Zapco Z-150.4 II — 4-Channel Class AB Car Amplifier

Zapco Z-150.4 II — 4-Channel Class AB Car Amplifier

The Z-150.4 II is a four-channel Class AB amplifier from Zapco's Z-II series, rated 165 watts RMS per channel at 4 ohms, 275 watts per channel at 2 ohms, and 550 watts bridged into 4 ohms per bridged pair. Signal-to-noise is better than 100dB with THD under 0.1%, across a 15Hz to 30kHz bandwidth.

It carries the same control architecture as the two-channel Z-150.2 II, adapted for four-channel use.

Front and Rear Channels Are Not Identical

Zapco split the crossover duties deliberately. The front channels have high-pass only — no low-pass filter — because they are expected to run full-range, or handle mids and highs, or drive tweeters.

The rear channels carry the full control set of the two-channel amplifier: high-pass, low-pass, full-range, and band-pass. That lets the rear pair run full-range, handle bass, or be band-passed for midrange.

The practical result is an amplifier that can run a complete two-way active front stage on its own — tweeters on the front channels, midranges band-passed on the rear — or a conventional front-and-rear installation.

Crossover Range and the X10 Multiplier

Both filters use a frequency selector with an X10 multiplier switch that shifts the range from 15Hz–500Hz to 150Hz–5,000Hz. That span is what allows one amplifier to cover subwoofer, midbass, midrange, or tweeter duty depending on how the channels are assigned.

A Clone position on the crossover mode selector makes the front and rear crossovers identical, which is useful when all four channels are doing the same job.

2Ch/4Ch Input Switch

The Z-150.4 II adds a 2Ch/4Ch input switch, allowing the Ch1/2 inputs to feed both front and rear channels. In a system running from a head unit with only one pair of preouts, all four channels can be driven without splitters.

Inputs use Zapco's proprietary RCA connectors with pass-through outputs for daisy-chaining additional amplifiers from a single front-to-back run. Front and rear have independent variable gain controls, plus variable bass boost, a port for the optional dash-mount bass control, and power and protect LEDs.

System Application

Four channels at 165 watts into 4 ohms suits a full component front stage plus rear fill, or a two-way active front stage using all four channels. At 2 ohms each channel delivers 275 watts, and a bridged pair produces 550 watts into 4 ohms — so one pair can run a subwoofer while the other handles the front stage.

In an active DSP-based system, the onboard crossovers can be set out of the way and the filtering handled upstream.

Installation Considerations

Four ohms is the minimum load when bridging. Each channel sees half the load bridged, so a 4-ohm bridged load presents 2 ohms per channel. Do not bridge into a 2-ohm woofer.

When band-passing the rear channels for midrange, the high-pass sets the bottom of the band and the low-pass sets the top. Reversed, there is no output.

Size power and ground wire from the total fuse value of the amplifiers on the circuit and the run distance from the battery. Match ground gauge to power gauge, keep the ground short, and secure it to clean bare metal on the vehicle frame.

Specifications

• Configuration: 4-Channel, Class AB
• Power: 165W RMS × 4 @ 4Ω
• Power: 275W RMS × 4 @ 2Ω
• Power: 550W RMS × 2 bridged @ 4Ω
• Minimum bridged load: 4Ω
• Frequency response: 15Hz–30kHz
• THD: <0.1%
• Signal-to-noise ratio: >100dB
• Front channels: high-pass only
• Rear channels: high-pass, low-pass, full-range, band-pass
• Crossover: 15Hz–500Hz or 150Hz–5,000Hz via X10 multiplier
• Input: 2Ch/4Ch switch, Clone crossover mode
• Optional: dash-mount bass control (sold separately)

HF Audio Perspective

The asymmetry between front and rear channels is the detail worth understanding before buying. This is not four identical channels — it is a two-channel amplifier's worth of full crossover capability paired with two high-pass-only channels, and that shapes what it can do.

For a two-way active front stage it is well matched: tweeters on the high-pass front channels, midbass band-passed on the rear. For four channels of identical duty, the Clone setting handles it. Work out the channel assignment first, and the crossover layout will tell you whether this amplifier fits the plan.