Clean power on every corner
80 watts to each speaker at 4 ohm, 135 at 2 ohm, or bridge to 270 watts a side. Under 0.02% distortion and a 99 dB signal to noise ratio.
4 x 80W Class D
NX125.4
Four Channels. Zero Distortion.
A compact Class D four channel that gives every factory speaker 80 clean watts, or bridges to 270 watts a side. Adjustable crossovers on both pairs, EPS high-level inputs, and a footprint the size of a paperback.
$529.95Free shipping.
Free nationwide shipping
3 year warranty included
30 day hassle-free returns
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2021 to 2026
Hi-Fi Product of the Year
100% German
Engineered and measured
3 Year
Warranty on every unit
Plug and Play
Factory-fit integration
Why drivers upgrade
Your speakers are fine. Your factory amp is not.
Factory head units push a few watts per speaker and clip early. The NX125.4 replaces that with clean power on all four corners while keeping your radio, screen, and controls.
Crossovers built in
Independent low or high pass filters on channels 1 and 2 and channels 3 and 4, adjustable from 50 to 5,000 Hz, so tweeters, mids, and a small sub each get the right band.
Fits where nothing else does
5.8 by 3.5 by 1.6 inches. Under a seat, behind a kick panel, or in the trunk corner, with auto turn-on from your factory speaker wires.
Built for the details
Full system control in a chassis that hides anywhere.
4 x 80W Class D.
80W at 4 ohm, 135W at 2 ohm, 2 x 270W bridged. Dynamic headroom to 170W per channel.
Adjustable Crossovers
Low or high pass on each channel pair, 50 to 5,000 Hz, for active or passive setups.
99 dB Signal to Noise
Under 0.02% distortion at 5W. Silent between tracks, clean at volume.
Remote Ba10 to 40,000 Hz Responsess Control
Full range from sub bass to beyond hearing for hi-res sources.
EPS High-Level Inputs
Type D inputs with error protection connect to factory speaker wires with auto turn-on.
Start-Stop Ready
Runs from 8.5 to 16.5 volts and stays stable through engine start-stop cycles.
Technical specifications
| Amplifier type | 4-channel digital Class D |
|---|---|
| Power at 4 ohm | 4 x 80W |
| Power at 2 ohm | 4 x 135W |
| Bridged at 4 ohm | 2 x 270W |
| Dynamic headroom | 170W at 2 ohm per channel |
| Frequency response | 10 to 40,000 Hz (-1 dB) |
| Signal to noise | greater than 99 dB |
| THD+N | under 0.02% at 5W |
| Input sensitivity | 425 mV to 8.0 V |
| Crossovers | low or high pass, 50 to 5,000 Hz, per channel pair |
| Operating voltage | 8.5 to 16.5 V |
| External fuse | 50 A |
| Dimensions | 5.8 x 3.5 x 1.6 inches |
| Warranty | 3 years |
| Box | 1x NX125.4 amplifier, 1x high-level input harness, 1x owner's manual, 1x mounting hardware |
| Note | A 50 A external fuse and 4 gauge power wire are recommended. Pair with the NX600.1 monoblock if you want a subwoofer channel. |
What is in the box
- 1xMusway M6 512K amplifier
- 1xPower harness
- 1xInput and output harness
- 1xUSB tuning cable
- 1xExtra 30 amp ATC fuse
- 1xMounting hardware
- 1xOwner's manual
Add the PK-RCA6 RCA input harness at checkout if you are feeding the M6 from an aftermarket head unit with RCA outputs.
Installation
Three steps from factory flat to full range.
1
Connect
Run power and ground, then plug the high-level harness into your factory speaker wires. Auto turn-on handles the rest.
2
Mount
At 5.8 by 3.5 inches it fits under a seat or behind a panel. Class D runs cool with no fan.
3
Tune
Set the front pair high pass around 80 Hz, match gains to your source, and let the rear pair run full range or bridged.
Compare
Why not just buy any four channel?
| Feature | Factory system | Generic amp | Musway NX125.4 |
|---|---|---|---|
| 80W per channel at 4 ohm | − | Varies | |
| Adjustable crossovers on both pairs | − | Varies | |
| 99 dB signal to noise | − | − | |
| Plug and play with factory wiring | − | ||
| Start-Stop ready | − | − | |
| 3 year warranty | − | Varies | |
| Compact 3.5 inch wide chassis | − | − |
Featured reviews
Drivers who stopped settling for factory sound.
★★★★★
Today's offer
NX125.4 with free nationwide shipping. 23 in stock.
Order the NX125.4 on its own, or pair it with Musway speakers or the NX600.1 monoblock so the whole system arrives in one box.
- Free nationwide shipping on every order
- 3 year warranty registered automatically
- 30 day returns if it is not the upgrade you expected
- DSP software, manual, and wiring diagrams included with your order
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QuestionsChoose your kit
Everything you want to know before you order.
Still unsure if the M6 512K fits your vehicle? Every order includes free fitment and tuning support from the Musway USA team.
Yes. The Type D high-level inputs with EPS accept factory speaker wire signals with auto turn-on, so the dash stays untouched.
Yes. Bridge channels 3 and 4 for 270 watts at 4 ohm and set the low pass around 80 Hz. For more bass add the NX600.1 monoblock.
Yes. Each channel pair has its own low or high pass filter from 50 to 5,000 Hz for active setups.
A 50 A external fuse and 4 gauge power and ground wire are recommended.
Yes. It runs from 8.5 to 16.5 volts and stays stable through engine start-stop cycles.
Return it within 30 days in its original packaging for a full refund.
Your next drive should sound like this.
Upgrade every speaker without replacing a single factory part. Free nationwide shipping, a 3 year warranty, and 30 days to decide.
30 day money back guarantee
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All reviews
Every review, straight from the driver's seat.
★★★★★
4.6 out of 5 from 86 verified reviews
NX125.4
$529.95
$529.95
