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Chord Mojo(1) DAC-amp ☆★►FAQ in 3rd post!◄★☆
Jul 16, 2017 at 7:08 PM Post #33,031 of 42,765
loghead said:
Thanks, before seeing this advice I was digging in this thread back to the beginning of May (following the bread crumbs of info i found searching keywords)... some people suggested just deleting UAPP and that worked.

My question is, why did I need UAPP in the first place? Was that a pre-requisite to allow my Galaxy S7 to play with a USB dac (ie, installing of certain drivers)? And if so, why does it still play nicely now that I uninstalled UAPP?
Click to expand...

not an Android user but I think you need UAPP because Android will upscale Tidal 44.1/16 streams and offline files to 48/16 and there’s nothing you can do it about it. not bitperfect.
 
Jul 16, 2017 at 7:09 PM Post #33,032 of 42,765
loghead said:
Thanks, before seeing this advice I was digging in this thread back to the beginning of May (following the bread crumbs of info i found searching keywords)... some people suggested just deleting UAPP and that worked.

My question is, why did I need UAPP in the first place? Was that a pre-requisite to allow my Galaxy S7 to play with a USB dac (ie, installing of certain drivers)? And if so, why does it still play nicely now that I uninstalled UAPP?
Click to expand...

UAPP is useful if you want bit perfect playback through USB for tidal and your locally stored music. As others have mentioned it’s important if you want to play directly to USB from other Apps (ie Tidal offline) you must make sure UAPP isn’t running as it will take control of your USB output. Do not allow UAPP to become the default player when USB is plugged in or it will take over the USB output every time you plug it in.
 
Jul 17, 2017 at 1:19 AM Post #33,034 of 42,765
loghead said:
Thanks, before seeing this advice I was digging in this thread back to the beginning of May (following the bread crumbs of info i found searching keywords)... some people suggested just deleting UAPP and that worked.

My question is, why did I need UAPP in the first place? Was that a pre-requisite to allow my Galaxy S7 to play with a USB dac (ie, installing of certain drivers)? And if so, why does it still play nicely now that I uninstalled UAPP?
Click to expand...

Only if you want bit perfect and correct frequency Playback otherwise Android sends all out scalled to 192/48 24bit I think.
 
Last edited:
Jul 17, 2017 at 3:13 AM Post #33,035 of 42,765
webzeb said:
Thank you for your reply.

Is this related to the voltage divider that output impedance of the Mojo forms with the (very frequency dependent) IEM impedance or is there something else happening?

Regarding distorsion, I was refering to a post of rob watts saying:
Reducing the output load only starts to increase distortion with 33 ohms - at this level it is very much lower than other headphone amps.
But I may have misunderstood if it actually applies the Mojo and in which scale.
Click to expand...

I have not covered this before, but it's fairly simple (well ok maybe not so simple). The output stage is the same as Hugo in that it uses the same discrete transistors. Now the output stage must be short circuit proof, and this is done normally by adding a current limit. The problem with current limits is that they start to function even with moderate OP stage currents, as the limiter starts to apply the brakes. And you can easily measure and hear this effect.

So to overcome this I use a series resistor instead. So when the OP stage is shorted, it will now see the series resistor, and it is safe. But you can't simply connect a series resistor to an amp OP stage; it will add to the output impedance, and it will mess up the damping of the headphone, giving you a soft bass. Also, adding a resistor in the signal path will directly degrade transparency. So what happens is the feedback is taken after this resistor; so the single feedback loop eliminates the consequences of the resistor being in place. But it means at RF frequencies, when the global feedback is not providing any effect, the resistor is functioning, and its there when the OP is shorted, so the OP stage is still safe. Because the resistor is present at RF, I also add a capacitor to ground, and this gives me another RF filter.

Now conventional DAC's have very complex out of band and RF filters, because DAC's create huge amounts of noise which must be filtered out (if you don't you get more noise floor modulation, and then things sound hard and bright). But adding these filters degrade transparency, simply because you have a lot more passive components in the signal path. Now with pulse array, I run the noise shapers at 104 MHz; and this means that the OP noise is much lower than conventional - but it still needs to be filtered out. So the adding of the OP resistor and the capacitor gives me another RF filter, and I get it for free, as there is no price to pay for it in terms of transparency, as the filter is inside the DAC's global feedback loop.

