Zapco Z-3KD II — Class D Mono Subwoofer Amplifier

Zapco Z-3KD II — Class D Mono Subwoofer Amplifier

The Z-3KD II is a Class D mono amplifier for the subwoofer section of a car audio system, and the highest-output of Zapco's three Z-II mono amplifiers. It is rated 900 watts RMS at 4 ohms, 1,800 watts at 2 ohms, and 3,000 watts at 1 ohm.

It shares its endplates and complete control set with the Z-1KD II and Z-2KD II.

Power and Impedance

The Z-3KD II's rated output separates most clearly at low impedance. At 4 ohms it produces 900 watts; at 2 ohms, 1,800; at 1 ohm, 3,000. The gap between the top two ratings is larger than the gap between the bottom two.

That makes final wired impedance the central planning question for this amplifier. A bass section designed to present a 1-ohm load uses the full rated output, while a 4-ohm load draws on a smaller portion of it.

Subwoofer-Specific Controls

The control section is the same across the Z-II mono line:

• RCA inputs
• Gain/sensitivity control
• Variable subsonic filter
• Variable low-pass crossover frequency control
• Variable bass boost
• Variable phase control
• Port for the optional dash bass control
• Master/slave switch for strapping
• RCAs for master output and slave input
• Power (green) and protect (red) LEDs

The subsonic filter protects the woofer from frequencies below the enclosure's usable range — roughly 25–30 Hz for a large woofer in a sealed box, and just below port tuning in a ported enclosure. At this output level that setting carries more weight, since excursion below tuning increases with the power available to drive it.

The variable phase control allows the subwoofer's output to be aligned with the rest of the system, letting you find the setting where the bass integrates with the front stage.

System Application

The Z-3KD II suits multiple subwoofers on a common low-impedance load, or a single competition-grade woofer rated to handle the output. It is a high-output bass amplifier, and the system around it — woofer power handling, enclosure design, and electrical capacity — needs to be specified accordingly.

As with the rest of the line, the onboard filters allow the bass section to be configured at the amplifier, or set aside in favour of upstream DSP processing in an active system.

Installation Considerations

Two Z-KD II amplifiers can be strapped to drive a single voice coil, with the master feeding the slave and the pair operating as one amplifier.

Each amplifier sees half the load when strapped. With a 1-ohm minimum per amplifier, the minimum for a strapped pair is 2 ohms, and Zapco specifies that two amplifiers must not be strapped to a 1-ohm load.

Electrical capacity is a real consideration at this output level. Sustained operation near rated power draws current accordingly, and the vehicle's charging system, battery, and power and ground cable should be sized for it.

Specifications

• Configuration: Mono, Class D
• Power: 900W RMS @ 4Ω
• Power: 1,800W RMS @ 2Ω
• Power: 3,000W RMS @ 1Ω
• Minimum load: 1Ω (2Ω strapped)
• Frequency response: 10Hz–350Hz
• THD: <0.1%
• Signal-to-noise ratio: >90dB
• Controls: gain, subsonic, low-pass crossover, bass boost, phase, master/slave
• Optional: dash bass control (sold separately)

HF Audio Perspective

The right amplifier is the one that fits the job. The Z-3KD II is built for bass sections that present a low-impedance load and have the woofer count or power handling to use 3,000 watts.

Because its rated output scales sharply with impedance, this is an amplifier worth selecting after the bass section is designed rather than before. Once the woofers, voice coil configuration, and final wired impedance are settled, the rated output at that impedance tells you whether the Z-3KD II is matched to the job or whether another amplifier in the line fits it better.