Hertz SP4-500 4-Channel Class D Car Amplifier

The Hertz SP4-500 is a compact four-channel car audio amplifier designed to add clean, configurable power where installation space is limited. It can operate in 4-, 3-, or 2-channel configurations, allowing it to drive a full speaker system, a front stage plus subwoofer, or bridged speakers or subwoofers. Its compact footprint makes it practical for motorcycles, under-seat vehicle installations, and behind-seat truck mounting locations.

With 90 watts RMS per channel at 4 ohms or 150 watts RMS per channel at 2 ohms, the SP4-500 is suited to aftermarket speakers that need more power and control than a factory radio can provide. Bridged operation supplies up to 300 watts RMS per pair at 4 ohms. It also supports a three-channel setup for powering two speakers and one bridged subwoofer channel.

The amplifier has a wide 10 Hz to 35 kHz bandwidth, a 100 dBA A-weighted signal-to-noise ratio, and less than 0.02% THD under its stated test conditions. Adjustable high-pass and low-pass filters on both channel pairs help tailor the signal for tweeters, full-range speakers, midbass drivers, or subwoofers. A selectable bass boost for channels 3-4 is available when their low-pass filter is engaged.

Hertz uses its ADC, or Advanced D-Class, output stage to provide efficient operation in a small chassis. The amplifier is rated for up to 85% efficiency and uses an IP55-rated aluminum chassis intended to help protect against humidity and external contaminants. Its sealed power, line-input, and speaker-output connections support installations exposed to vibration or changing conditions.

The SP4-500 accepts both preamp-level and speaker-level input signals, making it suitable for aftermarket receivers as well as many factory head units. Hertz USS, or Universal Speaker Simulators, is built into the high-level input section to support source units with speaker-load detection circuitry. The included wire-to-RCA adapters and selectable two- or four-channel input mode provide flexibility when integrating it into a new or existing system.

Key Features

• Four-Channel Flexibility: Operates in 4-, 3-, or 2-channel configurations for multiple system layouts.
• ADC Class D Output: Delivers compact, efficient amplification with up to 85% rated efficiency.
• 90W x 4 RMS: Supplies rated power at 4 ohms for aftermarket full-range speakers.
• High-Level Input With USS: Integrates with compatible factory radios using speaker-level signals.
• Adjustable Crossovers: High-pass and low-pass filters help match channels to speaker roles.
• IP55 Aluminum Chassis: Provides a compact enclosure designed for humid and demanding installations.

Design & Installation

The SP4-500 uses an IP55-rated aluminum chassis with a compact 192.7 x 130 x 49 mm footprint. Hertz specifies sealed power-cord, line-input, and speaker-output connections to help limit oxidation at connection points. The amplifier does not use an internal cooling fan, helping avoid internal dirt accumulation.

Install the amplifier in a dry, ventilated location within its stated 0°C to 55°C operating range, allowing clearance around the chassis for airflow. Use the supplied power and speaker-output harnesses, select either preamp or speaker-level input as appropriate, and set the input mode for two- or four-channel source signals. A 30A fuse is recommended on the power-supply line, positioned close to the battery positive terminal.