{"id":44571,"date":"2026-09-26T20:35:04","date_gmt":"2026-09-26T18:35:04","guid":{"rendered":"https:\/\/www.hifi-advice.com\/blog\/?p=44571"},"modified":"2026-09-26T21:34:07","modified_gmt":"2026-09-26T19:34:07","slug":"grimm-pa1-mono-power-amplifiers","status":"publish","type":"post","link":"https:\/\/www.hifi-advice.com\/blog\/amplifier-reviews\/phono-preamp-reviews\/grimm-pa1-mono-power-amplifiers\/","title":{"rendered":"Grimm PA1 mono power amplifiers"},"content":{"rendered":"

Review sample provided by Grimm Audio<\/a>
\nRetail price including VAT: \u20ac23.999 per pair<\/h4>\n

PA1 description<\/h3>\n

Designed by Michiel Uylings, who also designed the MU1 and PW1, the PA1 features a seemingly simple yet intriguing design that marries a classic square shape to modern asymmetrical curves, resulting in a highly elegant appearance. The cooling fins are perfectly integrated, flush with the sides and top panel, with no screws or perforations in sight. With its small 25 cm x 25 cm footprint, two of these beauties will fit side by side on most shelves.<\/p>\n

The PA1 mono-block power amplifier minimizes dynamic signal distortion that many overlook, but that greatly affects sound quality. The Grimm engineers took an ingenious amplifier concept to the next level through a meticulously optimized design that takes full advantage of modern technologies. The amplifier delivers what may seem like a modest 100 watts into 8 Ohms, but it doubles to 200 Watts into 4 Ohms, indicating a very low-impedance output and high stability.<\/p>\n

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Technical Details<\/h3>\n

One of the most striking design choices in the PA1 is its output power stage. It is a traditional \u2018Class AB\u2019 design, but with a unique twist. The output stage is a fully symmetrical circuit, with no fewer than 96(!) small, fast power transistors to achieve very high bandwidth. This technique became possible with modern aluminum printed circuit board technology, which provides extremely tight thermal coupling among all the power transistors. A special output driver circuit, mounted on the same aluminum printed circuit board, sets the quiescent current point (Bias) of the output-stage transistors.<\/p>\n

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This circuit is derived from an original design by the late Henk ten Pierick, dating back to 1985. His concept provides an extremely well-defined power-output-stage setting point, through which the impedance remains constant across the full crossover region, resulting in the lowest possible distortion of dynamic signals. The tight thermal coupling of the output-stage transistors with the driver stage ensures this ideal setting point is maintained even when large (low-frequency) currents are delivered to the loudspeaker. The PA1 name refers to Henk\u2019s genius; the \u201cPierick Amp\u201d.<\/p>\n

The importance of an extremely stable crossover region in the transfer curve can hardly be overstated, since music signals naturally contain large amounts of low-frequency content. This low-frequency content modulates the output transistors’ temperature, causing an offset from the amplifier\u2019s optimal bias via thermal runaway. Standard 1 kHz waveform THD measurements do not capture the resulting distortion because this signal’s simple and predictable nature has an even-handed effect on the transistors. However, even small changes in an amplifier\u2019s crossover-distortion footprint are audible and degrade true fidelity. The tight thermal coupling of all output devices in the PA1, combined with their clever driving circuit design, prevents such problems fundamentally \u2018by design\u2019.<\/p>\n

Another often-overlooked type of distortion is phase modulation, which occurs when the circuit’s speed varies with the audio signal’s amplitude. Like crossover distortion, phase modulation produces a distortion profile that varies across the different frequency components of the music signal. For instance, the (usually large) low-frequency components of a bass instrument can cause time smearing in the higher-frequency components of instruments and voices. In the power stage and other signal stages of the PA1, dedicated design techniques, including feedforward corrections, keep this type of distortion extremely low.<\/p>\n

With this highly optimized and fast amplifier circuitry, an appropriate amount of global feedback is applied. Grimm developed a second-order feedback loop for the PA1, which further reduces the last remnants of distortion. The very careful and unique design of this feedback circuitry \u2013 again preventing phase modulation and thermal errors in this part \u2013 further strengthens the fidelity of the amplifier.<\/p>\n

In addition, the input signal path is designed without series coupling capacitors, preventing any audio degradation of the incoming signal. A meticulously optimized multilayer PCB layout preserves input signal integrity. The input signal routing to the circuitry is kept as short as possible, as is the critical output-signal wiring. To prevent output-signal degradation, PA1’s clever protection circuitry is designed to work without relay contacts in the output signal.<\/p>\n

A large Amplimo toroidal power supply transformer ensures minimal capacitive coupling from the mains rails while providing ample current. The transformer current is buffered by a massive 90.000uF supply decoupling capacitance. In addition, the power supply to the driver and feedback circuitry is stabilized locally, ensuring stable operation independent of the output current drawn by the loudspeaker.<\/p>\n

Specifications<\/h6>\n