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IPod 5th Gen Headphone capless output MOD:
Feb 28, 2014 at 3:41 PM Thread Starter Post #1 of 27
beyondwind

beyondwind

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I will call it IPod 5th Gen Headphone capless output  MOD ,  iPHD
 
With this mod you will have the best audio quality ( if not, the simplest audio path ) that can be achieve with the Wolfson audio codec. The capless headphone output is achieved by using modifed rockbox firmware to enable WM8758's capless output configuration. 
 

For how to perform the mod, please check the details:
 
http://beyondwind.duckdns.org/?page_id=95
 
 
If you want to keep the dock pin lineout, either stock or iMod, A swapped mod is available, check this MOD with lineout
 
http://beyondwind.duckdns.org/?page_id=119
 
Neither mod is compatible with stock firmware, nor the original rockbox. The two versions of rockbox firmware are not compatible, so choose one according to wiring.
 
Feb 28, 2014 at 5:35 PM Post #2 of 27
So just to clarify - is this an option in the firmware so you can chose to turn it off and use the line out or is the line out disabled by the hardware mod?
 
Feb 28, 2014 at 6:21 PM Post #3 of 27
suicidal_orange said:
  So just to clarify - is this an option in the firmware so you can chose to turn it off and use the line out or is the line out disabled by the hardware mod?
Click to expand...

No, this is hardware mod with software configuration change, the coupling capacitor can't be bypassed by firmware. 
 
To keep the dock pin connector line-out, the solution is to swap out1 and out2, use out1 as the virtual ground driver.  I will compile a different version of rockbox firmware and update the hardware mod instructions later, just for whoever need it. 
 
The original version will have the best audio path IMO, for its simplicity.
 
Feb 28, 2014 at 6:57 PM Post #4 of 27
This is an interesting mod and thanks for sharing. I am gonna try it.
 
Is this mod bypassing internal amp? Are you getting some DC offsets from the HO after this mod? What kind of cap you put there and is the cap surface mounted?
 
Does the modified RB firmware for this mod also work for the mSATA mod?
 
Thanks
 
Feb 28, 2014 at 8:21 PM Post #5 of 27
dminor said:
  This is an interesting mod and thanks for sharing. I am gonna try it.
 
Is this mod bypassing internal amp? Are you getting some DC offsets from the HO after this mod? What kind of cap you put there and is the cap surface mounted?
 
Does the modified RB firmware for this mod also work for the mSATA mod?
 
Thanks
Click to expand...

Yes, this firmware will work with either HDD ipod or mSATA mod. 
 
No DC offset, some pop at startup due to registry initialization sequence. Very clean and tight bass!  Sound is neutral for my taste. I use ear buds so the 40mW output level is not a problem for me.
 
The Cap is kemet 47uf, 6V, tantalum, The exact cap used on other part of the logic board,  I harvest it from another broken logic board. 
 
Feb 28, 2014 at 8:42 PM Post #6 of 27
Thanks. So this mod does not bypass internal amp, correct?
 
In your pic below, it appears the two pads are bridged near the DAC where the two Z caps are removed, correct?
 
How do you mount the cap to the board or it just stays loose there?
 
It appears to be a challenge to put the headphone jack back to the case after the mod and close it. It may be also a challenge to open the ipod in the future with the headphone jack wired to the board.
 
Sorry for asking so many questions.
 
 

 
Feb 28, 2014 at 9:08 PM Post #7 of 27
There is no such thing as by pass internal amp. You can read the wm8758b datasheet, audio path, there is no way to do it, and from my point of view, it should not be done, all DAC output have to be buffered for line_out or Headphone.
 
The iMod has created the misconception,  what iMod do is to by pass the internal low quality zCap, replaced by a better cap in the LOD cable.
 
The cap is secured to the board by hot melting glue,
 
The HP_COM connection at the Zcap for this mod is bridged, both pin are at the same DC level, acting as mid point reference driver, which made the sound extremely well controlled.
 
