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Line level out vs headphone out... what's the difference?

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  • Line level out vs headphone out... what's the difference?

    I know that line level signals are quite low in output, to be then boosted by an amplifier...

    So how is a headphone output any different? (which is also quite low in output).

    This question occured to me when considering whether I should use a headphone amplifier when hooking my headphones up to my laptop, which has a typical headphone jack...

    Or, assuming I did choose to use a headphone amp, should I get a soundcard that has a line level out?

    I'm totally confused about the difference between a line level out and a headphone out... particularly considering that many ipod devices use the headphone out to feed an amp.

    Thanks
    Form does not follow function
    Form is simultaneous to function

  • #2
    Re: Line level out vs headphone out... what's the difference?

    Line level is usually high impedance output 10k ohms or greater, and not near as much drive level. A laptop headphone/ line level output IMO is really neither and both! Itís a compromise the manufacturers are implementing to make it "usable" for both applications. I have yet to hear a computer headphone output that will drive a set of cans to painful levels like a REAL headphone circuit would . . unless your using a set of Sennheiser 414s or something with really high input impedance. Likewise, I havenít heard too many "headphone" jacks on laptops I thought produced true, clean, line level output. You will undoubtedly have to fiddle with the gain control on the Volume Control panel for whichever application you want to use.
    Dave H

    Comment


    • #3
      Re: Line level out vs headphone out... what's the difference?

      Line level outputs typically have a source impedance of 50 to a few hundred ohms. They are intended to drive loads that have a high input impedance, usually greater than 5k ohms. They are typically optimized for very low noise and low distortion when used with high impedance loads.

      Headphone outputs typically have a source impedance less than a hundred ohms and the better ones have a source impedance of a few ohms or less. They are intended to drive the lower impedances presented by headphones which typically range from 16 ohms to 300 ohms. They are optimized for being able to drive higher current and for delivering reasonable distortion and noise with low impedance loads.

      Line level outputs usually do poorly when driving headphones because their higher source impedance will not properly damp the driver at low frequencies and they can suffer from high frequency rollof when loaded with significant capacitance.

      Headphone outputs can be used to drive line level loads and can provide good noise and distortion performance but are typically not as good as line level outputs.

      I know I made a lot of generalizations here and that there will always be exceptions, but these are just some rules of thumb.

      Louis

      Comment


      • #4
        Re: Line level out vs headphone out... what's the difference?

        I doubt you see this on many laptops, but my portable CD player has both line level and headphone out. The line level is not attenuated by the volume control, same as the tape loop on traditional receivers.

        I was a bit disappointed to find that the headphone jack on my home theater receiver was driven by the speaker amps which were switched into a voltage divider to drive the head phone. (I perceive the speaker amps to be the weak link for sound quality in this device.)

        The take away point is that you have to look at the specs and circuit diagram if possible to understand the features and limitations of any device.

        Comment


        • #5
          Re: Line level out vs headphone out... what's the difference?

          There are some cool headphone amps out there, including one designed by GMilitano, a poster here. Check it out:

          http://diyaudioprojects.com/Solid/IR...Headphone-Amp/


          http://www.headwize.com/projects/

          I was giving some thought to one of these, it looks pretty easy and inexpensive.

          http://headwize.com/projects/showfil...=cmoy2_prj.htm

          There are also some rather neat "hacked" enclosures out there including an emptied CD-ROM drive and a caffeinated peppermints box.

          Cheers / Robert

          Comment


          • #6
            Re: Line level out vs headphone out... what's the difference?

            Oops . . Louis is correct on the source impedance of line level. Either I should pay more attention to what I type, or not do it after havng a couple of Sierra Nevada Bigfoot 2009 brews! :D :o
            Dave H

            Comment


            • #7
              Re: Line level out vs headphone out... what's the difference?

              Originally posted by robert View Post
              There are some cool headphone amps out there, including one designed by GMilitano, a poster here. Check it out:

              http://diyaudioprojects.com/Solid/IR...Headphone-Amp/


              http://www.headwize.com/projects/

              I was giving some thought to one of these, it looks pretty easy and inexpensive.

              http://headwize.com/projects/showfil...=cmoy2_prj.htm

              There are also some rather neat "hacked" enclosures out there including an emptied CD-ROM drive and a caffeinated peppermints box.

              Cheers / Robert


              This one wasn't easy or inexpensive... about $150 is what it cost me, and the design didn't have a layout. I had a schematic and a fuzzy picture of what went where, so I could verify the connections in the schematic. He didn't have any nodes, or visual indications of what was a connection and what wasn't in the AudioXpress article I used.

              Tell you what though, that was well-spent, and this amp sounds really good!! Class A, 320 mW at 32 ohms, and will drive a set of vintage 8 ohm cans with 100mW. The PSU is good for a 25W x 2 Class A power amp, so it is extremely overbuilt. If the wall-AC is clean, the sound is clean. Period.

              I did update the wiring with an IEC connection, BTW.
              Later,
              Wolf
              "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
              "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
              "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
              "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

              *InDIYana event website*

              Photobucket pages:
              http://photobucket.com/Wolf-Speakers_and_more

              My blog/writeups/thoughts here at PE:
              http://techtalk.parts-express.com/blog.php?u=4102

              Comment


              • #8
                Re: Line level out vs headphone out... what's the difference?

