Zapco ST-1B — Mono Class AB Car Amplifier

Zapco ST-1B — Mono Class AB Car Amplifier

The ST-1B is a single-channel Class AB amplifier from Zapco's ST-B series, rated 200 watts RMS at 4 ohms and 300 watts at 2 ohms. Signal-to-noise is 90dB with THD under 0.2%, across a 15Hz to 30kHz bandwidth.

The wide bandwidth is worth noting on a mono amplifier. Many single-channel amplifiers are bass-only by design; the ST-1B's response extends to 30kHz, so its role is set by the crossover rather than by the hardware.

Controls

The input end carries RCA inputs and RCA pass-through outputs for daisy-chaining another amplifier, a variable gain control, and a crossover function selector with low-pass operation for subwoofer duty.

Set the gain to minimum before first power-up and bring it up against the source.

System Application

Two hundred watts at 4 ohms, or 300 at 2 ohms, suits a single subwoofer in a sealed or ported enclosure — the bass section of a system where the front stage is doing the primary work.

It also pairs naturally with a two- or four-channel amplifier from the same series, sharing the pass-through RCA run so one signal cable feeds both.

Installation Considerations

Final wired impedance determines available power: a dual 4-ohm woofer wired to 2 ohms sees the 300-watt rating, while the same woofer wired to 4 ohms sees 200. Decide the wiring alongside the woofer rather than after.

Size power and ground wire from the amplifier's fuse rating and the run length from the battery. Use the same gauge for ground as power, keep the ground short, and secure it to clean bare metal on the vehicle frame.

Specifications

• Configuration: Mono, Class AB
• Power: 200W RMS @ 4Ω
• Power: 300W RMS @ 2Ω
• Frequency response: 15Hz–30kHz
• THD: <0.2%
• Signal-to-noise ratio: 90dB
• Inputs: RCA with pass-through output
• Crossover: low-pass

HF Audio Perspective

The ST-1B is the bass channel for a system built around the ST-B series rather than a standalone high-output subwoofer amplifier.

Matched to a single woofer of appropriate power handling, in an enclosure designed for it, 200 to 300 watts is a complete answer for a great many systems. What decides whether it fits is the woofer and the box — check its output at your actual wired impedance against what the driver is rated to take, and the rest follows.