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Infinity Reference 551a

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

Item # 108R551A

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

Read more from Crutchfield writer, Buck P.

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$199.99

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About the Infinity Reference 551a

Power delivered in style

Infinity's Reference 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 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 REF-551a

Reference 551a inputs 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
  • fuse rating: 30A x 2
  • 8-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • 9-3/8"W x 2-1/4"H x 7-5/16"D
  • warranty: 1 year
  • Our 60-day money-back guarantee
  • MFR # Reference 551a
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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 551a Reviews

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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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Customer Q&A

Q
Crutchfield asked: Why did you buy this?
A
Price, function and size. [ Jason  Nov 27, 2018 ]
A
This amp is a killer holiday deal! [ T  Nov 24, 2018 ]
A
Clear bass amp, with low distortion and at a bargain price for infinity [ MICHAEL  Nov 25, 2017 ]
A
pricing and brand [ John  Nov 24, 2017 ]
A
On sale [ JOHN W  Nov 24, 2017 ]
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2 questions already asked

Q
Will this amp push 2 jl w0 10s?
[ Skyler  Feb 11, 2019 ]
1 answer
A
Thanks for your question. For information on selecting the best amp for your subs I would recommend reaching out to an Advisor by phone (1-800-324-9695) or online chat. They will be able to help determine the differences between the amp models and help you make the best choice for your system.
[ Krissy  Feb 14, 2019 ]  Staff
Q
How to wire this amp to output to single 2ohm stable ? The amp has 4 speaker terminals.
[ cal800  Dec 21, 2018 ]
3 answers
A
You must use positive for left speaker and negative for right speaker. Output is 4 ohm load in order to achieve 2 ohm load you must use dual 4 ohm voice coil subwoofer.
[ JASON  Dec 31, 2018 ]
A
There is no clear answer on infinity and I bridged the outer terminals and ran my speakers in series it sounds great my speakers are at 2ohm so I believe it's right
[ thomas  Dec 31, 2018 ]
A
The positives and negatives are on rails internally in the amp. Just pick one positive and one negative and go with it. I picked the outside positive and outside negative.
[ Anthony  Dec 30, 2018 ]

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