Chord Electronics Mojo D/A headphone amplifier Measurements

Sidebar 3: Measurements

I measured the Chord Mojo with my Audio Precision SYS2722 system (see and the January 2008 "As We See It"). The Mojo's battery was fully charged at the start of the measurements. The data sources were USB from my 2012 MacBook Pro running on battery power, using Pure Music 2.0 to play the files, and S/PDIF on TosLink from the SYS2722. Macintosh's USB Prober utility reported the Mojo's product string as "Mojo" from "Chord Electronics Ltd," and confirmed that its USB port operated in the optimal isochronous asynchronous mode. Apple's AudioMIDI utility confirmed that the Mojo operated at all sample rates from 44.1 through 768kHz with 32-bit integer data. The TosLink input operated reliably up to a sample rate of 96kHz; above that rate, whether the Mojo locked to a datastream sampled at 176.4 or 192kHz depended on the quality of the optical interlink used.

When I first turned on the Mojo in headphone mode, its output level was set to 774.5mV. With both volume buttons illuminated dark blue, the output level was the CD standard's 2V. When I turned on the Mojo in Line mode, the output was fixed at 3.08V. With digital data at 0dBFS, the Mojo's output was 7.425V with the volume control set to its maximum, which is much higher than I expected. However, the waveform was well into clipping. The maximum output level before waveform clipping was 4.887V; except where noted in the text, all measurements were performed with the volume control set so that this output voltage was the reference level.

The Mojo preserved absolute polarity (ie, was non-inverting). The output impedance at low and middle frequencies was extremely low, at 0.7 ohm including the interconnect cable, and though it had increased at the top of the audioband, this was to just 1.8 ohms. The Mojo will have no problem driving even the lowest-impedance headphones.

Tested with a "digital black" 44.1kHz WAV file that included one sample raised to 0dBFS, the Mojo's impulse response (fig.1) revealed the reconstruction filter to be a time-symmetrical FIR type—although, as with Chord's Rob Watts–designed Hugo TT, with more coefficients than I usually find. The ultrasonic rolloff associated with this filter is indicated by the red and magenta traces in fig.2, taken with 44.1kHz-sampled white noise at –4dBFS (footnote 1). The output drops sharply just before the Nyquist frequency (half the sample rate: vertical green line), and other than low-level spurious tones at 31, 62, and 93kHz, the filter's stop-band behavior is very clean. The rolloff is very fast, so with a full-scale tone at 19.1kHz (fig.2, blue and cyan traces), the aliasing product at 25kHz (44,100–19,100) is suppressed by >120dB. The harmonics of this tone can also be seen to be very low in level.

Fig.1 Chord Mojo, impulse response at 44.1kHz (4ms time window).

Fig.2 Chord Mojo, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).

Fig.3 shows a more conventional frequency-response graph, taken with data sampled at 44.1, 96, and 192kHz. The overall response conforms to the same basic shape at all three sample rates, with a sharp rolloff just below half the rate at 44.1 and 96kHz. I haven't shown the frequency response with data sampled at 384kHz, as it overlaid the 192kHz response up to 96kHz. Above that frequency, the response followed the same gentle rolloff, reaching –20dB at 165kHz. Channel separation below 1kHz was superb, at >114dB in both directions, and was still >100dB at 20kHz (fig.4). The Mojo's low-frequency noise floor was also superbly clean and free from spurious tones (fig.5).

Fig.3 Chord Mojo, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red) (2dB/vertical div.).

Fig.4 Chord Mojo, Channel separation.

Fig.5 Chord Mojo, spectrum with noise and spuriae of dithered 1kHz tone at 0dBFS with 24-bit TosLink data (left blue, right red) (20dB/vertical div.).

