Diamond Audio MICRO81U Monoblock Class D Subwoofer Amplifier

One job. Done right. The Diamond Audio MICRO81U is a monoblock Class D amplifier purpose-built for subwoofer duty — delivering 300W RMS at 2 ohms or 175W RMS at 4 ohms in a chassis small enough to disappear into almost any install. If you're adding a sub to a motorcycle, boat, UTV, or a car with limited real estate, this is the amp that makes it happen without compromise.

The Class D design is the right choice for a dedicated sub amp: high efficiency means less heat, less current draw, and more usable power delivered to your woofer. The variable 40–400Hz crossover (12dB/oct) gives you a wide tuning range to dial in the rolloff point for your specific sub and enclosure, and adjustable input sensitivity (0.2–10V) handles everything from a factory head unit to a high-output aftermarket deck.

Built on the same platform as the rest of the MICRO-U series, the MICRO81U features a conformal-coated circuit board that stands up to moisture, salt air, vibration, and dust. That makes it a real option for marine audio builds, motorcycle installs, ATVs, UTVs, and any outdoor application where a standard amp would eventually fail. The all-weather rating isn't a checkbox — it's baked into the design.

Selectable REM, VOX, and DC turn-on modes keep integration simple whether you're working with a factory source unit or a full aftermarket setup. Selectable 2CH or 4CH input modes add flexibility for different signal configurations, and the 10Hz–33kHz frequency response ensures the amp isn't the limiting factor in your low-end extension.

At 9.1" x 4.1" x 1.46", the MICRO81U fits in spaces where a conventional monoblock simply won't. Same footprint as the MICRO84U — so if you're building a mixed system, the amps stack and mount cleanly together.

Key Features

• 1-channel monoblock Class D amplifier
• 300W x 1 @ 2Ω / 175W x 1 @ 4Ω RMS
• Conformal-coated PCB — all-weather rated for marine & powersports
• Variable 40–400Hz crossover (12dB/oct)
• Adjustable input sensitivity: 0.2–10V
• Selectable REM / VOX / DC turn-on modes
• Selectable 2CH / 4CH input modes
• Compact chassis: 9.1" x 4.1" x 1.46" — same footprint as MICRO84U
• RCA input & speaker output harness kits included