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2003 Harley Davidson FLSTSI Heritage Springer

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Use our shopping filters to find the right 2/3/4-channel amp to power upgraded speakers properly.

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Amps for Adding Speakers for 2003 Harley Davidson FLSTSI Heritage Springer

Some vehicles require an amp bypass module, a line-output converter like the NVX XLCA2 or AudioControl LC2i, or a DSP to integrate with your factory radio and avoid bass roll-off. Bass roll-off occurs when a factory radio's crossover is designed only for the original equipment speakers, resulting in a not complete signal being sent to your new aftermarket amp.

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Number of Channels
Each channel on an amplifier will power one speaker using a positive and negative cable. There are various types of amplifiers, each designed to power a certain number of speakers. Monoblock amplifiers, also known as single channel, are designed to power one or more subwoofers. These amplifiers often have very high power ratings. On the other hand, multi-channel amplifiers power multiple speakers, usually at lower power ratings. 2-Channel and 4-Channel amplifiers can power car speakers or low powered subwoofers. Occasionally you might see a 5 or 6-channel amplifier that can power speakers and subwoofers at the same time. The most common setup is a monoblock amp to run subwoofers and a 4-channel amp to run door speakers. Check out our Knowledge Base for more information.
Amplifier Key Features
Amplifiers can offer a diverse array of features. If you select more than one feature, then you will view amplifiers that have ALL features selected. These include speaker-level inputs that facilitate seamless integration with factory audio systems, Bluetooth connectivity suitable for ATV/UTV or Classic vehicle setups, built-in DSPs that provide enhanced control over your audio signal, and a host of other functionalities to explore.
Amplifier Class

An amplifier increases the power of the signal being fed to it by taking energy from its power supply and matching the signal but increasing its amplitude. Amplifiers use many different methods for converting these electrical signals and have been categorized into classes.

Class A/B: Greater than 50% of the input signal is amplified while the other percentage is “off”. These amplifiers have a small amount of current flowing through the output transistors all the time which almost eliminates crossover distortion. Class A/B has great sound quality but is not as efficient as class D. These amps are most commonly used to drive speakers.

Class D: Also known as switching amplifiers, class D amps have output transistors that are completely turned “on” or “off”. This means that when the transistors are on, there is almost no voltage across them but when they are off there is significant voltage but no current flowing through it which makes these amplifiers very efficient at the cost of sound quality. These amps are most commonly used to drive subwoofers.

Other Classes: You may see classes such as GH, bD, X, FD, etc. by some manufactures. These amplifiers tend to be either class A/B, D or a hybrid of the two but with improvements to their designs that can make them more efficient or offer better sound quality.
Total RMS Power Output
Total RMS power is measured by multiplying RMS power per channel by the number of channels, and is calculated at the lowest level of operating impedance.

RMS power is the amount of continuous power, measured in watts, that an amplifier produces is called RMS power. The higher the RMS figure, the louder and cleaner your music sounds.

The RMS output figure is much more accurate than the peak rating when comparing products.
Total Peak Power Output
The total peak power output is measured as the wattage per channel multiplied by the number of channels, and is calculated at the lowest level of operating impedance.

It is measured during a brief musical burst, such as a sudden drum accent. Some manufacturers display peak power ratings on the face of their products to increase the appeal.

The RMS power rating is more accurate, and we recommend using it for product comparison.
Series
Many brands group their products into series or lines of products to help customers know the level of quality (good, better, best for example). You can filter by series and the brand using our guided browsing.
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Minimum Impedance Unbridged
The lowest impedance the amplifier will handle when it is not bridged.
Minimum Impedance Bridged
The lowest impedance the amplifier will handle when it is bridged.
Remote bass/level controller
If the amp comes with a bass/gain remote you will be able to control the level of your bass from your dashboard. Typically bass remotes also include a 16-20 ft. wire for installation.
Sonic Certified Amplifier
Sonic Certified amplifiers have been tested by the experts at Sonic Electronix to meet or exceed the wattage ratings provided by the manufacturer. If this is marked as Yes, then you can trust the wattage ratings. If marked as No, then we have tested the amplifier and it did not meet the advertised wattage ratings. If marked as Not Tested, then the Sonic Electronix experts have not yet been able to test the amp.
Preamp Outputs
Many amplifiers are equipped with RCA preamp outputs which pass the original music signal from the source to additional amplifiers. This is known as daisy chaining because the source connects to the first amp, and the first amp connects to the second amp, etc. The advantage to daisy chaining is you only need one 2-channel RCA cable to transfer the signal from the head-unit to the amplifier, and then one additional cable for each amp being daisy chained.
Built-in Crossover

