iPod Line Out Quality

[Hase]

Ok, I just got my Sik Din and thought I would try something; I plugged my headphones into the "Line Out." It was much louder than I expected. I wasunder the impression that a "line out" was low power and high quality. I was also under the impression that the point of using any line out was to avoid a lower quality power amp (such as is included in the iPod). Does the iPod (or other DAPs) use a variable resistor to adjust volume down? Unfortunately, the line out wasn't as loud as the highest volume from the headphone out. So what exactly does the amp in the iPod do to both increase and decrease volume? Does the line out run through the built in power amp too, just at a set volume? Don't most line out lines completely avoid going through a power amp?

 

[allenf]

Quote:

Originally Posted by Hase Ok, I just got my Sik Din and thought I would try something; I plugged my headphones into the "Line Out." It was much louder than I expected. I wasunder the impression that a "line out" was low power and high quality.

I did that with my NJB3 by accident once..."why isn't the vol control working..." duh!

I guess it just "bypasses" the volume control with a fixed level output.
It may be quieter bcause it isn't designed to drive 'phones??

Memory is hazy here, but IIRC a "true" (high output impedance) line out should not be able to power headphones

Edit: typical hi-fi component line-outs are designed to deliver max level into excess of approx 10 Kilohms load.

 

[Hase]

Quote:

Originally Posted by allenf I did that with my NJB3 by accident once..."why isn't the vol control working..." duh! I guess it just "bypasses" the volume control with a fixed level output. It may be quieter bcause it isn't designed to drive 'phones?? Memory is hazy here, but IIRC a "true" (high output impedance) line out should not be able to power headphones Edit: typical hi-fi component line-outs are designed to deliver max level into excess of approx 10 Kilohms load.

So we think that the iPod line out does not preempt the power amp, just the volume control? How does this improve sound quality at all?

It doesn't make sense that it would be worth using as opposed to just using the headphone out.

Your statement about "Hi-Fi" components, does this apply to the iPod? I wouldn't think so...

 

[allenf]

Quote:

Originally Posted by Hase So we think that the iPod line out does not preempt the power amp, just the volume control? How does this improve sound quality at all? It doesn't make sense that it would be worth using as opposed to just using the headphone out.

Consensus seems to be that the iPod sound better from the line-out than the headphone out - though this isn't a universal opinion - apparently the sound is very similar if the volume is adjusted up to 98% or so to improve the S/N ratio.
I haven't tried the same headphones via my amp as I usually use in the headphone out - so I won't comment on this - though bypassing volume circuitry might well make a significant difference.

Quote:

Originally Posted by Hase Your statement about "Hi-Fi" components, does this apply to the iPod? I wouldn't think so...

No - the iPod's line out doesn't appear to meet a "Hi-Fi" line out spec re: voltage/impedance load.
I wouldn't want to interpret your comment as "iPod doesn't qualify as a "Hi-Fi" component because the sound quality isn't good enough - because it is.
Apologies if "my bad"

 

[Hase]

I didn't mean that iPods are not "Hi Fi." I just meant in regards to your comment about the line out out-put on "Hi FI" devices. I bought my iPod because of what I had read about the "High Fidelity" of the unit.

 

[allenf]

Quote:

Originally Posted by Hase I didn't mean that iPods are not "Hi Fi." I just meant in regards to your comment about the line out out-put on "Hi FI" devices. I bought my iPod because of what I had read about the "High Fidelity" of the unit.

I apologise again

 

[jpr703]

The iPod gets a good rep from its Wolfson DACs. I'm not sure about the engineering of the line out but it sounds pretty good to me (when used with an external amp) and I definitely think it's better than using the headphone jack.

 

[TWIFOSP]

I think you guys are kind of missing the point of the line out.

The line out is just a line, literally, from the DAC output to "out". Where as the headphone jack is a line from the DAC, to an amplification circuit with digital volume control.

There really isn't much of a point in listening to a line out with headphones directly connected to it, unless the volume happens to be exactly perfect for you and you never want to change it. Otherwise, the headphone jack will likely sound better anyway due to the fact that it'll have more power and gain coming out of it and into your headphones.

The advantage of a line out is due to the low quality amplification circuits and volume control noise that is introduced by running the signal through those circuits to go to the headphone out. The line out does not go through these circuits. So when you connect the line out directly to an amplifier, the signal is cleaner than it would be coming from the headphone out. This allows much higher quality amplification components to grab the same signal your headphone jack would have gotten, but run it through much better components; thus altering and improving (hopefully) the sound. Not to mention being able to provide more actual power to the headphones.

The best analogy I can come up with is filtering water from your tap for brewing coffee.

The taste of the coffee is the sound, the coffee maker is the source, the filter is the amp, and the tap is the headphone out, and the water is the audio signal. The grounds I suppose are the music.

Your setup is a kitchen sink, with a tap faucet and a seperate filtered faucet (not filtered through the same tap faucet), that both bring out water from a pipe.

