Zapco ST-105D — 5-Channel Class D Car Amplifier

Zapco ST-105D — 5-Channel Class D Car Amplifier

The ST-105D is a five-channel Class D amplifier from Zapco's ST-D Compact series — four full-range channels plus a dedicated subwoofer channel. It is rated 80 watts RMS × 4 plus 200 watts on the subwoofer channel at 4 ohms, and 130 watts × 4 plus 300 watts at 2 ohms. Signal-to-noise is better than 90dB with THD under 0.1%, across a 20Hz to 20kHz bandwidth.

The chassis measures 262mm net and 303mm overall, by 124mm wide and 50mm tall.

A Complete System From One Chassis

Five channels covers front stage, rear fill, and subwoofer from a single amplifier — one power run, one ground, one mounting location. In vehicles where space or electrical capacity is limited, that consolidation frequently decides the system design.

The subwoofer channel at 200 watts into 4 ohms or 300 into 2 is genuinely useful output, not a token fifth channel.

Three Filter Modes

The ST-105D offers low-pass, high-pass, and flat filter modes across a 35Hz to 250Hz range. The flat position takes the crossover out of the signal path entirely, which matters when an external processor is handling the filtering and the amplifier should not add a second stage of it.

Input sensitivity is separately specified for the two sections: 0.4 to 13V on channels 1–4 and 0.2 to 9V on channel 5, with input impedance of 12K on low and 50 ohms on high. Different ranges for the main and subwoofer channels reflect that factory sources often deliver those signals at different levels.

System Application

Eighty watts per channel drives a component front stage and rear speakers, with the fifth channel handling a single subwoofer at 200 to 300 watts depending on wiring.

Two channels can also be bridged at 250 watts into 4 ohms where the layout calls for it.

Installation Considerations

Bridged loads must be a minimum of 4 ohms.

The amplifier operates from 9.5 to 16.5 volts with a 40A fuse rating. Size power and ground wire from that fuse value and the distance from the battery, match ground gauge to power, keep the ground short, and secure it to clean bare metal on the frame.

Set the input sensitivity ranges independently for channels 1–4 and channel 5 — they are specified separately for a reason, and matching each to its source makes gain setting far more straightforward.

Specifications

• Configuration: 5-Channel, Class D
• Power: 80W RMS × 4 + 200W × 1 @ 4Ω
• Power: 130W RMS × 4 + 300W × 1 @ 2Ω
• Power: 250W RMS × 2 bridged @ 4Ω
• Minimum bridged load: 4Ω
• Frequency response: 20Hz–20kHz
• THD: <0.1%
• Signal-to-noise ratio: >90dB
• Filter mode: low-pass / high-pass / flat
• Filter frequency range: 35Hz–250Hz
• Input impedance: 12K (low), 50Ω (high)
• Input voltage: 0.4–13V (Ch 1–4), 0.2–9V (Ch 5)
• Working voltage: 9.5–16.5V · Fuse: 40A
• Dimensions: 262 / 303 × 124 × 50 mm

HF Audio Perspective

Five-channel amplifiers trade flexibility for integration, and whether that is the right trade depends on the vehicle more than the specification.

Where one power run and one mounting location matter — a daily driver, a lease, a vehicle with a stock electrical system — the ST-105D covers a complete system cleanly. The flat filter mode is worth noting if you plan to add a DSP later: it lets the amplifier step out of the crossover role entirely rather than fighting the processor. Where the subwoofer stage is likely to grow well beyond 300 watts, separate amplifiers leave more room to expand.