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?

 

[liamstrain]

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

 

[PurpleAngel]

Quote:

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

 

[Anaxilus]

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

 

[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.

 

[liamstrain]

Quote:

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. 

 

[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.

 

[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. 

 

[Norman314]

Ah, that makes sense, I think.

 

[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".

 

[liamstrain]

Quote:

 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?

 

[Anaxilus]

Quote:

 
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?

 

[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.

 

[Anaxilus]

Quote:

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.

 

[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).