Hardware Reviews

Quiescent T100MPA: a unique approach

Quiescent T100MPA monoblock amplifiers https://the-ear.net

Quiescent T100MPA monoblock amplifiers

Jason Kennedy reviewed Quiescent’s T100SPA stereo power amplifier in February this year. A second review sample was doing the rounds at the same time and I was able to add a short note on my own thoughts at the end of that review.

Both Jason and I felt the T100SPA to be notable, disruptive even. The extensive use of Quiescent’s patented EMI and microphony reduction technology results in undoubtedly the quietest background either of us have ever experienced. The passive technology behind the quietness bestows upon the T100SPA an ability to reveal unprecedented levels of musical detail, including the timing intent of performers along with a muscularity that is out of proportion with the modest claimed output power of 130 Watts per channel. The word unprecedented is not used casually there. Through the T100SPA, I heard musical information that no previous amplifier of our respective acquaintance has been able to transcribe. So when Quiescent told me about the T100MPA monoblocks I was more than interested.

Quiescent T100MPA monoblock amplifiers https://the-ear.net

Noiseless ecosystem

Quiescent is the continuation of what was formerly named Vertex AQ, a developer of EMI and vibration absorbing interconnects, speaker and mains cables. The name was changed four years ago when the company passed into the hands of Nigel Payne, a microwave scientist turned entrepreneur. Payne’s Quiescent is nothing if not ambitious. He has assembled an international team of experts who, under his technical lead John Cheadle, are evolving technologies pioneered by Vertex AQ to create a new form of audio eco-system within which the mitigation of EMI and vibration is a key goal.

Payne’s contention is that conventional audio system performance has reached a virtual brick wall. Gain stage noise floors so low that they cannot be measured even with the best of test equipment are technically admirable, but they are compromised because they do not address the systemic vibration and EMI that lead to microphony and high frequency hash. Go-to engineering solutions such as cable screening and feedback loops are not the answer. Screened cable efficiently conducts the music signal already mixed with the noise (and makes it worse by adding microphony). Feedback merely ensures that unwanted pollution surrounding the signal as it arrives at the gain stage input is faithfully present at the output. What makes the problem even knottier is that amplifiers themselves can be efficient generators of unwanted EMI and vibration-induced microphony. Capacitors operate as microphones in reverse, inductors ring, voltage regulators and transistors emit EMI.

Quiescent’s EMI and vibration mitigation technology was first made available in a series of unitary stand-alone devices and cables. We can buy Quiescent interconnect, ethernet, mains and speaker cables that absorb EMI and resist vibration, and modules that do the same for use between amplifiers and speakers, and for the mains feeds to components. Rather oddly-named, Couplers are sold in sets of three and go underneath equipment on the kit table where they too absorb and dissipate EMI, and vibration that would otherwise turn into microphony.

Quiescent T100MPA monoblock amplifiers https://the-ear.net

Amplifiers

The T100SPA was not only Quiescent’s first amplifier, but also the first anywhere with the company’s EMI and vibration technology, some of it patented, deployed directly inside. Now the company has unveiled a pair of monoblocks, the T100MPAs (the M denotes monoblock, S denotes stereo). They deliver 130 Watts per channel and a constant 10 Amps into a 2 Ohm load, just as the stereo amplifier, but in return for a doubling in price we get two impeccably built units with, overall, three times the amount of noise reduction technology inside.

Quiescent’s absorptive matrixes, which soak up vibration and EMI, can be found at every logical stage inside the monoblocks. The signal input buffer is built directly onto its own matrix, the UK-made 700VA peak toroidal transformer has three, while the AC capacitor bank, the unique discrete bridge rectification circuit and the gain stage board also each get their own dedicated matrixes. Mains power enters through a dedicated absorptive matrix while at the business end the amplified music signal leaves the amplifier having itself first passed through another pollution-stripping matrix. This last element acts on any EMI and vibration created by the speaker load, lessening the likelihood of the noise causing intermodulation in the output stage of the amplifier.

In all, it is a unique approach to EMI and vibration mitigation, unique both because it is so comprehensive, and because it uses patented passive technology quite different from conventional active filtering, or passive approaches such as LCR networks. It also presents FFT (fast Fourier transform), the industry-standard measurement technique, with a problem. Noise floors across the audio sector have crept steadily lower and lower to the point where Johnson-Nyquist noise – the unavoidable result of thermal agitation of electronic components as they are energised – becomes significant. The Quiescent T100MPA amplifiers measure well too – better than -120dB – but an interesting gotcha emerged during development when Cheadle’s team found that while FFT shows the presence of the patented quietening technology, it fails to provide metrics that track the scale of the sonic benefits it brings.

