Chord Mojo(1) DAC-amp ☆★►FAQ in 3rd post!◄★☆

[miketlse]

  ...and there is no difference between an Amp and Headphones?
"Driving" means what it means but as I'm no expert, I don't want to jump to conclusions...

 

 
The Mojo is driving an electrical load  (headphones or amp), so no difference up to that point. The difference comes in that the impedence of headphones will change with frequency (they are a mini version of speakers), but I am not sure about the input impedence of amplifiers.
 
The Mojo is happy driving low impedence phones such as shure SE846 (9 ohms I think) and high impedence phones (eg Sennheiser HD600 and HD800 are 300 ohms).
 
beyer offer some headphone families with different impedences, eg the DT 770 pro is available at 16 ohms, 32 ohms, 80 ohms, and 250 ohms). With this design strategy, phones are basically the least impedence model, with an inline resistor added either in the headphone lead or the earpiece. Why all these versions of basically the same headphone? Firstly the 16 and 32 ohms are easier on the battery life of mobile phones, but this must be balanced by the fact that as the impedence increases, the control over bass notes improves - so it is swings and roundabouts.
 
But this is digressing from the Mojo, I am sure that I saw posts by Rob Watts that state that higher impedence headphones draw less power than lower impedence models, but I cannot find them yet.   

 

[Rob Watts]

  ...and there is no difference between an Amp and Headphones?
"Driving" means what it means but as I'm no expert, I don't want to jump to conclusions...

 

Strictly speaking there is a difference - the impedance of headphones can be reactive, so there could be a phase shift between current and voltage, thus slightly increasing power drain. But don't worry about that. The max power being drawn within Mojo is with 8 ohm IEM's - as although the power in the load is low, the current is higher and that will increase power dissipation on Mojo's discrete OP stage, even when you are running say at red on the volume.
 
Oh another point - power loss within the battery is 0.2% of Mojo's total, so it is insignificant.
 
And another one - power loss whilst charging is because of a use of a linear charger - so when the battery is fully depleted, we get max power loss in the charger, and very little power loss whilst at the end of the charge cycle. Why do I use a linear charger and not a switcher based charger? I have yet to find a switcher charger that allows full RF filtering, so it will upset the sound quality whilst charging. My design goals were to have no loss in sound quality whilst listening and charging and going to the current range of switcher chargers won't do that.
 
Should you find the thermal trip operating whilst charging and listening, then as a poster recommended, putting Mojo on its side fixes that possibility.
 
Rob

 

[miketlse]

   
Windows allows so much unnecessary hijacking of resources, by every man and his dog, that it's not surprising some people eventually find they are getting intconsistent performance with some devices.
 
There was some discussion about that in the following thread, which at a massive 2 pages long, is worth a quick read, before taking the huge step of reinstalling windows:
 
http://www.head-fi.org/t/812759/how-to-eliminate-stuttering-in-audio-players
 

 
Oh dear, prepare for incoming questions from iOS 10 beta users.
 
http://www.head-fi.org/t/702787/chord-hugo/13560#post_12750581

 

[Rowethren]

Strictly speaking there is a difference - the impedance of headphones can be reactive, so there could be a phase shift between current and voltage, thus slightly increasing power drain. But don't worry about that. The max power being drawn within Mojo is with 8 ohm IEM's - as although the power in the load is low, the current is higher and that will increase power dissipation on Mojo's discrete OP stage, even when you are running say at red on the volume.

Oh another point - power loss within the battery is 0.2% of Mojo's total, so it is insignificant.

And another one - power loss whilst charging is because of a use of a linear charger - so when the battery is fully depleted, we get max power loss in the charger, and very little power loss whilst at the end of the charge cycle. Why do I use a linear charger and not a switcher based charger? I have yet to find a switcher charger that allows full RF filtering, so it will upset the sound quality whilst charging. My design goals were to have no loss in sound quality whilst listening and charging and going to the current range of switcher chargers won't do that.

Should you find the thermal trip operating whilst charging and listening, then as a poster recommended, putting Mojo on its side fixes that possibility.

Rob

Nice information! So which linear usb power supply do you use?

 

[Traveller]

 

  ...and there is no difference between an Amp and Headphones?
"Driving" means what it means but as I'm no expert, I don't want to jump to conclusions...

 

 
The Mojo is driving an electrical load  (headphones or amp), so no difference up to that point. The difference comes in that the impedence of headphones will change with frequency...
... Why all these versions of basically the same headphone? Firstly the 16 and 32 ohms are easier on the battery life of mobile phones, but this must be balanced by the fact that as the impedence increases, the control over bass notes improves - so it is swings and roundabouts.

