[depon]

Hi,
I have been reading this forum for a while ( but quite a lot I must admit!)
This is my first post (and thread of course). Forgive me if I seem a bit lost here, this seemed the only place in the forum where I could start a thread.
I have a question I would like to ask. I would like to know if the following cablings are valid. This is about experimenting. I would like to hear the actual difference between those two cable setups. I also want to hear how the sound changes ( crosstalk (?) etc) when I change some variable in the setup (e.g. increasing the cable length before or after the headphone amp) but before I test this I would be grateful if someone could answer the following question(s) about cabling #2 :
Will anything explode?
Is cabling #2 valid?
 
Cabling #1 is the default cabling
Cabling #2 involves not passing the grounds through the amp but connecting directly to the audio source and headphones.
 
CABLING #1
                                    __________                 ___________
Left-------------------------|Portable     |--------------|headphones|
Right-----------------------|Headphone|--------------|                    |
Left ground-----______|Amp          | _____------|                   |
Right ground---            |_________|           ------|__________|
 
CABLING #2
                                    ____________                   __________
Left-------------------------|Headphone     |--------------|headphones|
Right-----------------------|Amp                |--------------|                    |
                                    |____________|                |                    |
                                                                              |                    |
Left ground--------------------------------------------------|                    |
Right ground------------------------------------------------|__________|
 
 
I am designing a cable for myself and I want to take several things into account. I have been reading a lot of stuff including things like the following
https://electronics.stackexchange.com/questions/175072/headset-input-crosstalk-or-how-to-mitigate-the-effects-of-common-ground-resista
http://www.rane.com/note151.html
Even though this experiment is about me hearing the actual difference , I would still appreciate any comments about those two setups.
 
As this will be driven by my mobile (smart)phone , I am also going to add a mic like in the following diagram. Is this diagram valid?
                                                                              ___________
Left-------------------------|Portable     |------------------|headphones|
Right-----------------------|Headphone|------------------|                    |
Left ground-----            |Amp          |           ----------|                   |
Right ground---            |_________|           ----------|_________|
                                                                              ___________
Mic-------------------------------------------------------------|microphone|
Mic ground---------------------------------------------------|__________|
 
 
The left ground, right ground and mic ground are finally merged in the ground ring on a trrs 3.5mm jack.
 
Thanks in advance

 

[Dulalala]

For the last diagram, wouldn't a 4 pole y splitter be much easier to deal with instead? 

 

[MindsMirror]

No, it won't work the way you are hoping.
 
The Left and Right wires contain a voltage signal. A voltage is a potential differential, meaning it is relative to some other point, which we usually usually define as ground. There is no voltage without a reference point. The amp can't do anything without a ground connection.
 
Another problem is that if the headphone is receiving power, current must be passing through it from the positive L or R lines to the negative or ground lines. That means that even if a signal somehow made it to the headphones in #2, the current must be returning to the ground connection, which in your diagram is your source ground, not your amp. If the current is returning to the source, it must also have been supplied by the source. If the source is supplying the current (power), then the amp is pointless.
 
The best way to avoid the common ground problem is to use a balanced amp. With a regular single ended amp, the best you can do is separate the ground line into L and R ground as early as possible to keep the effects of the common ground to a minimum. That means, use a balanced cable with separate isolated L(-) and R(-) wires, and connect them both to the ground point on the jack that plugs into the amp. Any voltage drop from current returning on the L(-) wire won't be seen on the R(-) wire, and vice-versa. There's nothing you can do about any common ground problems inside the amp itself.
 
As for the source to amp or the source to microphone connection, there is practically zero current on these wires so you shouldn't be concerned about those, just wire those as standard.

 

[depon]

Thank you very much both Dulala and MindsMirror ! 
 
At Dulala:
Thank you very much for your feedback! My short reply to your suggestion is that convenience is very much pursued but not first priority !    
Sound quality (or at least playing and experimenting around it) , comfort, visual simplicity and aesthetics is my main fun at this point !  
 
At MindsMirror:
 
Your answer would be what a junior would hope to get having the "head-fi" experience in mind!! I really appreciate your guidance !!
You will be sparing me some experimentation time. I am also very happy to know that you actually consider that separating the L(-) R(-) (and of course M(-) ) is a good idea to foresight. Especially if it gives you the choice to use a balanced amp (I hadn't thought of it ! ). That is a very good idea.
I will very much look into the portable balanced amp as a meaningful choice. Being portable is a main concern. 
 
To sum up in order to keep the thread useful for everyone, the currently ideal setup (for use with an unbalanced amp) up to current discussion is the following:
                                         __________                 ___________
Left (+)-------------------------|Portable     |--------------|headphones|
Right (+)-----------------------|Headphone|--------------|                    |
Left (-)----------------______|Amp          | _------------|                   |
Right (-)--------------            |_________|   ------------|__________|
                                                                              ___________
Mic-------------------------------------------------------------|microphone|
Mic (-)---------------------------------------------------------|__________|
 
Having read this thread:
https://electronics.stackexchange.com/questions/253546/how-does-stereo-audio-signal-works-with-shared-ground-e-g-headphone-cables
 
user Dampmaskin comments:

As a side note, in headphones/earbuds some crosstalk is desirable (at least IMO), because most mixes are made for speakers. The air between the speaker and the listener's head introduces lots of crosstalk between the left and right channel. In headphones, this does not happen, leading to exaggerated stereo separation. – Dampmaskin Aug 22 '16 at 10:23  

 
Then again having read this article
http://www.soundonsound.com/sound-advice/q-it-normal-get-crosstalk-appearing-headphones
Technical Editor Hugh Robjohns says:

The Grace Design m903 (and many other high-end headphone amps) does have a 'crossfeed' mode, and this does deliberately introduce crosstalk. However, the crosstalk in question is carefully frequency-shaped and delayed, to simulate the way that sound from one loudspeaker reaches both ears, the amount varying with frequency (and time) due to the shape of the head. Obviously, with headphones, each ear can only hear the sound generated by the earpiece serving that ear, and that results in the typical 'sounds on a line between the ears inside the head' effect that we all know. The crossfeed system (sometimes also called HRTF processing) creates a stereo presentation on headphones that more closely emulates loudspeaker listening, by deliberately reintroducing the acoustic crosstalk that occurs in that situation.

 
Some even enjoy introducing crossfeed with much cheaper and readily-accessible alternatives like using the "virtual room" software features of dsp software smartphone-DAP features.
http://www.head-fi.org/t/518925/to-crossfeed-or-not-to-crossfeed-that-is-the-question
 
Introducing your own desirable amount and type of crossfeed into one's portable setup and comparing the differences will be put to the test. I wonder if anyone has anything to say on those comments.
It will be fun to observe acoustically the differences (if significant at all for some at the end of the day????).