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Review and Measurements of Musical Fidelity M2si Amp

amirm

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#1
This is a review and detailed measurements of the Musical Fidelity M2si integrated stereo amplifier. It was kindly sent in by a member. I think the list price is US $999. However I see it selling for just US $599 from the outfit the owner purchased it. Other places have it as high as US $700.

From the pictures, the M2si looked very elegant and high-end. In person in black, it looks a bit less so and somewhat industrial:

Musical Fidelity M2si Integrated Stereo Amplifier Audio Review.jpg

Still, head and shoulders above DIY enclosures or budget products. To wit, it came wrapped in thick velvet and even came with white gloves!

The back panel shows what you would expect:
Musical Fidelity M2si Integrated Stereo Amplifier Back Panel Connections Audio Review.jpg

Sadly no balanced inputs. but we do get preamplifier out. I did not see that until this morning when I took pictures of it. So I put it back on the bench and took a quick snapshot of that too.

The unit is heavy being a class AB amplifier with toroidal transformer and such. In use the left side remains almost room temperature. The right side though gets warmer but nothing resembling hot.

I liked that the protection circuit was not latching in that when the overload conditions when away, it would reset itself and the amp was functional again. I see too many AVRs and amps these days that shut down and require power cycle to work again.

And oh, plastic remote comes with it which I did not use. But I don't see it listed on the MF website.

Anyway, overall impression is positive for an amplifier in this price range from brand name company sold through dealers.

Preamplifier Audio Measurements
As noted, I only got a chance to run the dashboard against the preamplifier section:
Musical Fidelity M2si Integrated Stereo Preamplifier Audio Measurements copy.png


This is good performance with SINAD that is 100 dB and dominated by noise, not distortion (distortion is near -108 dB).

Integrated Amplifier Audio Measurements
It is a bit of a quandary how to measure integrated amplifiers. Do I feed it the full output of 2 volt and then bring the level down with volume control to measure 5 watts? Or do I set the gain high (e.g. common 29 dB) and feed it much lower level to simulate what we get in power amplifier testing? I ran both:

Musical Fidelity M2si Integrated Stereo Amplifier 2 volt in Audio Measurements copy.png


Musical Fidelity M2si Integrated Stereo Amplifier Audio Measurements copy.png


The difference fortunately is not much because as I showed earlier, the pre-amplifier is much cleaner than the power amplifier. I used an average SINAD (signal over noise and distortion) of 82 which places the M2si slightly above average:
Best Stereo Amplifiers Measured copy.png


Frequency response is flat in audible band and extends fair bit past that:

Musical Fidelity M2si Integrated Stereo Amplifier 2 volt in Frequency Response Audio Measureme...png


Here is our 32-tone input response:

Musical Fidelity M2si Integrated Stereo Amplifier 2 volt in Multitone Audio Measurements copy.png


Really like to see 16 bits here to clear the most common CD/download format.

Distortion rises with frequency which is typical.

Amplifier Power Measurements
There has been discussions recently about how to measure power output from amplifiers. First, let's start with our usual graphs starting with 4 ohm load:

Musical Fidelity M2si Integrated Stereo Amplifier Power into 4 ohm Audio Measurements copy.png


I was surprised to see the protection circuit kick in and shut the amp down before anything clipped. Seems too aggressive to me. Regardless, this makes power measurement easy as there is only one max power level at 80 watts.

Switching to 8 ohm, we get our classic clipping response at max power:
Musical Fidelity M2si Integrated Stereo Amplifier Power into 8 ohm Audio Measurements copy.png


As is typical we are shy of reaching manufacturer's 72 watt spec. Looking at the clipping portion of the graph you see that if I went to the right some, I would get more power -- as much as 100 watts.

Question is, how far do we want to go to the right if any? And how about different test frequencies? Above are all at 1 kHz which is common testing criteria but with music, most of energy is at lower frequencies. I grabbed a few tracks from my music library and analyzed their spectrum. Highest peaks were around 40 to 45 Hz so we are way off the mark with 1 kHz tone.

Let's run a sweep to measure power for the full audio band and change the criteria for amount of distortion we allow for 8 ohm load:

Musical Fidelity M2si Integrated Stereo Amplifier Full Bandwidth Power into 8 ohm Audio Measur...png


I have included the control panel so you can see all the parameters. The top line separated from the rest is at THD+N of 10%. The rest that are bunched up on top of each other are 1%, 0.5% and 0.1%. For this amplifier at least, it seems that it makes no difference what we pick between 0.1 and 1% THD. An amplifier that would soft-clip would be different.

With respect to frequency sensitivity, we do have some power droop at low frequencies. The reservoir capacitors cannot catch their breath due to slow rate of change at lower frequencies. So maybe we should change my THD+N versus power graph to use 45 Hz? We would lose the data we already have if we did that.

One thing that has been bothering me is that peak power is measured at 1% THD but my regular power specs have been at onset of clipping, making comparison of those two values hard. Alas, I could not do that for 4 ohm with this amp because it never clips. So I set the continuous power threshold to 0.1% to get the max power:

Musical Fidelity M2si Integrated Stereo Amplifier Power into 4 ohm Maximum and Peak Power Audi...png


We see quite a bit of headroom as is typical of class AB amplifiers versus class D.

With 8 ohm I could use the same 1% THD+N for both:

Musical Fidelity M2si Integrated Stereo Amplifier Power into 8 ohm Maximum and Peak Power Audi...png


Notice how our maximum power is around 75 watts which beats the spec and my graph measurements of 66 watts.

Like to see some feedback on what to measure in the future. While I could run all of these, in case of devices with multiple functionality (e.g. AVRs), it would increase my workload more than it already is. With simple amplifiers like this I could run them all.

