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Line out dock vs. headphone out

Discussion in 'Sound Science' started by norman314, Jun 22, 2012.
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  1. OJNeg
    Is it 2 Vrms? or 2 Vp-p? I think my CD player is 2 Vrms....
  2. alperkocatas
    I seet this is a rather an old topic, but I wanted to put out my observations about the dock-out of iphone 3Gs.
    When connected to a sony micro hi-fi system via the dock connector, I can see that the eq setting of iphone still is effective.
    For example while the music is playing, when I change the eq setting of iphone from off to rock, I hear the difference. 
    This makes me belive that iphone dock connector line out does not give "untouched" sound. 
    May be it skips some headphone final amplification circuitry, which I am not sure, but I am sure that the sound output from the dock connector is not untounched.
    Any similar observations??
  3. stv014
    It is untouched by the built-in headphone amplifier, but not DSP (which, however, can normally be made lossless with the right settings, flat EQ, 100% digital volume, etc.). Having said that, there are a lot of myths and hyperbole regarding "double amping".
  4. autumnholy
    Speaking of "double amping", is that really a bad thing?
  5. stv014
    It depends on what you compare it to, the original amplified output, or amplifying that vs. a dedicated line output if one exists ?
    In the first case, it is a matter of how good each amplifier is, and may be a good or bad thing in practice. "Double amping" a bad headphone output that struggles to drive headphone loads with a high quality and transparent headphone amplifier can easily improve the overall sound quality. But if the original amplified output is already good enough (it can be with a decent DAP), then it might not make a useful difference.
    The second case is often a bad (and usually pointless) thing technically, but the difference might not necessarily be enough to be audible in practice.
    One important thing to keep in mind is that many "bad" headphone outputs improve significantly when they do not have to drive a difficult low impedance load.
  6. autumnholy
    My question would be, is there a case where the first headphone output (the internal amp for the DAP) is bad, thence when connected to the second amp (the external amp) and to the headphone, would the sound quality degrades?
  7. stv014
    It depends on exactly how it is "bad", and whether it improves significantly enough when it only has to drive a line input at a fixed volume setting, instead of a headphone. It also depends on the second amplifier how much potential there is for degradation (i.e. a very good external amp would either improve the quality, or at least not make it audibly worse).
  8. alperkocatas
    In my earlier post, I was asking if the sound from the dock port is untouched, because the eq settings are still in effect, and stv014 replied that line-out from dock skips the internal headphone amp, but it does not skip DSP, which puts the eq effect. Thanks for the answer, which is correct I think. 
    Now, I am trying to figure out more about the sound output of iphone from the dock port.
    I am connecting my phone to a Sony micro hifi system "CMT-G1IP", which does not have a dock station but a standard USB port instead. From the USB port, system can read flash disks and play audio files, and it can also play music from iphones and ipods. (I use the standard data cable of iphone for connecting to the system)
    From what I read so far, I think there is another component, which is DAC in between iphone DSP and the internal headphone amp.
    So, the sound path througn the headphone jack is like:
        "RAW DATA"  -> DSP  -> DAC -> Internal Headphone amp. 
    Ok, receiving the sound via the dock port line out ensures that the sound is not processed by the "Internal headphone amp."
    Now, I want to know if my system is receiving audio signal in digital or analog format. Is the internal DAC of iphone used or not?
    Iphone and Ipods can deliver either digital or analog audio via the 30 pin dock port. And many docking speakers use the analog output. 
    I have looked at the pinout diagram of Apple 30 pin connector. From there, I saw that pins 3 and 4 are used for analog audio output for left/right channels respectively. Additionally, pin 2 is used for ground signal. That makes totally 3 pins for the audio only. 
    And, additionally, this micro hifi system also charges the iphone through the usb port, which must then be using pins 16 and 23, which are for 5V and Ground. Adding these 2 pins, device totally needs 5 pins.  
    Finally, hifi system can also control the ipod, so that you can play/pause/etc.. And that signal is carried by other 2 pins. 
