– Drew Kalbach, The Absolute Sound
I don’t have a ton of experience with NuPrime, but here’s a quick, high-level history lesson: The company was founded back in 2014 by Jason Lim, the former CEO of NuForce, and it specializes in boutique Class D amps, media streamers, and many other products. I was very excited to get a nearly complete system of its AMG STA power amplifier and AMG PRA preamp. The amp and preamp combination have the same form factor and were clearly designed to work in tandem. While I’m a fan of mixing and matching equipment from a wide range of manufacturers, there’s something special about listening to the products from a single line, and getting a sense of how they work in tandem.
Diving in, the NuPrime AMG STA ($1695) is a sleek, compact Class D power amplifier with a Class A preamp stage and linear power supply. The chassis is simple, with only a metal switch on the front for power, a small white LED indicator, and the NuPrime logo. My review sample came in dark gray, and looked good in my relatively tight equipment rack.
As power amps go, the AMG STA never gets overly hot—likely a product of its very efficient Class D output module—though it does get somewhat warm. The back is relatively cramped, and it took a little contortion to get everything hooked up, but that didn’t matter much once it was plugged it and powered on. The power amp supplies a solid 130Wpc into 8 ohms in stereo mode and 300Wpc into 8 ohms in mono mode. That’s one of my favorite features of the PRA—its ability to work as either a single stereo amplifier or in tandem with a second STA as part of a monoblock setup.
The AMG PRA ($1795) looks almost exactly like the AMG STA power amp—sorry for the vaguely confusing names—but with two knobs and an LED indicator for channel and volume setting on the front panel. The left knob controls the unit’s loudness compensation feature, which is something I’ll talk about in a second. The right knob plays a bigger role—push and hold for standby mode, push briefly to select inputs, and turn to adjust volume. Two toggles on the front switch between high and low gain and between normal and inverted phase. On the back, the PRA includes one set of balanced inputs and three unbalanced RCAs, along with a balanced and unbalanced out. The remote is heavy enough to break a toe if dropped and seems to be milled from solid aluminum; it performed all the functions I could possibly want—from power to volume control to input switching. Overall, the PRA’s design is simple, but attractive and effective.
Before I dive into listening, it’s time to look at the “Active Low Frequency and Harmonic Gain” control feature. To put it very simply, this knob is somewhat like Ye Olde Loudness switch of yore. When turned on it very noticeably boosts bass, without increasing the overall volume. It is an interesting EQ effect, and definitely achieves NuPrime’s stated goal of giving smaller speakers a bit more natural low end. It worked well with my Wharfedale 225s, and actually sounded fairly nice with my Omen Dirty Weekend on its lowest setting. However, through the Polk L600 (review forthcoming), the knob made the bass a little too flabby, which makes sense. (The L600 have a very deep low end, and compensating made the bass a little too intense.) Each setting on the knob is a different EQ curve, and it may be worth experimenting with them to find the one that works best in your setup. For the following review, I kept the knob turned to the left, which turns the feature off.
First up, I plugged in a single AMG STA amplifier with the AMG PRA preamp. (I was sent two STAs by NuPrime, so I did half my listening with one, and half with the dual-mono setup.) The single STA was more than enough to power my Zu Omen Dirty Weekends, and made my copy of the recent Ray Charles vinyl reissue Genius + Soul = Jazz sing and scream and shout. Lows were suitably solid, and the midrange really shone with an extremely pleasant smoothness. I never felt as though the AMG STA lagged behind or ran out of headroom powering the Zu DWs, even on this very dynamic recording. Ray Charles sounded fantastic, and his organ really grooved in tight and exciting lines.
