Grimm Audio PA1 Monoblock Power Amplifier

Wide-bandwidth class-AB circuitry, 200 W into 4 ohms, and exceptionally low dynamic distortion

The Grimm Audio PA1 is a compact monoblock power amplifier designed to minimize forms of dynamic distortion that conventional measurements can overlook. Its fully symmetrical class-AB circuit delivers more than 150 W into 8 ohms and more than 200 W into 4 ohms, with the current capability and low output impedance required to maintain control over demanding loudspeakers.

The PA1’s output stage is an evolution of a circuit developed by the late Henk ten Pierick in 1985. Its name stands for “Pierick Amp.” The design uses 96 small, fast power transistors mounted on an aluminum circuit board that provides extremely close thermal coupling between the output devices and their driver circuit. This arrangement maintains a stable operating point as loudspeaker current and transistor temperature change, minimizing residual crossover distortion and other errors that vary with the music signal.

Designed for Low Dynamic Distortion

Dedicated circuit techniques, including feed-forward correction, reduce phase modulation throughout the PA1’s power and signal stages. Grimm Audio then applies a carefully designed second-order feedback loop to address the small amount of distortion that remains. The result is a measured total harmonic distortion of less than 0.0001% and a damping factor greater than 800 into 8 ohms.

The input signal path contains no series coupling capacitors, while multilayer circuit boards keep critical signal paths short. The protection system is designed without placing relay contacts in series with the amplified output signal. A large Amplimo toroidal transformer and 90,000 µF of power-supply capacitance provide ample current, while separate local regulation isolates the driver and feedback circuitry from changes in loudspeaker demand.

Flexible Gain and Automatic Operation

The PA1 provides balanced XLR and unbalanced RCA inputs, selected by a rear-panel switch. Its standard 26 dB gain setting suits most preamplifiers, while the 18 dB setting accommodates high-output preamplifiers, professional converters, and systems using high-sensitivity loudspeakers.

A selectable automatic power mode switches the PA1 on when it detects an input signal and returns it to low-power standby after approximately 40 minutes of silence. Thermal, DC-offset, short-circuit, and clipping protection help safeguard the amplifier and connected loudspeakers.

Features

• Fully symmetrical class-AB monoblock design
• More than 150 W into 8 ohms and 200 W into 4 ohms
• 96 fast output transistors mounted on an aluminum circuit board
• Close thermal coupling minimizes residual crossover distortion
• Feed-forward correction reduces phase modulation
• Second-order global feedback circuit
• No series coupling capacitors in the input signal path
• Linear power supply with a large Amplimo toroidal transformer
• 90,000 µF of power-supply capacitance
• Balanced XLR and unbalanced RCA inputs
• Selectable 18 dB or 26 dB gain
• Selectable automatic on/standby operation
• Extensive thermal, DC, short-circuit, and clipping protection
• Designed and made in the Netherlands
• Five-year limited warranty with registration

Specifications

Amplifier Type: Monaural class-AB power amplifier

Inputs: 1 x balanced XLR; 1 x unbalanced RCA

Input Impedance (XLR): 33 kΩ

Input Impedance (RCA): 16 kΩ

Gain: 18 dB or 26 dB, selectable

Output Power (8 Ohms): >150 W

Output Power (4 Ohms): >200 W

Output Impedance: <10 mΩ

Damping Factor (8 Ohms): >800

Frequency Response: 0.1 Hz–300 kHz

Signal-to-Noise Ratio (1 W, 8 Ohms): 96 dB

Signal-to-Noise Ratio (150 W, 8 Ohms): 118 dB

THD (1 W, 8 Ohms): <0.0001%

THD+N (1 W, 8 Ohms): -96 dB

Speaker Connections: Binding posts compatible with bare wire, spade connectors, and 4 mm banana plugs

Operating Power Consumption: 65–600 W

Standby Power Consumption: <5 W

Dimensions (W x D x H): 9.8" x 9.8" x 9.4" (250 x 250 x 240 mm)

Weight: 33.1 lb. (15 kg)