[GrussGott]

https://www.head-fi.org/threads/chord-mojo-dac-amp-☆★►faq-in-3rd-post-◄★☆.784602/page-1284#post-12685665

Yeah, except it seems not that based on Rob's explanation:

[great sound is] complicated and depends upon a number of factors - principally the amount of RF noise injected into the Mojo, and the amount of correlated noise that gets in. It will depend upon the source device as to which sounds best. My preference is optical, as this has the smoothest sound quality and best depth, as it does not suffer from both of the aforementioned problems ...

... all my DAC's up-sample to 2048 times that is at least 16 times more than typical. What does this do? Well its not just about up- sampling but filtering out the RF noise that is present on a digital signal. Its essential to do this, as it gets you closer to the original analogue signal in the ADC (and this is the DAC's job to recover the analogue signal not the digital data). This extensive filtering reduces jitter sensitivity by a factor of 64, and allows the DAC to eliminate noise floor modulation. Now this is a very important problem, as it makes the DAC sound hard and less smooth and is a major problem with DACs - all other DACs have very large noise floor modulation, Mojo has zero measurable noise floor modulation (I have plots at home proving this). This is a major reason why Mojo sounds so smooth and natural.
​

So I read that as Rob saying he's using beaucoup processing power to get rid of that noise.

That noise that's still there.

That no other portable DAC/Amps have.

 

[Mython]

Spoiler: Quoted text by Mython, regarding RFI

Could the Mojo have been built in a way that would prevent RF/EMI interference, like with some kind of shielding? I'm ignorant about such things, so pardon me if this is a stupid question.

Even with shielding of the circuitboard, the signal cable (microUSB cable) can pick-up RF from the phone (which is in almost-continual communication with local cell towers, even when not making a call or streaming) and carry that into the circuit.

Even with the best will in the world, there's only just so much one can do to minimise RF.


I do appreciate that it may be tempting to assume that some of us may be 'just making excuses' for Mojo, but that's not the situation, here.

RF is a major problem for many devices, and Mojo is not magically 100% immune, either.


As has been mentioned, certain frequencies can cause more issues than others, and another major factor, also mentioned, a few times in this thread, is the distance one's phone happens to be from the nearest cell-tower(s). It's tempting to believe that a tiny smartphone can't kick-out much RF, but actually, they have to broadcast around half a mile or so, to a cell-tower, and when one considers that Mojo is having to sit just a few inches away, and with a digital cable that accidentally behaves as an antenna for all that stray RF, it puts into perspective how impossible it is for Mojo to reject 100% of that RF. Wi-fi may involve less broadcast distance, but it's still orders of magnitude further away than the few inches between the phone and Mojo.

Yeah, except it seems not that based on Rob's explanation:

Spoiler: Quoted text by Rob Watts

[great sound is] complicated and depends upon a number of factors - principally the amount of RF noise injected into the Mojo, and the amount of correlated noise that gets in. It will depend upon the source device as to which sounds best. My preference is optical, as this has the smoothest sound quality and best depth, as it does not suffer from both of the aforementioned problems ...

... all my DAC's up-sample to 2048 times that is at least 16 times more than typical. What does this do? Well its not just about up- sampling but filtering out the RF noise that is present on a digital signal. Its essential to do this, as it gets you closer to the original analogue signal in the ADC (and this is the DAC's job to recover the analogue signal not the digital data). This extensive filtering reduces jitter sensitivity by a factor of 64, and allows the DAC to eliminate noise floor modulation. Now this is a very important problem, as it makes the DAC sound hard and less smooth and is a major problem with DACs - all other DACs have very large noise floor modulation, Mojo has zero measurable noise floor modulation (I have plots at home proving this). This is a major reason why Mojo sounds so smooth and natural.

So I read that as Rob saying he's using beaucoup processing power to get rid of that noise.

That noise that's still there.

As any competent DAC designer should, Rob has tried to minimise the influence of RF on his DAC designs.

However, the first remark you emboldened above, in the quoted text from Rob Watts, mentions a preference for optical. In relation to Mojo and RF, optical is ideal because an optical cable cannot act as an aerial capable of inadvertently picking up RF. Of course, RF may still attempt to get in directly through Mojos casework, even when optical is the chosen digital connection, but it should be vastly more difficult for RF to interfere with Mojos circuitry than in the scenario of a metal-conductor cable as would be the scenario with USB or Co-Axial.


