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Monoprice Monolith 7 Amplifier Measurements & Analysis

By

by: Gene DellaSala

Design Overview

Inside the Monolith 2 you will find a lot of empty space. This is NOT a bad thing mind you as there is plenty of space for ventilation.  The power modules are constructed as monoblocks; each having 6 output devices per channel and 4x 5,600uF, 80V capacitors in parallel to yield a total of 22,400uF of capacitance per channel. 

Monoprice Monolith 2 Two Channel Amp

Interior view of the Monolith-2 two-channel amplifier.

The power modules are constructed as monoblocks; each having 6 output devices per channel and 4x 5,600uF, 80V capacitors in parallel to yield a total of 22,400uF of capacitance per channel.  The parts are rated at 85 deg C which,is pretty standard fair for a product of this caliber.  The entire amp is fed off one large 800VA transformer.  This amp has all the right hardware to deliver its rated power honestly, and then some.  The same principles remain as you move up the model line-up with their Monolith7 boasting dual torrodial power transformers (1,230VA and 1,025VA) to maintain rated power with all channels driven.

Bench Test Results

All measurements were conducted on a Monolith-2 using our Audio Precision APx585 8 Channel HDMI Audio Analyzer following our rigid Amplifier Measurement Test Protocol.

All of the amps in the Monolith series feature the same gain blocks and similar power output.  The following test results were conducted on the Monolith-2 two-channel amplifier.  All Monolith series amplifiers use exactly the same amplifier modules and will yield the same measurement results. And as you'll read below, the power supply in the Monolith 7, seven-channel version is sized to deliver rated power to all channels. Voltage gain is spec'd to be 28dB which allows the amp to reach full rated power output with 1.6Vrms input.  I actually measured closer to 28.8dB voltage gain allowing the amp to reach full rated power (200 watts) with 1.43Vrms input.  Most AV receivers with preamp outputs should be able to deliver this.

Signal to Noise Ratio

Monoprice Monolith 2 SNR measurements

Monolith-2 SNR (A-wt) @ 1 watt 

The Monolith-2 exhibited an incredibly low noise floor which isn't surprising given the quality of the guts inside and the expert design of the folks at ATI behind it.  At full rated power (200 watts), the noise floor was around 121dB.  If there is noise in your system, rest assured it's not caused by this amplifier.

Frequency Response

Monoprice Monolith-2 Frequency Response

Monolith-2 Frequency Response @ 1 watt

The frequency response of the Monolith-2 was ruler flat at virtually every power level within the audio band and down only -1dB at 10Hz and the limit of my measurement system (80kHz). 

Power Measurements

Using our Audio Precision APx585 8-channel HDMI analyzer, I conducted a full barrage of power tests on the Monolith-2 using 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 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.

Monoprice Monolith 4 Ohm sweeps

Monoprice Monolith Full Power Bandwidth Continuous Sweep (335 watts, 4 ohms)

The Monolith-2 delivered a whopping 335 watts/CH full bandwidth with both channels driven at less than 1% THD+N.  It's nice to see a manufacturers product deliver more than rated power as its uncommon today in the AV receiver market.  

 

Monoprice Monolith 1kHz Power test 8 and 4 Ohm loads

Monolith-2 1kHz Power Test

Top Pic: 8 ohm load;  Bottom Pic:  4 ohm load

The power sweep tests revealed the Monolith-2 to be a powerhouse comfortably delivering more than its rated output power with both channels driven.  We measured 221 watts/ch at 1% into 8 ohms and 356 watts/ch at 1% into 4 ohms, both channels driven.

Monoprice Monolith Dynamic Power Test 8 Ohm

Monolith Dynamic Power Test 4 Ohm Load

Monolith-2 Dynamic Power Test (1kHz)
Top Pic: 8 ohm load;  Bottom Pic: 4 ohm load

The CEA-2006 burst tests simulate musical program material.  The Monolith-2 proved have incredible dynamic headroom partly due to its very beefy power supply.  Into 8 ohms, the Monolith-2 produced over 1.5 dB of dynamic headroom for 8 ohm loads and 2.5 dB for 4 ohm loads. 

Monolith Power Measurement Table

Monolith-2 Power Measurement Table

Monoprice rates the Monolith-2 as follows:

  • 200 watts: 20Hz - 20kHz < 0.03% ; 8 ohm load
  • 300 watts: 20Hz - 20kHz < 0.03% ; 4 ohm load

The Monolith-2 easily delivered rated power and then some.  It's refreshing to see an amplifier manufacturer conservatively rating its products.