Fed dithered TosLink data representing a 1kHz tone at –90dBFS with first 16-bit data (fig.6, cyan and magenta traces), then 24-bit data (blue, red), the increase in bit depth dropped the noise floor by more than 20dB, suggesting resolution of better than 19 bits. However, repeating this test with 24-bit USB data produced a large number of spurious tones and a random noise floor 3–4dB higher in level (fig.7). While these tones are well below the threshold of hearing, it is still behavior that I don't like to see. By contrast, 24-bit data sourced from an iPad showed a cleaner spectrum and a lower noise floor (fig.8). And with its high resolution and overall low level of noise, the Chord DAC's reproduction of undithered 16-bit data describing a sinewave at exactly –90.31dBFS was exemplary (fig.9), with zero DC offset and the three DC voltage levels well differentiated. With undithered 24-bit data, the Mojo output a well-formed sinewave despite the very low signal level (fig.10).

Fig.6 Chord Mojo, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit TosLink data (left channel cyan, right magenta), 24-bit TosLink data (left blue, right red) (20dB/vertical div.).

Fig.7 Chord Mojo, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 24-bit USB data (left channel blue, right red) (20dB/vertical div.).

Fig.8 Chord Mojo, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 24-bit data sourced from an iPad 2 (left channel blue, right red) (20dB/vertical div.).

Fig.9 Chord Mojo, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).

Fig.10 Chord Mojo, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right red).

Harmonic distortion at 2V into 300 ohms was very low (fig.11), with the second harmonic the highest in level and lying at –110dB (0.0003%). Even with the volume control set to its highest level before clipping into this load, the second harmonic had risen by only 7dB. Intermodulation was also extremely low (fig.12), with the 1kHz difference tone produced by an equal mix of 19 and 20kHz tones lying at –120dB (0.0001%). However, this graph shows some modulation of the Mojo's noise floor. This is very similar to what I found last month with the Apogee Groove, which, like the Mojo, has a much higher maximum output voltage than what would be expected from something powered by or compatible with 5V USB power.

Fig.11 Chord Mojo, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 300 ohms with volume control set to 2V output (left channel blue, right red; linear frequency scale).

Fig.12 Chord Mojo, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 300 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).

Perhaps this modulation is a function of a DC-to-DC converter in the power-supply circuitry, but the effect can also be seen in the narrowband spectral analysis of the Mojo's output while it decoded 16-bit J-Test data (fig.13). The high-order odd harmonics of the low-frequency LSB-level squarewave are all very close to their correct levels (green line). This graph was taken with TosLink data; when I repeated the analysis with USB data (not shown), the noise-floor modulation could still be seen—but, as anticipated from fig.6, the noise floor was a few dB higher than in fig.10. I very much doubt that this behavior will have audible consequences.

Fig.13 Chord Mojo, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit data via TosLink from AP SYS2722 (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Overall, the Chord Mojo offers measured performance that is superb for a portable device, and would not be out of place in a high-priced conventional D/A processor.—John Atkinson

Footnote 1: This test was suggested to me by Jürgen Reis, chief engineer of MBL.
Chord Electronics Ltd.
US distributor: Bluebird Music Ltd.
275 Woodward Avenue
Buffalo, NY 14217
(416) 638-8207

tonykaz's picture

nice piece of Journalism.
People tell me the same sort of things about the Chord stuff, I'm coming to the idea that the Mojo is "today's" version of the 1970's Linn LP12 discovery, a simple device that "sounds" better. ( the LP12 retailed for around $1,000 back then)

Everywhere I look, I see civilians using the iPhone as a music source, they'll buy after-market earphones from the Apple Store, then they're pretty much done.

Those wanting or having discovered better performance from something like the JDS combo might decide to ( or not to ) bother with extra electronic little boxes.

I suspect that when these civilians encounter that MOJO they'll want one, it's a charismatic kind of thing.

But it's more than that, isn't it, it's a Linn/Naim set-up that fits into a shirt pocket and can sit on a Coffee Shop table. It's a totally attractive little thing that everyone will want to touch and try.

So, I'm thinking, it's the Gateway device into the Future of High-End music performance. The same price as the Phone itself but with no monthly service contract.

I think that Franks & Team hit a Home Run.

