Connecting headphones to a PC - Page 1
Forum section: electronics / general

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 26, 2015, 04:50:37 pm
content: Hello!This question would be better suited to the audio forums i am registered at but i would like real advise and not a audio voodoo priest chant.Audio stuff is not new to me, i have build my own proper speakers, made a little class AB amp, repaired a lot of audio gear and worked with this stuff for many years.But i just barely know what i am dooing most of the time when it comes to analog stuff.I ordered myself headphones a few hours ago, they will be used only on my computer and it just dawned on me, that i do not know what sort of output the on board soundcard has.The headphones are rated with 40Ohms impedance, at lower frequencys that will be way less.The soundcard outputs about 4Vpp max, with a static resistive load the clipping starts at 0.6Vpp at 50Hz that comes to about 9mW.The sensitivity of the headphones is rated at 105 dB/mW.So, there should be no problem connecting the headphones straight to the soundcard, right?As long as i ignore possible higher THD(+N) at lower resistive loads, right?Most integrated headphone audio amps i came across have horrible THD+N ratings at lower impedance loads.So maybe it still would be a good idea to build a simple small headphone amp?Greetings,Peter

author: linux-works
author_rank: Super Contributor
timestamp: May 26, 2015, 05:31:39 pm
content: my preferred setup: usb dac (external box) and that will have an HP amp in it or you may still need one if its just line-level only.stronger line-stages can drive phones but most do not. you need current drive for phones, usually.there are lots of diy phones amps and some diy dacs. those are cost effective and you can spend as little as you want and still get good results. even a simple 'cmoy' stage on the output of a dac will be enough for most.better sound cards are going to have good analog-outs but few will really be meant to drive phones -well-. they'll do ok but you can do better with outboard dac and outboard phones driver/amp.

author: German_EE
author_rank: Super Contributor
timestamp: May 26, 2015, 05:31:47 pm
content: Assuming that you have a decent soundcard there will be no problem. 4V P-P is a MASSIVE signal into a pair of headphones and you will probably cause hearing damage if you try listening at such a level. I'm listening to music on headphones right now and just out of curiosity I connected my scope and a 16 ohm dummy load to see what the level was, comfortable volume is 150 mV.

author: linux-works
author_rank: Super Contributor
timestamp: May 26, 2015, 06:03:56 pm
content: without saying what the range of loads are, 4v may or MAY NOT be 'massive'.for high-z phones (senn hd600 or similar) you need much more voltage swing. for earbuds, 4v is probably more than enough.the OP did say he was using low-z so that's fine; but later if you try other phones, you may find there is not enough voltage swing or current to drive the bass well.

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 26, 2015, 09:42:19 pm
content: Quote from: linux-works on May 26, 2015, 05:31:39 pmActually that is something i have planned for some time in the future.Do you have a recommendation on a chip, all in one, simple layout?I had a external USB device on loan once, that had a tremendous line out, but everything else i hever had had terrible noise on the output.As does this on board soundcard, you can hear nearly hear everything that the CPU does if you crank it to eleven.QuoteThat is why i mentioned the 4Vpp, that is way more then a line output.So this seems to be designed to drive headphones in some manner or the other.Quote from: linux-works on May 26, 2015, 06:03:56 pmQuote from: German_EE on May 26, 2015, 05:31:47 pmThe current source capabillity is the main thing to look out for, i have had another look. The waveform looks horrible with a 50Hz signal even with a higher resistance load.So, it looks like it will work but i should build myself a headphone amp...Seems like the output is designed to drive headphones but but not with decent quality.

author: Lightages
author_rank: Unknown
timestamp: May 26, 2015, 10:12:27 pm
content: It is a good idea to use an outboard headphone amp f you can afford/build one. This way you can adjust the output of the sound card for the lowest noise and distortion, an then use the headphone amp to get the sound level you want. Headphone amps will also deliver a more stable output impedance than most generic sound card output stages.Sorry, I have no idea what reasonably priced no BS headphone amps you might have available to you in Germany. I purchased mine a long time ago in North America so I am out of the loop of these things right now.