Conclusions
The Musical Fidelity M2si is a well built and nice looking, branded integrated amplifier. Its preamplifier performance is very good but the power amp holds it back. The price is reasonable and inclusion of remote control is very nice in my book. I can't recommend it on pure performance but you have all the data to decide for yourself.

------------
As always, questions, comments, recommendations, etc. are welcome.

A kind member is building me a PC and I have to pay him soon. Alas, I looked in my paypal account and it is darn near empty given the use of funds for the last few wild parties we have had (had to drown out the sorrow after a few bad review results). So please donate as much money as you can using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Rja4000

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#3
I have an M6 PRX, which I like a lot.
I wonder how it measures...
(Given for 0.003% THD 20Hz-20kHz, <0.007% THD+N 20Hz to 20kHz, and SNR 120dBA)

I like the idea of power vs frequency, by the way.
 
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Herbert

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#4
I am even a litle bit surprised that A/B amps are still being made.
What power transistors are used?
I had a 2N3055 based Musical Fidelity B1 for almost two decades,
got unsatisfied with the sound and tried some amps for replacement.
I know amplifiers do not "sound" but I got very happy with a used
Nakamichi IA-3 which has a pair of 2SA1695 / 2SC4468 as power transistors.
The trannies are still being produced so I am curious if they are implemented in the Musical Fidelity...
 

Matias

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#6
images (9).jpeg
 
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#7
I am even a litle bit surprised that A/B amps are still being made.
What power transistors are used?
I had a 2N3055 based Musical Fidelity B1 for almost two decades,
got unsatisfied with the sound and tried some amps for replacement.
I know amplifiers do not "sound" but I got very happy with a used
Nakamichi IA-3 which has a pair of 2SA1695 / 2SC4468 as power transistors.
The trannies are still being produced so I am curious if they are implemented in the Musical Fidelity...
2N3055... Brings back memories. Built an AB amp with those and a complement, maybe c1968? 1972? Schematic out of ARRL handbook...
 

audimus

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#8
The back panel says Feb 2017. Don’t know when this was first released. But in 2019, it seems so outdated in interfaces that one can only see these amps as dead men walking. Tuner, tape inputs etc. Only analog sources.

I am sure there are some households that can still use these.

With regards to the measurements...

The pre-amp is an analog only unit with measurements from analog in to analog out with just a switching and volume control circuit. Except for discovering a totally incompetent design or manufacturing defect, does it even make sense to rate the “pre-amp” performance as good?

This is pretty much just an amp with volume control for its common use and testing. Integrated amps these days provide digital inputs and a DAC whose performance is worth evaluating as they involve significant circuitry that may vary a lot and difficult to get great performance.

As an amp with volume control, it is an average amp that is way overpriced. Unless to some ears it sounds golden over other mass market brands and makes them happier.
 

restorer-john

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#11
Question is, how far do we want to go to the right if any?
Standardize on either -60dB/0.1% or -40dB/1%. Standard position on the cross-hairs every time.

Reason: If you have a "knee" at 0.0001% or a "knee" at 0.1% on two different amplifiers, the power output numbers cannot be compared on the same playing field. The super low THD amplifier is at a distinct disadvantage in power numbers.

And how about different test frequencies?
Stated distortion number at X watts per channel, both channels driven at R ohms for any frequency from 20Hz-20Khz. (as per the FTC spec). Each end of the spectrum is where the amplifiers will fall off- don't give them a free ride. :)

The other parameter to test is channel balance across the volume range- you do it with D/A converters, and yet pre/main (int) amplifiers are where the troubles will lie, especially with cheap twin gang carbon track pots used in a lot of "lower cost" amps. This unit appears to use a motorized Alps RK-27.
 
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amirm

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#12
Maybe I should make three power measurements:
No clipping
Maximum Power (1% THD)
Peak Power (1% THD but short duration)
 

amirm

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#13
Stated distortion number at X watts per channel, both channels driven at R ohms for any frequency from 20Hz-20Khz. (as per the FTC spec). Each end of the spectrum is where the amplifiers will fall off- don't give them a free ride. :)
Do you want the graph or just worse case number?
 

amirm

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#14
The back panel says Feb 2017. Don’t know when this was first released. But in 2019, it seems so outdated in interfaces that one can only see these amps as dead men walking. Tuner, tape inputs etc. Only analog sources.
I was surprised how long this unit has been sitting seeing how it was just purchased and drop shipped to me. The shop that sells it has a video saying they had too many and gave him a discount to sell them cheaper. Likely it is for reason you mention.
 

restorer-john

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#16
Maybe I should make three power measurements:
No clipping
No clipping is open to interpretation and also must be measured against the rated spec which will be different for each amplifier.

Test each against their rated spec and call it out if they fail or are considerably better. Do your other two tests as they are (sadly) becoming industry standard.
 

amirm

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#17
Worst case. ie. everything else is the same or better than that number.
Putting aside confusing the reader with so many wattage values, worst case will likely be at 20 Hz. That is fine for home theater products but I don't think there is much content in music down low.
 

restorer-john

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#18
The AVRs' PSUs will run out of steam really fast in the low end, particularly with multiple channels at once.

But then again, 20Hz-20K has been the standard forever. I remember low end amplifiers 'cheating' by quoting their power outputs at 40Hz-20K or even 50Hz-20K to get a few extra watts on the spec sheet.
 

Another Bob

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#20
Like to see some feedback on what to measure in the future.
After the standard dashboard and multi-tone IM test, my favorites are the max power vs. frequency (could limit this to one or two distortion levels, but no more than 1%) and the power vs. distortion at various frequencies (as in the Schiit Aegir review, for example). I recognize these show very similar things, so no problem if you want to do just one or the other.
 
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