So this resistor and cap is very valuable arrangement; I get an RF filter with no cost in transparency; I get a an OP stage that is safe under shorts but does not require a limiter which would add distortion. But getting back to Mojo - why does adding a low impedance load subtly change the frequency response at 20 kHz? Its because I wanted to use the same OP stage as Hugo; but the transistors I use are way too big physically for Mojo, so I use the same transistors but packaged in a tiny package. But these have less power dissipation, and that forces me to use a safety resistor that is three times larger in value; and the larger value gives a bigger change in frequency response with low impedance loads. But we are talking about frankly trivial changes; at 33 ohms it is only -0.1dB down at 15 kHz; with 16 ohms it is -0.3 dB at 15 kHz.

But in terms of distortion, because there is not a current limit used for shorting, the current delivery is extremely linear and is the same as Hugo. With IEM's the impedance is low, but the actual voltage is trivial, and you certainly won't be able to measure or hear any distortion with such low voltages.

I hope this gives you a flavor of the complexities involved in designing Mojo's output stage; successful design for optimum sound quality is actually very complex, often involving competing pressures.

Rob
 
Jul 17, 2017 at 3:52 AM Post #33,036 of 42,765
Rob Watts said:
I have not covered this before, but it's fairly simple (well ok maybe not so simple). The output stage is the same as Hugo in that it uses the same discrete transistors. Now the output stage must be short circuit proof, and this is done normally by adding a current limit. The problem with current limits is that they start to function even with moderate OP stage currents, as the limiter starts to apply the brakes. And you can easily measure and hear this effect.

So to overcome this I use a series resistor instead. So when the OP stage is shorted, it will now see the series resistor, and it is safe. But you can't simply connect a series resistor to an amp OP stage; it will add to the output impedance, and it will mess up the damping of the headphone, giving you a soft bass. Also, adding a resistor in the signal path will directly degrade transparency. So what happens is the feedback is taken after this resistor; so the single feedback loop eliminates the consequences of the resistor being in place. But it means at RF frequencies, when the global feedback is not providing any effect, the resistor is functioning, and its there when the OP is shorted, so the OP stage is still safe. Because the resistor is present at RF, I also add a capacitor to ground, and this gives me another RF filter.

Now conventional DAC's have very complex out of band and RF filters, because DAC's create huge amounts of noise which must be filtered out (if you don't you get more noise floor modulation, and then things sound hard and bright). But adding these filters degrade transparency, simply because you have a lot more passive components in the signal path. Now with pulse array, I run the noise shapers at 104 MHz; and this means that the OP noise is much lower than conventional - but it still needs to be filtered out. So the adding of the OP resistor and the capacitor gives me another RF filter, and I get it for free, as there is no price to pay for it in terms of transparency, as the filter is inside the DAC's global feedback loop.

So this resistor and cap is very valuable arrangement; I get an RF filter with no cost in transparency; I get a an OP stage that is safe under shorts but does not require a limiter which would add distortion. But getting back to Mojo - why does adding a low impedance load subtly change the frequency response at 20 kHz? Its because I wanted to use the same OP stage as Hugo; but the transistors I use are way too big physically for Mojo, so I use the same transistors but packaged in a tiny package. But these have less power dissipation, and that forces me to use a safety resistor that is three times larger in value; and the larger value gives a bigger change in frequency response with low impedance loads. But we are talking about frankly trivial changes; at 33 ohms it is only -0.1dB down at 15 kHz; with 16 ohms it is -0.3 dB at 15 kHz.

But in terms of distortion, because there is not a current limit used for shorting, the current delivery is extremely linear and is the same as Hugo. With IEM's the impedance is low, but the actual voltage is trivial, and you certainly won't be able to measure or hear any distortion with such low voltages.

I hope this gives you a flavor of the complexities involved in designing Mojo's output stage; successful design for optimum sound quality is actually very complex, often involving competing pressures.