I recall first hearing a Linn, playing Sweet Georgia Brown from a Sheffield Labs Vinyl. wow, what an eye opener that was! and thru Naim Nait & Linn Kanns, right up against the wall. I can still remember the "sticker shock" I felt. ( I bought the LP12/Ittok/Asak right then and there ).

Now we have digital music sounding wonderful and we have the Mojo introducing folks to affordable high-end.

I love the British Stuff.

Tony in Michigan

dalethorn's picture

The fact that headphones are a craze with the young who are budget-constrained doesn't change history. The Mojo is a natural evolution from things long ago - the 1960's Philips compact cassette recorder for example. Today, for $50 USD, you can buy a FiiO K1 DAC/amp for iPhones that will audibly improve even the latest and best iPhone sound, but the tiny thumb-sized DAC, powered by the phone itself, is suitable only with reasonably efficient headphones. I don't doubt the superiority of the Mojo (and other DACs), but when you hold the very, very tiny FiiO in hand and experience what it does, you'll better understand where all this is going.

tonykaz's picture

Nice reporting,
Looks like the Audiophile iPhone Race is on but I don't think the Phone people think of themselves as Audiophiles, do they?
I just checked to discover FiiO K1 pricing around $39 USD, not that it matters, the price is well down into the impulse range!
I think that we're seeing a whole new Channel opening up, one that promises to be the dominant music delivery system for the next few years, (dominant in the Global sense).
The next generation of Audiophiles will be say'n things like "I first discovered good sound from my iPhone & K1".
I wonder how many will want to ( or be able to ) make Sound Quality a priority.
What loudspeakers will an iPhone based person own?
Probably none of this fits into the High-End, at least for now. Audio hobbyist's grannies will be the ones that own this K1 type stuff, my wife would look at it thinking it's a Lip Stick!

The Phone is a mandatory component to Social Integration and Mobility. We have to take this Channel seriously.

Tony in Michigan

dalethorn's picture

Psychology plays the big role in portable audio, for several reasons. The long-term success of manufacturers in that business is recognizing where their priorities are going to be. Portable headphones approaching $1000 and portable DAC/amps approaching the mid-$2000's are already reality. As early as 1984 I demonstrated a full-up desktop computer system based around a pocket computer with a serial interface that supported all the necessary components, and when work was over, the pocket computer would be detached and placed into a pocket where (get this) it could be pulled out at any moment and used like today's iPhone with tiny screen and keyboard on-the-go. That's 32 years ago. So I know very well where the potentials are for growth in this business.

tonykaz's picture

Apple made 700 Million phones, so far, and they're not the largest. They have made Music part of the phone experience!
Lethargic Audio Industry philosophy apart, the phone & google have become an integral component of the Auto Industry and now have a place in our daily lives.
I'm sitting here, watching and waiting for our Audio Industry wake up from a long sleep to emerge from the doldrums of Vinyl.

Music is "Everyman's Dopamine", billions upon billions of Dollars will be spent for it.

And, it's up for grabs!

Oh, to be young again & "in the game".

Tony in Michigan

dalethorn's picture

Large numbers does not make the producer 'right', any more than the fallacy of appeal to the majority or authority is right. Steve Jobs did commit the miracle in raising Apple from those very doldrums to the biggest of the big. They did a lot of things right, and I dare say that it wouldn't have happened with anyone except Steve Jobs. Jobs had his limits unfortunately, and from the beginning with his billboards all over the U.S. proclaiming the iPod Nano to be "impossibly small", to today's iPhones and Macbooks being "incredibly thin", his focus (and now Apple's focus) on thinness long since achieved its target, and I have doubts that *anyone* at Apple knows exactly why Jobs was so neurotic about thinness. After all, those Macbooks are carried in bags or cases that are pretty much just as fat as carries any other laptop. Do you understand the extreme devotion to thinness?

