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iBasso D42 "Mamba" with dual dacs! !! Hey Hey! Improved Starting on Page 76 . - Page 62

post #916 of 1153

Haven't read all 61 pages, but has anyone else come across what sounds like clipping when using the DAC? Tried two different headphone, battery and usb power, all the USB ports on my Mac, and a powered usb hub. Happens at high and low volumes. Still better than the headphone jack on the computer, but its just enough to bug me. Haven't noticed this at all when using the iPhone as a source.

post #917 of 1153
Thread Starter 

What Mac do you have? The Mac computer pre Pro models, like my MacBook Pro and the previous one, had a lower than standard output, which is why many external 2.5 hard drives could not run from the USB port of the earlier Mac's like the G4 etc. 

post #918 of 1153

You can check this thread from page 39, there are people who can hear the clipping and some who could not,

Attached are the 2 quotes from Madwolf describing the problem and a possible cure, there are more detail in this thread.
 

Quote:
Originally Posted by JeestersMandelbrot View Post

Haven't read all 61 pages, but has anyone else come across what sounds like clipping when using the DAC? Tried two different headphone, battery and usb power, all the USB ports on my Mac, and a powered usb hub. Happens at high and low volumes. Still better than the headphone jack on the computer, but its just enough to bug me. Haven't noticed this at all when using the iPhone as a source.





Quote:
Originally Posted by madwolf View Post

This is the measurement from the Output of the AD8616
At the input of the AD8616/output of WM8740 the Signal I pump in using the computer is a Triangle wave. Level set at 100%


Sorry for the poor image, I have one hand on the probe and hand on the camera.


So confirm there is clipping.
Straight off I have not regain from my shock, this is happening to me again.


So how to solve this problem ?

1) You could up the voltage of the AD8616. (Possible to tap from the 5V amp or from WM8740, but could be noisy, need to break traces as well )
2) or reduce the Gain of the AD8616 so that the output voltage is below clipping.

The second option could be easier just change 2 resistor value. Easy mod for anyone who solder. When I finally get to do that will post the solution.

A temporary solution would be to set the volume of your computer to about 80% of max so that the clipping does not occur.

I would need to go through the D4 design again, Look like I would have to keep the D4 for a while longer as my friend would likely ask me to solve this before passing to him.




Quote:
Originally Posted by madwolf View Post

Initial Solution, quick remedy, (Have not spend much time thinking of the best solution). I decided the quickest solution to the problem is to reduce the gain of the AD8616. It original gain of the AD8616 is 2, by adding a resistor from the output of the 8616 to the negative input we could adjust the gain.
The original resistor across is 2.2K ohm.



The Gain resistors are located on the top side of the board, and to solder on that you need to remove the Big Nichicon HZ cap (On my case it is Rubycon ZL) to troublesome, to fix this way.

So instead of changing the resistor, I found a compensation capacitor beside the AD8616 which is connected in parallel to the feedback resistor. By adding a 2.2K ohm across this I reduce the gain to about 1.5. From the Picture the 2.2K resistor is sitting on top of the capacitor. label C26 and C28.

You could also solder the resistor directly on PIN 6,7 and PIN 1,2 on the AD8616. (If I do that I would be tempted to change the AD8616! )

I so happened to have a 2.2K 1% SMD 0805 resistor at home. How lucky.
So after adding the resistor I test it again and the Clipping would not occur.
Now I could feed signal at 100% resolution to the D4 instead of just 80%

It should be placebo, on initial testing I could hear more details from the DAC now. Sweet. Well in theory it is 100% now instead of 80%, so might not be placebo.

Quote:
Originally Posted by qusp View Post
very cool madwolf, the crowd is easily impressed though as they are not from the dark side I feel your pain on finding this area after thinking you were done though. what I find most impressive is that you were able to take a photograph with one hand while using the probe with the other
The power is definitely stronger on the dark side.
post #919 of 1153

You could read more about the clipping problem from page 39 of this thread.

