# Line out dock vs. headphone out



## Norman314

So, a lot of people on head-fi seem to say that plugging an amp in through a line-out dock of an iPod/iPhone will give better results than using the headphone out. Is there any scientific basis for this claim ? In what way is the signal processed differently?
   
  Amazon reviewer SRH thinks it's better to not use an LOD: http://www.amazon.com/review/R3H4HRUK6UL5Y3/ref=cm_cr_pr_perm?ie=UTF8&ASIN=B004QVNNI0&linkCode=&nodeID=&tag=. Are his claims correct?
   
  Also, suppose I am hooking up an amp to an Android device that doesn't have an iPod style line out dock. Would the sound quality somehow be worse? Could I hook it up through the HDMI port instead, and would this give an improvement?


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## liamstrain

Using a line out dock prevents "double amping" - whether this is important depends very much on the amps in question.


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## PurpleAngel

Quote: 





norman314 said:


> So, a lot of people on head-fi seem to say that plugging an amp in through a line-out dock of an iPod/iPhone will give better results than using the headphone out. Is there any scientific basis for this claim ? In what way is the signal processed differently?
> 
> Amazon reviewer SRH thinks it's better to not use an LOD: http://www.amazon.com/FiiO-L9-L-Shaped-Cable-iPhone/product-reviews/B004QVNNI0/ref=cm_cr_pr_hist_2?ie=UTF8&filterBy=addTwoStar&showViewpoints=0. Are his claims correct?
> 
> Also, suppose I am hooking up an amp to an Android device that doesn't have an iPod style line out dock. Would the sound quality somehow be worse? Could I hook it up through the HDMI port instead, and would this give an improvement?


 
  Deleted


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## Anaxilus

Went through this little yesterday.
   
http://www.head-fi.org/t/495931/westone-es5/4665#post_8475311


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## Norman314

Why does daisy chaining amplifiers produce noise?
   
   
  The amazon reviewer whom I linked (just now I changed the link in my original post, original link pointed to the wrong place) claims that using an LOD does not actually bypass the iPod amp. I guess he is just flat out wrong. I looked at a few of his other reviews, and he doesn't seem to reliable.


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## liamstrain

Quote: 





norman314 said:


> Why does daisy chaining amplifiers produce noise?
> 
> 
> The amazon reviewer whom I linked (just now I changed the link in my original post, original link pointed to the wrong place) claims that using an LOD does not actually bypass the iPod amp. I guess he is just flat out wrong. I looked at a few of his other reviews, and he doesn't seem to reliable.


 
   
  It's not that it so much produces noise, as 1. Amplifies any noise in system, *twice*. 2. means you have to control two volumes... 3. May play with electrical damping on low impedance phones and IEMS, affecting the bass*
   
  *not sure about 3, but my memory is tweaking on something there.


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## Norman314

What you said about amplifying noise twice doesn't really make sense. What matter should be the degree to which the noise is amplified, not the number of times it is amplified.


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## liamstrain

the most common place for noise would be distortion in the amplifier circuit though. Minimizing the number of those, rather than amplifying another amps distortion, for instance, seems the better plan.


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## Norman314

Ah, that makes sense, I think.


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## Mauricio

The benefits of line-out over head-phone out usually boil down to i.) better impedance matching and ii.) better amplification by an outboard amplifier as opposed to the stock intergrated circuit chip amp in the device.  It has nothing to do with "double-amping".


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## liamstrain

Quote: 





mauricio said:


> ii.) better amplification by an outboard amplifier as opposed to the stock intergrated circuit chip amp in the device.


 
   
  I don't disagree. But why bother with the line out, rather than the headphone out?


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## Anaxilus

Quote: 





liamstrain said:


> I don't disagree. But why bother with the line out, rather than the headphone out?


 
  Huh?  I thought he explained that.....
   
  Why would you hook up a 1 inch garden hose to the end of a 3/4 inch hose and expect more flow?


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## Mauricio

Because line-out:
  i.) gives you a signal (more or less) untouched by the device's internal amp and volume control mechanism;
  ii.) has an output impedance well matched to the input impedance of line-in on devices that accept line-level inputs;
  iii.) provides a standard peak voltage of no more than 2.1 volts, thereby providing a standard voltage of sorts around which devices are designed and built.


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## Anaxilus

Quote: 





mauricio said:


> Because:
> i.) line-out gives you a signal (more or less) untouched by the device's internal amp;


 
   
  And potentiometer.  For those that don't think it matters go listen to a DACPort vs. a DACPort LX.  The only difference is a volume pot.  Substantial difference to my ears.


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## liamstrain

Right, my point with "double amping" was the same - you don't want to amplify a signal that's already been amplified (distorted) by the internal IC and it's gain controls... you just amplify any mess it has created and lose any benefit of using the better external amp (unless all you need is massive gain for some reason).


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## OJNeg

Quote: 





mauricio said:


> Because line-out:
> i.) gives you a signal (more or less) untouched by the device's internal amp and volume control mechanism;
> ii.) has an output impedance well matched to the input impedance of line-in on devices that accept line-level inputs;
> iii.)* provides a standard peak voltage of no more than 2.1 volts, thereby providing a standard voltage of sorts around which devices are designed and built.*


 
   
  Is it 2 Vrms? or 2 Vp-p? I think my CD player is 2 Vrms....