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 26, 2015, 10:32:25 pm
content: Quote from: Lightages on May 26, 2015, 10:12:27 pmI know of a few good ones but they are 19" studio gear, designed for distribution, with that function in mind they are resonably priced.But when it comes to single channel headphone amplifiers, no chance in hell to find one that is not blessed by a virgin in pale light of a blue moon.Building one myself is no problem, i had a look and found a few nice TI parts.PCM270n USB DAC and with a output stage that can drive a 30 Ohm load at with a resonable SNR and THN+N.

author: linux-works
author_rank: Super Contributor
timestamp: May 26, 2015, 11:13:55 pm
content: the current trend is to go 'direct' from usb to dac (usb to i2s and i2s to dac, all inside 1 box).more flexible is to go usb to spdif, then out of the box and into another box, the spdif/dac. those 2 are more standard functions and give as good sound in almost all cases as the 'direct' usb method.if you do go with usb, the new format is called 'uac2' (usb async audio, class 2). class 2 means 'pull data' model; and that has the dac pulling data out of the computer, as it needs it, with the dac doing the local clocking of the digital data to analog. uac2 can support 192k where uac1 stops at 96k (if you care). uac1 pushes data from computer to dac and the timing is derived from the host cpu and usb data stream, which is not optimal. we're talking a percent or so, in diff, so nothing huge at all. but if you are buying new gear, look for 'driverless' uac2 usb/dac devices.I've had good enough luck with $10 usb/spdif dongles, though. if you care only about 44/48 audio and not 'high res' the $10 usb cm102 (cmedia) are fine enough. they are the chips inside the gear, so you'd want to see what chip the usb/spdif dongle is using. cmedia is good, reliable, cheap and supported on all platforms.once you get the usb/spdif side done, you now have the rest of your time and money to spend on dacsbut again, even a $20 dac is probably going to be hum-free and noise-free compared to anything inside your pc.one exception is the juli@ ('juliet'? strange company or product name) sound card. its pci and now pcie. from what I'm told, its studio quality (ie, even measurement quality). its onboard a/d and d/a are as good as it gets under $1k and it also has spdif out. if you are looking for the best non-pro audio card, that would be the one I'd pick.but, really, usb is the new way to go. usb2 (don't need 3) and do NOT use the last 2 intel chipsets; sadly, they messed something up and I've had nothing but trouble with both linux and win7 (so its not really the os, but its the haswell chipset and the one before that). after that, I don't know. way before that, things were fine. but some intel usb chips really suck when it comes to audio and realtime data. not sure why. I end up using older mini-itx fanless pc's for my sound system

author: hayatepilot
author_rank: Frequent Contributor
timestamp: May 27, 2015, 11:28:48 am
content: Some Headphone outputs are built with a large cap so they can get away with a single ended supply.Those tend to roll of at low frequencys if the headphone impedance is low or if the capacitor isn't big enough.You can make a loopback measurement of the headphone output with a 40 Ohm resistor as a dummy load to test this. If the signal doesn't roll of, then your soundcard is good.If the frequency response changes considerably if you add the load, you should use a dedicatet headphone amp.Greetings

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 28, 2015, 06:26:37 am
content: Just try plugging it in. In many cases, it will just work, especially on desktops that are not particularly power or space constrained. 40 ohms is not particularly low.Where you often run into problems is when you use headphones designed for low voltage mobile devices (low impedance, as in less than 32 ohms) on a desktop. The low impedance gives a very unlevel output (bass seems weak) and highlights the noise. (Modern mobile devices are typically direct drive which is how they handle low impedance.) Before resorting to more dramatic measures, try the simple solution of adding series resistors. I suggest 100 ohms for a start, the goal being to find a value such that the optimum listening volume is achieved with the hardware volume control set to around 70-85% and software volume controls (which are a bad idea!) maxed out.