  Strictly speaking there is a difference - the impedance of headphones can be reactive, so there could be a phase shift between current and voltage, thus slightly increasing power drain. But don't worry about that. The max power being drawn within Mojo is with 8 ohm IEM's - as although the power in the load is low, the current is higher and that will increase power dissipation on Mojo's discrete OP stage, even when you are running say at red on the volume... Oh another point - power loss within the battery is 0.2% of Mojo's total, so it is insignificant...
 

Thank you very much for your time and info gents!

 
Rob, I'm sorry, I don't understand the point about the 0.2% battery-loss... should I understand it to mean that this is the total cost of actually driving any headphones and that the remaining 99.8% processing (DAC)?

 
Mike, thanks for pointing out what is certainly a basic principle of impedance vs. FR but I was not aware of the direct affect (of impedance) on LF and bit now I am much appreciated 

 

[Mojo ideas]

GreenBow, sorry you feel that way. I'm not trying to be dismissive of you in particular and find that you've been helpful in the thread and I appreciate your posts.

With regard to the battery, no, I don't think you'll find a better solution than the one Chord has come up with. If you wish to try that's entirely up to you. I wish you luck. However, the heat isn't just generated from the battery, but also from the FPGA chip and pulse array DAC, and the output stage. IMO you won't be making much of a dent in the heat generation by changing out the battery, but you will be changing the source of the Mojo's power, and may be risking thermal issues with a battery not meant to tolerate the heat within the case. I simply feel that trying a different battery is a fools errand to making the Mojo run cooler in hot climates.

IMO, a better solution would be to run the device on its side (as has been recommended already), or manage the charging/listening time better so it isn't charging constantly when running. Shoot, even the giant heat sink is a better idea in my opinion over trying to change out the battery yourself, especially since Chord has mentioned time and again that this is not a typical battery in the Mojo. Who is to say another battery won't melt and explode... But hey, IMO, YMMV, Just my perspective man. We can disagree you know.

Guys we at Chord really did extensive studies into batteries before we chose the optimised solution we have in Mojo. We even looked at up and coming battery technologies like lithium sulphur which potentially could extend Mojo's playing time by a factor of four but unfortunately the newer chemistry's are just not there yet. Be aware the battery technology we've chosen is good and above all its safe being a higher spec than most. Remember that mojo is designed for a pocket or a hand to carry and a poorly deigned lithium ion battery could be chemically very volatile. Look up lithium batteries catching fire I don't want one of those in my pocket!

 

[Rob Watts]

  Thank you very much for your time and info gents!

 
Rob, I'm sorry, I don't understand the point about the 0.2% battery-loss... should I understand it to mean that this is the total cost of actually driving any headphones and that the remaining 99.8% processing (DAC)?

 
Mike, thanks for pointing out what is certainly a basic principle of impedance vs. FR but I was not aware of the direct affect (of impedance) on LF and bit now I am much appreciated 

The 0.2% is the power loss due to the battery supplying the current that Mojo needs. So its the power loss within the battery itself and is negligible compared to the power loss of USB, FPGA, oscillators, discrete DAC and OP stages, references, power regulation and charging. All these things had to be heavily optimized during the design phase.
 
Rob 

 

[Mython]

 

...power loss of USB, FPGA, oscillators, discrete DAC and OP stages, references, power regulation and charging. All these things had to be heavily optimized during the design phase.

 
Rob 

 
 
So, if I'm understanding you correctly, DAVE was easy to design, since it doesn't need to worry about battery duration. Is that correct, Rob?

 

 

[canali]

  The 0.2% is the power loss due to the battery supplying the current that Mojo needs. So its the power loss within the battery itself and is negligible compared to the power loss of USB, FPGA, oscillators, discrete DAC and OP stages, references, power regulation and charging. All these things had to be heavily optimized during the design phase.
 
Rob 

 
 Rob: a brief aside, but revisiting something we touched upon last week:
the new module coming out this or next week: will an accompanying case be offered at the same time?

 

[audi0nick128]

Strictly speaking there is a difference - the impedance of headphones can be reactive, so there could be a phase shift between current and voltage, thus slightly increasing power drain. But don't worry about that. The max power being drawn within Mojo is with 8 ohm IEM's - as although the power in the load is low, the current is higher and that will increase power dissipation on Mojo's discrete OP stage, even when you are running say at red on the volume.

Oh another point - power loss within the battery is 0.2% of Mojo's total, so it is insignificant.