The HP jack mounting is easy to me, just two screws.

 
 
 
 

 
Feb 28, 2014 at 9:25 PM Post #8 of 27
Sorry I have no electrical background so I won't understand the wm8758b datasheet & audio path.
 
Are you saying the LOD output is already amped regardless of the stock ipod or the iMod?
 
How about sending the signals directly to the LOD pins from the two pads near the DAC where the Z caps are removed?
 
Feb 28, 2014 at 9:39 PM Post #9 of 27
dminor said:
  Sorry I have no electrical background so I won't understand the wm8758b datasheet & audio path.
 
Are you saying the LOD output is already amped regardless of the stock ipod or the iMod?
 
How about sending the signals directly to the LOD pins from the two pads near the DAC where the Z caps are removed?
Click to expand...


Correct, LOD output is always amped. In stock ipod or imod, the firmware just configure the line_out Amp gain at 0db. In my modded compilation, the Amp gain can be software configured. So to use the lineout, simply crank up the volume to anything less or equal to 0db.  The only penalty of setting the LOD output to less than 0db is some loss on S/N, while having a gain in THD performance.
 
The second version of the mod with line out can have zCap bypassed, ,send Lout2 and Rout2 directly to the corresponding LOD pins, the same as iMod.
 
Feb 28, 2014 at 9:48 PM Post #10 of 27
beyondwind said:
 
Correct, LOD output is always amped. In stock ipod or imod, the firmware just configure the line_out Amp gain at 0db. In my modded compilation, the Amp gain can be software configured. So to use the lineout, simply crank up the volume to anything less or equal to 0db.  The only penalty of setting the LOD output to less than 0db is some loss on S/N, while having a gain in THD performance.
 
The second version of the mod with line out can have zCap bypassed, ,send Lout2 and Rout2 directly to the corresponding LOD pins, the same as iMod.
Click to expand...

 
How about this mod - wired directly to the LOD pins (L & R output) from where the two Z caps are removed? Is this cleaner since the board is bypassed?
 

 
Feb 28, 2014 at 10:06 PM Post #11 of 27
dminor said:
   
How about this mod - wired directly to the LOD pins (L & R output) from where the two Z caps are removed? Is this cleaner?
 
Click to expand...

Yes, this is one way of dong iMOD, yet I think the wiring scheme is not optimum in my opinion. On wire on the top left is arranged next to the inductor, will be picking up lots of noise.
 
I my opinion, by-pass the Zcap is enough for the iMOD, if not carefully thought after, a wiring scheme can be worse than the stock PCB traces.
 
People tends to focus on the signal line mod, without realize that grounding is equally important (how the dockpin AGND is connected to the WM chip AGND).
 
That's why a pseud balanced line-out setup as i proposed from the modded audio jack will have the best performance in theory, no grounding issues.
 
Feb 28, 2014 at 10:17 PM Post #12 of 27
Oh I forgot to mention on that direct-out mod (shown in the pic above), those two LOD pins are lifted off board so the board is bypassed.
 
 
In that pic for your iPhD MOD, there seem to be no pads on the board (can't see any even with a magnifier) for soldering the two wires for AVDD2 & AGND. How did you solder those and can you blow up that detail? Thanks
 
In the pic below, it seems the HP_COM and HP_left were bridged with a trace of solder. Maybe it just looked like that in the pic.
 

 
Mar 3, 2014 at 7:39 AM Post #14 of 27
Just bought a dodgy cheap mainboard to give this a go, supposedly sound only works if you hold the bottom corner?!  Doesn't sound like an issue modding up near the DAC...
 
Mar 6, 2014 at 12:06 AM Post #15 of 27

 
I just put a few dots on the possible soldering points, The green dots are for AGND,  pink for AVDD. With a very fine tip soldering iron, soldering pads of existing components can be utilized. , otherwise just scrape off the soldering mask to expose the copper if needed. 
 
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