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Whether you're using the Niles SI-2125 as a part of a multi-room audio system or as the amplifier in your main listening room, you'll find that it delivers plenty of pristine, dynamic stereo power.

This amplifier also offers enough flexibility to make it perfect for a wide variety of applications. Its 4-ohm stability means that the SI-2125 can easily drive 2 pairs of speakers at once. Or you can bridge its two channels to drive a single speaker with 300 watts of power.

Niles uses quality parts throughout to ensure that you'll always get top-notch performance. Independent power supplies for each channel prevent cross-talk interference, ensuring especially clean sound. Oversized heat sinks keep the amp cool even when driving heavy loads, elimating the need for a noisy cooling fan and guaranteeing silent operation.

Product Highlights:

  • 2-channel amplifier
  • discrete, high-current design
  • power output (20-20,000 Hz):
    • 125 watts RMS per channel at 8 ohms (0.05% THD, both channels driven)
    • 200 watts RMS per channel into 4 ohms (.03% THD, both channels driven)
  • channels are bridgeable to 300 watts RMS (mono) into 8 ohms
  • stable into low-impedance loads
  • three turn-on modes: music-sensing, voltage trigger, and manual
  • gold-plated binding posts spaced to accommodate dual banana plugs
  • 12-volt control output
  • voltage trigger input accepts 3-30V AC/DC
  • detachable AC power cord
  • cascade output lets you easily connect additional amplifiers to your system
  • left and right channel adjustable level controls
  • DC, short circuit, and overload protection with automatic reset
  • 17"W x 5-3/4"H x 15-5/8"D
  • warranty: 2 years
  • Our 60-day money-back guarantee

Niles SI-2125 Reviews

Average Customer Review:

5 Reviews

Excellent power amp for bi-amping

Written by: JBaudiophile from Charlottesville, VA on April 12, 2011

I recently acquired a pair of Polk RTI-A9 speakers for my front mains. Even when bi-amping these speakers by using the assignable channels of my Yamaha RX-V3900, the speaker low-end response was not satisfactory. Connecting the SI-2125 in bi-amp mode to power the low-end drivers of the RTi-A9s, and using the RX-V3900 to power the mid and upper drivers has dramatically opened up the soundstage and clarity of sound production of the A9s. Bass response is now strong and crisp. The dynamics of the 4th movement of Mahler's Titan symphony are now awe-inspiring. A tremendous upgrade in sound! I am very happy with the improvement gained by adding SI-2125.



Love This Amp

Written by: Anonymous from Syracuse, Ut on June 23, 2010

Crutchfield Customer Review (What's this?)

I have to say this amp performs great. Using it in a Bi amp situation with a Pioneer elite reciever. My pioneer is running the upper section of my speakers and The Niles is running the low,s. Much improved bass performance in the low end. Cleans the sound up nicely. Cant wait to buy another!




Written by: GERALD from East Hampstead, N.H. on August 13, 2009

Crutchfield Customer Review (What's this?)

Using the SI-2125 to bi-amp a pair of Polk LTi12(s), with my Denon DRA-
697CIHD (all form Crutchfield). While not true bi-amping, this set-up
provided a much improved Sound Stage, better Mids and Highs from the
Denon, and nice Base Sound now provided by the SI-2125. The SI-2125
provides me some flexibility if I ever want to change my set-up. Thanks
Crutchfield for fast shipping and a great product, and Dave B. on the
Crutchfild Blog page for advice and info on bi-amping.



The Truth

Written by: busterlemons from Albuquerque, NM on March 29, 2009

I think this amp is good if you have an older radio system that you are just so amazed with that you do not want to get any of the new systems.

I have an Onkyo 805s that has 130 watts per channel, I have two speakers that are 500 watts each, I just wanted something a little better to push the bass and what not.

I had friends over and switched back and forth from the amp and non amped and no one could tell me that they heard a differance. I will admit the sound was a more clear to me. I pick up on sounds more then others it seems, but this clearness was not enough to warrent the price for the item. I got this to boost my stero but in truth its made to hook up more speakers for your amp.