dalethorn's picture

BTW, none of this has anything to do with the music industry per se being lethargic. It goes back as I said to the 1950's with pocket radios, to the 1960's with small cassette recorders, and then especially to the 1970's with real pocket computers (not calculators -- computers). HP for one example produced those advanced pocket gizmos, which soon evolved to support a modest graphic and sound capability. Still, nobody in *any* industry understood handheld computing and its applicability to graphics and music, until Steve Jobs noticed the digital revolution and the proliferation of MP3's, and made an art of it. A wise man who led the first personal computer club (handheld computers BTW) stated that "The only truly personal computer is one that is with you at all times, like a wristwatch." He said that in 1974, and it took decades for the "Industry" to get behind it.

dalethorn's picture

I forgot to note that the iPhone (or similar device) could be the CPU of your high-fidelity home system, but at this point there are limitations, on the Apple side at least. One, to avoid Apple's resolution limit of 44-48 khz, you need a player that doesn't access the iPhone's music files. That means the player app you choose would have to have its own 'container' for the files, which would not be seen by any other apps. And the maximum memory is 128 gb, or ~3500 4-minute FLAC-format tracks at 44 khz. Or only 1600 tracks at 96 khz resolution. I've always (for > 30 years) seen this as an ideal - use the pocket device as the core player of my home system, and take the same player with a portable amp on the road.

tonykaz's picture

It is coming down to the Wrist Watch, ( the Star Trek communicator ) sort of thing. Home systems will wirelessly connect to Powered Speakers.

I can even envision eyeglasses as our monitors.

How far away are we, time wise?

Is it true that Ben Franklin gave us the Lightning Rod only 250 years ago, why didn't God give it to Moses? ( along with the Periodic Table and the Germ Theory )

The Apple Story says they had 1,000 talented people working on the Phone in 2004, 4 years before it's introduction.

Apple seems to be our largest Engineering Company, it looks like they're designing our futures.

Tony in Michigan

dalethorn's picture

If I picked the developers for the iPhone, we could have done it with 30 people, not 1000. Look up some of the fun texts on the original Unix developers, or the people who patched a wealth of instructions into 300 bytes on a trans-solar-system craft. There are miracles, but it requires people who 'know' to perform them.

tonykaz's picture

Canadians havta pay $800 bucks unless they come to the States where they'll pay only $600.

And they don't have all that Military expense to cope with.

Tony in Michigan

ps. it don't seem right somehow!, wonder what they cost in London England?

spacehound's picture

I purchased mine mainly to go from the Onkyo HF Player app on a 128Gb iPod via the Lightning connector/Camera cable to the Chord and then via its Line output to the Aux socket on the car audio system.

192/24 WAV/FLAC/ALAC or whatever and DSD if you like it. What more do you need? (I don't have any music greater than 192/24.)

PERSONALLY I LIKE THE FPGA. I will NOT pay crazy prices (up to 20,000 dollars) for a box containing a 10 dollar DAC chip which does all the real work plus a power supply, a simple clock, and a little audio amplification for the other 19,990 dollars. So my 'fixed' DAC is a dCS for the same reason.

Tony - 399 UK Pounds. (Less about 21% tax if you tell them you are taking it back to the USA).

tonykaz's picture

It's tricky getting that VAT scrubbed off, I've done it though.
FPGA is the telling thing, how many outfits have the Engineering talent?
I'm figuring Apple will include something nice in the next few years or less.
High Quality Music reproduction has been democratized.

I lived in the UK when VAT was only 13%

Tony in Michigan

dce22's picture

Throw your Pono's into the trash bin.

Competitiors need to watch and learn how to make a proper portable Audio DAC.

Ktracho's picture

To be fair, Pono can store your music, so you don't need to tether it to another device. (Of course, on the flip side, you can't stream to it from your computer or phone.)

dce22's picture

Mojo sound quality exceeds many more expensive desktop dac's and it's a class above Pono.

You will always carry your phone regardless so it's not an issue.

Pono music store is good but Pono Player?

Not. iPhone 5/6 has better headamp.

