Why line out?
Nov 17, 2005 at 6:37 AM Thread Starter Post #1 of 22

jagorev

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I apologize if this is a stupid newbie question, but I honestly haven't been able to figure this out:

Why is it recommended to connect headphone amplifiers to the line out of CD players, soundcards, or iPods/DAPs? What do you lose by connecting another amplifier to the headphone jack?

I'm asking because I'm thinking of buying a Micro amp, and was wondering if it would be blasphemy to hook that up to the (really high-quality) headphone jack on my Echo Indigo, or do I need to get a separate USB DAC with a "pure" line out?
 
Nov 17, 2005 at 7:52 AM Post #2 of 22

Jeff Wong

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A line out will generally provide a purer signal as it goes through less circuitry; a headphone jack is probably going to have a volume control in the circuit and may be driven by a cheap and crappy sounding op amp.
 
Nov 18, 2005 at 1:51 AM Post #3 of 22

fewtch

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Quote:

Originally Posted by jagorev
I'm asking because I'm thinking of buying a Micro amp, and was wondering if it would be blasphemy to hook that up to the (really high-quality) headphone jack on my Echo Indigo, or do I need to get a separate USB DAC with a "pure" line out?


You would probably get an improvement, but you'd get even more of an improvement using a "true" line out.
 
Nov 18, 2005 at 6:01 AM Post #4 of 22

socrates63

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The main point of using an external amp is to bypass the presumably inferior internal amp of the player or source. Connecting the external amp to the headphone jack on the Indigo kinda defeats this purpose and you're amplifying an inferior signal than that which is possible from a line-out.
 
Nov 18, 2005 at 6:06 AM Post #5 of 22

fewtch

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Quote:

Originally Posted by socrates63
The main point of using an external amp is to bypass the presumably inferior internal amp of the player or source. Connecting the external amp to the headphone jack on the Indigo kinda defeats this purpose and you're amplifying an inferior signal than that which is possible from a line-out.


But the thing is, see... the internal amp may not be "inferior" driving such an easy load as an external headphone amp. What makes most built-in amps inferior is their poor ability to drive a lower impedance load like headphones. Hook an amp to the headphone out jack, and many of those inferiorities may vanish.
 
Nov 18, 2005 at 6:15 AM Post #6 of 22

Teerawit

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Quote:

Originally Posted by socrates63
The main point of using an external amp is to bypass the presumably inferior internal amp of the player or source. Connecting the external amp to the headphone jack on the Indigo kinda defeats this purpose and you're amplifying an inferior signal than that which is possible from a line-out.


Unless you need more current, voltage swing, or raw power to use hard-to-drive or inefficient headphones..

It is preferable to use a line out over a headphone out because you want to have less things in the signal path processing it. However, if all you have is the headphone jack, use what you got...
 
Nov 18, 2005 at 6:23 AM Post #7 of 22

xand1x

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Quote:

Originally Posted by Jeff Wong
A line out will generally provide a purer signal as it goes through less circuitry; a headphone jack is probably going to have a volume control in the circuit and may be driven by a cheap and crappy sounding op amp.


Took the words out of my mouth
tongue.gif
, Jeff's right on the ball here!
 
Nov 18, 2005 at 6:45 AM Post #8 of 22

jagorev

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Yeah, I was thinking along the same lines as fewtch or Teerawit. I don't think the headphone out on the Indigo is crappy by any stretch of the imagination - it is really very clean and noise-free even at max volume. It just plain isn't powerful enough to drive something like the HD 600. I thought it could provide a relatively "clean" signal for an amp to work with...

Are there any more technical reasons than the assumption that integrated jacks are crappy or noisy? Something to do with tone shaping or frequency balance? ie, does one op-amp change the actual character of the sound such that any further amping results in distortion, while line outs don't have this effect?

Admittedly, if all I had was AC'97 audio, I would think that a USB DAC with a line out would be a far more preferable option - in that case, amping out of the onboard headphone jack would be a waste of an amp
smily_headphones1.gif
 
Nov 18, 2005 at 7:15 AM Post #9 of 22

sxr71

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Quote:

Originally Posted by fewtch
But the thing is, see... the internal amp may not be "inferior" driving such an easy load as an external headphone amp. What makes most built-in amps inferior is their poor ability to drive a lower impedance load like headphones. Hook an amp to the headphone out jack, and many of those inferiorities may vanish.