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 28, 2015, 08:20:42 am
content: Hello everybody and thank you very much for your replys!Quote from: NiHaoMike on May 28, 2015, 06:26:37 amOf course it will be just tested, i just wanted to get it a bit sorted to get some lead time in building the amp.So, i fiddeled a bit with it, i know the output is fairly linear because i dit loopback test and used it to measure some speakers with a microphone i have a calibration file for some time ago even though it is not recommendet with those cheap on board sound cards.Annybody wants to comment on these two pictures?Fist one is no load on the output, second one is with a 30 ohm resistor.No settings changed, the voltage drops considerabely, at lower levels i does not pick up on the scope annymore, hence the high output. And the waveform looks not so much like a sine wave annymore.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: May 28, 2015, 08:49:58 am
content: Hello PeterFWIs this drop the same on other frequencys?The drop probably comes from a output resistor in the amplifier. It's probably there to protect from short circuits (happens when the jack is not properly plugged in).Since the impedance curve of a headphone is not linear, the output resistor has different voltage drops depending on the frequency. So it will distort your frequency response.You can test this with a loopback measurement with a cheap pair of earbuds as a load. A good software for this isARTAorREW. REW is easier to use but ARTA has more capabilities.So it seems that you would benefit from a headphone amplifier. You can even build your own simple amp using just a opamp and a couple of passives. Search fos CMOY amplifier.Greetings

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 28, 2015, 09:02:40 am
content: Quote from: hayatepilot on May 28, 2015, 08:49:58 amIt was pretty consistent up to 1kHz, there i abandoned the test.QuoteI thought the headphoes would not arrive til saturday but i just got a mail that they should be here today.Somewere i even have a few suitable cables from when i dit my own TSP measurements on drivers and Arta is still installed annyway.QuoteNever would i thought id have to build such a thing, allways thought they were audio voodo accessories.So... i was wrongThere may be a chance i should have all the parts i need at hand, somewere i should have a suitable opamp left over.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: May 28, 2015, 09:21:18 am
content: On many headphone outputs a dedicatet amp is voodoo, but others don't have a linear frequency response if they should drive a "low" impedance headphone.I once had a usb soundcard that used a single ended supply amplifier so it had a capacitor on the output. This formed a highpass first order with the headphones. The amplitude started to drop below about 100hz.I hacked the thing and swapped the capacitor with one 10 times larger so the drop starts not until about 10hz. A amplifier would have worked too since those have a high input impedance.Greetings

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 29, 2015, 01:32:07 am
content: If you directly plugged it in, about how far up on the hardware volume control does it have to be to get your desired volume level? The series resistors are a good way to boost SNR and flatten the frequency response.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 29, 2015, 02:02:33 am
content: Would guess it'll be quiet but understandable.Sound cards are usually suitable for headphone use, as-is. If you need more loudness (probable?), a preamp would be desirable. Just a voltage follower, really, or a little gain.I put a gain-of-3 amp on mine, I think, and it's painfully loud at 20%; most listening is in the <5% range (on the Windows sound volume slider, that is).Tim

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 29, 2015, 06:53:09 am
content: Hello and thanks for your replys!Quote from: T3sl4co1l on May 29, 2015, 02:02:33 amQuote from: NiHaoMike on May 29, 2015, 01:32:07 amI am happy with rather low spl levels, since id like my ears to survive a bit longerThe headphones are here and all my questions were answered, i will have to build a headphone amplifier and i can tell without measuring annything.Well, it could be the headphones but i do not think so.The low end distorts horribly on thumbs and longer notes, quite noticeable on low sound effects.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: May 29, 2015, 09:46:06 am
content: It would be very interesting to see if those distortions can be confirmed by measurements.I.e. make some loopback measurements:1. no load frequency response and distortion curve (with Arta Steps)2. same curves but with headphone as a load.3. with a simple cmoy amp in between.That would certainly make for a very interesting analysis.Would be great if you could do that.Greetings

