Nakamichi NHMD100.4 4-Channel Class-D Amplifier - Compact Efficiency

Experience efficient, cool-running power with Class-D technology—ultra-compact amplifier delivers 125W x 4 in just 48mm height and 1.4kg weight.

Product Overview

The Nakamichi NHMD100.4 is a professional 4-channel Class-D amplifier engineered for maximum efficiency, minimal heat generation, and exceptional space savings. Delivering 125W x 4 RMS at 2-ohm loads or 100W x 4 at 4-ohm loads using advanced Class-D switching technology, this amplifier produces less heat than traditional Class A/B designs while maintaining audiophile-grade performance across the full 20Hz-20kHz frequency range. The bridgeable design allows 200W x 2 configuration for high-power applications. With adjustable sensitivity (0.15-8V), less than 0.1% THD distortion, and greater than 90dB signal-to-noise ratio, the NHMD100.4 delivers clean, powerful audio in an ultra-compact 222 x 120 x 48mm package weighing just 1.4kg—among the smallest and lightest 4-channel amplifiers available. The efficient Class-D design reduces electrical load on vehicle charging systems while minimizing heat output, allowing installation in tight spaces with limited ventilation. Perfect for Australian drivers seeking professional speaker amplification in utes, sedans, SUVs, and 4WDs without the thermal management challenges, space consumption, or weight penalties of traditional amplifiers.

Key Specifications

• Professional 4-channel Class-D amplifier
• 125W RMS x 4 at 2Ω (500W total)
• 100W RMS x 4 at 4Ω (400W total)
• Bridgeable: 200W RMS x 2 at 4Ω
• 2500W maximum total power output
• Full-range frequency response: 20Hz - 20kHz
• Greater than 90dB signal-to-noise ratio (A-weighted)
• Less than 0.1% total harmonic distortion
• Adjustable input sensitivity: 0.15V - 8V
• Ultra-compact dimensions: 222 x 120 x 48mm
• Lightweight construction: 1.4kg
• Class-D topology (high efficiency, low heat)
• Cool-running operation

Features & Benefits

Class-D Efficiency Advantage: Advanced switching amplifier technology operates at 80-90% efficiency compared to 50-60% for Class A/B—wastes less energy as heat, reducing thermal load on vehicle electrical systems and allowing installation in locations with limited ventilation like under seats, behind panels, or tight enclosures without overheating concerns during Australian summer conditions.

Ultra-Compact Dimensions: At 222 x 120 x 48mm and just 1.4kg, this is among the smallest and lightest 4-channel amplifiers available—fits under seats with minimal clearance, behind door panels, in side trim areas, glove boxes, or other tight spaces where standard amplifiers won't accommodate, preserving cargo space in utes and wagons.

Reduced Electrical Load: Class-D efficiency means less current draw from battery and alternator for same power output—125W x 4 performance with electrical consumption comparable to 75W x 4 Class A/B amplifier, ideal for vehicles with modest alternators, older electrical systems, or when running multiple accessories like lighting, fridges, or communication equipment simultaneously.

Cool-Running Operation: Minimal heat generation eliminates need for large heatsinks, active cooling fans, or extensive ventilation—allows mounting in enclosed spaces, under seats, or behind trim panels without thermal protection shutdowns common in Class A/B amplifiers during extended high-volume use on long Australian highway drives or outback touring.

Powerful Speaker Amplification: Four channels delivering 125W RMS each at 2Ω provide substantial power for component speakers, coaxial speakers, or full-range systems—significant upgrade from factory headunit power (typically 15-25W), ensuring speakers reach full dynamic potential with improved clarity, bass control, and maximum volume.

Bridgeable Configuration: Connect channels in bridged mode for 200W x 2 at 4Ω—ideal for powering high-performance front component speakers requiring more power or rear fill speakers in systems with separate subwoofer amplification, providing installation flexibility as audio systems evolve.

Low Distortion Performance: Less than 0.1% THD ensures clean amplification without audible distortion—maintains audio quality at all volume levels during extended listening sessions without listening fatigue, proving Class-D technology delivers audiophile performance, not just efficiency benefits.

Adjustable Input Sensitivity: Wide 0.15-8V sensitivity range accommodates factory headunits with low voltage outputs and aftermarket headunits with high-voltage pre-outs—allows proper gain matching for balanced system performance preventing distortion or weak output.