                Thanks guys...

                If I do use a headphone amp with my laptop, I shouldn't simply be connecting it to the crappy headphone jack, right? I'll just be amplifying crap, right?

                I see that being done sometimes, and I don't get it... like in this picture from headwize (thanks Robert!), which shows the amp connected to the headphone jack of a portable CD player... isn't that just amplifying a crappy signal?



                There are a couple of guys at work who are using headphone amps connected to the headphone jacks of their laptops... when asked if the amps make a difference, they both sheepishly say "I can't really tell a difference, but the external volume control is convenient" :rolleyes:

                Anyways, I think I see 4 different paths to upgrading the sound quality from my laptop to my headphones... and I'm not sure which path to take, care to comment?

                1. Upgrade the internal sound card, which would then have a simple headphone jack like the current sound card.

                2. Use an external sound card, (which tend to be small and cheap) which has it's own headphone jack and connects to a usb port... not sure how much of an upgrade this would be, but it does make some sense, as it bypasses the crappy sound card, right?

                3. Use a headphone amp connected to the headphone jack (which, as I just explained, doesn't make sense to me, as aren't you then just amplifying crap?)

                4. Use a headphone amp connected to a usb port.... this seems to me to make the most sense, since it creates a strong signal, and a clean signal since it bypasses the crappy sound card.

                Which of these options would you recommend?

                Thanks
                Form does not follow function
                Form is simultaneous to function

                Comment


                • #9
                  Re: Line level out vs headphone out... what's the difference?

                  My opinion . . .

                  Maybe 2 or 4 (though I've never actually done it.) There are those here who have. I sent Dirk a Behringer UCA200 USB Audio Interface. IIRC it worked pretty well. Now the model is UCA202.

                  I just can't see getting really good audio out of any card either internal or external with a few exceptions.

                  The other problem I've experienced is the incredible noise generated on the audio out jack from the switching power supply when it's plugged in. Ya just about have to operate on batteries only to have a chance of making it work.
                  Dave H

                  Comment


                  • #10
                    Re: Line level out vs headphone out... what's the difference?

                    Thanks Hack...

                    I've decided that if I get a headphone amp, it's gotta have an actual knob on it to adjust the volume... constantly adjusting a tiny little knurled dial will drive me nuts...

                    I'm reading good things about the Fubar III... although it's a bit on the expensive side at $230... anyone have any experience with it?

                    Form does not follow function
                    Form is simultaneous to function

                    Comment


                    • #11
                      Re: Line level out vs headphone out... what's the difference?

                      If it's for sound for your PC, I'd probably go with one of the less expensive builds like on headwize. Fun, amusing, and if you are using it at work, small. If it's for the equipment rack, then maybe something a little more expensive. Plus, you can review it! Also, if you want to hear it from your home system, you only need a dual RCA - 1/8" stereo adapter.

                      Robert

                      Comment


                      • #12
                        Re: Line level out vs headphone out... what's the difference?

                        Originally posted by robert View Post
                        If it's for sound for your PC, I'd probably go with one of the less expensive builds like on headwize. Fun, amusing, and if you are using it at work, small. If it's for the equipment rack, then maybe something a little more expensive. Plus, you can review it! Also, if you want to hear it from your home system, you only need a dual RCA - 1/8" stereo adapter.

                        Robert
                        I don't see any builds on Headwize that connect to the computer via usb... I don't wanna amplify the crappy sound card.
                        Form does not follow function
                        Form is simultaneous to function

                        Comment


                        • #13
                          Re: Line level out vs headphone out... what's the difference?

                          Lunchmoney,

                          Its tough to get really clean audio from a laptop's headphone jack because the power supply and ground are contaminated with a lot of noise which falls into the audible band; CPU switching through various processes, WiFi TX/RX burstiness, hard drive motor and R/W head cycling through various states, and display scanning, just to mention a few. It is very challenging to keep this noise out of any piece of electronics that you connect to the laptop. Good external sound cards even use an isolation transformer on the USB port to provide some immunity to all this c**p.

                          What I use, and it is a bit of overkill, is a USB to optical converter like the M-audio Transit card. The USB port connects to your laptop and the optical port then connects to an external DAC with an optical input. The optical link provides complete ohmic isolation of the DAC from the noise generated by the laptop. For the DAC I use the Benchmark DAC-1, which is a bit pricey, but makes one heck of a sound card. The only drawback I've read about with using the optical link this way is that TosLink has relatively low bandwidth and can introduce some jitter into the digital audio stream. The Benchmark DAC-1 uses a PLL to retime the audio data and claims to be able to reduce the magnitude of this jitter.

                          Louis

                          Comment


                          • #14
                            Re: Line level out vs headphone out... what's the difference?

                            Use #2! Behringer makes a U-Control ext SC, that PE sells for $30. It has RCA outs, ins, SP/DIF, and a built-in headphone output for monitoring. This way you could try it as a HP amp, and if you want more, go the RCA route, and get/build an amp. It gives you lots of options. The SC sounds quite good, as I have one.
                            Later,
                            Wolf
                            "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                            "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                            "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                            "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                            *InDIYana event website*

                            Photobucket pages:
                            http://photobucket.com/Wolf-Speakers_and_more

                            My blog/writeups/thoughts here at PE:
                            http://techtalk.parts-express.com/blog.php?u=4102

                            Comment

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