[Kelvie1234]

Quote:

Originally posted by waffenschmidt OK, looks like the last few posts got this right. I don't consider myself an expert on this, but I think there were some misconceptions stated earlier in this thread. As I understand it, the difference between a line out and a headphone out is that the line out delivers the signal to the jack before it goes through the internal headphone amplifier circuitry (which is usually not that great in most portable devices). The fact that device's volume control and equalizer impacts the line out does NOT mean it is not a "true" line out. Again, as I understand it, in many modern devices the volume control and equalization is done digitally (I think in the chip with the DAC circuitry). The difference is where the signal goes after that. For a line out, the signal goes directly to the jack. For the headphone out, it goes through the internal amplifier and then to the headphone jack. Now, I got into trouble from Jazz on this next point in another thread, so I'll state it carefully. A line out is not designed to drive headphones directly. I'm not saying it can't or even that it won't sound better driving headphones than a headphone out (that part's for you, Jazz), but it isn't designed to drive headphones. It is designed to feel a line-level signal to the high impedance input of an external amp. Again, I don't claim to be an expert on this, so if anyone knows differently, please feel free to correct me. But if you don't know, please keep your thoughts to yourself. There is way too much disinformation being spread on this forum lately, and it's getting to the point where the usefulness of many threads is marginal. [Edited for clarity.]

I'm no expert either, but to give you a bit more credibility, I'll confirm this.

People always seem to bash iRivers for not having a true line out. It does.

I'll summarize waffen's points..

1. The line out was NOT designed to plug straight into headphones... the white noise at high volumes shows that it is at line level, and is indeed unamped.

2. The volume control and EQ do affect the lineout (however recent firmwares might have disabled EQ from affecting the line-out, yet to be confirmed).

To get a true line out, you have to turn the volume all the way up--that's right, all the way up to 40.

The whole point of a line out is so that you get the "raw" audio data, and if the volume is anything lower than 40, then the Digital Attenuator (aka. digital volume control) kicks in and makes the audio quieter; in the end, it won't be the "true" audio signal.

At these high volumes, the EQ has negligible effect, thanks to the EQ limit that the iRivers have.

The volume control affects the line out because of this:

Headphone out:

DAC -> DSP manager -> built-in opamp -> headphone out

Line out:

DAC -> DSP manager -> line-out

I am most probably skipping a few steps.. but the DSP manager(s) (don't know how many chips there are exactly) control the EQ and the volume.

You want the line out to plug your amp into, because you want to bypass the generally (for lack of a better term) crappier built in opamp (audio quality-wise anyways, they are usually much more power effeicient), and use your own amp.


So again.. to those that say the iRiver has no true line out.. not knowing some of the above, how useful is a true line out to you?

[edit: minor grammar adjustments]

 

[rodbac]

Excellent info, guys. Thanks.

Now my only worry is about kicking my battery in the nuts by having the volume pegged. I'm thinking I may have to see if I hear any difference at lower levels, just for the sake of being able to brag about 16 hours of continuous use...

 

[ASDFer]

The recent firmware (1.4) does not change the EQ behavior at the line out port as measured by RMAA (and it's very apparent when listening too.)

I don't know if I quite agree with your assessment of the volume control Kelvie. The volume could be controlled by just setting the maximum voltage on the DAC instead of, say, dividing the data by some constant to change the volume. I'm not sure which approach iRiver uses. I would guess they use the first approach because this would not collapse the dynamic range so much, and my measurements show that the dynamic range doesn't collapse very much at lower volumes. Could be wrong though... Any ideas how to elucidate the volume control method?

 

[JaZZ]

I agree with most of the previous posters. The fact that the iHP's line-out is affected by volume control and EQ doesn't tell it's no true line out in the essential sense of bypassing the internal headpone amp. My only concern would be that the maximum resolution possibly is only given with maximum-level setting (which may in turn affect the battery operation time). Since this is a (minor) problem even with some high-end gear with digital volume control, I wouldn't wonder if there is a slight loss in sound quality with lower volume settings (although also present with the headphone out, of course). Nevertheless, ASDFer could be right with his speculation about a «DAC-voltage control», although I don't understand how exactly this is meant.
Quote:

Originally posted by waffenschmidt Now, I got into trouble from Jazz on this next point in another thread, so I'll state it carefully. A line out is not designed to drive headphones directly. I'm not saying it can't or even that it won't sound better driving headphones than a headphone out (that part's for you, Jazz), but it isn't designed to drive headphones. It is designed to feed a line-level signal to the high impedance input of an external amp.

My then opposition was based on the generalizations which have been made pointing out that line-outs are «not designed» to drive headphones as a substantiation for their general unability to do so. Many soundcards in fact prove the opposite: their line-outs can be «misused» as headphone amps without negative consequences in the form of level limitations, overly distortion, colorations or bass roll-off. My SB Live Platinum's line-out plays louder and cleaner than the built-in true headphone out.