If you think that the built-in headphone jack does a good job then you might be better off going ampless. However if you choose to use an external amp then you should give it exactly the same signal that your built-in headphone jack (amp) is getting. Otherwise you will get a mix of characteristics of both amps and presumably the external amp was designed to sound good with a line out signal.
 
Nov 18, 2005 at 10:17 AM Post #10 of 22

saint.panda

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As fewtch and Teerawit have said, using the headphone out is not that bad. One big problem with cheap amp sections is distortion and distortion increases as the load it is driving gets harder to drive and decreases when the load gets easier to drive. So, a dedicated headphone amp put after the player's internal amp will act sort of like a buffer that takes the load of the player's internal amp.

Therefore, while you still have the potentionmeter and some other components in the way, connecting an amp to the headphone out will often sound better than using the headphone out directly, even if you're basically amplifying the signal twice unnecessarily. This is certainly a compromise but often a good one.

Of course, a line out is the better solution but modern headphone outs often underlie design constraints that even if there's no line out, it is often better to use a dedicated external headphone amp on top of the player's internal amp via the headphone out. Ipods for instance use undersized output coupling capacitors which lead to bass roll-off with low impedance headphones.
 
Nov 18, 2005 at 6:45 PM Post #12 of 22

chrisfromalbany

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Quote:

Originally Posted by jagorev
I apologize if this is a stupid newbie question, but I honestly haven't been able to figure this out:

Why is it recommended to connect headphone amplifiers to the line out of CD players, soundcards, or iPods/DAPs? What do you lose by connecting another amplifier to the headphone jack?

I'm asking because I'm thinking of buying a Micro amp, and was wondering if it would be blasphemy to hook that up to the (really high-quality) headphone jack on my Echo Indigo, or do I need to get a separate USB DAC with a "pure" line out?



I do use the line out on the ipod, I find the differences when running the amp from the jack out to be unnoticeable. I do it because it is best practice. But when I forgot my Sik Din lineout adaptor and needed to use the jack of the ipod, I can't tell the difference. The volume level of the line out and the jack out at max volume is about the same. And I have never tried to power headphones alone from line out. I dunno.. The ipod isnt the best source and using the line out should be best practice but loss is very slight when using jack out to amp.
 
Nov 18, 2005 at 8:08 PM Post #13 of 22

sxr71

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The iPod headphone out has that documented bass roll-off issue that the line-out is immune from. That is due to the poor design of the iPod headphone out. Apparently they couldn't put as big of a capacitor as they needed to prevent bass roll-off.
 
Nov 18, 2005 at 9:16 PM Post #14 of 22

Tyll Hertsens

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I think one of the issues here is that technology is moving so rapidly in this sector that there are a lot of different things out there. Is the volume control an attenuator befor the headphone amp stage? Or is it a thing that truncates number in the DAC somehow? Or is it some semi digital variable resistor as the volume control? What are the chipmakers making for audio devices? In the real world devices show up with all sorts of schemes for volume control. Some DAC parts have digitally controlled resistive attenuators that work very well, technically.

I use what ever is available. However...

Quote:

Originally Posted by saint.panda
So, a dedicated headphone amp put after the player's internal amp will act sort of like a buffer that takes the load of the player's internal amp.


That's he truth of it. The power margins on all these players are slim and load signals often end up on the power supplie rails. Sort of like the tree falling in the forest thing; portable players sound best when no headphone is plugged in. So an amp does indeed act like a buffer and will make the player sound better.
 
Nov 18, 2005 at 9:59 PM Post #15 of 22

kwitel

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you guys just confused the heck outta me...lol. (not that I knew much about amps in the first place)
Isnt there ONLY a headphone ajck on an IPOD, where exactly is there a "line-out"?? Thta may seem like an incredibly stupid question to many of you;please be patient with me
blink.gif

Im assuming that the plug that goes from the amp to your source should go in a "line-out" jack?
I only have a "line-out" on my laptop, not on my Ipod or stereo...what am I missing here?
 

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