There are some solution to it as well. It is all in this thread
 

Quote:
Originally Posted by JeestersMandelbrot View Post

Haven't read all 61 pages, but has anyone else come across what sounds like clipping when using the DAC? Tried two different headphone, battery and usb power, all the USB ports on my Mac, and a powered usb hub. Happens at high and low volumes. Still better than the headphone jack on the computer, but its just enough to bug me. Haven't noticed this at all when using the iPhone as a source.

post #920 of 1153

Thanks Alden, very helpful. Kind of glad it wasn't just me.

post #921 of 1153

anyway to improve the bass of the d4 with the hiflight opamp?

post #922 of 1153
Quote:
Originally Posted by playingwithfire View Post

anyway to improve the bass of the d4 with the hiflight opamp?


Try using the LMH6655 stock buffers in place of the Topkit dummies.  Combined with the Topkit LR module, the 6655's will yield a bit warmer SQ with slightly more bass impact.   This seems to work well with brighter sounding phones and IEMs. 

Ron

 

post #923 of 1153
Quote:
Originally Posted by HiFlight View Post




Try using the LMH6655 stock buffers in place of the Topkit dummies.  Combined with the Topkit LR module, the 6655's will yield a bit warmer SQ with slightly more bass impact.   This seems to work well with brighter sounding phones and IEMs. 

Ron

 


With the stock buffers and topkit opamp it's a virtual P-51 clone.

post #924 of 1153

Sorry, when I put in the highflight kit I took out 3 different chips and they all look identical to me. Is there any instruction to do this?

post #925 of 1153
Quote:
Originally Posted by playingwithfire View Post

Sorry, when I put in the highflight kit I took out 3 different chips and they all look identical to me. Is there any instruction to do this?


To a cursory look, they do look identical, but if you use a magnifier and hold the opamps at an angle to the light, you can read the numbers on the top.  The 2 LMH6655's are the buffers.  Sometimes the numbers are not all on one line....sort of like this:

 

  LMH 66

           55

 

Hope this helps.  

 

Please use great care to ensure that the opamps are inserted with the correct polarity when swapping them in and out of the sockets.  Otherwise your opamp will act as a very quick-blowing fuse!

 

Ron

 

post #926 of 1153
Quote:
Originally Posted by HiFlight View Post




To a cursory look, they do look identical, but if you use a magnifier and hold the opamps at an angle to the light, you can read the numbers on the top.  The 2 LMH6655's are the buffers.  Sometimes the numbers are not all on one line....sort of like this:

 

  LMH 66

           55

 

Hope this helps.  

 

Please use great care to ensure that the opamps are inserted with the correct polarity when swapping them in and out of the sockets.  Otherwise your opamp will act as a very quick-blowing fuse!

 

Ron

 

All white square on top left?
 

post #927 of 1153
Quote:
Originally Posted by playingwithfire View Post



All white square on top left?

The white squares point to the capacitors on the left side of the amp when looking at it from the front. I guess you would say they are closest to the front and point to the left when one faces the front of the amp.

 

Ron

post #928 of 1153
Quote:
Originally Posted by HiFlight View Post



The white squares point to the capacitors on the left side of the amp when looking at it from the front. I guess you would say they are closest to the front and point to the left when one faces the front of the amp.

 

Ron

seems like a tradeoff of bass vs. soundstage after switching. I'll have to think this over.
 

post #929 of 1153

Is a 9.6v rechargeable bad for the D4? 

 

I'm a little worried since I blew a cap the first time I used one last week, but I'm not sure if it was just a coincidence, due to the 9.6v battery or due to the really crappy USB cable I was using...

post #930 of 1153
Quote:
Originally Posted by airs View Post

Is a 9.6v rechargeable bad for the D4? 

 

I'm a little worried since I blew a cap the first time I used one last week, but I'm not sure if it was just a coincidence, due to the 9.6v battery or due to the really crappy USB cable I was using...

 

Been using 9.6v's for two months now with absolutely no problems.  Sound fantastic.
 

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