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## 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??


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## stv014

Quote: 





> Originally Posted by *alperkocatas* /img/forum/go_quote.gif
> 
> This makes me belive that iphone dock connector line out does not give "untouched" sound.


 
   
  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".


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## autumnholy

Quote: 





stv014 said:


> 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".


 
   
  Speaking of "double amping", is that really a bad thing?


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## stv014

Quote: 





autumnholy said:


> Speaking of "double amping", is that really a bad thing?


 
   
  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.


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## 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?


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## 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).


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## 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. 
   
  Conclusion:
   
*...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??


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## fubar3

Quote: 





norman314 said:


> So, a lot of people on head-fi seem to say that plugging an amp in through a line-out dock of an iPod/iPhone will give better results than using the headphone out. Is there any scientific basis for this claim ? In what way is the signal processed differently?


 
  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.


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## 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...


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## nick_charles

derekdog said:


> 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...


 
  
 There is a subforum dedicated to cables, docks etc, that would be a much better place to ask.


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## 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!
  
 Thanks!
 Nathan


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## womenyiqi

thereby providing a standard voltage of sorts around which devices are designed and built.


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## Happy Camper

portal2poe said:


> 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?
> ...


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.


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## 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?
  
 Nathan


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## bigshot

The DAC that is built into your iPod is as good as anything you will find in an external DAC. Save your money and put it into better headphones and music. Those are the things that make more of a difference.


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## Spyro

bigshot said:


> The DAC that is built into your iPod is as good as anything you will find in an external DAC. Save your money and put it into better headphones and music. Those are the things that make more of a difference.


 
   + 100!


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## jsplice

bigshot said:


> The DAC that is built into your iPod is as good as anything you will find in an external DAC. Save your money and put it into better headphones and music. Those are the things that make more of a difference.


 

 I have to disagree with this.  Primarily, this may be due to the amplification inside the iPod, but when I went from my iPod 5th gen to an iBasso D2 Boa back in 2008, I noticed a substantial difference in sound quality.  I'm referring to listening to the same music on the iPod, then listening to it via foobar in Windows, with the iBasso connected to the PC via USB.


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## castleofargh

there is difference, and there is better. 
  
 I'm one of those apple haters, so even if the next ipod was a little wonder, I guess my brain would still decide to not like the sound. but I still agree 100% with bigshot here.
  
  
 you pick your music, then try to find the headphone that makes it shine. and only then if the said headphone has needs of its own, provide to those needs.
 I'm saying this but I'm one to shoot in all directions at once ^_^. my audiophile trip is like some zen quest, I know what to do from the start, but it takes years to actually be able to apply it on myself.


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## jsplice

castleofargh said:


> there is difference, and there is better.
> 
> I'm one of those apple haters, so even if the next ipod was a little wonder, I guess my brain would still decide to not like the sound. but I still agree 100% with bigshot here.
> 
> ...


 

 When we're talking about just ranking items according to their importance and impact on sound, yes, no one can really argue that headphones make the most difference.  The same applies to speakers.  I was just saying that I don't agree with the comment that the DAC/amp inside the iPod is hard to improve on.  There's also a balance to be achieved.  You can't just say "use the iPod with your $1000 LCD-2s".  There's certain point where if you don't upgrade other items in your arsenal, then you won't be getting anywhere near the full sound of of the headphones.  With that being said, I was able to hear an improvement in sound going from the iPod to the iBasso D2 when using even a relatively cheap pair of headphones, the Beyerdynamic DT-770.  With much more efficient earphones, the difference isn't as great, but it's definitely still there.  I'll do a better comparison with my Westone 3's once they arrive from Amazon this week.


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## bigshot

jsplice said:


> I have to disagree with this.  Primarily, this may be due to the amplification inside the iPod, but when I went from my iPod 5th gen to an iBasso D2 Boa back in 2008, I noticed a substantial difference in sound quality.  I'm referring to listening to the same music on the iPod, then listening to it via foobar in Windows, with the iBasso connected to the PC via USB.


 
  
 Try it out of the line dock. The line out on an iPod is audibly transparent. No coloration. It's as good as a standalone CD player. The problems people experience with iPods are usually due to impedance mismatches with headphones that the iPod's headphone jack isn't meant to work with. The headphone out is for portable headphones. The line out amped is for many home phones.
  
 You might be interested in this... http://www.kenrockwell.com/apple/ipod-touch-5g/audio-quality.htm
  
 Quoting:
  
 the iPod Touch 5G is a wonderful high-fidelity audio source. While publications funded mostly by advertisements from makers of expensive cables, power conditioners and outboard DACs don't want you to know this, the iPod Touch 5G is a better audio source than most DACs will be when connected to a computer or CD transport. The only difference is that the iPod Touch has a level 6 dB lower than a proper CD player, but the iPod Touch still has more output at 1 V full-scale than some outboard audiophile DACs
  
 Stereophile review: http://www.stereophile.com/content/apple-ipod-portable-music-player-measurements


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## castleofargh

bigshot said:


> You might be interested in this... http://www.kenrockwell.com/apple/ipod-touch-5g/audio-quality.htm


 
  
 (off topic sorry) wow I remember reading with passion everything he posted in the early years of 2000 on photography I feel like I'm doing some internet archeology ^_^.


