[Kentajalli]

I'm interested to know more about this; without going too deep into details, can you briefly summarize which factors are involved in making direct coupling superior to capacitor coupling, thank you.

I also wonder why the original Mojo wasn't designed with direct coupling if it is more transparent than a coupling capacitor, but that's a question for Rob Watts if he wants to tell us...

I believe Mr. Watts has already answered this.
capacitor coupling is usually used as a means of DC current blocking.
in theory a capacitor will not allow DC currents to pass through, but AC currents can pass.
But nothing is perfect, a capacitor couple, can in conjunction with other components in the circuit behave in a non linear manner.
Also, you need a transparent system to begin with to be able to distinguish the audible effects of this behaviour.
As Mr. W says, in a lesser device, the direct coupling or not won't make much difference.
In my tube amp which is capacitor coupled, you can easily tell by listening, what type of capacitor it is! A plastic capacitor is cold and bright, paper-in-oil types sound fuller and smoother and so on, but that is another story.
My 2 pence, if Mr. W can elaborate , I shall learn thing or two too.

 

[vlach]

I believe Mr. Watts has already answered this.
capacitor coupling is usually used as a means of DC current blocking.
in theory a capacitor will not allow DC currents to pass through, but AC currents can pass.
But nothing is perfect, a capacitor couple, can in conjunction with other components in the circuit behave in a non linear manner.
Also, you need a transparent system to begin with to be able to distinguish the audible effects of this behaviour.
As Mr. W says, in a lesser device, the direct coupling or not won't make much difference.
In my tube amp which is capacitor coupled, you can easily tell by listening, what type of capacitor it is! A plastic capacitor is cold and bright, paper-in-oil types sound fuller and smoother and so on, but that is another story.
My 2 pence, if Mr. W can elaborate , I shall learn thing or two too.

Very interesting and informative, thank you so much!

 

[Kentajalli]

Just an observation !
did Mojo2 really need an extra USB input? I mean for a mobile joy device it already had three inputs , two more than a lot of competitors .
Was it just a political decision to silence up those who considered any device without a C-type as obsolete & inferior?
Was it a lost opportunity not to use C-type's power capabilities for charging and desktop mode?
The deed is done, I am sure they had good reasons for what they did, I just hope it wasn't for the sake of Poly.

 

[Bleach-Free]

Just an observation !
did Mojo2 really need an extra USB input? I mean for a mobile joy device it already had three inputs , two more than a lot of competitors .
Was it just a political decision to silence up those who considered any device without a C-type as obsolete & inferior?
Was it a lost opportunity not to use C-type's power capabilities for charging and desktop mode?
The deed is done, I am sure they had good reasons for what they did, I just hope it wasn't for the sake of Poly.

On Darko's podcast Rob Watts explains (early on in the podcast around the two minute mark) that there were a couple requirements in the design brief when planning Mojo2. One, that it needed to be compatible with Poly, and two, there were plans originally for two USB-C inputs (one charging, one data) but in order to fit it in the same physical size it would have sacrificed the TOSLINK optical input and that was something Rob was not going to consider.

 

[ecwl]

On Darko's podcast Rob Watts explains (early on in the podcast around the two minute mark) that there were a couple requirements in the design brief when planning Mojo2.

Thanks for posting this. Just listened to the podcast. Very educational. Even if Darko sounds lost
Like I didn't realize Chord Mojo 2 would make a much better desktop DAC compared to the original Mojo.
Or more importantly, there is a secret project that requires 140-bit DSP. I'm guessing it's probably the ADC although it could be the pulse array amplifier.

 

[Kentajalli]

On Darko's podcast Rob Watts explains (early on in the podcast around the two minute mark) that there were a couple requirements in the design brief when planning Mojo2. One, that it needed to be compatible with Poly, and two, there were plans originally for two USB-C inputs (one charging, one data) but in order to fit it in the same physical size it would have sacrificed the TOSLINK optical input and that was something Rob was not going to consider.