A crossover is a type of filtering system that permits only certain frequencies to play. A Low-Pass (LP) crossover allows only frequencies below its setting to get through which is good in the case of some subwoofers. A High-Pass(HP) filter allows frequencies above its setting to pass through, this is normally used on speakers.

When a crossover is set to FULL it means no filtering is added and the full frequency spectrum is allowed through the amplifier. Filtering is important because feeding a speaker frequencies it cannot reproduce effectively creates distortion.

Amp Bluetooth Connectivity
This feature will tell you if the amplifier has the capability to connect to a Bluetooth device.
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Wet Sounds SYN-DX 2 (Like New (Open Box))

750W RMS SYN-DX Series Bridgeable Full Range 2-Channel Class D Marine Amplifier (WetSounds)

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Wet Sounds SYN-DX 2 (Like New (Open Box))

750W RMS SYN-DX Series Bridgeable Full Range 2-Channel Class D Marine Amplifier (WetSounds)

• 200 watts x 2 chan. @ 4 Ohm
• 375 watts x 2 chan. @ 2 Ohm
• 750 watts x 1 chan. @ 4 Ohm
• Total power output: 750 watts RMS
• Variable low-pass filter: 50 - 250 Hz, 12 dB/octave
• Variable high-pass filter: 50 - 250 Hz, 12 dB/octave
• Fuse Rating: 30 A x 3

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Cerwin Vega B54 (Like New (Open Box))

1200W Peak (600W RMS) Class D Stealth Bomber Series 4 Channel Car Amplifier

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Cerwin Vega B54 (Like New (Open Box))

1200W Peak (600W RMS) Class D Stealth Bomber Series 4 Channel Car Amplifier

• 80 watts x 4 channel @ 4 ohm
• 150 watts x 4 channel @ 2 ohm
• Bridged: 300 watts x 2 channel @ 4 ohm
• Total RMS Power: 600 watts
• Class D 2 ohm Stable 4-Channel Amplifier

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2026-06-16 09:46:00
Save 30% off an NVX XKIT84 Amp Kit at Checkout! Add a qualifying amplifier to your cart and save 30% on the NVX XKIT84 Amp Kit! No code needed — discount applies automatically at checkout.
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Rockford Fosgate Punch PM300X2 + FREE $75 Gift Card

300W Punch Series Class A/B 2-Channel Marine Amplifier With Gift Card

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Rockford Fosgate Punch PM300X2 + FREE $75 Gift Card

300W Punch Series Class A/B 2-Channel Marine Amplifier With Gift Card

• RMS: 100 watts x 2 chan. @ 4 ohm, 150 watts x 2 chan. @ 2 ohm, 300 watts x 1 chan. @ 4 ohm Bridged
• CEA-2006 Compliant
• Features C.L.E.A.N. Set-up
• Protected against Dust, UV, & Corrosion
• Marine grade two part epoxy coating on circuit boards

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• RMS: 100 watts x 2 chan. @ 4 ohm, 150 watts x 2 chan. @ 2 ohm, 300 watts x 1 chan. @ 4 ohm Bridged
• CEA-2006 Compliant
• Features C.L.E.A.N. Set-up
• Protected against Dust, UV, & Corrosion
• Marine grade two part epoxy coating on circuit boards

Rockford Fosgate M2-300X4 + FREE $75 Gift Card

300 Watt 4-channel marine amplifier

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Rockford Fosgate M2-300X4 + FREE $75 Gift Card

300 Watt 4-channel marine amplifier

• 50 Watts x 4 @ 4 ohm<
• 75 Watts x 4 @ 2 ohm
• 150 Watts x 2 @ 4 ohm Bridged/Mono
• 4-Channel Marine Amplifier
• Top Mounted Control Panel
• 2/4 channel input switch