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 29, 2015, 12:55:58 pm
content: Quote from: hayatepilot on May 29, 2015, 09:46:06 amNo promises but that sounds like a good idea, might do thatThere is only one thing that is bothering me, i bought a "Technica ATH-T400" and while it certainly sound good i am unhappy with how they fit on my head.They sit fairly loose. The loose fit seems to be intentional, most other headphones look like they will not fit snugly either.The next model i like would be double the price, the "Beyerdynamic DT-770 M" are designed to fit snugly and have a awesome 30dB ambient sound attenuation.Maybe i can still return these...

author: Lightages
author_rank: Unknown
timestamp: May 30, 2015, 12:27:34 am
content: I don't know what your price range is but I can highly recommend Audio Techica ATH-M40X headphones. They are very hard to beat for the price, or for even much more.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 30, 2015, 04:13:17 am
content: Quote from: PeterFW on May 29, 2015, 06:53:09 amIf you have to set the volume level really low to get the right volume, you have too much voltage (and current), not too little. An amplifier with a greater than unity gain would only make matters worse, lowering your SNR. Whether or not you add an amplifier, you'll need an attenuator to end up with less than unity gain. So you might as well make an attenuator with some series resistors, then if it turns out the frequency response is still unlevel, add a unity gain buffer between the sound card and attenuator.

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 30, 2015, 07:40:02 am
content: Quote from: NiHaoMike on May 30, 2015, 04:13:17 amI know how speakers work... what i am hearing is distortion either caused by the driver reaching its linear excursion limit or clipping of either the voltage or current source capability of the "amplifier".Hence the comment about lowering the output volume (lowering the voltage into the load), wich should reduce those distortions.Have not had time to wire a suitable adapter, thought i had one, i dont.

author: dom0
author_rank: Super Contributor
timestamp: May 30, 2015, 03:23:20 pm
content: - To maximize the systems' SNR you really want to always use the DAC's full output swing or it's dedicated digital volume control (which usually gives better results on the first 20-40 dB attn than the same attenuation applied to the input stream). The latter is usually not used by the operating systems' volume control, or not even available.- A dedicated line driver / headphone amplifier makes sense if the output amplifier of the integrated sound card is crap. A simple line driver with any audio op and a discrete buffer stage will easily drive any headphone to complete and utter destruction of the voice coil, so neither swing nor power is really an issue. If you want 0 dB gain in the "power stage" make it inverting (always invert) and overcompensate grossly (if you don't use a capacitive test load - or just compensate appropriately with a capacitive test load).

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 30, 2015, 10:17:22 pm
content: You want to do the attenuation after the DAC, and ideally at the last possible moment. The series resistors on the opamp outputs can do it and also make it short circuit proof and ESD resistant, at the cost of requiring a more voltage on the opamp supplies. That's not an issue for a mains powered unit (though a low noise mains powered PSU is not exactly trivial - those cheap wall warts are worse than a half decent PC PSU!), but if you do want to make it battery operated, you'll probably want to do the attenuation just before the opamps. (Just a simple voltage divider, try to target about 1-10k input impedance.)

author: PeterFW
author_rank: Frequent Contributor
timestamp: June 03, 2015, 01:35:54 pm
content: Hello and thanks your your replys NiHaoMike and DomThe idea of the DAC and amp is slowly simmering on the back burner, i think i found a few very nice parts with a very low external component count.When(/If) i build something, i will be back with measurementsQuote from: Lightages on May 30, 2015, 12:27:34 amOne i had a set of ATH-M40fs that died many, many moons ago and i had indeed looked at the M40X this time around.But i deemed them a bit too expensive and they have the same design feature that makes repairing them a pain in the arse.But... well... over the weekend i found headphones that had everything i wanted and ordered them but they cost a lot more.Today they were delivered and i am very happy with the "Beyerdynamic DT-770 M" right now, they have a ambient noise attenuation of 35 dBA and sound very good.Since my main goal was nice sound and to isolate myself from the outside world, this might be a winner. Now i just have to forget how expensive they were...

