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Review and Measurements of Grace Design m900 DAC & Amp

amirm

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#1
This is a review and detailed measurements of the Grace Design m900 DAC and headphone amplifier. It is on kind loan from a member and was drop shipped to me. It costs USD $575 but I see it on sale for USD $545.

The unit has a substantial feel to it despite being small. Its design highlight is the metal rotary control for the volume control:
Grace Design m900 DAC and Headphone Amplifier Review.jpg

The rotary control feels a bit light to me but otherwise, it is one of the best controls in the business. Unlike similar looking ones from JDS Labs, this one has a metal knob giving it more of a luxurious feel. A couple of bright white LEDs show the current volume level as you see in the picture.

The unit comes with an optional external USB power supply which is beefier than the typical mobile phone one. The manual says it will work without it but it will sense the lack of sufficient current from the USB port and throttle the output. For my testing, I left the power supply plugged in.

Typical of modern DACs, the device is UAC2 compliant so no need for drivers or anything. Plug it in and you are in business.

There are three inputs in the back: USB, S/PDIF and Toslink. I only tested the USB port.

Massdrop sells a version of this called m9xx. A local member has offered that for testing so I will be able to verify how different they may be.

Strangely, the web page for m900 is missing from Grace Design's own website.

Let's get into measurements and see how she does.

DAC Measurements
As usual, I test the DAC portion of these combo units before testing the headphone output. Here, the RCA out is variable and goes to multiples of what we need (2 volts) indicating RCA outs are just tapped from the headphone amplifier. In these cases I adjust the level to 2 volts to match DACs normally tested and run the dashboard:

Grace Design m900 DAC and Headphone Amplifier Measurements.png


Wow, these are excellent numbers! Second harmonic distortion is down to -115 dB or so. Combined and added to noise level, the Grace Design m900 lands solidly in our tier 1 performance chart:
Grace Design m900 DAC and Headphone Amplifier SINAD Measurements.png


Likewise dynamic range is quite good with 2 volt output:

Grace Design m900 DAC and Headphone Amplifier Dynamic Range Measurements.png


Story gets even better with the m900 nailing the jitter test with very low noise level and almost total absence of spurious tones.

Grace Design m900 DAC and Headphone Amplifier Jitter Measurements.png


The good news doesn't end there. Here is linearity:
Grace Design m900 DAC and Headphone Amplifier Linearity Measurements.png


Intermodulation distortion and noise doesn't quite match match our reference Topping DX3 Pro in noise level (sloping down part of the curve) but has almost no level related distortion, beating the DX3 Pro that way at max volume (of again, 2 volts):
Grace Design m900 DAC and Headphone Amplifier IMD Measurements.png


Can this keep going when we run the 32-tone test?
Grace Design m900 DAC and Headphone Amplifier Multitone Measurements.png


Oh, what happened here? We have those intermodulation between our spikes going down to the lowest frequency and accumulating heavily as we go up in frequency. Why didn't this show up in previous tests? I am not 100% but this test is run at 192 kHz sampling rate so perhaps there is a problem there?

To make sure the setup was not the cause, I ran the identical test on Topping D50 and got the expected clean results:
Topping D50 DAC Amplifier Multitone Measurements.png


As you see, we used the same power supply as Grace Design.

Let's see if we can get a clue as to what may be wrong by running the THD+Noise versus frequency:

Topping D50 DAC Amplifier THD vs Frequency Measurements.png


Look at that massive rise in THD+N starting at 5 kHz. Note that this test uses a wide spectrum of 90 kHz versus the dashboard which runs at 22.4 kHz. Let's look at the wideband spectrum at different frequencies and see if we can find the source of this problem:

Grace Design m900 DAC and Headphone Amplifier FFT Measurements.png


On the left is 1 kHz and all is well more or less. But notice what happens when I switch to 8 kHz on top right. We have that large spike at 40 kHz. The more I increase the frequency, the taller it gets. To wit, the inset is at 16 kHz and by then the 40 kHz tone is at very high levels.

The frequency of the 40 kHz tone is not changing with source frequency. It is its amplitude that increases. I wonder if the output stage is oscillating at that frequency?

EDIT: The above issue was due to selection of filter F4 which provides no filtering in transition band. Selecting F1 filter remedied that: https://www.audiosciencereview.com/...of-grace-design-m900-dac-amp.6470/post-144171


Headphone Amplifier Measurements
Let's switch to the headphone out jack and run our usual power versus distortion+noise at 300 ohm:

Grace Design m900 DAC and Headphone Amplifier THD versus power at 300 ohm Measurements.png


The m900 matches the power output of Topping DX3 Pro but can't keep up with it with respect to distortion. Distortion sets in earlier and climbs higher. On noise level, due to lack of gain settings, it loses a lot to the DX3 Pro in low gain mode.

Changing the load to 33 ohm gets us this:
Grace Design m900 DAC and Headphone Amplifier THD versus power at 33 ohm Measurements.png


We get nearly 1 watt of power but distortion sets in pretty early (around 2 milliwatts). Clearly the amplifier in m900 is less at home with a low impedance load than high.

Output impedance is a low and comfortable 1.2 ohm:
Grace Design m900 DAC and Headphone Amplifier Output Impedance Measurements.png


This shouldn't give you trouble with any headphone.