Quiescent T100MPA monoblock amplifiers https://the-ear.net

As part of the beta-testing process Quiescent pitted its stereo amplifier against alternatives that have achieved class-leading noise figures when measured with ultra-sensitive (and ultra-expensive) test equipment. In comparison, the T100SPA was heard to reveal superior tonal, dynamic, spatial and timing detail; evidence that intermodulation of the musical signal with microphony products and HF hash holds back the performance of even top-measuring conventional amplifiers. It also showed, as Cheadle notes, that a new, perhaps still to be invented measurement technique is required. For now we will just have to make do with our ears.

Disorientation

In February the Quiescent T100SPA rocked my world with its unprecedented levels of dynamic, tonal and timing detail. The T100MPA monoblocks did the same, but more so, sounding even more agile and powerful, and more tonally informative with even lower apparent levels of distortion. They are single channel of course, but otherwise feature the same power supply and gain stage design used in the stereo amplifier. All things thus being equal, the credit for the further uplift in sonic performance can only be laid at the door of the even more extensive use of Quiescent’s EMI and vibration mitigation technology.

Listening to a system powered by the T100MPA monoblocks (and to a slightly lesser extent the stereo amplifier) is initially a rather disconcerting experience. Musical events emerge from a greater depth of blackness and with more energy than we are undoubtedly used to, but what really unsettles is the comparative absence of something we might up to that point have taken for granted. We might call it ‘air’ or ‘ambience’, but we are describing a sonic halo around voices and instrumental events. It can be more apparent at some frequencies more than others, but it is generally so pervasive and present that we regard it as a natural part of the so-called high-end listening experience.

In all, it is a unique approach to EMI and vibration mitigation, unique both because it is so comprehensive, and because it uses patented passive technology quite different from conventional active filtering, or passive approaches such as LCR networks. It also presents FFT (fast Fourier transform), the industry-standard measurement technique, with a problem. Noise floors across the audio sector have crept steadily lower and lower to the point where Johnson-Nyquist noise – the unavoidable result of thermal agitation of electronic components as they are energised – becomes significant. The Quiescent amplifiers measure well too – better than -120dB – but an interesting gotcha emerged during development when Cheadle’s team found that while FFT shows the presence of the patented quietening technology, it fails to provide metrics that track the scale of the sonic benefits it brings.

The Quiescent T100MPA amplifiers reveal it to be a corruption, the product of intermodulation between the music signal and HF noise. Quiescent’s quietening technology supresses it to the point where initially we might think that the amplifiers lack openness because the halo of ‘air’ is absent. Then we then realise that we are hearing familiar recordings afresh, with a purity and completeness of tone and timing that tracks more closely than before the sound of live voices and instruments. The intriguing corollary of this is that when a recording does contain genuine recorded acoustic ambience, we hear it with a clarity that is simply arresting.

Conclusion

Once heard, the closer-to-the-truth delivery of Quiescent’s T100MPA amplifiers cannot be unheard. From that point on our senses, having been alerted to the corruption wrought by intermodulation artefacts, now home in on it wherever it occurs. We find that all other amplifiers, no matter how much or how little they cost, are more or less as prone to it. They lack the ability to effectively mitigate vibration and EMI, and so intermodulation pollution of the music signal just comes as part of the package.

Quiescent has shown the audio industry that chasing further noughts to the right of the decimal point in THD specifications only gets us so far. What’s required for the next level of performance is a focus on the damage that vibration and EMI do to the music signal. At the moment Quiescent’s approach is unique and the T100MPA is their finest work, amplification does not get much better.

Specifications:

Type: mono power amplifiers
Analogue inputs: WBT nextgen Ag silver RCA, silver conductor XLR
Speaker terminals: WBT nextgen Ag silver conductor binding posts
Grounding: M5 binding post and single-end RCA socket (signal ground)
Power output: 130W/8 Ohms, 200W/4 Ohms
Frequency response: 0.5Hz – 600kHz (-3dB)
Sensitivity: 1.6V
Gain: 26.5dB
Distortion: 0.03% at 24W into 8ohm, input 1kHz
Signal to Noise Ratio: >120dB
Dimensions (HxWxD): 140 x 440 x 400mm
Shipping weight: 31kg each
Warranty: 5 years

Price when tested:
£40,000/pair
Manufacturer Details:

Quiescent
http://www.quiescent.co.uk

Type:

monoblock power amplifiers

Author:

Kevin Fiske

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