Zapco Z-2KD II — Class D Mono Subwoofer Amplifier

Zapco Z-2KD II — Class D Mono Subwoofer Amplifier

The Z-2KD II is a Class D mono amplifier built for the subwoofer section of a car audio system. It is the middle of Zapco's three Z-II mono amplifiers, rated 800 watts RMS at 4 ohms, 1,400 watts at 2 ohms, and 2,100 watts at 1 ohm.

It shares its endplates and complete control set with the Z-1KD II and Z-3KD II. The difference across the three is rated output at a given impedance.

Power and Impedance

Rated output roughly doubles as impedance halves, so the woofer's voice coil configuration and final wiring determine how much of the amplifier is available. A pair of dual 4-ohm woofers wired to a common 1-ohm load sees 2,100 watts. The same pair wired to 2 ohms sees 1,400.

Because the output range is broad, the practical question is not whether the amplifier has enough power but which wiring option matches the woofers you intend to run.

Subwoofer-Specific Controls

The control section is designed to set up and adjust a bass section at the amplifier:

• 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 what the enclosure is designed to reproduce. Zapco's guidance is roughly 25–30 Hz for a large woofer in a sealed box, and just below port tuning frequency in a ported enclosure, where the port stops loading the cone and excursion rises quickly.

The variable phase control allows the subwoofer's output to be aligned with the rest of the system, which matters more as the bass section grows — with two woofers in play, the relationship between the bass and the front stage is easier to get wrong.

System Application

The Z-2KD II suits a two-woofer bass section wired to a common load, or a single woofer rated to absorb 1,400 watts or more. It works in sealed or ported enclosures.

The onboard crossover, subsonic, and bass boost allow the bass section to be configured without external processing. In an active DSP-based system, those filters can be set out of the way and the crossover work handled upstream.

Installation Considerations

Two Z-KD II amplifiers can be strapped to drive a single voice coil. The master receives the input signal for both and feeds the slave; the only control used on the slave is its master/slave switch, and the pair then operates as one amplifier.

When strapped, each amplifier sees half the load. Since the minimum load for a single amplifier is 1 ohm, the minimum for a strapped pair is 2 ohms. Zapco specifies that two amplifiers must not be strapped to a 1-ohm load.

Specifications

• Configuration: Mono, Class D
• Power: 800W RMS @ 4Ω
• Power: 1,400W RMS @ 2Ω
• Power: 2,100W 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-2KD II covers bass sections that have outgrown a single moderate woofer — two drivers on a common load, or one driver with a high enough power rating to use what the amplifier delivers.

What decides whether it is the correct choice is the woofer count, the voice coil configuration, and the enclosure. Establish those first, calculate the final wired impedance, then check the amplifier's rated output at that impedance against what the woofers are built to handle.