Channel balance was excellent as is typical of these DAC and Amp combos where they can control the level digitally through the DAC chip:
Grace Design m900 DAC and Headphone Amplifier Channel Matching Measurements.png


Listening Tests
By accident, I started my listening tests with the m600 running purely on USB power (i.e. no external power supply). With my Sennheiser HD-650s, the m900 barely got loud enough and fidelity was just OK. Switching to much lower impedance Hifiman HE400i caused additional trouble. Getting close to anywhere close to max volume would cause distortion. In addition, the unit would shut down with "OC" indicator which I assume to be over current.

Scratching my head that the above should not be happening, I realized my power strip was shut off so the power supply was off as well. Turned that on and there was a larger transformation. Bass became thundering with both headphones and I could not detect any distortion even at the limit. As such, I highly recommend that you run the m900 using its external power supply with power hungry headphones such as the ones I used.

Conclusions
The Grace Design m900 starts the show well with excellent measured performance. It was hard to find a fault until I tested the unit with wider bandwidth than 22.4 kHz I normally use. There, there are high frequency oscillations which sharply reduce performance. Mind you, the problem is ultrasonic and not audible but from engineering point of view, they should not be there. It is amazing how close to winning the m900 the measurement crown for dac+amp but didn't quite get there at the end.

Subjectively, performance is excellent. There is plenty of volume there to drive just about any headphone. No, it is not distortionless like some of the other products we have measured but subjectively, it is fine.

Price is high of course but with it you get excellent build, super nice volume control and attractive and unique packaging.

For those of you wanting to find a western design version of Topping DX3 Pro, the Grace Design m900 is it. On that basis, I am going to recommend the product even though I wished there were no ultrasonic distortions visible in measurements.

------------
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amirm

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#3
I have a M9xx which I picked up for roughly half price. It's great with HD6xx phones.
Wow, was it that cheap? That would have made it a very good purchase.
 

Ron Texas

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#4
Wow, was it that cheap? That would have made it a very good purchase.
It was supposedly a factory refurb. Condition was like new, but the cables were not the ones with ferrite beads and the USB wall wart was missing. The chokes cost me $3 for 2 at a nearby electronics store and I am using a spare iPad charger for power. I keep it on the night table as my second system, but I can pack it and take it on a trip with an external HD and my laptop.

The volume control is super convenient and it's nice to have a single box solution.

I am not surprised by the test results as other Grace products measure well.
 

Roen

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#9
Would you rather use this on battery or a Modi 3 + O2, both on batteries, subjectively speaking?

It seems like this is a good DAC, but should be paired with a capable amp to extract the same level of performance as some of the top tier products.

I wish it had a dedicated line-out circuit, as well as analog volume control as I am (philosophically) not a fan of digital attenuation as volume control.
 
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Ron Texas

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#10
Would you rather use this on battery or a Modi 3 + O2, both on batteries, subjectively speaking?

It seems like this is a good DAC, but should be paired with a capable amp to extract the same level of performance as some of the top tier products.
My opinion is it works better in the high power mode. It certainly drives low sensitivity cans better. That means you will need a largish battery to provide at least 1.5 A @ 5V.
 

graz_lag

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#11
A 20,000mAh / 74Wh Power Bank gives you up to 3.4A @ 5V ...
 

BYRTT

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#13
Hi Amirm
Thank you for the review.

How do you think is it going to traslate in termns of sound that sky rocketing result at THD+N chart ?

Pretty disappointing the USB low power mode has this problem. Do you think that with low impedance headphone, even at low volumes, fidelty is going to be good enough or just ok ?
 

Ron Texas

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A 20,000mAh / 74Wh Power Bank gives you up to 3.4A @ 5V ...
I have one almost that large to use if power goes out from a storm. Nearly all of these 5V battery packs use switching power supplies, so I don't see any likely improvement in SQ, and never heard one with mine. The M900 does not have an on off switch, so the battery will discharge if you forget and leave it connected.
 

Blumlein 88

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#16
Would be nice to see a wideband spectrogram as you run a sweep from 20-20 khz on the Grace. Might illuminate what the interaction is with the strange behavior at higher frequencies.
 

m8o

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#17
Ya, their website seems to be a bit 'messy' (this review proves they're experts in physical audio electronics, not necessarily websites -hehe- ). The M900 page is here:

https://gracedesign.com/products/monitor-controllers/m900/

Owner of a M9xx here. I look forward to hearing confirmation it performs on par with Grace's own offering. I see no reason it won't, but emperical evidence is always welcome. As the M9xx only has toslink spdif in, I do wish my unit had the coax spdif in of the M900 at times tho.
 
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amirm

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Why do you compare to the Topping DX3 and then run 32 tone test on the D50?
The DX3 Pro is in my measurement templates so it is always there. I also use it for listening tests so for new data, I don't use it. Music comes first, measurements second. :)
 

amirm

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#19
The Y axis is a different unit for the grace chart.
Yeh, I used to show voltage there but changed to dB to make it easier to interpret. The scale is the same though.
 

amirm

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Hi Amirm
Thank you for the review.

How do you think is it going to traslate in termns of sound that sky rocketing result at THD+N chart ?
Hi there. No impact on sound because the cause of THD+N is the spike at 40 kHz that by itself is not audible. The only concern there is if you used speakers and the extra energy there started to cook the tweeter. I have to see if its level is proportional to signal or not.
 
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