In any event, the issue of RF and Mojo primarily relates to the potential influence of RF noise on the analogue circuitry (and many customers do not experience RF issues).

 

[Yourmomm]

(and many customers do not experience RF issues).

I'm obviously lucky, then, in that I'm one of them who doesn't... I wonder what the difference is between those that do, and those that do not experience this problem? It can't be distance from cell tower, as I'm constantly on the move, in poor reception areas, too, and still don't ever suffer with it. Is it the quality of the OTG cable? (mine's a fairly cheapo, no name brand, micro USB-to-micro USB one, which is definitely OTG, as it only works in one direction); or is it variations in source (apple/windows phones vs Android?), or variations in the Mojo units themselves? (doubtful)...it seems a bit odd...

 

[GrussGott]

In any event, the issue of RF and Mojo primarily relates to the potential influence of RF noise on the analogue circuitry (and many customers do not experience RF issues).

I'm not trying to poop in anybody's bowl of morning mojos, I'm just pointing out that the radio interference is real and is the result of poor design, at least when it comes to a portable, mobile DAC/amp - and that's not opinion, that's a fact - which is why I don't think we should try to come up with reasons why it's not poor design.

Torq over at SBAF posted a fantastic write-up comparison of portable DAC/Amps and here's what he found:

Despite the heavy metal casing, Mojo is surprisingly susceptible to EMI. For a device that is intended to be used with a phone, this is unfortunate. While the degree of interference is dependent on what radio bands your particular phone is using and, as a result, can change markedly depending on where you’re using it, there’s a good chance you’ll need to put your phone in “Airplane” mode if you want a clean listening session.

It’s curious to note that none of the other units I compared here exhibited these issues at all.

Also, I think this has the worst USB implementation I’ve come across. It results in frequent dropouts when playing multi-rate DSD via every macOS machine I’ve tried and some Surface devices, and seems excessively affected by electrical noise on the USB connection.

If evaluated as a DAC/amp, again irrespective of price/value, then things change a little bit:
iDSD BL > GOV2+ Inf > Mojo > Explorer 2 > Dragonfly Red
​

So, yeah, relative to EMI, The mojo is unique is this drawback - and similar in performance - which means it's 100% a design flaw. Of course there are many trade-offs with these things including who makes them and where, which in this case, these are two UK companies in the top (AMR the parent of iFi is). I knew all of this and still bought a Mojo vs the iFi.

But, yeah, one of Mojo's unique flaws is an EMI problem and, yes, this is 100% Chord's fault as others of similar (or better) performance have designed for it, or not had to worry.

 

[Mython]

I'm not trying to poop in anybody's bowl of morning mojos, I'm just pointing out that the radio interference is real and is the result of poor design, at least when it comes to a portable, mobile DAC/amp - and that's not opinion, that's a fact - which is why I don't think we should try to come up with reasons why it's not poor design.

Torq over at SBAF posted a fantastic write-up comparison of portable DAC/Amps and here's what he found:

Despite the heavy metal casing, Mojo is surprisingly susceptible to EMI. For a device that is intended to be used with a phone, this is unfortunate. While the degree of interference is dependent on what radio bands your particular phone is using and, as a result, can change markedly depending on where you’re using it, there’s a good chance you’ll need to put your phone in “Airplane” mode if you want a clean listening session.

It’s curious to note that none of the other units I compared here exhibited these issues at all.

Also, I think this has the worst USB implementation I’ve come across. It results in frequent dropouts when playing multi-rate DSD via every macOS machine I’ve tried and some Surface devices, and seems excessively affected by electrical noise on the USB connection.

If evaluated as a DAC/amp, again irrespective of price/value, then things change a little bit:
iDSD BL > GOV2+ Inf > Mojo > Explorer 2 > Dragonfly Red
​

So, yeah, relative to EMI, The mojo is unique is this drawback and similar in performance which means it's 100% a design flaw. Of course there are many trade-offs with these things including who makes them and where, which in this case, these are two UK companies in the top (AMR the parent of iFi is). I knew all of this and still bought a Mojo vs the iFi.

But, yeah, one of Mojo's unique flaws is an EMI problem and, yes, this is 100% Chord's fault as others of similar (or better) performance have designed for it, or not had to worry.