Technical Specs

• Type: 4-channel automotive amplifier
• Amplifier Class: Class-D (high-efficiency switching design)
• Total Channels: 4 (full-range)
• Power Output at 2Ω: 125W RMS x 4 (500W total)
• Power Output at 4Ω: 100W RMS x 4 (400W total)
• Bridged Power at 4Ω: 200W RMS x 2 (400W total)
• Maximum Power Output: 2500W peak
• Frequency Response: 20Hz - 20kHz (full audible range)
• Signal-to-Noise Ratio: Greater than 90dB (A-weighted)
• Total Harmonic Distortion: Less than 0.1%
• Input Sensitivity: 0.15V - 8V (adjustable)
• Input Impedance: Not specified (verify from documentation)
• Load Impedance: 2-4Ω per channel
• Crossover: Built-in high-pass and low-pass (verify specifications)
• Bass Boost: Verify from product documentation
• Remote Level Control: Verify compatibility
• Fuse Rating: Not specified (verify from documentation)
• Operating Voltage: 12V DC nominal (10.5-16V range typical)
• Dimensions (L x H x W): 222mm x 120mm x 48mm
• Net Weight: Approximately 1.4kg
• Box Dimensions: 295mm x 218mm x 75mm
• Gross Weight: Approximately 2.5kg (with packaging)
• Cooling: Minimal heatsink (Class-D efficiency)
• Connections: RCA inputs (channels 1-4), speaker outputs
• Protection: Short circuit, thermal, DC offset (typical features)

Frequently Asked Questions

What's the advantage of Class-D amplifiers over Class A/B?

Class-D amplifiers operate at 80-90% efficiency vs 50-60% for Class A/B—less energy wasted as heat means cooler operation, reduced electrical load, smaller size, lighter weight, and ability to install in tight spaces without ventilation concerns. Modern Class-D delivers audiophile sound quality previously only from Class A/B while providing significant practical advantages.

Will this ultra-compact amplifier provide enough power for my speakers?

At 125W x 4 RMS (2Ω), this amplifier provides substantial power for most aftermarket speakers. Perfect for Nakamichi NSA-CS1721 components (70W), NSE1658 coaxials (55W), or NSE6958 6x9" speakers (75W). The compact size doesn't compromise power—Class-D efficiency allows high output from small package.

Does Class-D amplification affect sound quality compared to Class A/B?

Modern Class-D amplifiers like the NHMD100.4 deliver audiophile-grade sound quality with <0.1% THD and >90dB SNR—specifications matching or exceeding quality Class A/B amplifiers. Early Class-D had audible artifacts, but current technology eliminates these issues. Most listeners cannot distinguish between quality Class-D and Class A/B in blind testing.

What electrical system requirements does this amplifier have?

Class-D efficiency reduces electrical load compared to equivalent Class A/B—approximately 50-60A draw at maximum output despite 500W total power. Use minimum 8-gauge power cable with appropriate fuse. Most factory alternators (80A+) handle this easily. Efficiency advantage particularly beneficial in vehicles with modest electrical systems.

Where can I mount this ultra-compact amplifier?

The 222 x 120 x 48mm dimensions and 1.4kg weight allow mounting virtually anywhere: under front seats, behind door panels, behind dash, in glove box area, side trim panels, or boot corners. Class-D cool-running operation eliminates ventilation concerns that limit traditional amplifier mounting locations.

Compatible With / Goes Well With

Ideal Speaker Systems:

• Nakamichi NSA-CS1721 6.5" components (70W, front channels)
• Nakamichi NSE1658 6.5" 3-way coaxials (55W, all channels)
• Nakamichi NSE1648 6.5" coaxials (40W, all channels)
• Nakamichi NSE6958 6x9" speakers (75W, rear channels)
• Nakamichi NSE1318 5.25" coaxials (25W, all channels)
• Most aftermarket 6.5" speakers rated 60-125W RMS

Subwoofer Addition Options:

• Nakamichi NBX251A 10" active sub (separate, built-in amp)
• Nakamichi NBX25M 10" active sub (separate, lightweight)
• Nakamichi NBS210A compact active sub (separate, remote)
• Upgrade to NKTA750.5 5-channel if want single amp solution

Essential Installation Accessories:

• 8-gauge amplifier wiring kit (power, ground, remote)
• Inline fuse holder (appropriate rating, verify)
• RCA audio cables (4-channel: 10-16 feet)
• Speaker wire (14-16 gauge, adequate lengths)
• Ground wire and ring terminals
• Wire management ties and loom
• Amplifier mounting brackets or board

System Enhancement Products:

• Digital sound processor (advanced tuning)
• Line output converter (if using factory headunit)
• Voltage meter (electrical monitoring)
• Bass remote control (if compatible)
• Sound deadening (improved audio quality)

Recommended Headunits:

• Aftermarket headunits with 2-4V pre-out voltage
• Digital media receivers with EQ control
• Apple CarPlay/Android Auto headunits
• Factory headunits (with line output converter)
• 4-channel pre-out headunits

Caution: Verify mounting location for secure installation of 1.4kg amplifier. Even though Class-D runs cool, ensure adequate airflow for any amplifier. Secure mounting prevents movement during driving. Professional installation recommended for proper electrical integration, gain adjustment, and optimal performance.

Weight

1.4kg (net), 2.5kg (with packaging).