If you take water directly from the tap and use it to brew coffee (headphone out) then the coffee can only potentially taste as good as the tap water. However if you take the water via the source and filter it (amp) it, the coffee can taste much better due to not having any pollutants (noise) from the tap water.

This analogy isn't perfect, because you can filter tap water, instead of having to use water from another point of source, but just pretend that once you run it through a tap faucet ONCE, the water is polluted forever. In the case of the amp from a headphone jack, the amp still has to deal with the noise and amplification circuits that are built in, so it's foundation isn't as good as the line out. Dirty water...

But just to illustrate:

Water from Pipe = Signal from DAC
Faucet = Headphone out.
Seperate Tap = Line out
Filter = Amplifer (from seperate tap in pipe)
Coffee maker = Source
Grounds = Music
Taste = Sound

That's about the best I can come up with.

 

[Hase]

Quote:

Originally Posted by TWIFOSP I think you guys are kind of missing the point of the line out. The line out is just a line, literally, from the DAC output to "out". Where as the headphone jack is a line from the DAC, to an amplification circuit with digital volume control. There really isn't much of a point in listening to a line out with headphones directly connected to it, unless the volume happens to be exactly perfect for you and you never want to change it. Otherwise, the headphone jack will likely sound better anyway due to the fact that it'll have more power and gain coming out of it and into your headphones.

I think I know what the point of a line out is. What I am saying is, that the line out from the iPod is much greater volume than I expected. I expected the line out to be unamplified, straight from the DAC as you suggest, but shouldn't that be almost too underpowered to run headphones? Much to my surprise, the headphones were quite loud. Like listening to the headphone jack, volume set at about 80% (very rough estimate). If you are right then the built in amp, with the volume set lower than 80%, actually just lowers the volume of what it is being fed from the DAC, which makes no sense. I seriously doubt the DAC is outputting as much power as is coming out of the line out. What I am wondering is, when using the line out, does it still go through the amplifier but bypass a volume control? This is the only scenario that makes sense to me given my experiences.

 

[Jahn]

it might be loud, but it's clean. a line out doesn't have to be a whisper like a phono line out to be a clean signal. let's put it this way. if you jack up an ipod from the headphone out to the point of clipping, and compare it to a line out from that ipod to a headphone amp like the SR71, i bet you that signal wont be clipping at the same volume level out of the headphone amp. the SR71 is taking that signal (it may be loud, but it's not "hot") and getting it to your ears in perfect blackness and detail with no clipping. for all i know the ipod may be running that signal through 15 hamster wheels to jack up the volume before it reaches the line out, but hey the signal is clean. but the headphone out definitely is an attenuated signal, bah.

 

[utdeep]

Every line out I've ever used has been loud if you plug directly in.
The iPod line out is friggin fantastic. The sound quality is remarkably better than without it if you use a decent headphone. It just has more richness and clarity when piped through a good amp like the SR-71.

 

[Hase]

Ok, so we accept that the line out on an iPod is cleaner than the headphone out. But are we saying that the DAC really put out that much power, or does the signal indeed go through an internal amplifier before it goes out the line-out?

 

[bigshot]

There has to be some sort of simple amplifier to bring the signal up to the industry standards for line level. Clean, low power amplifiers like that are simple to make. As I understand it, the noise is introduced with the variable transformer (i think that's what it's called... I'm no expert in electronics.) that pots the volume up and down.

A very efficient set of headphones might be able to operate off of line level. Generally a volume pot will boost volume above zero as much as it cuts it below. So theoretically, line level is roughly halfway up the scale. That doesn't mean that line level is necessarily as noisy as the headphone out at the same volume level though. The electronics of the volume pot are introducing noise at all volume levels.

See ya
Steve

 

[Hase]

Thanks Bigshot, I think that was the explanation I was looking for. That would make sense of everything. Anyone contest what he had to say?

 

[vranswer]

Dr. Xin has this to say about line-out:

[size=x-small]Generally, line out port has high voltage output with very limited current, compared to headphone out. Usually the coupling caps of line-out are about 10uF; if you plug headphones right into it, bass is cut off sharply.

Howerver, to reduce cost or limited by size, many home CD players and portables use a single strong amp for both line out and headphone out. In such a case, the headphone jack is nothing but two resistors (about 100-600 ohm) added to the line out. With these two resistors in the headphone out, volume is actually lower than line out. But without these two resistors, the amp cannot drive some low impedance phones very well. I think IHP-120 has exactly such a fake line out. If this is the case, yes, you'd better plug headphones to the line out jack, except some low impedance phones. If you use an external amp, you won't hear any difference between the two ports while a true line-out always sounds much better.

Standard line-out is a voltage type port and does not require high current capacity. Therefore, an amp for it can be easily designed to be very good with very low distortion. With the improvements in amplifier technology, it is now possible to make a very good line-out amp with quite high current capacity so it can meanwhile be used as a headphone amp. If IHP-120's amp is not too bad, you can still use a good external amp to get better sound. Just don't expect a better sound from the line out than the headphone jack - they are the same[/size].

Excerpt taken from Xin's Cool Talk.