Zapco Z-150.4 AP — 4-Channel Class AB Competition Amplifier

Zapco Z-150.4 AP — 4-Channel Class AB Competition Amplifier

The Z-150.4 AP is a four-channel Class AB amplifier from Zapco's AP competition series, rated 150 watts RMS per channel at 4 ohms, 275 watts per channel at 2 ohms, and 400 watts per channel at 1 ohm. Bridged it produces 550 watts into 4 ohms or 800 watts into 2 ohms per bridged pair. THD is under 0.1% with signal-to-noise better than 110dB, across a 10Hz to 30kHz bandwidth.

It carries the AP series measurements across four channels rather than two.

Four Channels at a 110dB Noise Floor

The noise specification is what distinguishes this from a conventional four-channel. Better than 110dB across all four channels means the amplifier stays out of the way in an active system where four separately filtered signals are being reproduced.

In a two-way active front stage — tweeters on one pair, midbass on the other — that matters, because any noise or distortion the amplifier adds appears in a band where the driver is working alone rather than masked by the rest of the range.

Low-Impedance Operation and Its Limits

The Z-150.4 AP runs to 1 ohm per channel and 2 ohms bridged, with Zapco's qualification attached.

Those ratings apply with music signal. Sustained output is limited by heat dissipation rather than by the load. Where the heat cannot escape, the amplifier goes into protection, and repeated protection cycles can damage it.

With four channels in one chassis the thermal load is concentrated, so mounting location and airflow deserve attention before committing to low-impedance operation.

System Application

One hundred fifty watts per channel into 4 ohms suits a two-way active front stage using all four channels, or a component front stage with rear fill.

A bridged pair at 550 watts into 4 ohms lets the rear channels drive a subwoofer while the front pair handles the stage — a complete system from one chassis at competition measurements.

Installation Considerations

Four ohms is the minimum load when bridging for the standard rating; the 2-ohm bridged figure carries the music-signal qualification above.

Four channels of Class AB produces sustained heat. Mount where air can reach the heatsink rather than in a sealed location.

Add up the fuse values, size power and ground wire from that total and the distance from the battery, match ground gauge to power, keep the ground short, and secure it to clean bare metal on the frame.

Specifications

• Configuration: 4-Channel, Class AB
• Power: 150W RMS × 4 @ 4Ω
• Power: 275W RMS × 4 @ 2Ω
• Power: 400W RMS × 4 @ 1Ω (music signal)
• Power: 550W RMS × 2 bridged @ 4Ω
• Power: 800W RMS × 2 bridged @ 2Ω (music signal)
• THD: <0.1%
• Signal-to-noise ratio: >110dB
• Frequency response: 10Hz–30kHz

HF Audio Perspective

Four channels at AP measurements is aimed at an active front stage where each driver is amplified and filtered on its own channel.

That is where a 110dB noise floor is worth paying for — an active system exposes the amplifier in a way a passive one does not. Where the system is a conventional four-speaker install running full range, the measurements are still real but much of what the amplifier offers goes unused, and a less specialised four-channel would serve the same purpose. Decide the architecture first; the amplifier follows from it.