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    SKU: SMP-300

    OSD SMP300500W Mono Class D Subwoofer Amplifier, Auto Sensing, 4 -8 Ohm ETL and CE Certified

    Purchase SMP300 Mono-Channel Class D Subwoofer Amplifier 500W, Auto Sensing, 4 -8 Ohm ETL and CE Certified
    • Outdoor Speaker Depot SKU: SMP-300 smp300-class-d-digital-subwoofer-amplifier-500w-osd-audio
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      Compare at: $563.99
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     OSD Audio's SMP300 is a Class D digital mono subwoofer that delivers up to 500W of peak power to beef up the bass in your home theater or audio sound system. Designed for use with passive subwoofers such as in-wall subs that require external power, the SMP300 provides continuous, stable power but measures only 3' high so it can fit inside any equipment rack or cabinet. Moderately priced with high-end features, this compact sub amp enhances the low frequency sound effects on music and movie soundtracks so you’ll experience highly accurate bass and a more intense surround sound experience. The SMP300 includes variable low pass filter control for balanced and seamless sound quality as well as variable phase control for additional fine tuning. Multiple connection options include LFE input, line-level and speaker-level inputs to cover newer and old school source equipment.

    • A compact and powerful digital subwoofer amplifier for home theater applications 
    • Efficient Class D digital technology runs cool under demanding loads 
    • Rated at 500W peak power and 250W continuous RMS 
    • Includes front-panel variable low-pass filter for balanced and accurate bass 
    • Additional front panel controls include phase and volume 
    • Multiple input options for older and newer receivers and pre-amps 
    • Auto sensing feature turns off amp when signal is undetected 
    • Dual voltage switchable (120V/230V) 
    Variable Low Pass Filter 
    A front-panel variable low pass filter allows you to adjust the upper frequency limit of the subwoofer to control the overlap of the subwoofer's upper frequencies and the main speakers' lower frequencies. This results in bass that complements the sound from the main speakers rather than overpowers. 

    Variable Phase Control
    The SMP300 also includes a front-panel variable phase control knob that operates over a range from 0 degrees to 180 degrees and allows you to match the arrival times of the sound waves from the subwoofer and the main speakers. This fine-tuning results in bass that is less muddy or thumpy but rather smooth and detailed. Many amp subwoofers in this price range include a variable phase switch that does not offer the same amount of audio precision. Includes 

    Class D Amp Technology
    The SMP300 uses Class D digital amplifier technology that combines the best qualities of both Class A and B amp protocols into a highly efficient compact chassis that is ideal for budget-minded users who want a feature-rich digital sub amp that does not run hot or take up a lot of space.

    Why Do You Need Subwoofer Amp? 
    A powered subwoofer has its own internal amplifier. A passive subwoofer requires external power, and most in-wall subs are passive. After all, it's not so easy to install a 100-pound powered subwoofer inside a wall. That's where an amp like the SMP300 comes into play. This amp not only adds necessary power but routes LFE away from your surround speakers, which in turn gives you much cleaner highs and midrange. This subwoofer amp does much more than supply power. It also improves the overall sound quality of your entire surround sound system.

    Warning: California's Proposition 65


    This product can expose you to chemicals, including vinyl chloride, which is known to the State of California to cause cancer. For more information, go to

    • Amplifier Type: Subwoofer
    • Amplifier Class: Digital Class D
    • Channels: 1
    • Power Output: 500 Watts @ 4 Ohm
    • Power Output: 150W RMS @ 8-ohm w/ 300W Peak
    • Power Output: 250W RMS @ 4-ohm w/ 500W Peak
    • Frequency Response: 20Hz-160Hz +/-1dB THD: 1%
    • Variable Crossover: 35Hz-180Hz
    • Variable Phase Switch: 0 to 180 Degrees
    • Impedance: 8 Ohm and 4 Ohm Stable
    • Signal to Noise Ratio: 95 dB
    • 12V Trigger Mode
    • Inputs: Speaker (High) Level / Signal (Low) Level RCA
    • Rack Mountable: 1U Rack Space Style / Mounts Included
    • Dimensions (L x H x D): 16.25" x 3" x 9.25"
    • Weight: 7 lbs.
    • Warranty: 2 Years
    3 Questions asked
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    What's on your mind?