I will give this a 2 star because I could see that someone would buy this item if they wanted to put sound though out their house, if they did not have a zoned amp or if they wanted to hook up like 12 speakers at once. Your going to get clear and good sound to ever speaker. I hate giving bad reviews, its a soild amp that is two channel for this price, if your getting this for your theater room because you want more power do not do it, instead get yourself a better reciver.



Excellent Results

Written by: Vinnie from Jersey City, NJ on January 19, 2009

Crutchfield Customer Review (What's this?)

I have speakers in 4 additional rooms and a balcony put the performance was extremely weak and the sound was horrible. I purchased the Niles SI-2125 and it worked terrific. The sound is so rich, clear and truly the best thing I have done to enhance the sound of my stereo throughout my Condo.

Honestly, everything I have purchased from Crutchfield has been terrific including their impeccable prompt service. I won't buy anywhere else but Crutchfield as they are very competitive in the pricing and their recommendations are right on target.



Hands-on research

What's in the box?

Download owner's manual

  • 2-channel amplifier
  • 6.25' AC power cord
  • Installation & Operation Guide
  • Warranty and Registration Card
  • Important Safety Instructions

Product Research



Power Output: The SI-2125 delivers 125 watts per channel at 8 Ohms, 200 watts per channel at 4 Ohms, and 300 watts bridged at 8 ohms.

Audio Circuitry Construction: The audio circuitry of the SI-2125 is constructed using 1% metal film resistors, high quality capacitors, and oversized heat sinks, allowing the amplifier to create sound that is clear and uncolored with great imaging.

Independent Power Supplies: Each channel of the SI-2125 is powered by its own independent power supply. This increases the isolation between the two channels and eliminates cross talk.

High-current Design: The toroidal transformer has two separate windings for each of the power supplies, providing more than ample current to your system.

Oversized Heat Sinks: The oversized heat sinks inside the SI-2125 allow the amplifier to stay cool even when operating into low impedance loads without the noise of fan-cooled amplifiers.

Independent Level Controls: Each channel has its own independent level control enabling you to precisely match the SI-2125 to the rest of your system.

Turn-On Modes: The Turn-On Mode selector switch gives you three options for turning the SI-2125 on and off:

  • Constant: the auto turn-on circuitry is off. The front panel power switch operates the amplifier.
  • Audio Sense: the power switch on the front panel must be in the "On" position. The amplifier is off when there is no audio signal present at either the left or the right input. If it detects a signal, the amplifier is turned on. Once the audio signal stops, the sensing circuit waits two minutes, then turns the amplifier off.
  • 3-30 Volt AC/DC Voltage Trigger: the power switch on the front panel must be in the "On" position. The amplifier is off when there is no 3-30V AC or DC voltage detected at the trigger input. Once the sensing circuitry detects a voltage, the amplifier is turned on. Once the voltage stops, the sensing circuit instantly turns the amplifier off.

Automatic Protection: The SI-2125 is equipped with sophisticated protection circuits. The red "Protect" LED indicates the amp has shut down because there is a fault in the speaker, the wiring, or with the SI-2125 itself. When conditions return to normal, regular operation resumes.


Trigger Input (3-30V): minijack

12V Control Output (150A maximum): minijack

Main Input: left and right RCA audio jacks

Cascade Output: left and right RCA audio jacks

Speaker Outputs: left and right gold-plated 5-way binding posts that will accept up to 12-gauge bare wire


Continuous Average Power Output:

  • 125 watts per channel RMS at 8 ohms
  • 200 watts per channel RMS at 4 ohms
  • 300 watts bridged channel RMS at 8 ohms

Input Impedance: 10k ohms

Input Sensitivity: 0.878V for 8 ohm rated input

Overall Voltage Gain: 33 dB

Frequency Response: bandwidth limited from 10 Hz to 100 kHz

Total Harmonic Distortion:

  • 8 Ohms: 0.05% THD from 20 Hz to 20 kHz @ full rated power
  • 4 Ohms: 0.03% THD from 20 Hz to 20 kHz @ full rated power

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.