IQ Audio M300 MonoBlock Amplifier Review

We’ve all heard the phrase “good things come in small packages” when receiving an unexpectedly small Christmas present as a child.  Sometimes this would ring true while other times it often wouldn’t.  At least that has been my experience growing up, since I always wanted large bulky audio gear.  The small stuff either wasn’t very good or easily available, unless it was a Walkman or a dreaded cube speaker system.  When IQ Audio contacted me to review their new M300 Class D MonoBlock audio amplifier I was intrigued, until I went to the product page on their website and saw the pint size casing.  I mean, what can one expect from a 7lb box measuring 3” x 7” x 7”?  I’m thinking flea watt amplifier power but their website spec claimed otherwise and they went to great lengths to explain their 150 watt @ 8 ohm and 300 watt @ 4 ohm rating was at full bandwidth.  Many Class D amplifiers are quietly rated at 1kHz to give the illusion of high power but tend to be very limited at driving low impedance loads over the full bandwidth.  This often isn’t revealed by most of the AV press since they typically only power test amplifiers at 1kHz.  I was dying to get this amp on my test bench, Audioholics style, and find out if this small package could really be a good thing or not.  Continue reading this review to find out the answer.

Design Overview

The IQ M300 was designed to be a compact, impeccably-built, audiophile-grade amplifier able to deliver real FTC rated power, all at a reasonably affordable price point.  IQ Audio claimed they also wanted a very quiet amplifier with a real black background. The M300 is said to achieve 40uV to 50uV micro-volts total noise which we will validate in the measurements portion of this review.

In speaking with company CEO Bruce Weisberg, he told me they used as design references, two of their favorite solid-state amplifiers from Spectral and Pass Labs. Their goal was to try to achieve maximum resolution while maintaining musicality.  The reference speakers they tested the M300 on were Quad electrostatics, Bruce’s personal long-time favorite.

Input Stage

The M300 utilizes a micro controlled input buffer stage. This section controls the start up of the amplifier, and allows for control over the amplifier and feature set. This buffer section is said to achieve high common mode rejection for excellent noise immunity to increase dynamic range.  The balanced and un-balanced inputs have 100K input impedances making the M300 very compatible with both tube and solid-state preamps.

The microprocessor allows 12V remote start up and shut down, without the use of energy wasting secondary transformers. In fact, the power supply meets all Energy Star requirements. 

Power Supply

To supply the rated 300 watts of FTC-rated power would require a hefty 10-12-pound transformer. Rather than using a conventional linear power supply which can inject hum or buzz on sensitive equipment, IQ Audio instead opted for a power supply based upon the efficient zero-voltage, zero-current switching technology, which IQ Audio claims yields ultra-fast response while greatly reducing radiated and conductive electromagnetic interference and high frequency noise on the DC power supply.

In the IQ design, the transistors turn on and off at zero-voltage and zero-current, reducing power supply stress, reducing the amount of filtering and shielding required, reducing heat, and lowering RF interference. Keeping RF noise and EMI interference low in a power supply was a fundamental goal. IQ Audio believes this contributes significantly to the transparent reproduction and increased dynamic range from the M300 amplifier.

In other conventional switching power supplies, the power transistor turns on and off with a lot of voltage present. This stresses the power supply and creates the need for greater filtering, shielding, etc. By integrating the power supply with the Class-D section IQ Audio engineering was able to shorten the electrical paths.

The Class-D Output Section

The IQ M300 Class D section is a self-oscillating design. Special attention was paid to the feedback control loops, which includes the Class D output filter. The goal was to maximize loop gain with utter stability.

The Class-D circuit runs at approximately 500Khz, and IQ Audio uses the fastest switching devices to achieve optimal results.  As you will see in our detailed measurements, the M300’s frequency response is independent of the impedance load, and the amplifier is stable with reactive loads and loads down to 2 ohms.

 

 

 IQ Audio M300 Top View with cover removed

 

 IQ Audio M300 Backview

The M300 comes with heavy duty 14AWG detachable power cord with ferrite beads attached to both ends, presumably a necessity to pass CE radiated emissions due to the high switching frequency of the Class D operation.  It sports a hospital grade 3-prong plug with a sticker claiming “grounding reliability can only be achieved when this equipment is connected to a receptacle marked hospital grade”.  Sounds serious, but I had no grounding issues plugged into my ordinary 15 amp household outlets.