Rob
Click to expand...
Rob,

Manu thanks!
 
Jul 17, 2017 at 10:09 AM Post #33,037 of 42,765
I know it's probably answered before but I can't find it.
How can I play DSD/DSF files with foobar through chord mojo? I've installed the DSD Decoder component and output preference is set to WASAPI event/push. But I can't play dsd files (mp3, flac works fine). Also JRiver Media Center has no problem.
What do I need to change?
 
Jul 17, 2017 at 10:14 AM Post #33,038 of 42,765
Arghavan said:
I know it's probably answered before but I can't find it.
How can I play DSD/DSF files with foobar through chord mojo? I've installed the DSD Decoder component and output preference is set to WASAPI event/push. But I can't play dsd files (mp3, flac works fine). Also JRiver Media Center has no problem.
What do I need to change?
Click to expand...
Mojo does not play native DSD, it plays DOP (DSD over PCM) instead.
Seriously RBCD sounds excellent, so why worry about DSD?
 
Jul 18, 2017 at 11:46 AM Post #33,041 of 42,765
LIVE_EVIL said:
Guys, i have a stupid question. I bought mojo and when i am using it I end up hearing distortion when going above certain physical headphones volume. I assume that this is headphones clipping or i am wrong and i am driving mojo too hard. i use mojo with AKG K240DF ( i assume DF should be capable of withstanding lots and lots of power, ER4S and HD600.
So are headphones or mojo at fault?
Click to expand...

Most likely your headphones clipping, but interestingly, above a certain volume (it varies depending on individuals) the tiny bones that transmit sound in your ears create their own distortion.
(tldr: your ears can clip)
 
Jul 18, 2017 at 4:48 PM Post #33,042 of 42,765
Please properly quote me or I may not see your reply!

I recently got my second Mojo. I had bought the 2Qute for $1,300, but I'm back to the Mojo. One reason is because I want to keep costs down for the time being. I more or less only use speakers now. (I think my speakers are better than any headphone I've heard.) I'm even more impressed with the Mojo's performance with speakers (using it as a DAC / digital preamp) than with headphones.

I'd say the Mojo is not as accurate as the 2Qute, but it has a unique magical sound. I do think it beats the non-Chord DACs I've owned, including the Schiit Modi Multibit and iFi micro iDSD.

Anyway, this is a used unit that is a little older than the new one I got earlier this year. It came with an aftermarket USB A to dual micro USB cable, which lets you do charging and playback at the same time. However, this Mojo overheats and shuts off when I do that, even when it's placed upright. (It works fine if I do charging and playback separately.)

Can anyone recommend something to charge it at the same time as playback without it overheating? I'd prefer one of those devices that plug into the wall, to have it separate from my computer.
 
Last edited:
Jul 18, 2017 at 5:53 PM Post #33,043 of 42,765
Music Alchemist said:
Please properly quote me or I may not see your reply!

I recently got my second Mojo. I had bought the 2Qute for $1,300, but I'm back to the Mojo. One reason is because I want to keep costs down for the time being. I more or less only use speakers now. (I think my speakers are better than any headphone I've heard.) I'm even more impressed with the Mojo's performance with speakers (using it as a DAC / digital preamp) than with headphones.

I'd say the Mojo is not as accurate as the 2Qute, but it has a unique magical sound. I do think it beats the non-Chord DACs I've owned, including the Schiit Modi Multibit and iFi micro iDSD.

Anyway, this is a used unit that is a little older than the new one I got earlier this year. It came with an aftermarket USB A to dual micro USB cable, which lets you do charging and playback at the same time. However, this Mojo overheats and shuts off when I do that, even when it's placed upright. (It works fine if I do charging and playback separately.)

Can anyone recommend something to charge it at the same time as playback without it overheating? I'd prefer one of those devices that plug into the wall, to have it separate from my computer.
Click to expand...

Try an older phone charger with a low enough output maximum to force a cooler trickle charge; maybe a 750mA or or even 500mA. Could be wrong but I think despite modern 5V chargers being 2.1A the Mojo only takes 1A max.
 
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