The Kicker KPX300.4 is a 4-channel powersports amplifier built specifically for motorcycles and other space-compromised installs — a 4-lb, compact-footprint design that fits under a fairing where a marine-style amp never would. It delivers 45W RMS per channel at 4-ohm (75W at 2-ohm, 150W bridged), and it's $299.99.
This isn't a marine amp, and it's not trying to be one. Every amplifier we've reviewed so far in this catalog — the KMA600.4 and KMA360.4 — was sized for a boat console cavity. The KPX300.4 is sized for the space under a motorcycle fairing, which is a completely different design problem.
Key Takeaways
- The KPX300.4 is purpose-built for motorcycles and space-compromised powersports installs — a compact, 4-lb footprint that fits under a fairing, not a boat console.
- Power output is 45W RMS per channel at 4-ohm, noticeably lower than either marine amp we've reviewed — intentional, sized to match motorcycle electrical systems rather than a boat's battery and alternator.
- It's weather-resistant, explicitly not fully waterproof — a real distinction from the ASTM-tested marine amps in this catalog, and appropriate for its actual use case.
- At $299.99, it costs more than either marine 4-channel amp despite lower power output — you're paying for compact engineering and low current draw, not raw wattage.
- It pairs closely with the Kicker PSM handlebar speakers' 50W RMS rating at the same 4-ohm impedance.
Built for Space You Don't Have
A boat console has room most motorcycles simply don't. The KPX300.4 is engineered around that reality: a genuinely compact footprint, 4 pounds total, specifically designed to fit under a motorcycle fairing rather than in a dedicated equipment bay.
That's not a minor spec — it's the entire premise of the product. If you've ever tried to find amp mounting space on a motorcycle, you already know the marine-style amps in this catalog (the KMA600.4 at 6.7 lbs, 16 inches long) simply won't fit anywhere on a bike. The KPX300.4 solves a mounting problem the marine amps were never built to solve.
Check current price and dimensions →
Weather-Resistant, Not Waterproof — And Why That's Actually Fine Here
Every marine amp in this catalog carries specific ASTM UV and salt-fog testing, built for an environment where the equipment sits exposed to spray and humidity constantly. The KPX300.4 doesn't make that same claim — it's described as weather-resistant, explicitly not fully waterproof.
That's a real, honest distinction worth understanding rather than glossing over. A motorcycle amp mounted under a fairing isn't taking direct spray the way a boat-mounted amp does; it needs to handle rain and general weather exposure, not sustained saltwater contact. Weather-resistant construction is the appropriate spec for this use case, not a corner cut — but if you're expecting the same marine-grade waterproofing as the KMA-series amps, this isn't rated to that standard, and you shouldn't mount it somewhere it'll take direct water exposure.
Power Output, and Why Less Can Be More Here
At 45W RMS per channel into 4-ohm (75W at 2-ohm, or 150W bridged to 2-channel), the KPX300.4 puts out meaningfully less power than either marine amp we've reviewed. That's not a shortcoming — it's sized to match what it's actually being asked to do.
Kicker specifically frames this amp as built “without taxing your charging system,” and that framing matters more here than it does in a marine context. A motorcycle's electrical system is a fraction of a boat's battery and alternator capacity. An amp that draws current like a full-size marine unit would be a real problem on a bike; the KPX300.4 is deliberately right-sized to avoid that, not underpowered by accident.
Pairing with the Kicker PSM Speakers
Since the KPX300.4 and the PSM handlebar speakers are both built for the same ATV/motorcycle use case, the pairing math is worth spelling out directly: the PSM is rated 50W RMS at 4-ohm per speaker, and the KPX300.4 delivers 45W RMS per channel at 4-ohm. That's a close, comfortable match — slightly under the PSM's rated maximum, which means headroom in your favor rather than a mismatch.
Four channels means you can run two pairs of PSM speakers off a single KPX300.4, or two speakers plus a bridged channel pair for something else, depending on how you're building out the system.
Building a handlebar-speaker system? See the PSM review for mounting details →
Installation Notes
The compact footprint is the whole point here, but Kicker doesn't publish detailed mounting dimensions or hardware specifics for the KPX300.4 the way it does for the marine amps — confirm exact measurements against your available space before ordering rather than assuming based on the “compact” description alone.
For wiring, the lower power draw here means you're not dealing with the same gauge requirements as a marine sub or high-power speaker run. Our marine speaker wiring guide's general gauge principles still apply even though it's written for marine installs — at 45W RMS per channel, a 16 AWG baseline is more than sufficient.
Where It Falls Short
Not fully waterproof. Weather-resistant, not marine-grade sealed. Mount it somewhere protected from direct water exposure, not out in the open the way you might a marine amp.
Lower power than the marine amps. If you're expecting KMA600.4-level output, this isn't that amp — it's intentionally scaled down for motorcycle electrical systems, not a bigger build.
Amplifier class not specified. Unlike the KMA600.4 (Class D) and KMA360.4 (Class A/B), Kicker doesn't publish the amplifier class for the KPX300.4 in its listing.
Costs more than either marine amp despite less power. $299.99 for 45W RMS per channel is a real premium over the KMA360.4's $239.96 for 65W RMS per channel — you're paying for the compact, motorcycle-specific engineering, not for more output.
1-year warranty, consistent with the rest of the amps and electronics in this catalog, not the 3-year coverage on Kicker's KM speaker lineup.
Frequently Asked Questions
Is the KPX300.4 a marine amplifier?
No. It's built specifically for motorcycles and other space-compromised powersports installs, not boats. It's weather-resistant but not rated to the same marine-grade waterproofing as Kicker's KMA-series amps.
Will the KPX300.4 fit under my motorcycle fairing?
Kicker markets it specifically for that use case, with a compact 4-lb footprint, but doesn't publish exact mounting dimensions — confirm your available space before ordering.
What speakers pair well with the KPX300.4?
The Kicker PSM handlebar speakers are a close match: 50W RMS rated at 4-ohm against the amp's 45W RMS per channel at the same impedance, comfortably within range.
Why does the KPX300.4 cost more than Kicker's marine amps if it's less powerful?
You're paying for the compact, motorcycle-specific engineering and low current draw designed not to tax a motorcycle's smaller electrical system, not for raw power output.
Is the KPX300.4 fully waterproof?
No. It's described as weather-resistant, not fully waterproof — appropriate for its typical mounting location under a fairing, but not rated for the same direct water exposure as a marine amp.
Bottom Line
The Kicker KPX300.4 solves a problem the marine amps in this catalog were never built to solve: finding amp space on a motorcycle. At 45W RMS per channel, it's not trying to match a boat amp's output — it's sized specifically to work within a motorcycle's electrical system and physical space constraints, and it pairs cleanly with the PSM handlebar speakers at nearly identical power ratings.
It's not the right choice if you're expecting marine-grade waterproofing or KMA600.4-level power — for either of those, look at the marine amp lineup instead. But if you're building out audio on a motorcycle or ATV and need something that actually fits, this is engineered for exactly that constraint.