Torque binding posts are used for the speaker connection terminals (same ones on the Pass Labs X350.5 amplifier we’ve recently reviewed).  I’m not a big fan of this connection type since I typically prefer banana terminations, but luckily I had some Kimber 8TC cables on hand with spade terminations that made a very firm connection to the M300 terminals once I tightened them down.  The M300 has both balanced and unbalanced input connections and 12v triggers.  The chassis is not your run-of-the-mill thin sheet metal found on AV receivers.  It’s significantly thicker giving the unit a very rugged build quality.  Potential owners should be particularly proud of the fact that this amplifier is fully designed and manufactured in the USA as you can see stamped on the back panel.  The CE mark is on the bottom of the unit and its rated power consumption (I assume a max rating) is 500 watts.

IQ Audio M300 MonoBlock Power Amplifier Sound Quality

Scenario #1: Office Room Desktop Listening

I initially connected up the M300’s to my desktop computer system featuring the EMP VT-40.2 Tube Amp / EMP E-41-SE/B bookshelf speaker system.  The E-41-SE/B’s are a very special speaker sporting RBH’s 4” phase plug beryllium-aluminum cone driver and a hot-rodded Scan-Speak 9500 tweeter I later added after my review. I bypassed the lousy computer soundcard with the Headroom Micro DAC and Headroom Micropreamp to drive the M300’s.   

Scenario #2: Audioholics Showcase Theater Room Listening

I connected the M300’s to my Marantz PM-11S3 Preamp outputs using the Oppo BDP-105 Blu-ray player and Marantz TT-15S1 turntable as the source devices.  The speakers were a pair of the new Status Acoustics Granite bookshelf system I currently have under review but I also tried them out on my $50k/pair Status Acoustics Titus 8T towers.  Cables were Kimber 8TC with spade terminations.

Listening Tests

Office Room

I honestly wasn’t expecting much of a sonic difference driving the little EMP E-41-SE/B speakers with the M300’s despite their much higher power rating than the EMP VT-40.2 20wpc tube amp in such a small room in a near-field listening environment, but the difference was significant..  The M300’s really brought new life to my little EMP speakers.  These EMP speakers are very revealing but a bit lacking in bass response due to their size.  However, driven with the M300’s, the bass they were producing was much snappier and had more weight.  The noise floor also seemed lower allowing me to extract details I previously wasn’t able to do with the EMP tube amp.  I did feel the VT40.2 had a bit more warmth in the top end but that didn’t mean the M300 was fatiguing by any means.  So far I was just using my paid subscription to Pandora.com for initial sound evaluations but it was time to move on to higher fidelity pastures. 

CD: Pat Metheny – Question & Answer

Track #1 “Solar” showed off the wonderful percussive genius of Roy Haynes.  The snares popped well and cymbals had a nice airy sound.  Metheny’s guitar was forward and clear. Track# 3, “H&H,” demoed more of the good stuff that I love about this jazz classic.  Bass line was tight and the M300’s didn’t run out of gas, sounding fully composed at insanely loud listening levels I’d dare not take my reference amp to for this system.  Instruments remained well separated and this song just begged for my full attention.

CD: Kem – Kemistry

I initially discovered the relatively new Soul/R&B singer Kem on my Pandora Michael Franks channel.    

The percussion sounded great in Track #1 “Matter of Time.”  The M300 drove my EMP speakers with authority.  The soundstage was deep and expansive and the reverb in Kem’s vocals sounded fabulous.  Track #9 “This Place” reminded just how incredibly accurate my desktop EMP speakers are at reproducing vocal timber.  The electric piano provided the accompaniment while Kem’s vocals came through with authority and utmost clarity.

IQ Audio M300's dwarfed in size by the Pass Labs X350.5

Audioholics Showcase Theater Room

I was quite surprised that the M300’s connected to my Marantz PM-11S3 preamp were dead quiet.  Usually the Marantz causes a slight hum heard with my ear against the grille of the speaker that even grounding the chassis’s together doesn’t completely eliminate.  This wasn’t the case with the M300.  Instead I “enjoyed the silence.”  Check out just how little the M300’s are next to the Pass Labs X350.5 two-channel monster amp I recently reviewed.