FFT Distortion Analysis

Distortion Analysis for Monoprice Monolith

Monolith-2 FFT Distortion Analysis

(Top pic: @ 1 watt ; Bottom pic: @ full power)

I ran FFT distortion plots at 1 watt (top pic) and full rated power (bottom pic) to determine how clean this amplifier really is. 

There was a slight ground loop that developed between the Monolith-2 and my test equipment I was unable to fully resolve which did have a negative effect on the distortion results.  That said, the noise floor was exceedingly low while the odd-order harmonics dominated the distortion profile.  The 3rd harmonic was still 96dB below the fundamental.  At full power, the distortion products rose as expected but the 3rd harmonic was still 83dB below the fundamental which was good.

Crosstalk

Crosstalk measurements for Monoprice Monolith

Monolith-2 Crosstalk (Channel to Channel Isolation)

The channel to channel isolation of the Monolith-2 is simply superb exhibiting -120dB at 20kHz with a very slow rise up to 80kHz.  This is about as good as it can get and allows you to get the monoblock type of isolation from a multi-channel amplifier.

Downside

There was little to fault in the performance of the Monolith-2 amplifier.  It offers text book measurements, and clean ample power with plenty of dynamic headroom.  The lack of balanced inputs was perhaps my biggest gripe with this amplifier followed by the closely spaced +- speaker terminals that can make it challenging to mate with some fancy speaker terminations.

 

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Recent Forum Posts:

tparm posts on June 16, 2020 16:14
With Class D amplification being en vogue and ATI having success with their AT52XNC series, how long until there is a Class D Monolith variant? Thoughts? Insider info????
RichB posts on June 14, 2020 15:51
Pogre, post: 1397880, member: 79914
Boom! Thanks Peng!

I am going to conclude that scooting a little closer will definitely take a little heat off my speakers at high volumes. The folks over at Ascend have been a little bit hit and miss to contact lately, with everything going on but they always eventually get back to me. I think I'm gonna shoot Dave an email and ask him ask about max spl at 1 meter, like you suggested I do with Ed for my Ultras.

You know what's interesting, tho maybe not overly surprising? My Monolith runs MUCH cooler powering my 4 ohm Sierra towers than it does my “8 ohm” Ultra towers. It's gets good and warm with the Ultras, but barely more than lukewarm with the Sierras. Even after some some very spirited listening sessions.

In general, when you consider stereo and room gain the volume at the listening position can be surprisingly close to rating at 1 meter (when accurately specified).
Ascends are among the best manufacturers at accurate sensitivity specifications.

Here is recent article on Audio Science Review:
https://www.audiosciencereview.com/forum/index.php?threads/speaker-sensitivity-advertised-vs-measured.14072/

Adding power to speakers that perform will with power (with good distortion characteristics) can lead to listening at higher levels. A small radio can seem too loud because the distortion is makes it unpleasant. That said, I have found I enjoy my Salons for casual listening at less than one watt. Of course, I'd like a near perfect 1'st watt

THX specifications are for a single speaker but this is not representative of any realistic listening session.
To estimate my power usage I used the following procedure.

I played 250Hz, 1kHz, and 2kHz 0 DBFS (maximum volume) sine-wave tones and measured the voltage at the speaker adjusting the processor until it was as close as possible to 2.83 volts. The volume matches the speakers sensitivity rating. While playing the tone, I measured the SPL at my listening position of 11 feet.

The Salon2s are rates are 86 dB at 1 meter. The measured SPL was also 86 dB (with two speakers playing). The Salon2s are basically 4 ohm speakers that doubles to power. For my spreadsheet, this means -31 is 86 dB at 11 feet. From there I computed the attached power levels. Since I know my habits, the left column indicates those levels. Fortunately, the AHB2 amplifiers have accurate and clip meters per channel that illuminate for 1/4 seconds when the amp hits 1% distortion.
With music, they clip as expected with recording that peak at full scale (too many recording are maximized for volume).

Into 4 Ohms, the AHB2s deliver 180 WPC and they are not clipping at -10 so these numbers are conservative.
I also plugged in these numbers into the Crown power calculator: 3.5 meters, 101 dB, 83 dB sensitivity (for 4 ohms) and the required power is 773 watts.
My measurements and calculation show 64 watts stereo or 128 watts for a single speaker.

37113
37114

The Aquaman 4K BD has some formidable bass and I turned it up -15 (which is 3 dB louder than I found comfortable) and there is no clipping and the Salon2 3 8 inch woofers are really moving.