And another one - power loss whilst charging is because of a use of a linear charger - so when the battery is fully depleted, we get max power loss in the charger, and very little power loss whilst at the end of the charge cycle. Why do I use a linear charger and not a switcher based charger? I have yet to find a switcher charger that allows full RF filtering, so it will upset the sound quality whilst charging. My design goals were to have no loss in sound quality whilst listening and charging and going to the current range of switcher chargers won't do that.

Should you find the thermal trip operating whilst charging and listening, then as a poster recommended, putting Mojo on its side fixes that possibility.

Rob

Hey Rob,

Did you try a high quality SMPS, like an Ifi Ipower? Oh and while we are at it, I read somewhere that the power supply being used to load a battery can have influence on the batterys performance. What do you think about that?

Cheers

 

[howdy]

Make sure the cable is an OTG one, and make sure the OTG end is plugged into the phone.

And there are a few other tips in post #3.

Let us know how you get on

I've tried everything, this phone definitely does not have USB out. Does you or anyone have a list of cellphones with USB out so I can narrow my search. The goal is to buy the cheapest Android device with USB out so I can use my Tidal offline with the Mojo.
Thanks in advance!

 

[canali]

I've tried everything, this phone definitely does not have USB out. Does you or anyone have a list of cellphones with USB out so I can narrow my search. The goal is to buy the cheapest Android device with USB out so I can use my Tidal offline with the Mojo.
Thanks in advance!

ipod touch 6   64-128gb..no, it's not android (and i have an android phone)
but imo a good gizmo to easily synch up w the mojo, dragonfly for tidal hifi (using senn's captune app even) 
btw, i thought you were getting an ipod touch6

 

[Mython]

 

Make sure the cable is an OTG one, and make sure the OTG end is plugged into the phone.

And there are a few other tips in post #3.

Let us know how you get on

I've tried everything, this phone definitely does not have USB out. Does you or anyone have a list of cellphones with USB out so I can narrow my search. The goal is to buy the cheapest Android device with USB out so I can use my Tidal offline with the Mojo.
Thanks in advance!

 
Did you read the 'connecting Mojo to MicroUSB devices' section of post #3?
 
It doesn't contain all the answers, but it does point you to a USB issue discussed recently, in this thread (error initialising USB system), as well as pointing to the compatibility list for USB OTG smartphones, on the UAPP homepage. That may get you nearer to finding an answer, and if it doesn't, then it may be that your phone simply isn't USB OTG compatible, or perhaps some other reason, but please check the aforementioned and see how far it takes you.
 
 
 
EDIT: good catch, @ canali - I overlooked the offline part of that question, as I was focused upon the USB connection aspect.
 
@ Howdy: Tidal offline content is encrypted and UAPP can't access it offline, which means, amongst other things, that you can't play Tidal offline, bit-perfect, to Mojo

 

[howdy]

Did you read the 'connecting Mojo to MicroUSB devices' section of post #3?

It doesn't contain all the answers, but it does point you to a USB issue discussed recently, in this thread (error initialising USB system), as well as pointing to the compatibility list for USB OTG smartphones, on the UAPP homepage. That may get you nearer to finding an answer, and if it doesn't, then it may be that your phone simply isn't USB OTG compatible, or perhaps some other reason, but please check the aforementioned and see how far it takes you.



EDIT: good catch, @ canali - I overlooked the offline part of that question, as I was focused upon the USB connection aspect.

@ Howdy: Tidal offline content is encrypted and UAPP can't access it offline, which means, amongst other things, that you can't play Tidal offline, bit-perfect, to Mojo

Yeah I did read post 3 about it which helped me get where I am and have concluded that the phone I bought for the mojo is just to cheap and does not have the USB out. I do have a OTG and still did not recognize it. I may just have to go with what I know works which is Apple. I have a IPhone 5s but it's only 16gb I would be happy with a 64gb iPod touch. My Onkyo DP-X1 hooks up nice with mojo but I don't what to use those 2 together. I have an OCD where I have to have a dedicated source.

 

[miketlse]

Yeah I did read post 3 about it which helped me get where I am and have concluded that the phone I bought for the mojo is just to cheap and does not have the USB out. I do have a OTG and still did not recognize it. I may just have to go with what I know works which is Apple. I have a IPhone 5s but it's only 16gb I would be happy with a 64gb iPod touch. My Onkyo DP-X1 hooks up nice with mojo but I don't what to use those 2 together. I have an OCD where I have to have a dedicated source.

 
OTG cables are directional (one plug has 4 pins, the other has 5) so the correct plug must be inserted into the phone - try reversing the cable, and seeing if that improves things.