LP:  Richard Marx

Richard Marx rocks and is very underrated in my opinion.  Side 2 of his first album contained songs rarely (if ever) played on the radio and they were much harder-hitting than his more well-known radio pop songs. Track #5 “Have Mercy” starts out with some great drumming and a catchy hard rock guitar theme.  Richard’s voice portrayed the same great clarity I’ve heard on my own reference amps.  I enjoyed the edgy sound of this song and felt like I was thrust into a live performance with the music enveloping all around me.  Track #6 “Remember Manhattan” is my favorite track on the album mostly because I really dig the bass line.  Bass extended deeper than I expected.  The M300s delivered a soundstage and depth that bellied their diminutive size.  I was nodding my head in disbelief as I cranked the volume up higher and the M300’s accommodated me.  If you’re not a Richard Marx fan, I can assure you will be after hearing the entire second side of this album.  Check it out!

LP:  Miles Davis: Kind of Blue (180G)

Still a benchmark for vinyl even by today’s standards despite being over 50 years old, Kind of Blue is also the best-selling jazz album of all time.  Accompanying Miles are jazz legends such as Bill Evans on piano and John Coltrane on tenor saxophone.  Track #1 “So What” sets the mode for this album, which is just a feel-good laid back experience that is best accompanied by a good glass of red.  Jimmy Cobb’s cymbal brushes were delicate and airy while the back and forth between Miles on trumpet and Coltrane on sax was exhilarating.  The M300’s did a bang up job pumping the juice to my Status 8T speakers as I turned the volume up to lifelike SPLs.  I did feel the dynamics were somewhat constrained compared to my 1kwatt reference amps but I still couldn’t believe these little darlings were handling my power hungry speakers with such grace and delicacy.  Track #2 “Freddie Freeloader” is my favorite song on the whole album.  It just oozes coolness and if you’re foot isn’t tapping on this tune, someone needs to check your pulse.  Bill Evan tickles the ivories with a surgeon’s precision.  I got instant goose bumps when Miles’ trumpet kicked in.  The M300’s were demonstrating excellent bass control and poise, never sounding harsh or grainy.

SACD/ Blu-ray:  Jienat - Mira

This is my go to disc for testing dynamic capabilities of speakers, and amplifiers.   The multi-channel Mira Blu-ray recording is second to none in this regard but the two-channel SACD is excellent as well.

In Track #4 “DanceHall”, you’re enveloped in the middle of the room with singers all around you. The percussion was full of life and vibrancy in a way that you rarely ever hear in any recording.  Most playback systems are incapable of reproducing the dynamic range of this album. The M300’s did a very good job delivering the power necessary for the Status 8T speaker system to accomplish this goal cleanly, but it lacked the punch and depth of my reference amps.  Still, I was quite surprised by their composure.  I never heard distortion or clipping.  The M300s were producing up to their power limits with such excellent behavior and composure.  Recall that when I tested this very track using the uber pricey and hefty Pass Labs X350.5 amplifier, the bass drivers from my Status 8T speakers were sucking the life out of the power supply on this track.  On smaller speakers such as the Status Granite bookshelf speakers, the 300-watt limit of the M300 mono amplifier wasn’t an issue. 

IQ Audio M300 MonoBlock Power Amplifier Measurements and Analysis

All measurements were conducted using our Audio Precision APx585 8 Channel HDMI Audio Analyzer following our rigid Amplifier Measurement Test Protocol.

I did some quick spot-checking on the IQ Audio M300 amplifier gain structure to ensure it could be properly driven with a wide assortment of preamps or receivers.  This was not an issue with the M300’s 28dB gain structure (same as THX rated amps).  It only took about 1.4Vrms to drive the M300 to full rated power (150 watts, 8 ohms).  Any receiver preamp out section should work fine with this amplifier.

Signal to Noise Ratio

 

IQ Audio M300 SNR (A-wt) @ 1 watt

I was expecting poor noise measurements on the M300 since it’s a Class D amp and I didn’t have a pre-condition filter to prevent slew-induced input distortion and noise for my Audio Precision test gear.  I was pleasantly surprised to get excellent SNR results nonetheless.  With 115mV input, I measured 96.5dB at 1 watt A-wt and 85db with no filter.  At 150 watts, the SNR was 118dB A-wt.  That’s impressively quiet and seemed to validate the manufacturer rating of 40-50uV. 