Thank you.
Evidently Chord and Mr. W had decided on a second USB input.
It is the "Why!" bit I don't get.
Most people, use one input and stick with it.
I suppose, if it had a remote (like Hugo2), then it could have acted as a center piece in a desktop system.
Does Chord have a large inventory of Poly's ?
I wonder.

 

[Rob Watts]

@Rob Watts you mentioned in a previous reply that the charger has been developed specifically for the Mojo's desktop mode. Which charger are you referring to?

“When the battery is fully charged it will go into desktop mode - and unlike Hugo 2 the battery is disconnected to preserve battery life. That meant I had to improve the PSU regulation/rejection and design the charger so that when in desktop mode it was a low impedance high current power source.”

I meant the FPGA charger circuit within Mojo 2, not the PSU charger. I should have been more precise - a lot of time and effort went into the FPGA charger, and I just refer to it as the charger.

Rob, is there any other measurement slides you can show? Jitter, linearity etc

Unfortunately I did not record my measurements, but I did do a 16 bit 3 level plot:

Note how similar the left and right plots are - the ringing you see is exactly what one should see for a bandwidth limited signal. The 16 bit levels are perfectly reproduced.

My question about future Mscalers was actually whether Mojo2 will be compatible with it/those as well?

Sure

Comforting to hear that M2 will drive "REAL" headphones like HD800 and Dan´s Stealth too.? Really? Have you auditioned Stealth yet?
If so,what is your take on it?

Unfortunately not. But will hear it at NYC CanJam. Am very much looking forward to that and Singapore CanJam.

But ,what about the quite a bit more difficult to drive HEKV2 which is the headphone I use on a daily basis, will it cope with that one as well?

You will get 99.3 dB SPL from the HEKV2 - almost identical to the HD800.

Regarding no charger I only auditioned Mojo a few times and realized it was not as good as my Hugo1 and was not aware that no charger was included with it.
Why not?
And how to charge it?

Cost - this is an audiophile product sold through normal audio channels. It would have meant an eye watering increase in retail price.

You can charge it with any USB port that is capable of 0.5A. Of course, if you want quick charge time and full charge you need a 2A charger with a decent USB cable.

I'm interested to know more about this; without going too deep into details, can you briefly summarize which factors are involved in making direct coupling superior to capacitor coupling, thank you.

I also wonder why the original Mojo wasn't designed with direct coupling if it is more transparent than a coupling capacitor, but that's a question for Rob Watts if he wants to tell us...

Coupling capacitors have a few problems - one is increased distortion at bass (20Hz I use as a test) and that's due to the capacitance value changing with applied voltage. The second is dielectric absorption, where charge is discharged some time later than it should do. These two effects accounts for the soft warm and slightly imprecise bass when using coupling caps.

The issue on Mojo was power dissipation, as it needs the FPGA ADC and the digital DC servo, which would significantly increase power dissipation. With the power savings made elsewhere I could now do this.

Thank you.
Evidently Chord and Mr. W had decided on a second USB input.
It is the "Why!" bit I don't get.
Most people, use one input and stick with it.
I suppose, if it had a remote (like Hugo2), then it could have acted as a center piece in a desktop system.
Does Chord have a large inventory of Poly's ?
I wonder.

Because some are crazy about USB C, and we had to make it compatible with Poly.

I don't understand it as every USB C device I have had had connector reliability problems. Indeed my son just came up to tell me just 5 minutes ago that his 18 month old phone won't charge - it's the USB C socket failing...

 

[Rebel Chris]

But with USB C I will plug it in 100% correct, instead of 50%...haha.

Thank you for telling us more over your products/technology.

 

[Kentajalli]

Because some are crazy about USB C, and we had to make it compatible with Poly.

I don't understand it as every USB C device I have had had connector reliability problems. Indeed my son just came up to tell me just 5 minutes ago that his 18 month old phone won't charge - it's the USB C socket failing...