Ktracho's picture

Personally, I've waited so long to upgrade my DAC, I might as well wait until there is more availability of MQA-capable DACs. It would be really nice if Chord jumped on the bandwagon. I hope I don't have to wait too much longer.

spacehound's picture

Wanting 'high quality' non-CD audio for my new car and having mistakenly not ordered the Burmester/Mercedes audio option (which cannot be retrofitted) I just purchased the Chord Mojo, a 128GB iPod, and the Onkyo HF player iOS app about ten days ago. The Mojo, set to 'line' output, plugs into the 3.5mm 'Aux' input on the 'standard Mercedes issue' audio system.

I thought of purchasing the Astell & Kern Junior but had doubts if its output was sufficient to drive the Mercedes audio system. Additionally it is very limited (no 'apps' and is effectively non upgradable).

The Pono has the same limitations. Additionally it was always hard to find here in the UK and now seems to have totally vanished.

In principle all three do the same job but though the Chord/iPod/Onkyo App solution was more expensive I KNEW it would work. I don't NEED any other iOS apps but the iPod might be a less heavy and clumsy solution for my Naim streamer iOS DLNA control point and/or the iOS JRemote (Windows 10/J River Music Center) software I use in my home system than the over large and too heavy iPad I currently use.

To me upgradeability without replacing it all, and flexibility, is more important than initial cost.

The Pono? Looks excellent to me for what it is intended. The fact that I think Neil Young is a pretentious old fool who produces high-pitched whining noises out of his nose rather than actual songs from his mouth SHOULDN'T influence me but it does.

Long-time listener's picture

John, instead of trying to convince us that this misshapen blob of black plastic with bulbous, walleyed blinking lights is "drop-dead gorgeous," why not just tell us how beautiful it sounds? We're audiophiles. We'll likely buy it no matter how ugly it is.

spacehound's picture

Not that any aircraft I am familiar with (as a pilot) has ever been made out of aluminium as it is far to weak unless alloyed with something else but never mind.

Chord stuff is usually weird-looking, with pointless 'windows' and is mostly silver colored. Purely to make it stand out in the shop. Get it home and it looks like over-styled hospital equipment.

regalar guy's picture

forgive my newb-ness to portable, and i know there are converting cables galore out there, but i'm struggling to understand how i could get this signal from the mojo into my amplifier if at all.

spacehound's picture

You buy a stereo 3.5mm jack to two RCA plug cable at Wal Mart or anywhere else you fancy and connect the jack to the Mojo earphone outlet and the two RCA plugs to any spare input on the amplifier.

Works fine.

Set the Mojo to 'Line' output when turning it on and its volume control is disabled leaving volume to the amplifier volume control as usual.

For 'safety' the 'Line' setting is NOT remembered by the Mojo as its full volume output might blow some earphones.

If your ANDROID phone DOESN'T have a USB music output (some only use the micro USB socket for data transfer and charging) don't buy the Mojo as you will be wasting your money.

If you have an Apple device the Mojo will work fine with the Lightning connector or the old 30 pin connector provided you buy the correct Apple Camera Adaptor or Camera Cable.

If you actually INTEND to use it in a 'mobile manner' with earphones don't forget to wear a dumb expression, walk into lamp posts occasionally, and cross the street without looking to see if a large truck is approaching. We wouldn't want Darwin to miss you, would we?

tonykaz's picture

Can you offer opinions as to the Amplifier Power usefulness in the Mojo?
I'm reading the device to have modest or very modest power output.
Although, nobody seems to complain about it but nobody seems to claim it has more than ample power.

Tony in Michigan

spacehound's picture

It will drive the two earphones (fairly low cost ones) I have to possibly damaging levels even when set to 'phones' rather than 'line'. This surprised me, I admit.

In fact Chord say NOT to switch it to fixed level 'line' output if you are using phones as it may damage them and it is so designed deliberately that your switching it to 'line' output is NOT remembered at your next switch-on and setting to 'line' level can only be done as part of switch-on so won't be 'accidental'. Whereas your previous earphone volume IS remembered so will not be at full and possibly damaging levels.