Frequency Response

 

IQ Audio M300 Frequency Response under various load conditions

The ruler flat frequency response (-3dB at 60kHz and -1dB at 10Hz) of the M300 was yet another surprise to me.  We’ve measured a few Class D amplifiers in the past and they’ve almost always been optimized for a particular load impedance.  The Axiom Audio A1400-8 Class D amp for example would oscillate unloaded and vary its high frequency response dramatically based on the load it was driving.  This wasn’t the case with the M300.  The frequency response did NOT change whether the amp was measured open circuit, or via an 8 ohm and even 4 ohm load. In fact the deviation was measured to be a mere +-0.094dB from no load to load.  Also the response didn’t brickwall above 20kHz either.  This was a clear indication that the engineers who designed this amplifier executed the post filter feedback circuit with sheer brilliance. 

Power Measurements
Using our Audio Precision APx585 8-channel HDMI analyzer, I conducted a full barrage of power tests on the IQ Audio M300 amplifier. The M300 was tested on a dedicated 120V / 20A line. 

We tested power using three methods, all of which were taken at < 0.1% THD + N:

• Continuous Full Power Bandwidth (CFP-BW) from 20Hz to 20Khz into 8 and 4-ohm loads
• 1kHz Power Sweep vs Distortion (1kHz PSweep) - popularized by the print magazines, this is an instantaneous power vs. distortion test at 1kHz. The problem with this test is it often masks slew-related and or frequency response problems some amplifiers exhibit at the frequency extremes, and thus inflates the measured power results. It does provide an instant gratification # for consumers to argue over on the forums, so we are now incorporating this test to please the masses.

• Dynamic PWR - 1kHz CEA-2006 Burst Method testing. This is a dynamic power measurement adopted from the car industry similar to IHF method, only a bit more difficult for an amplifier and more representative of real musical content.

Keep in mind most review publications don't do continuous power measurements and they usually publish power measurements into clipping at 1% THD + N. Our measurements are very conservative as we use a dedicated 20A line with no Variac to regulate line voltage.  We constantly monitor the line to ensure it never drops more than 2Vrms from nominal which in our case was 120Vrms. 

For more info on amplifier measurements, see:  The All Channels Driven (ACD) Test

 

IQ Audio M300 Full Power Bandwidth Continuous Sweep (100 watts, 8 ohms)

 

IQ Audio M300 Full Power Bandwidth Distortion Sweep (100 watts, 8 ohms)

 The IQ Audio M300 exhibited excellent bandwidth linearity even at high output levels; in this case 100 watts continuous.  Distortion did rise with frequency but it was still below 0.1% at 20kHz.

 

IQ Audio M300 Full Power Bandwidth Continuous Sweep (307 watts, 4 ohms)

The M300 delivered a whopping 307 watts continuously from 20Hz to 20kHz.  Now that is big power from a Mighty Mouse sized amplifier.

 IQ Audio M300 1kHz Power Test
Top Pic: 8 ohm load;  Bottom Pic:  4 ohm load

The M300 produced great results with our 1kHz power sweep test.  Into 8 ohms, I measured 190 watts (1% THD + N) and 166 watts (0.1% THD + N), respectively.  At 4 ohms, I measured a whopping 371 watts (1% THD+N) and 317 watts (0.1% THD+N). 

We used the SMPTE IMD multi-tone distortion tests to see how the M300 amplifier reacts to non-harmonically related signals.  This is important since these artifacts can make music sound harsh or fatiguing.   The test signal consists of a 60Hz and 7kHz test signal summed together at a 4:1 amplitude ratio.  60Hz is an important frequency to show how well the power supply can reject residual noise coming from the AC line.  7kHz represents about the midband point of the human audio range and it's also a region where a lot of harmonic content is present in music.

 

IQ Audio M300 SMPTE IMD Distortion Test; 8 ohms

The harmonic residuals were well below the fundamental indicating good power supply noise immunity.

