Zapco Z-1KD II — Class D Mono Subwoofer Amplifier

Zapco Z-1KD II — Class D Mono Subwoofer Amplifier

The Z-1KD II is a Class D mono amplifier designed specifically for the subwoofer section of a car audio system. It is the first of three mono amplifiers in Zapco's Z-II series, rated 450 watts RMS at 4 ohms, 700 watts at 2 ohms, and 1,050 watts at 1 ohm.

All three Z-II monos — the Z-1KD II, Z-2KD II, and Z-3KD II — share the same endplates and the same control set. What separates them is rated output, not feature set.

Power and Impedance

Rated output changes substantially with load, so the woofer's voice coil configuration and how it is wired determine how much of the amplifier you actually use. A dual 4-ohm woofer wired to 2 ohms sees 700 watts. The same woofer wired to 1 ohm sees 1,050.

Worth deciding at the design stage rather than after the amplifier is mounted, since the wiring option is a function of the woofer you choose.

Subwoofer-Specific Controls

Zapco designed the control section of the Z-KD II amplifiers specifically to set up a bass section. The endplate carries:

• 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. In a ported enclosure it matters more, and should be set just below the port tuning frequency — below tuning, 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. Where a fixed 0/180 switch gives two options, a variable control lets you find the setting where the bass integrates with the front stage rather than working against it.

Because the low-pass crossover, subsonic, and bass boost are all adjustable at the amplifier, the bass section can be set up without a DSP in the signal path.

System Application

The Z-1KD II suits a single-subwoofer bass section in a sealed or ported enclosure, driven at 4, 2, or 1 ohm depending on the woofer and its wiring.

It works in systems with or without external processing. In a simpler build running from a factory head unit, the onboard filters handle crossover and protection duties directly. In an active DSP-based system, those filters can be set out of the way and the processing handled upstream.

Installation Considerations

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

Note the load requirement when strapping. Each amplifier sees half the load, and because 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: 450W RMS @ 4Ω
• Power: 700W RMS @ 2Ω
• Power: 1,050W 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-1KD II covers the bass section of a system across a useful range — 450 to 1,050 watts depending on wiring — with the adjustment range to integrate that bass with the front stage properly.

What determines whether it is the right choice is the woofer and the enclosure, not the amplifier's headline number. Match its output at your actual wired impedance to what the woofer is rated to handle, and the Z-1KD II gives you a bass section you can set up and tune without adding processing you do not otherwise need.