NuPrime STA-9 Power Amplifier

One Amplifier, or Half a Pair of Monoblocks

The STA-9 does two jobs. As a stereo amplifier it makes 120 watts per channel. Bridged to mono it makes 290 watts, and a pair of them becomes a monoblock rig.

That flexibility is the point of buying one. Start with a single STA-9 driving both speakers, and if the system grows, add a second and run them as monoblocks instead of selling the first.

The design is Class A+D: a Class A input stage feeding a Class D output stage. NuPrime tunes the input circuit for even-order harmonics, which is the part of tube sound most listeners actually want, without the heat, the bias or the retubing.

Inside the Chassis

THD+N measures 0.02% in stereo and 0.01% in mono, with signal-to-noise better than 95dB at 1, 10 and 100 watts. Frequency response runs 10Hz to 50kHz, and dynamic range spans 115dB at 1kHz.

Input impedance is 47k ohms, which NuPrime notes should suit virtually any preamplifier, and both balanced XLR and unbalanced RCA inputs are fitted. Gain is 26.85dB in stereo and 32.46dB in mono.

A linear power supply with a high-efficiency toroidal transformer sits behind it, and the switching frequency is 600kHz. The whole amplifier is 235mm wide and weighs 4kg. NuPrime covers it with a 1-year warranty.

What Reviewers Are Saying

The Absolute Sound named the STA-9 an Editors' Choice in its Power Amplifiers Under $1,000 category, published 29 March 2018. "Producing 120Wpc and weighing just under 10.5 pounds, the STA-9 uses a Class A input circuit along with a Class D output circuit," the citation reads.

On the mono option it was specific: the amplifier is "easily bridgeable into 290Wpc monoblocks, and its 47k-ohm input impedance should work with virtually any preamplifier." In monoblock mode, TAS found, "the STA-9 produced powerful bass, even with small KEF speakers."

Who Is This Amplifier Best For?

• Your system is going to grow — one STA-9 is a 120-watt stereo amplifier; two are 290-watt monoblocks. The upgrade path costs you a second purchase rather than a trade-in.
• You want tube character without tubes — the Class A input stage is tuned for even-order harmonics, which is the part of tube sound people actually want, with no bias to set and nothing to retube.
• Space is tight — 235mm wide and 4kg means it fits a desk, a shelf or a cupboard, and it runs cool enough to sit somewhere with little air around it.
• Your preamplifier is unusual — 47k ohms of input impedance and both XLR and RCA inputs mean it sits behind almost any preamp, valve or solid-state, without loading it down.
• You want a preamp voiced alongside it — PRA-9X supplies the volume and the input switching for this power stage

How Does It Connect to Your System?

Connect your preamplifier by balanced XLR or unbalanced RCA. Speakers go to the stereo outputs. If you are running two STA-9s as monoblocks, use the mono speaker output on each and set them to bridged mode first.

Short-circuit protection is built in, and the amplifier is stable with no load connected, so a mistake during setup will not damage it.

Pairs Well With

Here are some great companions:

• Preamplifier: Required, and the natural next decision — see our Preamplifiers.
• Speaker Cables: Carry the current properly — see our Speaker Cables.
• Interconnects: Balanced XLR is the better run from preamp to amp — see our Interconnect Cables.
• Audio Rack: Give the amplifier a proper shelf — see our Audio Racks.

Frequently Asked Questions

How much power does it make?

120 watts per channel into 8 ohms in stereo. Bridged to mono, one STA-9 makes 290 watts.

Can I use two as monoblocks?

Yes, and that is the usual upgrade path. Each bridges to 290 watts of mono, so a second unit doubles the system rather than replacing the first.

What does Class A+D mean?

A Class A input stage feeding a Class D output stage. NuPrime tunes the input circuit for even-order harmonics, which is the character tube amplifiers are known for.

Does it take balanced inputs?

Yes. One balanced XLR pair and one unbalanced RCA pair, at 47k ohms input impedance.

How big is it?

235mm wide, 281mm deep and 55mm high, weighing 4kg, in black or silver.

What warranty does it carry?

NuPrime covers the STA-9 with a 1-year warranty.

See It in Action

Machina4K reviews the NuPrime STA-9:

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Want to learn more about power amplifiers, bridging an amplifier to mono, or building a separates system? Visit our Learning Center for guides, tips, and expert advice.