Harmony HB 104D II — 4-Channel Class D Car Amplifier

Harmony HB 104D II — 4-Channel Class D Car Amplifier

The HB 104D II is a four-channel Class D amplifier rated 100 watts RMS per channel at 4 ohms, 150 watts per channel at 2 ohms, and 250 watts bridged into 4 ohms per bridged pair. Signal-to-noise is better than 90dB with THD under 0.1%, across a 20Hz to 20kHz bandwidth.

Input impedance is 22 kilohms, and the chassis measures 170mm in length — a compact four-channel that mounts in spaces a full-size amplifier will not reach.

Four Channels in 170 Millimetres

Length is the practical specification here. At 170mm the amplifier fits under a seat, behind a panel, or in a factory amplifier location — the installations where physical dimensions decide what is possible.

Class D is what allows that footprint. The efficiency of the output stage means less heat to dissipate, so the chassis can be smaller and can tolerate an enclosed mounting position that a Class AB amplifier of the same output could not.

Load Requirements

Each channel is rated for 2 to 4 ohms, and bridged pairs for 4 to 8 ohms. Those are the useful operating ranges rather than absolute survival limits — wiring within them is what keeps the amplifier delivering its rated output rather than working against the load.

A 22-kilohm input impedance suits any standard line-level source without loading the preamp stage.

System Application

One hundred watts per channel into 4 ohms covers a component front stage plus rear fill, or a two-way active front stage using all four channels.

At 2 ohms each channel delivers 150 watts, and a bridged pair produces 250 watts into 4 ohms — so one pair can handle a subwoofer while the other drives the front stage, keeping the whole system on one compact chassis.

Installation Considerations

Bridged loads should be 4 to 8 ohms. Each channel sees half the load when bridged, so a 4-ohm bridged load presents 2 ohms per channel.

Compact amplifiers usually end up in enclosed locations. Class D produces less heat than Class AB, but give the chassis some airflow rather than sealing it into an unventilated space.

Size power and ground wire from the fuse rating and the run distance from the battery. Match ground gauge to power, keep the ground short, and secure it to clean bare metal on the vehicle frame.

Specifications

• Configuration: 4-Channel, Class D
• Power: 100W RMS × 4 @ 4Ω
• Power: 150W RMS × 4 @ 2Ω
• Power: 250W RMS × 2 bridged @ 4Ω
• Speaker load: 2–4Ω per channel, 4–8Ω bridged
• Frequency response: 20Hz–20kHz
• THD: <0.1%
• Signal-to-noise ratio: >90dB
• Input impedance: 22 kΩ
• Length: 170 mm

HF Audio Perspective

The HB 104D II is a straightforward four-channel for installations where the amplifier has to fit somewhere specific.

One hundred watts a channel is enough to drive most component sets to their intended output, so the compact format is not costing you the power the speakers actually want. Measure the mounting location first — if a full-size chassis fits and nothing is pushing you toward compact, you have more options at this power level. Where it does not, this covers a complete system, front stage and bridged bass, from a single 170mm box.