Zapco REF 250.2 — 2-Channel Class AB Reference Amplifier

Zapco REF 250.2 — 2-Channel Class AB Reference Amplifier

The REF 250.2 is a two-channel Class AB amplifier from Zapco's Reference series, rated 250 watts RMS per channel at 4 ohms, 350 watts per channel at 2 ohms, and 800 watts bridged into 4 ohms. Measured at 1kHz into 4 ohms at 70% rated power, THD is under 0.02%, with A-weighted signal-to-noise better than 104dB at full power and channel separation of 63dB.

Frequency response is 10Hz to 40kHz within ±3dB.

What Those Measurements Mean

The Reference specifications are stated more rigorously than most. THD is quoted at a defined frequency, impedance, and power level rather than at an unspecified operating point, and signal-to-noise is A-weighted at full power rather than at an arbitrary reference.

The figures themselves are the point. Distortion under 0.02% and noise better than 104dB describe an amplifier engineered so that its own contribution sits well below what the rest of the system introduces — which is what a reference-grade design is for.

The 40kHz upper limit is well beyond audibility. Its practical value is that response remains flat through the audible band rather than beginning to roll off inside it.

Socket-Mounted Operational Amplifiers

The Reference amplifiers ship with MUSES8820 operational amplifiers mounted on sockets rather than soldered. They can be replaced with the higher-specification MUSES02, or with other op-amps to suit preference, without desoldering.

The original parts are surface-mount devices carried on a small PCB adapter to fit the socket. Orientation matters when fitting replacements — the marked terminal on the op-amp must line up with the marked pin on the socket. Zapco recommends the work be done by a qualified technician.

This is a genuine tuning avenue at this level, where the op-amp is one of the few remaining components that measurably shapes the signal stage.

System Application

Two hundred fifty watts per channel into 4 ohms drives a high-performance component front stage with substantial reserve. At 2 ohms it delivers 350 per channel, and bridged it produces 800 watts into 4 ohms for a subwoofer channel.

Two low-level input channels with 0.5V to 8V sensitivity and greater than 20K input impedance suit any line-level source, including processors with high output.

Installation Considerations

The amplifier operates from 9 to 16 volts with a 2 × 40A fuse rating and measures 416 × 210 × 62 mm — a full-size chassis that needs planned mounting space.

Size power and ground wire from the total fuse value and the distance from the battery. Use the same gauge for ground as power, keep the ground short, and secure it to clean bare metal on the vehicle frame.

Class AB at this output produces meaningful heat. Allow airflow around the heatsink.

Specifications

• Configuration: 2-Channel, Class AB
• Power: 250W RMS × 2 @ 4Ω
• Power: 350W RMS × 2 @ 2Ω
• Power: 800W RMS bridged @ 4Ω
• THD (1kHz, 4Ω, 70% rated power): <0.02%
• Signal-to-noise (A-weighted, full power): >104dB
• Channel separation: 63dB
• Frequency response (±3dB): 10Hz–40kHz
• Low-level input channels: 2
• Input sensitivity: 0.5V–8V · Input impedance: >20K
• Working voltage: 9–16V · Fuse: 2 × 40A
• Dimensions: 416 × 210 × 62 mm
• Socket-mounted MUSES8820 op-amps, upgradeable

HF Audio Perspective

The Reference series is where Zapco's measurements stop being competitive and start being the reason to choose the amplifier.

Distortion below 0.02% and noise better than 104dB matter in a system built around accuracy — where the drivers, processing, and installation are already good enough that the amplifier's own contribution becomes audible. In a system that is not there yet, those numbers will not be the limiting factor and the money is better spent elsewhere.

The socket-mounted op-amps are worth understanding before you buy. They mean the signal stage is not fixed at the factory, which suits a builder who intends to experiment. If that is not something you plan to do, the amplifier performs to specification exactly as it ships.