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

Oct 13, 2016 at 10:53 AM Post #24,001 of 42,916
light - man said:
  Why don't you do that and come back to us in 25 years?  
wink_face.gif
Click to expand...

 
Latency for a 100k tap filter would be ridiculously long (100k * 1/Fs to be exact), yes... but that's not the point.
 
Designing the filter would be simple... boxcar in the frequency domain and IFFT will give the coefficients. 100k point (well, 131072) IFFT is nothing for matlab.
 
Oct 13, 2016 at 11:26 AM Post #24,002 of 42,916
grumpyoldguy said:
 
light - man said:
  Why don't you do that and come back to us in 25 years?  
wink_face.gif
Click to expand...

 
Latency for a 100k tap filter would be ridiculously long (100k * 1/Fs to be exact), yes... but that's not the point.
 
Designing the filter would be simple... boxcar in the frequency domain and IFFT will give the coefficients. 100k point (well, 131072) IFFT is nothing for matlab.
Click to expand...

May i know, what's your day job :)
 
Oct 13, 2016 at 11:34 AM Post #24,004 of 42,916
Oct 13, 2016 at 12:50 PM Post #24,007 of 42,916
jarnopp said:
I can't find the post right now, but Rob has said Mojo actually uses twice the taps that Hugo does, but at half the speed, for the same result. Something like that. And, more taps correlates to a warmer sound.
Click to expand...

Yes, the first part is true.The second part I am not sure about.
John Franks replied to my post and said:
 
"Actually it's about twice as many as Hugo but run at half the speed giving approximately the same number crunching power in terms of DSP ..... We have mentioned this before, but didn't want to put much focus on it as this is a small only part of the over design of Rob's overall topology."
 
And
 
"it was always our intention to try to match the performance of Hugo To do this without using as much power as Hugo. Therefore Rob used more DSP cores but run differently to match the performance of Hugo but at far lower power demands. JF"
 
Oct 13, 2016 at 12:59 PM Post #24,008 of 42,916
maxh22 said:
Yes, the first part is true.The second part I am not sure about.
John Franks replied to my post and said:

"Actually it's about twice as many as Hugo but run at half the speed giving approximately the same number crunching power in terms of DSP ..... We have mentioned this before, but didn't want to put much focus on it as this is a small only part of the over design of Rob's overall topology."

And

"it was always our intention to try to match the performance of Hugo To do this without using as much power as Hugo. Therefore Rob used more DSP cores but run differently to match the performance of Hugo but at far lower power demands. JF"
Click to expand...


A length N filter requires N parallel multiplies and an adder tree to produce an answer every clock cycle when running at Fs.

If I now run at Fs/2, I'm processing twice as much data every clock cycle... I get two input samples every clock instead of just one. In order to keep up and not drop data I need to process both every clock. Hence the doubling of resources.

Of course the Mojo is running at many, many times the sampling rate... Ostensibly to partially serialize the design and take advantage of timesharing DSP48s. But the concept is still the same... halving the clock rate requires a doubling of resources.

The structure doesn't change the frequency response, the coefficient values do.
 
Oct 13, 2016 at 1:35 PM Post #24,009 of 42,916
If you throw some angled velour pads on the HE400i the mids tame a bit and bring out some more punch and sparkle. It's not so.. flat sounding. More rounded imo with the Brainwavz velour angled pads. I found the Brainwavz leather (all type) to be too bright and didn't absorb any of the upper and mids. 
 
Oct 13, 2016 at 4:44 PM Post #24,010 of 42,916
jarnopp said:
I can't find the post right now, but Rob has said Mojo actually uses twice the taps that Hugo does, but at half the speed, for the same result. Something like that. And, more taps correlates to a warmer sound.
Click to expand...


Actually, as I quoted in my previous post on the previous page, Rob has said the warmth and smoothness was from improving the noise, most notably the noise floor modulation. It wasn't from increasing TAPs.
 
Oct 13, 2016 at 5:09 PM Post #24,011 of 42,916


No, the Mojo, and all Chord DACs, are single ended. There is no benefit to plugging the separate headphone jacks to your stereo. Even the RCA output measures better, except for Voltage output, than the XLR output (which is derived from the SE out) in the Hugo TT and DAVE.

As for your connection to the phone, you are likely hearing cellular interference and/or a loose connection with the USB cable in the Mojo input. Unfortunately this loose connection can happen with some USB connectors.

As for charging, yes, you would connect to both the USB ports to charge and listen at the same time. The fact that it takes a long time to charge is not surprising as PC USB ports are not high current ports, especially when you are drawing power while listening. Try using a sperate 2A 5V USB charger plugged in to the wall instead. Often times manufacturers may overstate their charger specs, so even though the charger is rated at 1A output they may not quite deliver that amount of current.
 
Oct 13, 2016 at 6:37 PM Post #24,013 of 42,916
x relic x said:
No, the Mojo, and all Chord DACs, are single ended. There is no benefit to plugging the separate headphone jacks to your stereo. Even the RCA output measures better, except for Voltage output, than the XLR output (which is derived from the SE out) in the Hugo TT and DAVE.

As for your connection to the phone, you are likely hearing cellular interference and/or a loose connection with the USB cable in the Mojo input. Unfortunately this loose connection can happen with some USB connectors.

As for charging, yes, you would connect to both the USB ports to charge and listen at the same time. The fact that it takes a long time to charge is not surprising as PC USB ports are not high current ports, especially when you are drawing power while listening. Try using a sperate 2A 5V USB charger plugged in to the wall instead. Often times manufacturers may overstate their charger specs, so even though the charger is rated at 1A output they may not quite deliver that amount of current.
Click to expand...

Rob Watts also recommends first fully charging the Mojo, then when connected to both USB sockets, the Mojo just needs enough current to trickle charge.
This approach has the additional advantage that it enables the Mojo to operate in a mode that generates the least heat, and will not cause thermal shutdown.  
 
Oct 13, 2016 at 7:01 PM Post #24,014 of 42,916
miketlse said:
Rob Watts also recommends first fully charging the Mojo, then when connected to both USB sockets, the Mojo just needs enough current to trickle charge.
This approach has the additional advantage that it enables the Mojo to operate in a mode that generates the least heat, and will not cause thermal shutdown.  
Click to expand...


Yes, good point, however it'll still take forever to charge from most PCs USB, even if they do deliver the 1A current. Personally, I recommend a wall charger capable of 2A 5V to be safe. :)
 
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