For the record, I stand by what I've written, this past hour. There are, as I've quite reasonably explained, many different factors influencing whether RFI might be experienced or not. I'm not mindlessly defending Chord or Mojo - I'm simply pointing out some of the factors which can be at play.

Furthermore:

Some experience RFI issues, some don't.

Some prefer an iDSD BL or other DAC over Mojo, and some don't.

Mojo is categorically not unique in experiencing occasional RFI - I consider that assertion (and it's only my opinion, of course) to be unsubstantiated.

That one individual, on another forum, might happen to post their experiences of comparing RFI susceptibility of several different DACs, and derive one set of findings, does not necessarily make that set of findings representative of a majority of many thousands of Mojo owners around the globe.


I respect that you have encountered some RFI issues, yourself, and I'm not belittling that at all, but it doesn't mean Mojo is a 'uniquely flawed' product.

 

[GrussGott]

I'm not mindlessly defending Chord or Mojo
I consider that assertion (and it's only my opinion, of course) to be unsubstantiated.
, but it doesn't mean Mojo is a 'uniquely flawed' product.

yeah but you are blindly [changing the word to blind] defending the Mojo given you have zero data to support your opinion - that's basically the definition of "blind".

Said differently, there's plenty of evidence to support the Mojo being uniquely flawed in this respect - if you have data disproving that, let's see it, otherwise there's actually not anything you're standing behind.

If you don't have any data then you're blind defending.

and, for the record, I just bought the mojo and I KNEW it had this design flaw, so I'm not blind attacking it, just responding to the data and not letting Rob off the hook for fixing an obvious and pervasive design flaw.

 

[bikutoru]

I just bought the mojo and I KNEW it had this design flaw

Why would you do that?
Masochistic tendencies?

 

[NaiveSound]

Anyone have comparisons of pha3 vs mojo?

 

[x RELIC x]

So basically its what you called "volume preset" and reviewers just haven't mentioned simplicity of amp section and called it "straight DAC section" ?


EDIT: and to be on a safe side just ordered 2Qute as well, to have all 3 devices compared side by side

Exactly. ‘Reviewers’ will typically use conventional terminology or just don’t understand the product they are reviewing.

I’m just passing on information from the designer, and he’s repeatedly informed these forums (and in PMs with me because I was curious and asked) the same info that I posted to you. I’m not sure why John said the RCA is different in that 2014 video, probably because it’s easier in a sound byte than getting in to the details of the unique implementation over conventional designs. In the end though it is as I mentioned to you. I’ll trust the designer.

If you like I can bring up multiple posts like the following (just for information purposes, of course). You can’t bypass the single I to V (Current to Voltage) stage or it would sound terrible. This is akin to other conventional DAC’s analogue out, but with much lower impedance. What Rob refers to as the amplifier stage is not the same as traditional conventional amplifiers and I believe this is where some confusion may be.

Line level mode is just a volume preset for the volume control - nothing else changes.

Mojo has an FPGA (which is digital logic only) a discrete DAC (turning digital signals to analogue via flip-flops and resistors) and a single output amplifier - and that is it.

Conventional DAC headphone amps use differential outputs and have two I to V converters (current to voltage), a differential to single ended converter, and an output amplifier. Wrapped up with that is a analogue filter. So that's a lot of passive components and four amplifiers in the signal path.

Because Mojo's FPGA has extensive digital filtering (at 2048 FS) and has a noise shaper that runs at a very high rate (104MHz) and uses a discrete DAC, I can keep the analogue section radically simpler, and this is one reason why Mojo is so transparent compared to all other DAC amps.

Rob

Yes it should be thought of as a preset level, rather than line out mode - even if you are indeed actually doing it for a line out function. All that happens is the volume is set to give 3V RMS at 0dBFS (or 3v RMS maximum possible).

So you may use it into power amps to drive loudspeakers... And line out is only a pre-set volume, physically nothing changes.

No, you need at least one amplifier to do the critical I to V conversion. Now it is possible to design a voltage only DAC (no amp at all), but they sound poor due to lots of problems - the largest being the huge amount of distortion you get doing it that way. Believe me, if I could make it simpler I would. The key that Mojo has is extremely low distortion and noise (0.00017% 3V 300 Ohms) but only one single amplifier in the signal path - and this amp combines headphone drive, filtering and I to V conversion in a single stage.

