– Philippe Daussin, qobuz.com
Translated from French.
The achievements of the manufacturer NuPrime enjoy an excellent reputation, including its digital amplifiers, including this STA-9 model with power stages using a brand design and preceded by class A gain stages, all providing excellent sound results, which should reconcile the supporters of opposing opinions on the amplification classes!
Before giving birth to NuPrime and Encore Audio, NuForce already imposed its quality in the world of digital amplifiers with, for example, the STA-100 which we rewarded in its time with a Qobuzissime.
But while this NuForce amplifier used International Rectifier integrated circuits driving the cutting transistors, NuPrime’s STA-9 abandons this structure for a self-oscillating circuit designed by the brand and preceded by a class A gain stage, its also grown, and realized in discrete components, thus offering a mix of the best of analog amplification with a switching power amplification already appreciated on the previous model ST-10.
This STA-9 amplifier is intended by its design to be the ideal companion of the DAC-9 which has been the subject of a recent test bench Qobuz and which can function as a preamplifier.
The casing of the NuPrime STA-9 amplifier is entirely made of black or silver satin aluminum and takes up the sober and elegant design adopted for a while by the brand and whose upper and lower edges of the facade are bevelled. Only a discreet blue LED power indicator brings a touch of light to the smooth uniformity of the facade.
The input of stereo analog signals will be either in unbalanced mode on Cinch sockets or in balanced mode on three-pin XLR sockets, by tilting the upper switch. The one below will make it possible to operate the STA-9 in monophonic mode in bridged mode, the input then being made on the lower Cinch socket, the loudspeaker then being connected to the upper terminals.
NuPrime has chosen to supply current to the amplification stages of the STA-9 with a linear power supply whose large toroidal transformer can be seen at the opening of the case. This has two 110V primary windings which will be put in series for operation on a 220V mains voltage and in parallel for a 110V mains voltage by moving the selector located under the case, and powered through a mains filter shielded.
Two 40V mid-point secondary windings capable of delivering a high current to supply the power stages are filtered, after rectification by a molded diode bridge, by two groups of two 2200 μF/80V Audio-Grade capacitors manufactured to specifications. NuPrime fillers.
Each of these capacitors is doubled with a lower value model, stamped NuForce, but whose capacitance is not indicated, presumably to improve dynamic behavior by reducing the (low) parasitic series resistance inherent in high value capacitors (called ESR or equivalent series resistance, in English).
Another secondary winding of 9V is used to make the voltage of +5V (seen below, lower left part), via an adjustable regulator LM317G (U3), to supply the relays and the indicator diode on the front.
Two other midpoint 15V secondary windings, with lower current capacity, will be used to power the gain stages. The filtering of the rectified voltages is ensured by high value electrochemical capacitors (not indicated) stamped NuForce. These voltages will be stabilized at ±15V by LM317G (U2) and LM337 (U4) regulators, followed by 1000 μF/25V electrochemical capacitors.
Below are the gain stages (Ultra Linear Class A Module) each of which uses two NPN FMMT489 Zetex transistors and two PNP FMMT589 (and no Fet as can be seen in the NuPrime schematic). The output stage works in real class A single end with an FMMT589 transistor mounted as a constant current generator in the collector of an MFFT489 transistor.
The phase inversion of the right channel signals for operation in bridged mode seems to be carried out by the two transistors that can be seen in the bottom of the display, just above the anti-copy marking.
Then come the class D amplification stages of NuPrime design, self-oscillating at a frequency of around 600 kHz, i.e. double that usually used by specialized circuits. The chopping transistors are IRFI4020H dual MosFets from specialist International Rectifier, mounted on a cooler which they share with two TIP31C bipolar power transistors, likely involved in the oscillation circuit with the chokes and capacitors that are on the other side of the cooler.
The filtering of the signals from these class D amplification stages is carried out by components mounted directly on the wires going to the terminal blocks for the loudspeakers and protected by heat-shrink tubing, components among which one can recognize the form of wound chokes.
As the NuPrime STA-9 amplifier forms a particularly homogeneous pair with the DAC-9, of which we very recently produced a test bench, it is this configuration that we have chosen to carry out our listening. The playback of audio files was entrusted to the Foobar2000 player in Kernel Streaming mode (bit perfect) and the speakers connected to the STA-9 were our usual Triangle Antal Anniversary.
When listening, there is no need to wait for hours to realize that the sound quality of the NuPrime STA-9 amplifier is of a high standard and this is evident from the first bars of the Sanctus of the Solemn Mass of Sainte Cécile extracted from the very nice album Meditation by Elína Garanča where all the depth of this sacred work is perfectly highlighted by the STA-9 which lets the music unfold with ease in a wide sound space where it is not necessary to push the volume to obtain an orchestra ample and present, while the voice of the soloist Elína Garanča is well defined and relatively soft, even during passages where she must show vehemence.
We also enjoy listening to excerpts from Vespri per l’Assunzione di Maria Vergine by Vivaldi by Rinaldo Alessandrini conducting the Concerto Italiano where the extreme vivacity of the STA-9 works wonders on the attacks of the strings which show no trace of harshness, while we also notice a very good differentiation of the instrumental groups, both in the musical flow than in space and that one cannot really say that it is the impression of power which dominates when one teases the volume a little, but that of great ease and breathing of the music.
Now, let’s panic the membranes of the woofers of our Triangle speakers a little with the titles North Star and Silent Space from the single Tale Of Us and their cataclysmic bass. Nay, it is not so, no panic of the membranes of the boomers despite the debauchery of watts sent to the speakers, the STA-9 firmly holds the boomers which send decibels in the bass like they have never sent and the rest of the spectrum, even if it is quite reduced on these titles, is not even disturbed!
With the title Paradis Perdus from the album Human warmth of Christine and the Queens, we still notice the very good definition of the singer’s voice, well nuanced, and which is in no way affected by a powerful and firm restitution of the low register, even at high level.
In conclusion, with the STA-9, NuPrime offers us an amplifier with a refined aesthetic and offering excellent sound performance thanks to exclusive and high-performance electronics, earning it our Qobuzissime award.
Link to the review --> https://www.qobuz.com/fr-fr/magazine/story/Hi-Res-Guide/Bancs-d-essai/Amplificateur-NuPrime-STA-9178808/