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• 50 Watts x 4 @ 4 ohm<
• 75 Watts x 4 @ 2 ohm
• 150 Watts x 2 @ 4 ohm Bridged/Mono
• 4-Channel Marine Amplifier
• Top Mounted Control Panel
• 2/4 channel input switch

Rockford Fosgate Punch PM600X4 + NVX XKIT44

600W 4-Channel Punch Series Class AB Marine Amplifier + NVX 4 Gauge 4-Channel Amp Kit

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Rockford Fosgate Punch PM600X4 + NVX XKIT44

600W 4-Channel Punch Series Class AB Marine Amplifier + NVX 4 Gauge 4-Channel Amp Kit

• RMS: 75W x 4 @ 4 ohm, 150W x 4 @ 2 ohm, Bridged 300W x 2 @ 4ohm
• CEA-2006 Compliant
• Features C.L.E.A.N. Set-up
• Protected against Dust, UV, & Corrosion
• Marine grade two part epoxy coating on circuit boards

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• RMS: 75W x 4 @ 4 ohm, 150W x 4 @ 2 ohm, Bridged 300W x 2 @ 4ohm
• CEA-2006 Compliant
• Features C.L.E.A.N. Set-up
• Protected against Dust, UV, & Corrosion
• Marine grade two part epoxy coating on circuit boards

Rockford Fosgate Prime R2-500X4 + Belva BAK44 4 Gauge Amp Wiring Kit

Rockford Prime 500W 4-Channel Full Range Class D Amplifier + Belva BAK44

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Rockford Fosgate Prime R2-500X4 + Belva BAK44 4 Gauge Amp Wiring Kit

Rockford Prime 500W 4-Channel Full Range Class D Amplifier + Belva BAK44

• 75 Watts RMS x 4 @ 4 ohm
• 125 Watts RMS x 4 @ 2 ohm
• Total Peak Power: 500 Watts
• CEA-2006 Compliant
• Top Mounted Control Panel
• 1.9" x "6.8" x "10.1"

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• 75 Watts RMS x 4 @ 4 ohm
• 125 Watts RMS x 4 @ 2 ohm
• Total Peak Power: 500 Watts
• CEA-2006 Compliant
• Top Mounted Control Panel
• 1.9" x "6.8" x "10.1"

Hifonics ZD-750.4D with Amplifier Wiring Kit

750W RMS Zeus Delta Series Class-D 4-Channel Car Amplifier

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Hifonics ZD-750.4D with Amplifier Wiring Kit

750W RMS Zeus Delta Series Class-D 4-Channel Car Amplifier

• 100 watts x 4 channel @ 4 ohm
• 175 watts x 4 channel @ 2 ohm
• Bridged: 375 watts x 2 channel @ 4 ohm
• Class D 2 ohm Stable 4-Channel-Channel Amplifier
• Includes Amplifier Wiring Kit

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• 100 watts x 4 channel @ 4 ohm
• 175 watts x 4 channel @ 2 ohm
• Bridged: 375 watts x 2 channel @ 4 ohm
• Class D 2 ohm Stable 4-Channel-Channel Amplifier
• Includes Amplifier Wiring Kit

Pioneer GM-DX874 with NVX 4 Gauge Amp Kit

1200W Peak (600W RMS) GM Series Class-FD 4-Channel Amplifier with Remote Bass Knob

GMDX874_XKIT44 big
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Pioneer GM-DX874 with NVX 4 Gauge Amp Kit

1200W Peak (600W RMS) GM Series Class-FD 4-Channel Amplifier with Remote Bass Knob

• 100 watts x 4 channel @ 4 ohm
• 150 watts x 4 channel @ 2 ohm
• Bridged: 300 watts x 2 channel @ 4 ohm
• Total RMS Power: 600 watts
• Class D 1 ohm Stable 4-Channel Amplifier
• Includes Amplifier Wiring Kit

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• 100 watts x 4 channel @ 4 ohm
• 150 watts x 4 channel @ 2 ohm
• Bridged: 300 watts x 2 channel @ 4 ohm
• Total RMS Power: 600 watts
• Class D 1 ohm Stable 4-Channel Amplifier
• Includes Amplifier Wiring Kit

JL Audio MV1000/5i - Open Box, Great

MVi Series Marine 5-Channel Class-D Amplifier

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JL Audio MV1000/5i - Open Box, Great