 

IQ Audio M300 Dynamic Power Test (1kHz); 4 ohm load

The CEA-2006 burst tests simulate musical program material.  The M300 produced some fine results for such a diminutive-sized amplifier.  At 8 ohms, it was able to deliver 195 watts at 1% THD + N.  Into 4 ohms, it belted out 367 watts at 1% THD + N.  

Because the M300 uses a Switch Mode Power Supply (SMPS) power supply instead of a linear supply, it has almost very little headroom at all beyond its continuous power rating.  This is a drawback of such a power supply and may explain why at times I felt the amp lacked dynamics when driving my reference speakers at loud SPL for highly dynamic program material.

# of CH	Test Type	Power	Load	THD + N
1	CFP-BW	150 watts	8 ohms	1%
1	CFP-BW	307 watts	4 ohms	1%
1	1kHz Psweep	190 watts	8 ohms	1%
1	1kHz Psweep	166 watts	8 ohms	0.1%
1	1kHz Psweep	371 watts	4 ohms	1%
1	1kHz Psweep	317 watts	4 ohms	0.1%
1	Dynamic PWR	195 watts	8 ohms	1%
1	Dynamic PWR	367 watts	4 ohms	1%

IQ Audio M300 Power Measurement Table

Note about CPF-BW:

I was unable to sweep full bandwidth at rated power below 20Hz as my APx585 produced erroneous results possibly due to limitations caused by the SMPS used in the M300.  When I tried to spot check discrete frequencies (10Hz to 20Hz) at rated power, the M300 went into obvious current limiting.

IQ Audio rates the M300 as follows:

• 150 watts < 0.02% ; 8 ohm load, 20Hz to 20kHz
• 300 watts < 0.02% ; 4 ohm load, 20Hz to 20kHz

Based on my measurements, I’d have to say the M300 amplifier is capable of delivering its stated power.  Weighing a meager 7lbs, it certainly offers the most power per pound I’ve seen in an audio amplifier.

FFT Distortion Analysis

 

IQ Audio M300 FFT Distortion Analysis; 1 watt, 8 ohms

I ran FFT distortion plot at 1 watt which overall looked fairly clean.  The 3rd order component was dominant, but still almost 90dB below the fundamental.  The M300 didn’t look so clean once the power level was driven up but that is to be expected of a Class D design, especially one using an SMPS power supply.   A precondition filter on the test gear is necessary for more accurate measurements in this case.

IQ Audio M300 MonoBlock Power Amplifier Conclusion

Downside

There is little not to like about a 300 watt amplifier I can literally hold in my palm of my hand.  However at $1500/pair, this gets you into a dangerously competitive price class of some seriously good two-channel amplifiers from the likes of Emotiva and Outlaw Audio.  If you need more power, and have the space for a much larger box, then the alternatives may better suit your needs.  However, if you want truly impressive performance from the smallest and most efficient package I’ve ever seen, the IQ Audio M300 has no equal.

IQ Audio M300 Stacked

Conclusion

I came into this review wanting to pick apart this little amp as nothing more than a gimmick.  Instead I was pleasantly surprised.  The IQ Audio M300 amplifier is the first Class D amplifier that I’d seriously consider for my own use. It offers better measurable performance than I’ve seen from the Axiom Audio Class D amp and the very popular ICE amplifier modules integrated into some AV receivers and standalone products.  It generates little to no heat making it ideal for stacking multiple units or cramming into tight spaces.

Most importantly, the M300 sounds fabulous, never misbehaving or losing composure.  It is a deceptively great little amplifier. I’d recommend this amplifier for small to medium sized speakers with reasonable sensitivity (>87 dB 2.83V/meter); not goliaths like my 2 ohm dipping $50k reference towers.  The M300 should be able to fill a medium sized room with clean SPL without a hitch.  I foresee the M300 fulfilling many applications splendidly like an office system, personal DJ system or to power speakers from an electric drum kit or digital piano.  This is the only amplifier offering IQ Audio currently produces but I sincerely hope that changes.  I’d love to see a multi-channel amp based on this design as well as a more powerful MonoBlock for power mongers like me.

IQ Audio Corporation
M300 Review
MSRP: 747.50/ea

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Frequency Response Linearity
SNR
Measured Power (8-ohms)
Measured Power (4-ohms)
Multi-channel Audio Performance
Build Quality
Fit and Finish
Performance
Value