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Infinity Reference REF-551a

Mono subwoofer amplifier — 550 watts RMS x 1 at 2 ohms

Item # 108R551AM

Infinity's Reference REF-551a mono amp will add some bass muscle to your music without breaking a sweat, and it'll...

Infinity's Reference REF-551a mono amp will add some bass muscle to your music without breaking a sweat, and it'll...

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About the Infinity Reference REF-551a

Power delivered in style

Infinity's Reference REF-551a mono amp will add some bass muscle to your music without breaking a sweat, and it'll look good doing it. This potent powerhouse will send up to 550 watts RMS to your subwoofer, and its Class D design ensures the amp's high output will put minimal strain your vehicle's electrical system.

Power delivered in style

Infinity's Reference REF-551a mono amp will add some bass muscle to your music without breaking a sweat, and it'll look good doing it. This potent powerhouse will send up to 550 watts RMS to your subwoofer, and its Class D design ensures the amp's high output will put minimal strain your vehicle's electrical system.

Works in almost any vehicle

Speaker-level inputs allow this amplifier to work in almost any system, even if you're hanging on to your factory radio. You can use the low-pass filter and variable bass boost to maximize the performance of your subwoofer and enclosure, while a phase switch ensures that the bass will blend well with your full-range speakers.

Infinity Reference 551a

Reference 551a input and control panel

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Product highlights:

  • mono subwoofer amplifier
    • 370 watts RMS x 1 at 4 ohms (550 watts RMS x 1 at 2 ohms)
  • Class D amp technology
  • variable low-pass filter (32-320 Hz, 12 dB/octave)
  • variable bass boost (0-9 dB at 45 Hz)
  • phase switch (0, 180 degrees)
  • preamp and speaker-level inputs
  • wiring and hardware not included with amplifier
    • 8-gauge power and ground leads recommended
  • fuse rating: 30A x 2
  • dimensions: 9-3/8"W x 2-1/4"H x 7-5/16"D
  • warranty: 1 year
  • Our 60-day money-back guarantee
  • MFR # REF-551AAM

What's in the box:

  • Monoblock amplifier with two 30A ATO fuses installed
  • Two spare 30A ATO fuses
  • 2 Speaker wire-to-RCA adapters
  • 4 Self-tapping screws (length=2.25")
  • Quick Connect Guide
  • 2 Infinity decals

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Infinity Reference REF-551a

Jonathan from Hawesville, KY on 2/28/2019

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Awesome Amp! Half the size and and all the watts! Infinity is awesome!

Pros:

Cons:

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Infinity Reference REF-551a

Paul from Spanaway, WA on 12/10/2018

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The sale price for this amp and the quality performance in a small package is amazing! You guys are top notch. I will continue my business with you on all of my future audio needs, thank you!

Pros: Quality, big power in a small package.

Cons: None

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Great little amp

John from Round Rock, TX on 12/10/2018

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Nice amp. Solidly built and many different ways to configure it.

Pros:

Cons: Remote gain control is expensive compared to other Amps i've looked into

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Nice Amp

Mark from 88001 on 5/27/2017

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Nice amp. Easy to install and access all controls and connectors. Pushes my 2 12" subs good with tight bass. Never gets hot, even when I push it.

Pros: Powerful Does not run too hot easy access to all controls

Cons: none

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Features
Controls
Connections

Features

Power Output: The Infinity REF-551a monoblock amplifier delivers the following power output (RMS Power Output @ <1% THD, 14.4 VDC):

  • 370 watts x 1 @ 4 ohms
  • 550 watts x 1 @ 2 ohms

Protection Circuitry: The amplifier features protection circuitry for thermal overload, over/under-voltage (<9V or >16V), amplifier output circuit failure, and short circuits. The Protect LED on the top of the amp glows red if the amp goes into protection mode.

Controls

Gain: The REF-551a's rotary gain control lets you match the amp's input sensitivity to the output of the source unit. The input sensitivity range of the amplifier is 200mV and up. A small screwdriver (not included) is required to set the gain.

Input Level: The amp will accept low-level (line level) or high-level (speaker level) input signals. The input level switch lets you select the type of input you are using. For a high-level input, there are two settings: Hi1 and Hi2. If the audio system fails to play with an amplifier connected to its output, set the switch to the Hi2 position. The Hi2 position includes a circuit design to fool this type of factory system into "seeing" a speaker connected to its output.

Crossover: The amp features a low-pass filter that is non-defeatable. It eliminates a range of high frequencies that are sent to the subwoofer. You can adjust the cutoff frequency of the low-pass filter from 32Hz to 320Hz using the rotary control. A small screwdriver is required to adjust the frequency.

Bass Boost: The REF-551a has a variable 0-9dB bass boost, centered at 45Hz. This allows you to dial in the amount of bass according to your personal taste.

Connections

Terminals: The Infinity REF-551a uses set screw terminals for the +12V power, ground, turn-on (remote) lead, and speaker outputs. The screws can be tightened/loosened with a Phillips-head or flat-head screwdriver (not provided).

Power/Ground: The +12V Power and Ground terminals will accept up to 4-gauge wire. It is recommended that you use a minimum of 8 AWG power wire to the battery, with an in-line 60A fuse installed no more than 18" from the battery terminal. An 8 AWG ground wire (minimum) is also recommended, and attached to a metal area close to the amplifier.

Fuses: The REF-551a has two 30A ATO (blade-type) fuses installed in the amplifier behind a removable panel. A small Phillips-head screwdriver (not included) is required to remove the panel. Two spare 30A ATO fuses are also included with the amp.

Remote Turn-On: The Remote screw terminal will accept up to 10 AWG wire. Typically, an 18 AWG wire is sufficient for the turn-on lead.

Speaker-Level Input: The amp includes two bare wire-to-RCA adapters for connecting the amp to a factory radio or aftermarket head unit without preamp outputs. You should attach the left and right speaker wires from the head unit to each adapter and plug the adapter's RCA plug into the amp.

Line-Level Inputs: The amplifier is equipped with one pair of RCA inputs for connecting stereo RCA patch cables from the head unit to the amp. If your source unit only has one subwoofer output, you will need a Y-adapter to split the signal and connect it to both left or right RCA inputs on the amp.

Speaker Outputs: The amp features screw terminals for connecting one or two speakers. (The terminals are internally wired in parallel). The amplifier's minimum speaker impedance is 2 ohms, so you can connect any combination of speakers that presents a 2 ohm load or higher. The terminals will accept up to 10 AWG wire.

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