Unfortunately AVR amps are seldom measured as diligently as dedicated power amps and not going into protection is not a good indicator of distortion driving reactive loads. Those measurements don't really exist. We know a lot about how amps play 1 kHz sine-waves into reactive loads.

- Rich
operamatt posts on June 14, 2020 08:31
Verdinut, post: 1397824, member: 80194
Those Monolith amplifiers are really well designed affordable amplifiers. You won't regret your purchase.

Are you an opera nut too? Because of my user name, it's not hard to guess who is my preferred Italian composer. If that is the case, maybe we could exchange comments at some point. In my collection, I have the complete Verdi Parma Opera series on Blu-ray, apart from all his operas on CD. That's only part of my opera collection.

I know quite a bit about opera singers and I am very critical about them. I studied classical singing. As a lyric tenor, I used to sing solos with choirs, and also sung in restaurants as a hobby. It was indeed a passion.

Cheers!
very cool, i also trained as a classical musician. my mane instrument was voice but i was a pianist & director as well. i’ve chosen a different path for my life but the love for classical music is still there.
PENG posts on June 13, 2020 09:23
Pogre, post: 1397880, member: 79914
Boom! Thanks Peng!

I am going to conclude that scooting a little closer will definitely take a little heat off my speakers at high volumes. The folks over at Ascend have been a little bit hit and miss to contact lately, with everything going on but they always eventually get back to me. I think I'm gonna shoot Dave an email and ask him ask about max spl at 1 meter, like you suggested I do with Ed for my Ultras.

You know what's interesting, tho maybe not overly surprising? My Monolith runs MUCH cooler powering my 4 ohm Sierra towers than it does my “8 ohm” Ultra towers. It's gets good and warm with the Ultras, but barely more than lukewarm with the Sierras. Even after some some very spirited listening sessions.

I just clarified my comments a little, but we were typing at the same time.

The Ascends are likely more sensitive and have better phase angles than the Ultras. I discussed power requirements with Ed before, you (may be not you but people who think amps are always needed for 4 ohm speakers) will be shocked if you know what he said..
Pogre posts on June 13, 2020 09:18
PENG, post: 1397878, member: 6097
Okay then, the Ascends in your system will still be the bottleneck as it is only rated 500 W maximum short term peak. You will need about 660 W to hit reference level with one speaker from 15 feet.

The Monolith can output only a little more than 500 W average short term dynamic peak, that's 1,000 W peak, two channel driven into 4 ohms.

Calculated results based on Ascend specs, for one single speaker:



Input data required:
Input data
Unit


1) Speaker nominal impedance (Ohms)
4.00
Ohm


2) Sensitivity in dB/W at 1 Meter


dB


3) Sensitivity in dB/2.83 V at 1 Meter
90.00
dB


4) Seating distance (1 foot = 0.3048 Meter, 1 Meter = 3.281 foot)
4.57
Meter


5) Room gain for speaker placement near walls/corners, enter 0 to 3 dB max., to err on the conservative side
3.00
dB


6) Desired additional amplifier headroom (dB) Recommended minimum is 3


dB


7) Target SPL - THX reference is 85 dB, with 20 dB of headroom
105.00
dB









Calculated values from the input data:
Calculated values



Sensitivity loss at seating distance (dB)
13.20
dB


SPL/W at seating distance calculated from the input data
79.80
dB


Amplifier power output based on 2.83 V and the assumed impedance at 1 Meter
2.00
Watt (W)


Power increase in multiples needed to achieve target SPL
331.46



Power increase in dB needed to achieve target SPL
25.20
dB









Calculated amplifier output power required:





For the target SPL at seating distance
663.66
Watt (W)


For the target SPL at seating distance, with the desired headroom included


Watt (W)


Boom! Thanks Peng!

I am going to conclude that scooting a little closer will definitely take a little heat off my speakers at high volumes. The folks over at Ascend have been a little bit hit and miss to contact lately, with everything going on but they always eventually get back to me. I think I'm gonna shoot Dave an email and ask him ask about max spl at 1 meter, like you suggested I do with Ed for my Ultras.

You know what's interesting, tho maybe not overly surprising? My Monolith runs MUCH cooler powering my 4 ohm Sierra towers than it does my “8 ohm” Ultra towers. It's gets good and warm with the Ultras, but barely more than lukewarm with the Sierras. Even after some some very spirited listening sessions.
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