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## portal2poe

Ha!  I came across that site just a couple weeks ago, and read through quite a few of the audio reviews.  But since I'm so new to all this headphone stuff, and haven't listened to any of the equipment he's reviewing, I didn't know how much salt to take with his opinions, which are pretty emphatic.  
  
 I then did some googling on him.....some people love love love him, and others hate hate hate, and there doesn't seem to be much room in the middle....


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## bigshot

The thing to look at in that review is the measurements. Every one exceeds the perceptual thresholds of human hearing by a fair margin. You're not going to find better sounding equipment than audibly transparent equipment.


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## harry501

I know this is an old thread, but I have the Fiio X1 which sounds great with headphones straight into the Headphone jack. I was just messing around the other day and tried the line out option with an external headphone AMP (Topping Nx2) and using the same headphones it sounded noticeably much better. I use Grado sr80es and Senn HD25iis and both sounded better, better bass control especially. Even my IEM HiFiman e400s had more bass (which they lack).
  
 I then tried the same thing using the same headphones with my Fiio e10k desktop amp. Used the line out to topping nx2, and then to headphones (not speakers). Again I enjoyed the sound much more, actually was giving up a bit with Hd25iis but now they sound great, the bass control is outstanding imo.
  
 Going by what is being said (i think), does that mean the X1's internal amp is being bypassed? Also, is using the line out option with the e10k going into another amp (nx2) considered 'double AMPing'?


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## castleofargh

harry501 said:


> I know this is an old thread, but I have the Fiio X1 which sounds great with headphones straight into the Headphone jack. I was just messing around the other day and tried the line out option with an external headphone AMP (Topping Nx2) and using the same headphones it sounded noticeably much better. I use Grado sr80es and Senn HD25iis and both sounded better, better bass control especially. Even my IEM HiFiman e400s had more bass (which they lack).
> 
> I then tried the same thing using the same headphones with my Fiio e10k desktop amp. Used the line out to topping nx2, and then to headphones (not speakers). Again I enjoyed the sound much more, actually was giving up a bit with Hd25iis but now they sound great, the bass control is outstanding imo.
> 
> Going by what is being said (i think), does that mean the X1's internal amp is being bypassed? Also, is using the line out option with the e10k going into another amp (nx2) considered 'double AMPing'?


 

 out of curiosity, a bunch of things to try:
 are you sure the EQ is off when using the HO?
 is the sound of the HO with volume maxed out into an external amp, also inferior to the LO into the same amp? (they should be pretty much at the same volume level that way if the EQ is OFF)
  
 double amping or not really doesn't matter if you have a preference in sound or usability with double amping, then just go for it IMO.


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## Sp12er3

2 question, 
1) when using a headphone out to an exteral amp, is it better to keep the Source volume at max or keep it slightly below that to keep distortion/ floor noise/ etc from happening?
2) Does the sound sig of the source's amp will be kept and amplified by the external amp? ie Wolfson internal to Sabre external, will the sound that come out of the HO of the external amp soumd warmer?


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## pinnahertz

sp12er3 said:


> 2 question,
> 1) when using a headphone out to an exteral amp, is it better to keep the Source volume at max or keep it slightly below that to keep distortion/ floor noise/ etc from happening?


 If you have your source up to max, and it distorts, what do you think you should do?  (Hint: if banging your head against the wall hurts, stop.) 





sp12er3 said:


> 2) Does the sound sig of the source's amp will be kept and amplified by the external amp?


 A good amp won't change any aspect of its input signal except to amplify it, and perhaps provide a different output impedance to the load. 





sp12er3 said:


> ie Wolfson internal to Sabre external, will the sound that come out of the HO of the external amp soumd warmer?


 
 How would you connect a Wolfson internal to a Sabre external using the headphone jack?


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## Sp12er3

I ask question 1 as I find myself not hearing much distortion at maximum volume from the source (maybe they set the limiter quite low?), thus wonder whether it's alright to keep it go at max. As that way I'd have better headroom. Ah well, I'd be the judge myself when the time comes whether to choose battery life or driving power. 
For 2nd, oops, Sabre is a DAC chip isn't it? My b, I mean to say Cirrus amp. 
Now then, So you mean to say, the 1st amp (lets just sa its more warm than neutral) will not be affecting the sound coming out of the external, yes? It won't act as a pre amp to the external amplifier?


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## pinnahertz

A good amp will amplify its input. The "color" you refer to could in some cases be the result of the inability of the internal amp to drive a particular load well (should be rare these days). In that case, connecting the headphone jack to an amp effectively removes the load from the internal amp, and whatever distortion the load may have caused.


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## Sp12er3

Oh ok that kinda hels explain stuff.. Thanks


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