    Mike • 12/17/2019, 2:17:43 PM Hi, I am building an outdoor sound system to stream music to our new patio/pool area. I already have a Yamaha Music Cast preamp and an older high current Onkyo av receiver. My 4 satellites are SnapAV, 8ohm and the subwoofer is a Niles Boom Tomb, buried 12 inch in-ground sub. It can eat 500w and is also 8ohm. The way I have it drawn up, I need a one channel sub amp - preferably with auto on/off feature - hanging off the receiver2;s Line Out. I would like to use LFE for passing the signal to the subwoofer amp. Question: what will this amp drive into 8 ohms? Second, is it bridgeable - if so what is the bridged (8ohm) output? Last, would you recommend any changes to how I have it drawn up? I have a 500 spool of OSD 12/2 wire ready to bury (equipment will be in a cabinet on our screened porch). Thanks
    Customer Service • 12/17/2019, 2:17:43 PM
    Hi Mike: The Boom Tomb was the name of a Speakercraft In-Ground Subwoofer that they recommended a 250 Watt amplifier. Niles has in an in-ground 10" subwoofer rated at 50Watts. At one time these companies were fierce competitors, but both were purchased by the same company back in 2007 along with 15 other companies including Elan, Proficient, Furman, Panamax, and Sunfire. Today both Niles and Speakercraft are part of the Core group a Nortek Company. I did find a 12" Niles in-Ground sub rated at 8-ohms and 500 Watts. Its Sensitivity Rating is 86 dB which tells us you need more power to reach full output. I would suggest that the SMP500 would be a better choice for the Niles in-ground sub. 1) The SMP500 will do 500 Watts peak at 8 ohms 2) It is Mono output already bridged. 3)12 gauge for your low level is ideal. I do not know enough about your configuration to comment. You do not mention anything about possible speaker selector, Volume Controls, Impedance Matching or the model number of the ONKYO and how you are connected. TL/5510
    Mark • 12/17/2019, 2:17:43 PM I just purchased this amp to drive my outdoor subwoofer, polk audio atrium 10.  As it was a subwoofer, I assumed a mono amp was required.  Upon reading further, I now see that the atrium 10 has 2 voice coils and a total of 4 wire inputs.  The sub is for an outdoor theater.  Sound is driven from denon avr s930h.  I want to use the subwoofer out from the denon to the line in through a y cable for pass through sound.  Then from the line out connect both positives from the atrium to to the positive line out of the amp.  Likewise for negatives.  I have polk atrium 8 speakers for rear channels for surround and definitive technologies aw6500 for front channels.  I do not want to wire in parallel from front channels.  Am I ok with wiring suggested.  Thank you.
    Customer Service • 12/17/2019, 2:17:43 PM
    Hi Mark:I would suggest returning the SMP300 in exchange for our XMP300 2 channel stereo amplifier. The Atrium Sub 10 has an internal crossover already, and most likely the sub output from the DENON should be an LFE (Low-Frequency Effects) where the DENON controls the full process low pass signal. You would connect to speaker A a stereo right and left stereo signal. Otherwise, before you do that, you could combine the SMP300 to just one of the inputs. I believe each voice coil is rated at 4 ohms and then wired in Series together to create an 8-ohm connection, but before you do that check with Polk and see what they say. Please let me know which option you might take.TL/5668
    Matt • 01/05/2021, 1:04:37 PM Hello! I am driving an SL800D with this Amp, fed by a Denon AVR-x3600h receiver. At present, I have the preout from the receiver wired with a Y cable to the Line In on this amp - which I believe is correct according to the instructions. In order to satisfy the 75db requirements of the Audyssey speaker setup, I have to bring the Low Pass Filter of this amp up to 155hz and set the volume control to max. This satisfies the decibel level of the Denon, but sounds awful. What am I doing wrong? Thanks in advance for your help!
    Customer Service • 02/04/2021, 1:22:11 AM
    HI Matt: Do you have the DENON connected to the LFE input on the SMP-300 The LFE input bypasses the SMP300's low frequency (low pass) crossover. Checkout page 222 of your DENON AVR Owner's Manual for Subwoofer LFE settings including 100HZ/120Hz/150Hz. Try a couple of different settings. TL/2-3-2021