After trying the Zu DWs, I gave the Polk L600s a shot in the single AMG STA configuration. The Polk speakers are much more difficult to drive than the Zu DWs, but the STA still had plenty of space and headroom to blast through those fiery Ray Charles licks. I decided to try the Analogue Productions vinyl reissue of the RCA release Witches’ Brew to see how it handled something dynamic that might stress its capabilities a bit. Even at its loudest, biggest moments, when the orchestra swells and cymbals crash, I never felt as though the AMG STA was lagging behind, even powering the difficult L600s. The low end was deep and slammed—not quite razor-sharp but not flabby, either. The midrange had an ease to it, a nice, relaxed presentation. Horns were sharp and evenly spaced, and their upper registers had a bit of sparkle. Of the two speaker pairs I tried out, I’d say the single AMG STA worked best with the Zu DWs, likely because they’re easier to drive, but also because they share a similar sound profile—relaxed, with a delightful midrange, a decently solid lower end, and a shimmery treble.
I switched over to the dual-mono setup next, which gave me a solid 300Wpc into 8 ohms. That’s way more than enough for the Zu Omen DWs, since they’re easy to drive, but I liked the limitless-feeling headroom that the dual-mono combination bought me. I didn’t find it necessarily sounded better, just more centered and solid, with no straining or restraint. Where this dual-mono configuration really worked was with the Polk L600s, the more difficult pair of speakers to drive. The AMG STA retained its signature relaxed and easy sound, but with that much power on tap really opened up the full potential of the Polks. The backgrounds were shockingly black, and it almost felt as if the AMG PRA preamp was nearly transparent, if you’ll forgive a reviewing cliché. That deep noise floor allowed the music to shine with a crispness and dynamism that I absolutely loved.
Sticking with the dual-mono setup and the L600s, I put on the Tone Poets vinyl reissue of My Point of View by Herbie Hancock. The tune “King Cobra” opens the B-side, and it features Tony Williams at only 17 years old showing off all his incredible potential, with dancing cymbals that really sparkled through the STA/PRA combo. Williams’ fills sounded exuberant and rhythmically complex, and the system never compromised or slowed down his fascinating drumming. In the midrange, the piano and horns were smooth and silky with a hint of nice, heavy warmth down in their lower regions. Hancock’s solo was quick and slithering, like the song’s namesake, and each note was clearly delineated. Attacks and decays were on point, which added to the whole rhythmic picture building throughout the song. When the horns massed for the theme, each instrument remained wholly itself and focused, creating a wide sense of soundstage. The STA/PRA dual-mono combo worked very well with the L600s, since the speakers have a very solid and deep lower end, and the amp/preamp shines in the lower registers. It was that deep heft that really brought a difficult song like “King Cobra” to life, and leant the entire ensemble a massive sound.
Next up, I listened to Iceage’s most recent album Seek Shelter,streamed via Tidal. On the opening track, “Shelter Song,” the fuzzy guitar had a solid growl, while the deep kick drum slammed. The choir added depth and texture without ever straying into chaos. There was a surprisingly strong sense of place and positioning. Despite the sheer number of sounds occurring at the same time, I could still pinpoint each voice and instrument, and I think the monoblocks’ massive amount of headroom went a long way to allowing the weight of the song to shine through. Later on the record, on the hard-rocking banger “Saint Cecilia,” the heavy guitars and screaming solos and choral shouts built into really epic, room-encompassing crescendos. The low end felt solid and intense, while the upper range of the twanging guitar had genuine dazzle. Overall, I felt the PRA/STA combo played very nicely with some serious rock and roll.
I really enjoyed the NuPrime AMG PRA preamplifier and the AMG STA power amplifier. I didn’t waste any time hand-wringing over Class D, and barely even mention it in my review—for good reason. The STA/PRA combination sounded great, with a heavy low end, a relaxed and pleasant midrange, and just enough sparkle in the upper end to make cymbals shimmer. The interesting loudness function on the PRA and the very nicely made remote control were the kind of simple but useful upgrades over a standard preamp that made this combination feel premium. For many folks, I suspect a single STA will provide enough power, but for those who have more difficult-to-drive speakers, or those who want a massive amount of power on tap and ready to go, the monoblock setup is fantastic. This is a system worth trying and comes highly recommended.