MVi Series Marine 5-Channel Class-D Amplifier

• RMS: 75W x 4 + 400W @ 4 ohm / 100W x 4 + 600W @ 2 ohm
• Contains the 2nd-Gen NexD2™ Switching Amplifier Technology
• Latest generation of DirectFET® MOSFET Output Devices
• Cast alloy chassis with marine-grade speaker connections and keyhole mounting design

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• RMS: 75W x 4 + 400W @ 4 ohm / 100W x 4 + 600W @ 2 ohm
• Contains the 2nd-Gen NexD2™ Switching Amplifier Technology
• Latest generation of DirectFET® MOSFET Output Devices
• Cast alloy chassis with marine-grade speaker connections and keyhole mounting design

Hertz HCP 4M with Free Premium NVX 4 Gauge Amp Kit

Class-D 4-Channel 2 Ohms Marine Stereo Amplifier

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Hertz HCP 4M with Free Premium NVX 4 Gauge Amp Kit

Class-D 4-Channel 2 Ohms Marine Stereo Amplifier

• 65 Watts RMS x 4 @ 4 ohm
• 95 Watts RMS x 4 @ 2 ohm
• CEA-2006 Compliant/Preamp Outputs/LPF
• Corrosion Protection
• Water jet tested
• Dimensions: 12.40" x 7.48" x 1.97"

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• 65 Watts RMS x 4 @ 4 ohm
• 95 Watts RMS x 4 @ 2 ohm
• CEA-2006 Compliant/Preamp Outputs/LPF
• Corrosion Protection
• Water jet tested
• Dimensions: 12.40" x 7.48" x 1.97"

Pioneer GM-DX975 with Amplifier Wiring Kit

2000 Watts Class D 5-Channel Amplifier w/ Gold-plated RCA Terminals and Bass Boost Remote

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Pioneer GM-DX975 with Amplifier Wiring Kit

2000 Watts Class D 5-Channel Amplifier w/ Gold-plated RCA Terminals and Bass Boost Remote

• 75 Watts RMS x 4 @ 4 ohm + 350 watts RMS x 1
• 100 Watts RMS x 1 @ 2 ohm + 600 watts RMS x 1
• 1200 Watts RMS x 1 @ 1 ohm
• 5-channel operation
• CEA-2006 Compliant/Preamp Outputs/LPF
• HQ Sound Parts
• Gold-plated RCA connections
• Includes Amplifier Wiring Kit
• 12-7/16"W x 2"H x 7-7/8"D

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• 75 Watts RMS x 4 @ 4 ohm + 350 watts RMS x 1
• 100 Watts RMS x 1 @ 2 ohm + 600 watts RMS x 1
• 1200 Watts RMS x 1 @ 1 ohm
• 5-channel operation
• CEA-2006 Compliant/Preamp Outputs/LPF
• HQ Sound Parts
• Gold-plated RCA connections
• Includes Amplifier Wiring Kit
• 12-7/16"W x 2"H x 7-7/8"D

Lowest price in 30 days

Rockford Fosgate Punch P600X4 + NVX XFLOC4 Line-Output-Converter + Amp Kit

600W 4-Channel Amplifier + NVX 4-Channel L.O.C. + 4 Gauge Amp Kit

P600X4, XFLOC4, BAK44 big
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Rockford Fosgate Punch P600X4 + NVX XFLOC4 Line-Output-Converter + Amp Kit

600W 4-Channel Amplifier + NVX 4-Channel L.O.C. + 4 Gauge Amp Kit

• 75W x 4-Chan. @ 4 ohm
• 150W x 4-Chan. @ 2 ohm
• Built In NOMAD "Real Time" Analog Computer
• 4/3/2/1 Channel Operation
• 4 Gauge Power and Ground Inputs
• MESHA3 Reduces MOSFET Temperatures for Improved Durability

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• 75W x 4-Chan. @ 4 ohm
• 150W x 4-Chan. @ 2 ohm
• Built In NOMAD "Real Time" Analog Computer
• 4/3/2/1 Channel Operation
• 4 Gauge Power and Ground Inputs
• MESHA3 Reduces MOSFET Temperatures for Improved Durability

