NuPrime STA-9 Stereo Amplifier

Class A+D Stereo Amp bridgeable into a 290W mono amp

The NuPrime STA-9, a 2 X 120W Class A+D stereo amp, bridgeable into a 290W mono amp, is designed with enhanced even-order harmonic circuitry that mimics the most attractive features of tubed-amp sound without incurring tubes’ drawbacks and limitations. The STA-9's spacious, transparent, dynamic and luxuriously textured soundstage has to be heard to believe.

The STA-9 amplifier is derived from the ULCAM (Ultra Linear Class A Module)+Class D design first introduced in the IDA-8. By joining a powerful high impedance singled ended amplifier circuit in the preamp stage with a well integrated Class-D power stage, the STA-9 delivers a rich tube-like sound with the remarkable speed and clarity of NuPrime Class-D design. Audio enthusiasts are bound to be impressed.

The NuPrime amp circuit improves on traditional Class-D design by using a self-oscillating circuit to generate pulse-width modulation. The amplifier switches at a frequency of 550kHz, well beyond the compact disc’s 44.1kHz sampling rate. Most class-D amps switch at 300kHz or lower. Completing the ensemble is NuPrime's new linear power supply with its high-efficiency toroidal transformer for reduced high-frequency noise and strengthened low-frequency performance. The damping effect of the NuPrime isolation feet (patent pending) absorbs and cancels vibrations that degrade audio performance. The overall result is unprecedented transient speed and an almost shocking level of dynamic impact.

The STA-9's frequency response to 50 kHz elevates vocals into emotional experiences; similarly, instrumental upper registers mimic a live performance’s shimmering heights.

Features:

  • Single End Class A + D amplifier design
  • Bridgeable allowing switch between stereo or mono mode.
  • Enhanced even-order harmonic (H2) circuitry resembling the most attractive features of tubed-amp sound without its drawbacks and limitations.
  • Highly reliable under no-load condition and enhanced short circuit protection.
  • High output current drive capability for low impedance speakers.
  • 550 KHz switching frequency for accurate reproduction of musical signal.
  • New linear power supply with a high-efficiency toroidal transformer. Reduced high-frequency noise and strengthened low-frequency performance.
  • Signal path avoids cross-linking capacitors, thus achieving a frequency response at DC level for pure musical enjoyment.

How did STA-9 achieve tubed-amp sound?
The front-end circuit of the STA-9 employs the same structure as that of the HPA-9: a single-end JFET structure that mainly simulates the sound characteristics of a triode by the addition of 2nd harmonics. The 2nd harmonic of a vacuum tube and STA-9 are high, resulting in an SNR measured value > 90DB. This does not mean that the STA-9 produces audible noise; rather, it is the effect of 2nd harmonic's appealing coloration.
The bandwidth of the front-end circuits of the STA-9 and HPA-9 are up to 300KHZ, which produce a more natural sound. With very low negative feedback, the sound is smooth and relaxed rather than harsh.

How did STA-9 mono achieve better sonic characteristic, in addition to more power than STA-9 stereo ?
The standard method for bridging a stereo amp into mono employs a series of op amps (OPA) in order to invert the input signals to one of the stereo amp, thereby creating an opposite phase, which can then be combined to increase power. Conversely, the STA-9's innovative bridging circuit utilises a design we call Single-Ended Direct-Inject Bridge Technology, in which the mono mode, in addition to acquiring more than double the power, sounds livelier and more dynamic.

The NuPrime Sound

  • Vast soundstage
  • Wide, lightning-fast dynamics
  • Ultra-low distortion and noise
  • Music emerges from a pristine background, with delicate details and nuances intact

In summary, NuPrime’s sonic character stands well apart from – and indeed above – the soft, cushy sound we often associate with most tubed amplification or the dry, clinically edgy sound we often associate with solid-state and switching technology. Rarely does an amp achieve an ideal balance of richly textured timbres and harmonics, bottom-end authority, startling dynamics, exquisite low-level detail, and a fully revealed, fully dimensional soundstage against a backdrop of mile-deep silence.

Specifications:

Inputs: RCA: Un-Balanced input x 1 XLR: Balanced input x 1  
Outputs: Stereo Speaker Out x 1 or Mono Speaker Out x 1  
Power: 2 X 120W / 1 X 290W @ 8 & 4 Ohms Peak Output Power: 2 X 280W / 1 X 320W @ 8 & 4 Ohms
Input Impedance: 47k Ohms Input sensitivity: 1.5Vrms at 120W 8ohm
Gain: 22db Signal to Noise Ratio: < -95dB at 1W, 10W, 100W
THD+N: 0.02% (Stereo) / 0.01% (Mono) Frequency Response: 10Hz to 50kHz
Worldwide AC voltage: (115 VAC / 230 VAC) with Voltage Select Switch AC Fuse: Slow-blow, 3A, 250VAC
Dimension: 235 mm W x 281 mm D x 55 mm H (including feet) Weight: 4.75 kg
Color: Black or Silver    

In a 110V outlet, the idle-power consumption is below 14W. In a 230V outlet, the idle-power consumption is below 16W.

Frequently Asked Questions

MCH-K38 front panel buttons and LED lights

The buttons on the front panel are toggle on/off switch. 

Power button:  Red means Standby and Green means power on.  No Light means AC power switch off.

Channel 1 ~ 8, Red light means the source is set to XLR and Green means the source is set to RCA.  No Light means the channel is turn off.

The light in between 1 & 2, 3 & 4, 5 & 6, and 7 & 8 are Mono indicators.  Red light also means the source is set to XLR and Green means the source is set to RCA.  No Light means the channel is turn off.  The mono channel can be toggled on/off with channel 2, 4, 6, & 8. 

Please make sure to press the buttons to turn on the channels.  Since our stereo lights are very small LED on the button top, so it might be easy to miss if its put inside the rack.

What some of the amps have the same power rating at 8 and 4 Ohms ?

There is two side to a coin. The truth is that the amp is capable of more power than the spec suggested. So if 4 and 8 Ohms are specified at 100Wx2, that means the power supply is a 200W PSU. And we are extremely conservative about our power rating (we provide conservative RMS rating, not peak power). A customer reported 180W for IDA-8 because he is using just one channel to do the measurement. So, if IDA-8 is in a bigger case, and we put in a 300W PSU, you will see a higher rating. In reality, you get more than 100W per channel from the 200W PSU, because not both channels are driven at the same time.

Why don't we put in a bigger PSU? Each model is designed for specific product position and adding more power will certainly increase the cost and size of the product.

Can the amplifier's speaker terminals be used as source inputs (e.g. to REL Subwoofer) ?

In some applications, the speaker outputs from the power amplifier are used as source signals for devices such as REL sub woofer. For such application, usually the receiving devices should have DC offset blocking capability because some amplifier by design has floating ground (DC offset) on the speaker outputs. 

The following models have no DC offset on the amplifier speaker outputs and the negative terminal is also the ground:

NuPrime STA-9, MCH-K38, IDA-16

The following models' speaker outputs can not be connected directly to sub woofer input:

NuPrime Reference 20, ST-10, IDA-8

What kind of trigger cable can be used for your products?

When a device has a 12V trigger input, it is designed to be turned on when a 12V is detected. You can use any standard male to male 3.5mm (3-pin type) cable.