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.
- 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.