Why did I buy it?
First - I bought it unseen and unheard on the strength of reviews here and elsewhere and because of its specified high level line output.
Actually I have little interest in earphones and bought it purely because the analog output from an iPod or similar was not high enough to drive my car audio system to satisfactory volumes whereas I knew the Chord 'line' output would be.

So after looking at the Astell & Kern 'Junior' and similar devices I decided that an iPod plus the Chord Mojo was the most flexible, though not the lowest cost, answer. I use the iPod only as a 'transport' via its Lightning connector and camera cable and used as such it goes to 192/24 AND 2X DSD with the Onkyo HF player app. I don't currently HAVE any other use for the iPod (mail, notes, iTunes whatever) but unlike the A & K or equivalents the iPod has those facilities should I ever want them.

Sound quality?
The iPod plus Mojo connected to my good but not crazy expensive home system is indistinguishable from my Naim streamer and dCS DAC. Thus I recommend such a setup both for value and portability. And like the dCS, Chord use their own methods of digital to analog conversion and don't depend on a 10 dollar 'high street quality' bought in chip. That was influential in my decision to buy it.

tonykaz's picture

Well, ok, I was curious about headphone power for Sennheiser HD 600s but I'm happy to accept your answer.
Chord is nice stuff.
I've heard that: Modules will be available for doing various things including SD Card reading & playing.
So, I'm interested.

Maybe interested in their other stuff too, 'in for a penny' sort of thing.

Betcha Franks gets a "K" for Chord's export success.

Tony in Michigan

spacehound's picture

with high impedance phones so with those Sennheisers I strongly suggest you try it first.

BTW: Naim (I use one of their streamers and one of their power amps) has got THREE "Queen's awards for exports". It's a pity they are now owned by the French (whom we dislike) company Focal, though Naim call it a 'merge' :)

tonykaz's picture

I can't share the French 'dislike', I even fly Airbus.

In fact I admire their Medical systems. They do speak a funny language which I can overlook. We never went to war with them!, and they did help us out a bit ( back in the late 1700s ), Focal is nice gear and they take better care of Naim than Linn ever did. I like the Focal Active monitors.

And it ain't Chinese!

Tony in Michigan

spacehound's picture

Chord and dCS stuff is made by real people earning real wages. That influences my purchasing decisions.

I've bought two Harley-Davidsons over the years for the same reason :)

BTW: You'd still be British were it not for the French. We were fighting them (as usual) at the same time as your War of Independence so our attention was not fully on it :)

As for Linn, they never owned Naim. They just co-operated to browbeat everyone else, mainly the British HiFi magazines, both Tiefenbrun of Linn and Vereker of Naim being very strong personalities. Naim was founded by an eccentric called Julian Vereker, a very good amateur racing driver with an interest in audio, who I knew slightly (they are only 15 miles from me). I don't buy Linn stuff. Their famous turntable was a rip-off of someone else's. Linn were a small engineering outfit who were contracted to make some parts for the turntable. They copied the design TOTALLY, even down to the shape of the plexiglass lid, and sold it under their own name. There was a court case about it at the time but neither outfit could afford to fully pursue it.

tonykaz's picture

I know the story. I liked the LP-12 and sold plenty of them and Linn certainly did own the press. Eventually I got a couple of the original AR tables in trades, they were crappy in construction but could be rebuilt to sound nearly as good as the LINN but they remained lesser cousins.

I think that we are still British! We have the language which is the DNA of societies. We enjoy our isolation and the absence of Papist influences, we are an amalgam of governable peoples ( I'm Russian and Swedish with a Polish name).

And we're heading off a Revolution, just now. Thomas Pketty describes the top 10% of us owning 70% of the Assets. He presents a history of revolts where the top 10% own 90%! I'm supporting a populist Bernie Sanders in hopes of heading off bloodshed.

I've been a Schiit person, now I'm admiring Chord design philosophies. The Mojo with it's little modules may become the heart of my music system. I've gone from Meridian M10s down to handheld devices. My world is changing, again!

Tony in Yankee Country