Power amplifiers stereo — Nuprime Audio AMG PRA

The AMG PRA is the analogue preamplifier of NuPrime's AMG series, the Taiwanese-American company's compact separates range, designed to stack with the AMG STA and AMG STA-SE power amplifiers in the same slim chassis. NuPrime describes the goal as a line preamplifier that alters the signal as little as possible, and it contains no digital section.

Key specs that matter

Every input, XLR or RCA, presents 1 Mohm. There are four inputs, one balanced XLR and three RCA, and two outputs, one XLR and one RCA. Gain is switchable between 2.1 dB and 3.2 dB. Frequency response runs from 10 Hz to 200 kHz, signal-to-noise is 95 dB and THD+N is 0.008%. The chassis measures 235 x 55 x 300 mm and weighs 3.5 kg.

Engineering and use context

Signal enters through wide-bandwidth, low-noise JFETs feeding NuPrime's single-ended Class A module without negative feedback and a MUSES8920 operational amplifier. Volume is controlled by MUSES72320 electronic attenuators, keeping the number of components in the signal path low. Both polarities of the signal travel through duplicated circuits, so the design stays balanced end to end. Power circuitry sits on its own board with star-topology power and ground layers, separated from the preamplifier board by an isolation layer, and the supply uses a C-core transformer. A four-step Active Low Frequency and Harmonic Gain control adds bass extension with a gradual roll-off, intended for small bookshelf speakers, rather than acting as a simple bass boost. A front-panel toggle inverts absolute phase, and a second toggle sets gain. The front panel is milled from 15 mm aerospace aluminium alloy on a four-axis CNC machine in a 48-step process, and the remote is machined from solid aluminium. Two knobs on the front handle the bass compensation and a combined volume and input control, and a push-and-hold on the right knob puts the unit into standby. An LED indicator shows the selected input and level. Because there is no DAC, digital sources connect through an external converter, which lets the owner upgrade the digital side independently.

Pairing

The very high input impedance is a light load for any source, including valve DACs and phono stages with high output impedance. The PRA's natural partners are NuPrime's matching AMG power amplifiers, which share its footprint, but its balanced output drives any power amplifier.

Alternatives

NuPrime's HPA-9 is a headphone amplifier that also works as an analogue line preamplifier.