DS18 SXE-4000.4D/RD (Red) with NVX 4 Gauge Amp Kit

4000W Peak (1500W RMS) Class D SXE Series 4-Channel Car Amplifier

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DS18 SXE-4000.4D/RD (Red) with NVX 4 Gauge Amp Kit

4000W Peak (1500W RMS) Class D SXE Series 4-Channel Car Amplifier

• 275 watts x 4 channel @ 4 ohm
• 430 watts x 4 channel @ 2 ohm
• Bridged: 750 watts x 2 channel @ 4 ohm
• Total RMS Power: 1500 watts
• Class D 2 ohm Stable 4-Channel-Channel Amplifier (Red)
• Includes Amplifier Wiring Kit

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• 275 watts x 4 channel @ 4 ohm
• 430 watts x 4 channel @ 2 ohm
• Bridged: 750 watts x 2 channel @ 4 ohm
• Total RMS Power: 1500 watts
• Class D 2 ohm Stable 4-Channel-Channel Amplifier (Red)
• Includes Amplifier Wiring Kit

Hertz SP 4.500 with NVX 8 Gauge Amp Kit

600W RMS SPL Show Series Class-D 4-3- 2-Channel Amplifier

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Hertz SP 4.500 with NVX 8 Gauge Amp Kit

600W RMS SPL Show Series Class-D 4-3- 2-Channel Amplifier

• 90 watts x 4 channel @ 4 ohm
• 150 watts x 4 channel @ 2 ohm
• Total RMS Power: 600 watts
• Class D 2 ohm Stable 4-Channel Marine Amplifier
• Includes Amplifier Wiring Kit

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• 90 watts x 4 channel @ 4 ohm
• 150 watts x 4 channel @ 2 ohm
• Total RMS Power: 600 watts
• Class D 2 ohm Stable 4-Channel Marine Amplifier
• Includes Amplifier Wiring Kit

JL Audio RD900/5 (Open Box, Great)

900W RMS Class D RD Series 5 Channel Car Amplifier

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JL Audio RD900/5 (Open Box, Great)

900W RMS Class D RD Series 5 Channel Car Amplifier

• 70 watts x 4 channel + 225 watts x 1 channel @ 4 ohm
• 100 watts x 4 channel + 500 watts x 1 channel @ 2 ohm
• Bridged: 200 watts x 2 channel @ 4 ohm + 500 watts x 1 channel @ 2 ohm
• Total RMS Power: 900 watts
• Class D 2 ohm Stable 5-Channel Amplifier

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• 70 watts x 4 channel + 225 watts x 1 channel @ 4 ohm
• 100 watts x 4 channel + 500 watts x 1 channel @ 2 ohm
• Bridged: 200 watts x 2 channel @ 4 ohm + 500 watts x 1 channel @ 2 ohm
• Total RMS Power: 900 watts
• Class D 2 ohm Stable 5-Channel Amplifier

Lowest price in 30 days

Rockford Fosgate Punch P300X2 + NVX Line-Output-Converter + Amp Kit

300W RMS 2-Channel Amplifier + NVX 2-Channel + 8 Gauge Amp Kit

P300X2, XLCA2, BAK82 big
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Rockford Fosgate Punch P300X2 + NVX Line-Output-Converter + Amp Kit

300W RMS 2-Channel Amplifier + NVX 2-Channel + 8 Gauge Amp Kit

• 100W x 2 Chan. @ 4 ohm
• 150W x 2 Chan. @ 2 ohm
• Built In NOMAD "Real Time" Analog Computer
• 2/1 Channel Operation
• 4 Gauge Power and Ground Inputs
• MESHA3 Reduces MOSFET Temperatures for Improved Durability

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• 100W x 2 Chan. @ 4 ohm
• 150W x 2 Chan. @ 2 ohm
• Built In NOMAD "Real Time" Analog Computer
• 2/1 Channel Operation
• 4 Gauge Power and Ground Inputs
• MESHA3 Reduces MOSFET Temperatures for Improved Durability

Rockford Fosgate R2-750X5 + FREE $100 Gift Card

350W RMS 5-Channel Prime Series Full Range Amplifier With Gift Card

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Rockford Fosgate R2-750X5 + FREE $100 Gift Card