So, in short I guessed it right !
it was for Poly and to silence up the few - a political decision.
Every now and then I get it right!
btw, C-type is reversible , so easier to plug in and out. and kids! they are just too rough with their gear sometimes, most of us swear by C-type reliability .
Just wait for some, to claim that the new port sounds better, more resolution, more ......
Next question:
Does the battery carry more juice?
if yes, I take it , it is physically bigger, right?

 

[vlach]

Coupling capacitors have a few problems - one is increased distortion at bass (20Hz I use as a test) and that's due to the capacitance value changing with applied voltage. The second is dielectric absorption, where charge is discharged some time later than it should do. These two effects accounts for the soft warm and slightly imprecise bass when using coupling caps.

The issue on Mojo was power dissipation, as it needs the FPGA ADC and the digital DC servo, which would significantly increase power dissipation. With the power savings made elsewhere I could now do this.

Thank you Rob for keeping up with all our questions and taking the time to explain these technicalities, i truly appreciate your feedback and participation!
Big congratulations on the Mojo2!!!

 

[mikecheck95]

Question about EQ filters on the Mojo 2. I'm wanting to use this to fix some upper mid recession on my headphones however don't want to end up elevating the 7k-8k area where does the upper-treble filter's "roll off" begin and where would the elevation begin and end for the lower-mid filter?

 

[Rob Watts]

So, in short I guessed it right !
it was for Poly and to silence up the few - a political decision.
Every now and then I get it right!
btw, C-type is reversible , so easier to plug in and out. and kids! they are just too rough with their gear sometimes, most of us swear by C-type reliability .
Just wait for some, to claim that the new port sounds better, more resolution, more ......
Next question:
Does the battery carry more juice?
if yes, I take it , it is physically bigger, right?

Yes it has 9% more capacity - partly from better battery tech, and from being slightly longer.

Question about EQ filters on the Mojo 2. I'm wanting to use this to fix some upper mid recession on my headphones however don't want to end up elevating the 7k-8k area where does the upper-treble filter's "roll off" begin and where would the elevation begin and end for the lower-mid filter?

The Q for the peak filters is set to 0.5, so it's quite broad. It means that -9dB at 20k, 10k is -4.5dB, and -3.5dB at 7.5 kHz.

My intent was that the EQ was for two reasons - compensating for low frequency problems from headphones/IEMs - which given the plots I have seen it does well; and to adjust the overall balance to taste (brighter/darker or sharper/warmer). It's not intended to solve headphone HF problems, as these tend to be sharper resonances. And even parametric EQ can't fix these issues perfectly anyway - using resonances to cancel headphone resonances never works properly.

 

[mikecheck95]

The Q for the peak filters is set to 0.5, so it's quite broad. It means that -9dB at 20k, 10k is -4.5dB, and -3.5dB at 7.5 kHz.

My intent was that the EQ was for two reasons - compensating for low frequency problems from headphones/IEMs - which given the plots I have seen it does well; and to adjust the overall balance to taste (brighter/darker or sharper/warmer). It's not intended to solve headphone HF problems, as these tend to be sharper resonances. And even parametric EQ can't fix these issues perfectly anyway - using resonances to cancel headphone resonances never works properly.

Thank you for the response! Sorry to pick your brain for a follow-up question you said that the Q for the peak filters is 0.5. This is for the 20hz peak filter as well? Also, are the shelf filters similarly broad? If I used the "lower treble" shelf filter would I be boosting frequencies below 1000hz?

 

[technobear]

Questions about the EQ are well answered by this post:

https://www.head-fi.org/threads/chord-mojo-2-thread.885405/post-16797432

 

[mikecheck95]

Questions about the EQ are well answered by this post:

https://www.head-fi.org/threads/chord-mojo-2-thread.885405/post-16797432

Those graphs are… rough to say the least