Hertz HDP4 Digital Power Series 4 Channel Amplifier

The Hertz HDP4 is a four-channel Class-D amplifier from the Hertz Digital Power series, rated 150 W RMS x 4 at 4 ohm and 250 W RMS x 4 at 2 ohm, that drives speakers from either a factory head unit through its high-level Speaker-In inputs or an aftermarket source through its RCA Pre-In inputs.

Key Benefits

• Runs as four, three or two channels: 150 W RMS x 4 at 4 ohm, 250 W RMS x 4 at 2 ohm, or 500 W RMS x 2 bridged at 4 ohm, so one chassis can cover a full stage or a stage plus a subwoofer.
• Speaker-In high-level inputs accept the speaker wiring from a factory radio, so no line-output converter is needed on a stock-head-unit build.
• ART automatic remote turn-on senses signal on the Speaker-In inputs and powers the amplifier up and down with the source, removing the need for a remote turn-on wire on OEM installs.
• Two independent crossover sections: the A channels run Full, Hi-Pass or Lo-Pass over 50 to 5,000 Hz and the B channels over 80 to 3,300 Hz, both at 12 dB/octave.
• Class-D output stage is 2 ohm stable on all four channels, so it holds up on dual-voice-coil and paralleled speaker loads.
• Rated 0.08 percent THD at 100 Hz into 4 ohm with a 100 dB A-weighted signal-to-noise ratio.
• Compact for the power: 11.18 x 6.73 in footprint and a 1.83 in profile at 5.4 lb.

Fitment

The HDP4 is a universal 12-volt amplifier rather than a vehicle-specific part. It suits any negative-ground 12 V system running 11 to 15 VDC, which covers cars, trucks, SUVs, side-by-sides and UTVs. Because it accepts high-level Speaker-In signal at 1.4 to 24 V RMS as well as 0.3 to 5 V RMS RCA Pre-In signal, it integrates with a factory radio or an aftermarket deck without an adapter.

Plan the electrical side around the published numbers: the amplifier carries two 40 A blade fuses on board and draws up to 50 A at 2 ohm on maximum musical power, so size the battery feed and the in-line fuse near the battery accordingly. Minimum load is 2 ohm per channel in four-channel mode and 4 ohm bridged.

Hertz does not publish an IP or salt-fog rating for the HDP4, so treat it as a dry-location amplifier and mount it where it is protected from spray and standing water. If the install is open to the weather, look at the marine-rated Hertz HCP 4M instead. Within the Hertz range, the HDP4 is the four-channel Digital Power model; the HDP1 is the mono subwoofer amplifier from the same series, and the smaller Compact Power HCP 4D and HCP 4DK are the shorter-chassis four-channel alternatives.