    So totally, 7, out of 30 pins must be used, if my system was receiving the audio in analog format. 
    But, USB bus only has 4 pins. 5V, Data Tx, Data Rx and Ground. So, you would not have enough pins if you wanted to carry the audio signal in analog format. 
    ...And this makes me believe that all devices which transmit audio from ipod/iphone by using a "USB cable", must transmit the audio in digital format.
    And for the systems receiving the audio direcly by docking the device using the dock port, it depends on the receiver system. It can be analog or digital. 
    Am I true, or am I missing something here?
    Any answers are welcome. 
    Note: By the way, analog output from the dock port is no more offered in iPhone 5 lightning port. Because of this, Apple had to put DAC into the lightning to 30-pin dock port adapter. 
    So, I can find  an iPhone 5 and try if it works with my system, I will be sure that audio is indeed transferred digitally. May be someone who has the latest iPhone can try a similar test??
  9. fubar3
    Consider the Sansa Fuze or Clip, for example. There is one battery with a bridge circuit or virtual ground which eliminates a big blocking capacitor to the phone jack. However, most of the circuitry runs on 3v such that the LOD lines rest at +1.2v (so blocking caps might be needed for some amps).
    Using the LOD gives a better sound since the distortion from the phone driver chips is bypassed.  I assume other players will have a similiar design.
  10. derekdog
    Speaking of line out dock cables...has anyone ever used or heard anything on the Trends CQ100 LOD? The price is not bad at $65.00 and it looks like a quality piece...I really need the dock to RCA for my Schiit Magni and those LODs tend to be higher in price...
  11. nick_charles Contributor
    There is a subforum dedicated to cables, docks etc, that would be a much better place to ask. 
  12. portal2poe
    I've read this whole post/thread with interest....I sit at my desk all day (computer programmer), and have used the apple dock with the line out connecting to a pair of Grado SR80s for 3 iPhones in a row, now, and have been pretty happy. (Ignorance is bliss maybe?)  But I'm wanting to upgrade my sound experience here at my desk....so for a desktop (non-mobile) environment, what should I be plugging into a Amp/DAC...
    Line-out from Dock -- (I love this solution because it looks nice, and it gets charged, but....)?
    USB through the Apple Camera Connection Kit for a pure digital signal?
    Headphone jack (doesn't sound like it, but just putting it here for completeness?)
    First post, so if this belongs in another forum, my apologies!
  13. womenyiqi
    thereby providing a standard voltage of sorts around which devices are designed and built.
  14. Happy Camper
    USB to DAC would be your cleanest option if you can get digital out, depending on the output implementation of the DAC. Then LOD to amp next. Headphone out last. This in the theoretical view. I've used my portable amp to boost the output of a headphone amp to increase gain in a noisy environment and inefficient open headphones. If I have more environmental noise than can be generated with two THD devices combined, it doesn't matter, I won't hear it. I've tried it at home and can hear my dogs snore more than any static or increased noise floor masking the sound. Now if I was in a dead quiet environment with high efficiency IEMs, I might possibly hear some hiss but then I wouldn't need to double amp them.

    In the signal chain, you want all the signal that is on the material(which sometimes can be pretty noisy background hiss). Supposedly, the LOD gives you that. The headphone amp will add some frequencies and take some away. That is then used in the final amp to add it's impact. If both amps are flat, you should have no other impact than raising the noise floor that would possibly mask any signal in that frequency range. That usually ends up being micro details (decay of instruments) and ambiance ques.

    The standard for portable devices is typically 1v and home devices 2v but I am sure there are exceptions since there are no fast standards.
  15. portal2poe
    Thanks so much Happy Camper!
    Yes, I've been continuing my research into this, and I had determined that the USB to DAC/AMP to headphones path is how I want to go.  So then I started the search for a Iphone 5 (lighntning dock) that charges AND provides a USB audio out....and one year into the existence of lightning....such an integrated device does not exist.   The only way to do this (charge and usb audio out) currently that I see is to use the Pure i-20 with the lightning to 30pin adapter...and even with that I'm not sure the phone will charge....seems like an sales opportunity to me?  Does anyone know if any companies are working on such a device?
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