350W RMS 5-Channel Prime Series Full Range Amplifier With Gift Card

• 50 Watts RMS x 4 @ 4 ohm
• 100 Watts RMS x 4 @ 2 ohm
• Total Peak Power: 600 Watts
• CEA-2006 Compliant
• Balanced Differential Inputs with RCA Pass Through Outputs
• Variable Infrasonic Filter
• ull Range Class D

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• 50 Watts RMS x 4 @ 4 ohm
• 100 Watts RMS x 4 @ 2 ohm
• Total Peak Power: 600 Watts
• CEA-2006 Compliant
• Balanced Differential Inputs with RCA Pass Through Outputs
• Variable Infrasonic Filter
• ull Range Class D

Cerwin-Vega XED4004D with Belva 4 Gauge Amp Kit

400W Peak (360W RMS) XED Series Class-D 4-Channel Amplifier

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Cerwin-Vega XED4004D with Belva 4 Gauge Amp Kit

400W Peak (360W RMS) XED Series Class-D 4-Channel Amplifier

• 60 watts x 4 channel @ 4 ohm
• 90 watts x 4 channel @ 2 ohm
• Bridged: 170 watts x 2 channel @ 4 ohm
• Total RMS Power: 360 watts
• Class D 2 ohm Stable 4-Channel Amplifier
• Includes Amplifier Wiring Kit

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• 60 watts x 4 channel @ 4 ohm
• 90 watts x 4 channel @ 2 ohm
• Bridged: 170 watts x 2 channel @ 4 ohm
• Total RMS Power: 360 watts
• Class D 2 ohm Stable 4-Channel Amplifier
• Includes Amplifier Wiring Kit

Deaf Bonce Apocalypse Atom 900.2 with Belva 4 Gauge Amp Kit

900W RMS Class D Apocalypse Atom Pro Series 2-Channel Car Amplifier

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Deaf Bonce Apocalypse Atom 900.2 with Belva 4 Gauge Amp Kit

900W RMS Class D Apocalypse Atom Pro Series 2-Channel Car Amplifier

• 350 watts x 2 channel @ 4 ohm
• 510 watts x 2 channel @ 2 ohm
• 900 watts x 2 channel @ 1 ohm
• Bridged: 1020 watts x 1 channel @ 4 ohm
• 1000 watts @ 2 ohm
• Total RMS Power: 900 watts
• Class D 1 ohm Stable 2-Channel-Channel Amplifier
• Includes Amplifier Wiring Kit

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-12% $254.39

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• 350 watts x 2 channel @ 4 ohm
• 510 watts x 2 channel @ 2 ohm
• 900 watts x 2 channel @ 1 ohm
• Bridged: 1020 watts x 1 channel @ 4 ohm
• 1000 watts @ 2 ohm
• Total RMS Power: 900 watts
• Class D 1 ohm Stable 2-Channel-Channel Amplifier
• Includes Amplifier Wiring Kit

DS18 SXE-2000.4D/RD (Red) with Belva 4 Gauge Amp Kit

2000W Peak (640W RMS) Class D SXE Series 4-Channel Car Amplifier

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DS18 SXE-2000.4D/RD (Red) with Belva 4 Gauge Amp Kit

2000W Peak (640W RMS) Class D SXE Series 4-Channel Car Amplifier

• 100 watts x 4 channel @ 4 ohm
• 160 watts x 4 channel @ 2 ohm
• Bridged: 320 watts x 3 channel @ 4 ohm
• Total RMS Power: 640 watts
• Class D 2 ohm Stable 4-Channel-Channel Amplifier (Red)
• Includes Amplifier Wiring Kit

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• 100 watts x 4 channel @ 4 ohm
• 160 watts x 4 channel @ 2 ohm
• Bridged: 320 watts x 3 channel @ 4 ohm
• Total RMS Power: 640 watts
• Class D 2 ohm Stable 4-Channel-Channel Amplifier (Red)
• Includes Amplifier Wiring Kit

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    FAQ for Multi-channel Amplifiers for Adding Speakers in 2003 FLSTSI Heritage Springer

    Q: Can I upgrade or change the Multi-channel Amplifiers for Adding Speakers in 2003 Harley Davidson FLSTSI Heritage Springer?

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