to play more quietly. The T100SPA has no such qualms and is blessed with an expansive dynamic range.

Hi-Fi News Verdict

If you’re looking for dynamics, detail and authenticity, then you’ll probably find much to appreciate in the Quiescent T100SPA. While it’s not quite the all-conquering all-rounder that I had been hoping for at the price, it still dazzles with high- quality recordings, leaving no stone unturned. The effort and ingenuity put into its design has clearly paid dividends, but there’s arguably more to come.

Sound Quality: 80%