As to the iHP: my then statement was based on Murasame's report about the line-out sounding better than the headphone out. Meanwhile I've heard it myself, and while I had no problem with the maximum undistorted level using ER-4P and PX-200, one thing that was very apparent was an attenuated bass compared to the headphone out (confirmed by ASDFer's measurement). So in this case I don't recommend it to drive headphones; maybe a Portapro or other bass-bloated headphones may benefit from the bass roll-off and at the same time of the bypassed amplification stage though.

 

[waffenschmidt]

Quote:

Now my only worry is about kicking my battery in the nuts by having the volume pegged.

Again, this is not my area of expertise, but I don't think cranking the volume while using the line out is likely to affect power consumption greatly, as long as the line out is connected to the high impedance input of an external amplifier. The intent of the line out is not to deliver a lot of power, just a good signal (high voltage, low current).

Sure, if you plug a pair of low-impedence headphones into a line out it might end up delivering a significant amount of power to the cans, and therefore impact battery life, but that's a lot different than connecting to an external amp.

Rodbac, if your goal is to maximize battery life on your IHP at the expense of battery life on your Supermini, you could just crank the volume down on the IHP. Maybe the sound won't be as good as if you cranked it up, but at least you'd have bragging rights. OTOH, who cares if you get 15 1/2 hours instead of 16.

Jazz, we're on the same page. You're right; if a line out sounds good when driving headphones, it really doesn't matter what it was "designed" to do. Personally, I worry a little about drawing too much current through circuitry that might not have been designed to handle it, but I don't have the electronics expertise to say that it's really a problem.

 

[JaZZ]

A higher power consumption with maximum volume setting even without a load (as reported by some members) makes sense -- since the amp still has to do some work, by amplifying the incoming signal. I'm not even sure to what extent the load (impedance) affects the power consumption at all.

A good solution would be to separate the headphone amp from the DAC when no headphone is connected. This would be easy to do, but I doubt this feature has a high priority on the manufacturer's side, because the number of users of external amps on the go is most likely very small.

My own interest for the iHP-120/140 has very much diminished. The only things that could bring me back on track would be a true shuffle play and a graphic (if not parametric) EQ instead of the poor «rock-, jazz-, user defined...» type with no possibility to decrease a certain frequency range. Is this all still the same with the latest firmware?

 

[rodbac]

What Waffen. says regarding the power-consumption issue seems to have just been supported by my highly credible, soon-to-be-published experiment- I ran the unit all night (7.5 hrs) at vol.40 and the battery is still at ~1/2 charge (with a Super Mini and KSC-35s).

 

[Kelvie1234]

I believe I read a long while back a thread talking about things like this; the poster stated that the volume control would have little to affect how long the battery life would last, it's more the impedance load.

Another post I've read a long time ago (if I recall correctly), is that even with the volume shifted, the difference in battery life is not noticeable (around the area of a few minutes?), because the VAST majority of the battery consumption comes from the accessing of the hard drive, so the power used by the amp becomes negligible.

However.. I forget the sources that back this up.... it was quite a while ago, and I've been reading posts here for almost two years now.

 

[Traveller]

Quote:

Originally posted by Kelvie1234 ...volume control would have little to affect how long the battery life would last, it's more the impedance load.

Speaking of impedence loads, let's not forget that the source's (iHP-120) o/p stage has to drive the portable amp's input stage. So like full-fledged audio systems, proper component-matching is necessary for best results.

As an example, my CD player has an o/p impedence of 47 Ohms and my preamp's i/p stage has an impedence of 10K Ohms. The preamp's o/p stage is rated @10 Ohms and my amp's i/p stage is rated @100K Ohms. Note that there is a relational difference between source components -> (pre)amps and amps -> loudspeakers (where impedence matching seems to be the goal).

(btw, Kelvie, it's Digital Signal Processor -> DAC -> ....)

 

[ASDFer]

Why would you want to match input impedance on an amplifier to the output impedance on the source? For modern amps, the goal is maximum voltage transfer; for this to happen you want a much higher input than output impdeance.

For the amplifier to speakers stage, impedance matching will give you maximum power transfer, but that's it. If you're worried about reflections or something, then you're not even taking into account the impedance of the cables, which act as very poor waveguides anyway and shouldn't even be an issue at such low frequencies.

 

[Traveller]

Quote:

Originally posted by ASDFer Why would you want to match input impedance on an amplifier to the output impedance on the source?

"Component matching" does not mean "impedence matching". It means making sure your source(es) are able to drive the preamp, etc. I thought the example with my own system made it clear what I was trying to get to (or maybe not

).

 

[ASDFer]

Ah yes, I thought you were one of those crazy directional wire-impedance matching guys. Apologies.

 

[Traveller]

Btw, the answer to our questions, or at least more info towards it, might be in Head-Fi's post, Inside the iHP-120.

cheers