Rob

 

[x RELIC x]

Yeah, except it seems not that based on Rob's explanation:

[great sound is] complicated and depends upon a number of factors - principally the amount of RF noise injected into the Mojo, and the amount of correlated noise that gets in. It will depend upon the source device as to which sounds best. My preference is optical, as this has the smoothest sound quality and best depth, as it does not suffer from both of the aforementioned problems ...

... all my DAC's up-sample to 2048 times that is at least 16 times more than typical. What does this do? Well its not just about up- sampling but filtering out the RF noise that is present on a digital signal. Its essential to do this, as it gets you closer to the original analogue signal in the ADC (and this is the DAC's job to recover the analogue signal not the digital data). This extensive filtering reduces jitter sensitivity by a factor of 64, and allows the DAC to eliminate noise floor modulation. Now this is a very important problem, as it makes the DAC sound hard and less smooth and is a major problem with DACs - all other DACs have very large noise floor modulation, Mojo has zero measurable noise floor modulation (I have plots at home proving this). This is a major reason why Mojo sounds so smooth and natural.
​

So I read that as Rob saying he's using beaucoup processing power to get rid of that noise.

That noise that's still there.

That no other portable DAC/Amps have.

The noise Rob is referring to in that quote is different from EMI emitted from a cellular device.

I'm not trying to poop in anybody's bowl of morning mojos, I'm just pointing out that the radio interference is real and is the result of poor design, at least when it comes to a portable, mobile DAC/amp - and that's not opinion, that's a fact - which is why I don't think we should try to come up with reasons why it's not poor design.

Torq over at SBAF posted a fantastic write-up comparison of portable DAC/Amps and here's what he found:

Despite the heavy metal casing, Mojo is surprisingly susceptible to EMI. For a device that is intended to be used with a phone, this is unfortunate. While the degree of interference is dependent on what radio bands your particular phone is using and, as a result, can change markedly depending on where you’re using it, there’s a good chance you’ll need to put your phone in “Airplane” mode if you want a clean listening session.

It’s curious to note that none of the other units I compared here exhibited these issues at all.

Also, I think this has the worst USB implementation I’ve come across. It results in frequent dropouts when playing multi-rate DSD via every macOS machine I’ve tried and some Surface devices, and seems excessively affected by electrical noise on the USB connection.

If evaluated as a DAC/amp, again irrespective of price/value, then things change a little bit:
iDSD BL > GOV2+ Inf > Mojo > Explorer 2 > Dragonfly Red
​

So, yeah, relative to EMI, The mojo is unique is this drawback - and similar in performance - which means it's 100% a design flaw. Of course there are many trade-offs with these things including who makes them and where, which in this case, these are two UK companies in the top (AMR the parent of iFi is). I knew all of this and still bought a Mojo vs the iFi.

But, yeah, one of Mojo's unique flaws is an EMI problem and, yes, this is 100% Chord's fault as others of similar (or better) performance have designed for it, or not had to worry.

With all due respect the Mojo isn’t the only device to have this issue (no defence here, just pointing it out). The Oppo HA-2 comes to mind. Yes, it’s unfortunate that the Mojo is susceptible to EMI from cellular phones and I’ve heard it myself. I get a lot of EMI from my 3G network but none from my LTE network. I’m sure every case will be different depending on the proximity to the transmition tower and the network used. I even get interference when I hold my phone near the Headphone cable on 3G, which acts like an antenna for the EMI that gets in to the Mojo.

 

[GrussGott]

Why would you do that?
Masochistic tendencies?

Mostly that.

But also because I like the mojo form factor better, I like the design better, and I do want to get to know the Chord stuff for myself. But I guess that's the masochist in me talking. And back to the design ... that hard core aluminum and those marbles ... that's pretty cool. But, gah! with the cheap USB connectors.

Also I've worked with a communications gear manufacturer in their labs and I have some experience with what to expect from cell interference, how it's caused and what the result is. Given there's no revolt I was pretty sure the problem was/is minor and that my use-case won't matter for it and I was right ... except for it's even less impactful that I thought!

I'll probably buy an iFi DSD BL next, but that's if I keep my P9s that are coming ... if not I may skip the iFi and spend the dough on a pair of ZMF Atticus which are 300 ohms ... I wonder if the poor little Mojo can drive those!

