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Measurements Of Chord Mojo

March Audio

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#1
I know Chords Mojo is on Amirs ToDo list, but I have decided to publish my measurements as another data point to compare our two measurement systems for consistency.

The Mojo is a well known and regarded unit, its in a small and robust aluminium case with usb, optical and electrical SPDIF inputs. It has 2 3.5mm headphone outputs and funky (read odd) power and volume control balls which change colour. The unit has a rechargeable battery as it is in essence a portable unit. A second usb input is used for powering and recharging the unit. Personally I find the idea of strapping this to your mobile phone is odd (just use the phones headphone output, it really is good enough for mobile use) and the battery just a long term maintenance liability.

The unit is different from most DACs as it doesnt employ an off the shelf DAC chip but utilises an FPGA to deliver a reconstruction filter with a very high number of taps and has discrete DA conversion. The designer says thats good, but also says other things that make me quizically raise one eyebrow.

The Mojo can be found on Amazon for around $570 USD
https://www.amazon.com/Electronics-ultimate-Headphone-Amplifier-Coaxial/dp/B016W1X94O

m1.jpg

M2.jpg



0dBFS - Output volume is set to 2V RMS. Note I have utlised the input attenuator on the QA401 to minimise its harmonic distortion contribution. The side effect of doing so means the noise floor rises slightly. Disengaged it is approximately -130dbFS (32k point FFT).
Low harmonic distortion is exhibited however there are two odd spuria at 10 and 12kHz.
upload_2018-3-10_15-6-53.png


-6dBFS
upload_2018-3-10_15-26-38.png


-60dBFS - Low noise floor
upload_2018-3-10_15-28-1.png


-90.31dBFS 24 bit waveform - pretty clean / low noise but some very low frequency fluctuation noted
upload_2018-3-10_15-30-40.png


Jitter - There is no jitter of significance.
upload_2018-3-10_16-19-31.png


IMD SMPTE - Nice and clean
upload_2018-3-10_15-41-46.png

upload_2018-3-10_15-43-34.png


FR and Imaging - Sharp anti image filter and good suppression
upload_2018-3-10_15-47-51.png


Linearity - Extremely good
upload_2018-3-10_15-49-18.png


I havent tested with headphone loads, just as it would be used as a line level source with the QA401 high imput impedance. I wouldnt hesitate to use this DAC as a primary source in a full system despite its portable pretensions. It measures very well.

Im always very cautious when offering subjective impressions, but IMO this DAC does sound a little bit different to most. I find most DACs boringly similar despite what some say. I dont think I hear more with this DAC than any other good DAC, but this has a slightly different tonality. It is my "daily driver" used with Oppo PM1 cans. Oh yeah, it goes loud!
 

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RayDunzl

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#2
I dont think I hear more with this DAC than any other good DAC, but this has a slightly different tonality.
How does it do that?
 

Sal1950

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#3
I dont think I hear more with this DAC than any other good DAC, but this has a slightly different tonality. It is my "daily driver" used with Oppo PM1 cans. Oh yeah, it goes loud!
Is there anything in the measurements that you believe would point to that "sound"? Maybe you need to test it with headphone loads to see if you can deduce the reason.
 

bunkbail

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#5
I have a Chord Mojo and it sounds great with speakers! These days I use it in my car as a replacement of my mediocre Cirrus Logic WM8731-based stereo head-unit.
 

Wombat

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#6
"It's got the Mojo workin' ........................... ".o_O

Check frequency response at listening level.
 

March Audio

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#7
Is there anything in the measurements that you believe would point to that "sound"? Maybe you need to test it with headphone loads to see if you can deduce the reason.
Apart from the fact that it measures well, nothing specific. Perhaps that is the difference. No two dacs measure the same, and maybe this particular gamut of differences, even if subtle, make the difference. Different loads will change the measurements and therefore the sound. To what extent that will be audible is a good / tough question. Amir has sorted out some load measurements so it will be intetesting to see what that throws up.

Rob Watts makes some comment below on the design. It is fundamentally different to most DACs. Note the comments about drive capability. As I alluded to above he does make some claims here and elsewhere that raise my eyebrows with incredulity, and as Amir has pointed out he doesnt perform blind controlled listening tests, so make of the marketing what you will :) .

http://www.the-ear.net/how-to/rob-watts-chord-mojo-tech

I will do a bit more investigating and testing.
 
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Sythrix

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#8
"Personally I find the idea of strapping this to your mobile phone is odd (just use the phones headphone output, it really is good enough for mobile use)..."

Now that I have my Note 8, I would agree for the most part, depending on your choice in headphones.

However, when I had my Nexus 6P, it was absolutely necessary to have an external amp/dac. Never have I encountered such a weak-sauce headphone port on a phone, not to mention the audio output seems to simply have no shielding. I am very intimate with the sounds its cellular radio makes. That's why I ended up buying a Sabaj Da3. I believe there are also several cheaper phones out there that can benefit as well.

Doesn't have to be a Mojo, but there are better options than stock on some phones, for more than superfluous reasons.
 

mindbomb

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#9
Another unusual thing about Chord dacs is that they aren't delta sigma dacs but pwm dacs afaik.
 

DonH56

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#10
Their website does mention noise shaping which is usually associated with delta-sigma designs. DS DACs are generally PWM type DACs.
 