author: Lightages
author_rank: Unknown
timestamp: June 03, 2015, 05:58:44 pm
content: What was it that broke and was hard to repair?

author: PeterFW
author_rank: Frequent Contributor
timestamp: June 03, 2015, 06:41:04 pm
content: Quote from: Lightages on June 03, 2015, 05:58:44 pmThe fault wich made me bin them was the broken wire wich connects both ear pieces.You could not just pull a new one through the polster on the padded head band since it was stuck and you could not get the padding of without tearing them completely apart, every single piece had to go.After that i could get a hold of a suitable long enough replacement wich was small enough to fit in the original place so i gave up, the padding was loosing structural integrity annyway and i allready had replaced the main cable.On the M40X it looks like the wire is burried even deeper in the guts of the swivel mechanism and polster wich should make it even more prone to failure.They do however feature a nice replaceable main cable.On the cheaper ATH-M30x they even look like they are designed to fail.

author: TMM
author_rank: Frequent Contributor
timestamp: June 06, 2015, 11:48:33 am
content: Any half decent PC sound interface will have the output buffered by an opamp. You can expect at least 20mA before you hit the current limit of the opamp which will drive some 32ohm headphones fairly loud (at least 1.28Vpp) before there is compression of the signal and audible distortion.I did some tests a while back comparing the onboard output of my motherboard (Gigabyte P67-DS3-B3 - can't remember what codec IC it uses), a reasonably priced PCI-e sound card (Asus Xonar DX) and a known low-distortion USB interface (E-MU 0204 USB).I compared the output level and distortion under HighZ (1Mohm) and LoZ (33ohm) with a 2Vpp signal. This represents a pretty loud volume. At 1Vpk/33ohm = 30mA, it will reveal the current limit of any piss weak output buffers.-The motherboard's onboard output showed perhaps a 10% drop in amplitude . Distortion rose significantly. While not unlistenable, the distortion was obvious if you compared it with a sound source that could drive the headphones adequately. If you only listened at low levels, the distortion problem wasn't present.-The reasonably priced sound card showed no change in level when loaded with a low impedance but distortion rose slightly. Distortion was still low enough that it would be inaudible.-The high end USB sound interface showed no change in level or distortion when either it's dedicated headphone output or line output were loaded with a low impedance.One thing to note is that the dedicated stereo line output (usually green coloured jack) is more likely to be opamp buffered. The other outputs are usually only intended to drive HighZ inputs such as for a surround sound speaker system. While they may be able to configured as the main stereo output, they may be driven directly from the DAC or through a low current amplifier, so won't have sufficient current drive for low impedance headphones.Perhaps check you are using the right output jack - 1.35Vpp HighZ to 0.25Vpp LoZ(30ohm) means that the output impedance of your sound interface is effectively 130ohm, that seems pretty high. The output impedance of the onboard sound in my tests was effectively 3ohms. I have never seen a seperate series output resistor on an PC sound interface. Usually they just rely on the current limiting of the output opamp.

author: dom0
author_rank: Super Contributor
timestamp: June 06, 2015, 02:54:49 pm
content: Quote from: TMM on June 06, 2015, 11:48:33 amNot necessarily, some vendors use a 120 ? output resistance for headphones outputs, based on some obscure standard from the 80s.

author: shanky887614
author_rank: Contributor
timestamp: June 09, 2015, 03:04:12 pm
content: Quote from: linux-works on May 26, 2015, 11:13:55 pmto be honest i swapped to optical and im really enjoying it now.optical -dac is better than usb, i dont know why but a lot of dacs dont have usb input and have optical

author: Kibi
author_rank: Unknown
timestamp: June 09, 2015, 03:27:31 pm
content: A few years ago I built the O2 Headphone Amp by NwAvGuy. It's really good, drives my AKG K550's very well.I even have spare PCB's.http://nwavguy.blogspot.co.uk/2011/07/o2-headphone-amp.html