 

[Leo-]

Mojo is categorically not unique in experiencing occasional RFI - I consider that assertion (and it's only my opinion, of course) to be unsubstantiated.

That one individual, on another forum, might happen to post their experiences of comparing RFI susceptibility of several different DACs, and derive one set of findings, does not necessarily make that set of findings representative of a majority of many thousands of Mojo owners around the globe.

Someone's findings may not be representative of the majority, but it does mean that it may be a concern for users interested in doing a similar thing. I have 3 DACs at work and a soon to be replaced Samsung 5s. I'm just thinking if the 5s is especially "dirty" due to having a plastic back, however an antenna is an antenna - not sure why it is especially bad, however the Mojo picks up any interference from the 3g/4g. One other dac used to pick up the "classic" network handshake (which the Mojo doesn't seem to bother with) and the third nothing. Also the Mojo picks up noise from a fairly long distance whilst the phone needs to be hugging the other Dac in order to have any interference.

I'm wondering from the comment above if the noise is picked up by the cable since I leave the cable in even if the Mojo is disconnected - I will give it a try without the cable and the Mojo disconnected. As it stands now it is bloody annoying since the noise is louder than my normal listening level on IEMs.

Regarding the Mojo and DSD comment above, I also have intermittent problems with the mobile (which I always use in airplane mode ) and the Mojo. However, it works fine if I plug it to my stereo up to dsd128 - couldn't get dsd256 to work yet, however I just want to point out that it is likely to be a source issue.

 

[GrussGott]

The noise Rob is referring to in that quote is different from EMI emitted from a cellular device.

Well then that's probably why there's a design flaw: the lead designer is unaware there's a problem. He can't fix what he doesn't know about.

In any event, Rob is pretty clear that his tech is upsampling "16 times more than typical" to filter out RF noise. Seems like if he was only focused on one type of RF noise he'd say so. It would also sound kind of odd if he said, "except cell RF noise, that shiit shoots right on through"

And, since we don't hear about this EMI flaw with, say, the iFi DSD BL, then either iFi is upsampling 16x more than Rob, and filtering out even more RF noise than Rob is, or Rob's got a design flaw.

If something primarily happens only with the mojo, then that something is primarily a mojo problem.

 

[x RELIC x]

Well then that's probably why there's a design flaw: the lead designer is unaware there's a problem. He can't fix what he doesn't know about.

In any event, Rob is pretty clear that his tech is upsampling "16 times more than typical" to filter out RF noise. Seems like if he was only focused on one type of RF noise he'd say so. It would also sound kind of odd if he said, "except cell RF noise, that shiit shoots right on through"

And, since we don't hear about this EMI flaw with, say, the iFi DSD BL, then either iFi is upsampling 16x more than Rob, and filtering out even more RF noise than Rob is, or Rob's got a design flaw.

If something primarily happens only with the mojo, then that something is primarily a mojo problem.

Of course he’s aware of the EMI from cellular networks and Chord and Rob have discussed this many times in this thread. You can search the topic if you want or not, it’s no skin off my teeth. I was just pointing out that what you specifically quoted from Rob was not an EMI filter from cellular networks.

You keep bringing up the iDSD BL, but like I mentioned there’s other devices that also have this issue even if the iDSD does not. There’s no argument from me that the Mojo is susceptible to EMI interference, just that it’s not exclusive to the Mojo. Does that make it any less painful? No.

 

[Mython]

yeah but you are blindly [changing the word to blind] defending the Mojo given you have zero data to support your opinion - that's basically the definition of "blind".

Said differently, there's plenty of evidence to support the Mojo being uniquely flawed in this respect - if you have data disproving that, let's see it, otherwise there's actually not anything you're standing behind.

If you don't have any data then you're blind defending.

No, I am doing nothing of the sort - I am simply pointing out that your claim that Mojo is 'uniquely' flawed in not being immune to RFI is unsubstantiated. The burden of proof is upon you to prove such an outlandish assertion, not on me to disprove it. Have you personally tested every other portable DAC on the market and found each and every one to be immune to RFI?

Nobody here, least of all me, is asserting that Mojo is a perfect device or that your experiencing RFI with Mojo is something to be swept under the carpet - the issue of RFI has been openly discussed in this thread. However, to extrapolate your RFI experience to the point of exclaiming that Mojo is 'uniquely flawed' is (IMO) a step too far, that's all.