NuPrime STA-9X Stereo Power Amplifier, Silver

The NuPrime STA-9X is a compact stereo power amplifier in Class-A+D technology that can be bridged by switch into a powerful mono power amplifier.

It turns a small footprint into a lot of control: 2 × 130 watts, 330 watts in mono mode, and all from a chassis that fits easily next to your router. If you believe a serious power amplifier has to be as heavy as an anvil, it is time to rethink.

Why the STA-9X?

The STA-9X combines a single-ended Class-A input stage, which according to NuPrime emphasizes even-order harmonics, with a Class-D output stage with dual feedback. It switches at 750 kHz – around twice as high as many other Class-D designs – and thereby keeps distortion well away from the audible range. Fast, clear, unexcited – three qualities you would also wish for in a good relationship.

NuPrime positions the 9X series for compact systems with natural sound and fair value for money. The STA-9X stands in it under the motto “Power that grows with you”: first one power amplifier in stereo operation, later a second one added and both bridged as mono – then it is 330 watts per unit.

What you get

• ✅ 2 × 130 W, mono 330 W: Stereo into 8 and 4 Ω (RMS), or bridged via the stereo/mono switch as a mono power amplifier with 330 W into 8 and 4 Ω – significantly more punch.
• ✅ Class-A input, Class-D at 750 kHz: The high switching frequency pushes typical Class-D distortion out of the audible range – fast transients, clear treble.
• ✅ Toroidal linear power supply: Classically built power supply instead of a switch-mode supply – a calm foundation for the fast amplifier.
• ✅ XLR and RCA: Balanced and unbalanced input, suitable for practically any preamp.
• ✅ Mono-capable for later: Stereo today, a second unit tomorrow – two STA-9X make a genuine monoblock pair.
• ✅ 12 V trigger on/off: Switches on and off cleanly with the rest of the system, ideal for tidy setups.
• ✅ Isolation feet: Purpose-developed feet keep vibrations away from the chassis and thus out of the sound.

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Who is the STA-9X suited for?

For anyone who wants to add a serious, space-saving power amplifier to their preamp or integrated amplifier with pre-out – and for anyone who wants to keep a clean upgrade path to mono power amplifiers open. Also a slim, fast solution in an active or bi-amping setup.

Honestly: The STA-9X is a pure power amplifier without volume control – without a preamp or an integrated amplifier with pre-out, nothing happens here. 2 × 130 W is plenty for the vast majority of speakers; with extremely low-impedance, power-hungry speakers in stereo operation it eventually reaches its limits – then mono mode with two units is the answer. If you are looking for a tube power amplifier, this is the wrong place: the STA-9X sounds fast and controlled, not romantic – even though NuPrime describes the Class-A input stage as emphasizing even-order harmonics.

Our verdict

The STA-9X is our insider tip for anyone looking for a lot of power amplifier in little space. At HD Zürisee in Wädenswil we value it because it stays quiet and controlled and still grips firmly – and because it offers an honest upgrade path with the later move to a pair of monoblocks. The trade press sees it similarly: according to NuPrime, the magazine Stereo included the DAC-9X and STA-9X in its Best Buy Components 2023 (result in January 2024), and HiFi-IFAs certified that the combination with the DAC-9X needs no audiophile elitism.

Technical specifications

• Amplifier type: Class-A input stage (single-ended) + Class-D output stage with dual feedback, 750 kHz switching frequency
• Power supply: Toroidal linear power supply
• Power (RMS): 2 × 130 W (stereo) / 1 × 330 W (mono, bridged) into 8 & 4 Ω
• Peak power: 2 × 170 W / 1 × 370 W into 8 Ω
• Inputs: 1 × RCA (unbalanced), 1 × XLR (balanced), trigger in 12 V
• Outputs: Stereo speaker, mono speaker, trigger out 12 V
• Operating mode: Stereo/mono switch
• Input impedance: 47 kΩ
• Output impedance: 20 mΩ
• Gain: 29.1 dB
• Signal-to-noise ratio: > 90 dB (at 1 W / 10 W / 100 W)
• THD+N: 0.005 %
• Frequency response: 10 Hz – 50 kHz
• Mains voltage: 115 / 230 VAC switchable; fuse slow-blow 3 A / 250 V
• Dimensions (W × H × D): 235 × 55 × 281 mm
• Weight: 4 kg
• Colour: Silver
• What's in the box: STA-9X stereo power amplifier, power cable, quick start guide

FAQ

How much power does the NuPrime STA-9X have?
In stereo operation the STA-9X delivers 2 × 130 W into 8 and 4 Ω. Bridged by switch it works as a mono power amplifier with 330 W. That is clearly enough for the vast majority of speakers; for particularly power-hungry speakers, two units can be combined as a monoblock pair.

Can I run two STA-9X as mono power amplifiers?
Yes. Each STA-9X can be bridged by switch into mono mode and then delivers 330 W. With two units you drive each speaker with its own power amplifier – this noticeably improves channel separation, control and spatial imaging. A clean, step-by-step upgrade path.

Do I need a preamp for the STA-9X?
Yes. The STA-9X is a pure power amplifier without volume control. You need a preamp or an integrated amplifier with pre-out. It combines well, for example, with a NuPrime preamp or a DAC with volume control. We will help you find the right match.

Does the STA-9X suit my speakers sonically?
The STA-9X sounds fast, controlled and clear – it rewards precise, dynamic speakers. NuPrime describes the Class-A input stage as emphasizing even-order harmonics, but that does not make it a substitute for a tube power amplifier. Whether it suits your speakers, your room and your listening taste, we are happy to assess together with you.

Why buy the NuPrime STA-9X at HD Zürisee?
Because we know which preamps and speakers the STA-9X thrives with – from practice, not just from the data sheet. You get personal advice from Andy and Maurizio, service through our own technician and support with setup and the mono upgrade. Reachable by phone, WhatsApp or in Wädenswil.

Goes well with

The STA-9X is the power stage of the chain – the rest grows with it step by step:

• Preamp: The STA-9X has no volume control. A preamplifier from the same series as the PRA-9X takes care of level, phono and headphones; if you listen purely digitally, take a DAC with volume control such as the DAC-9X.
• Digital: With a streamer such as the Stream 9X you add network and streaming services – DAC behind it, STA-9X at the end of the chain.
• Expansion: A second STA-9X, both bridged as mono, gives 330 W per side. No rebuild, no throwing away: the first unit stays, the second is added.
• Speakers: Speakers that appreciate fast, precise drive.
• Connection: Cables & connectors – XLR if the preamp can do it, otherwise RCA.
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