RayDunzl

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#11

Blumlein 88

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#12
You mention you think this DAC sounds different. Can you use the QA401 to record some bits of music with the Chord and a different sounding DAC so we could hear for ourselves? Maybe record at 96 or even 192 khz in case it is a case of some ultrasonic intermodulation or imaging that the steep deep filters of the Chord filter out.

Also are you doing linearity measurements by using a signal for each bit and plotting it or is it done some other way? And if so, I wonder if one gets different results when a signal that fades to silence is used instead?

Good review and measurements so kudos for that. Don't mistake my questions for complaints.
 

amirm

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#13
I know Chords Mojo is on Amirs ToDo list...
I am glad you reviewed it as the person who promised me one did not come through....
 

mindbomb

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#14
Their website does mention noise shaping which is usually associated with delta-sigma designs. DS DACs are generally PWM type DACs.
I believe the Chord dacs are still 1 bit dacs, so I think they still need noise shaping, but they can change pulse width unlike delta sigma dacs.
 

March Audio

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#15
"Personally I find the idea of strapping this to your mobile phone is odd (just use the phones headphone output, it really is good enough for mobile use)..."

Now that I have my Note 8, I would agree for the most part, depending on your choice in headphones.

However, when I had my Nexus 6P, it was absolutely necessary to have an external amp/dac. Never have I encountered such a weak-sauce headphone port on a phone, not to mention the audio output seems to simply have no shielding. I am very intimate with the sounds its cellular radio makes. That's why I ended up buying a Sabaj Da3. I believe there are also several cheaper phones out there that can benefit as well.

Doesn't have to be a Mojo, but there are better options than stock on some phones, for more than superfluous reasons.
Perhaps others mobile use is different to mine, but the thought of having this lump (or other similar unit) in your pocket as well as your phone while on a noisy bus, tube, train or plane seems pointless to me. Its inconvenient and the environment (and probably the cans) simply dont lend themselves to more than casual listening. As you say, if its that important to you buy a phone that has a good reputation and audio measurements :) . I appreciate that in your case your Nexus 6 really was a deficient design, but in my experience thats not typical of most decent phones these days.
 
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March Audio

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#16
You mention you think this DAC sounds different. Can you use the QA401 to record some bits of music with the Chord and a different sounding DAC so we could hear for ourselves? Maybe record at 96 or even 192 khz in case it is a case of some ultrasonic intermodulation or imaging that the steep deep filters of the Chord filter out.

Also are you doing linearity measurements by using a signal for each bit and plotting it or is it done some other way? And if so, I wonder if one gets different results when a signal that fades to silence is used instead?

Good review and measurements so kudos for that. Don't mistake my questions for complaints.
On no I dont take it as complaints :) I cant record using the QA, it doesnt have standard audio drivers so wont interface with recording software, however I do have two ADCs to try this with, my Motu 8A and TI evm4222 board. Whether you will hear the subtle difference via this route is an interesting question.

The linearity test is performed at 1kHz and those discrete signal levels shown in the graph. I use a high resolution FFT with flat top window (262k points for long sample time not frequency resolution) and averaging to minimise the impact of random noise and make sure there are no spuria visible at/around the test frequency
 

Blumlein 88

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#17
On no I dont take it as complaints :) I cant record using the QA, it doesnt have standard audio drivers so wont interface with recording software, however I do have two ADCs to try this with, my Motu 8A and TI evm4222 board. Whether you will hear the subtle difference via this route is an interesting question.

The linearity test is performed at 1kHz and those discrete signal levels shown in the graph. I use a high resolution FFT with flat top window (262k points for long sample time not frequency resolution) and averaging to minimise the impact of random noise and make sure there are no spuria visible at/around the test frequency
Yeah, I say try the Motu 8A. You can listen to the recordings and see if you discern a difference. If you think you hear it, then let us listen to see what we can hear.

Well I was putting together some test signals for linearity of my own wondering how you did yours. I think I am going to try a 12 khz tone. With perfect timing you'll get all your samples at one bit level and others at zero. Yes noise and such would get in the way, but it seems it might be cleaner to find the peak bit value recorded. I realize you never match the ADC to the nearest bit, but the overall output level should be stable to see if you get 6.02 db between bits.
 

Blumlein 88

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#18
Perhaps others mobile use is different to mine, but the thought of having this lump (or other similar unit) in your pocket as well as your phone while on a noisy bus, tube, train or plane seems pointless to me. Its inconvenient and the environment (and probably the cans) simply dont lend themselves to more than casual listening. As you say, if its that important to you buy a phone that has a good reputation and audio measurements :) . I appreciate that in your case your Nexus 6 really was a deficient design, but in my experience thats not typical of most decent phones these days.
That is how it seems to me. I have a portable Headroom amp, and yet its portability was never really portable enough for phone use. I have taken it to the beach or things like that. Even then a phone with a good output is better.

Also as a user of a Nexus 6P it does have a pitiful output level. It really only works with efficient IEMs. The good side is you'll not damage your hearing. I seem to remember I measured it and it was .2 volt or .25 volt peak output on the headphone jack. I ran it thru a microphone pre with gain turned down when I recorded some signals off of it.
 

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#20
That linked thread has two posts linking to much cheaper DIY replacement batteries. One poster has personally, successfully, tried them.
 
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