Topic: notebook headphone output - how to amplify?

Hello,

when I plug the headphone output of my notebook into a line input of my Yamaha mixer, the signal is week and muddy. But with low impedance headphones the signal is rich and very pleasing from Pianoteq.

My guess is an impedance mismatch between the headphone output of the notebook and the line input of the mixing console. How do you face this problem? Do some kind of preamplifiers exist, that can bring the weak  headphone outs to line level? And change the impedance to avoid a loss of treble? Or have you heard from DIY solutions?

Thanks

P.S. notebook with soundchip Realtek ALC270 --> Yamaha MG82cx

Re: notebook headphone output - how to amplify?

Hello Groovy,

You are on the right track when you mention impedance mismatches between the headphone output of your notebook and the line input of your mixing console.  Signal level also needs to be addressed.

The following link addresses your problem and offers home-made and commercial fixes.

http://beavishifi.com/articles/headphonejack/

Hope this helps.

Cheers,

Joe

Last edited by jcfelice88keys (13-02-2012 04:39)

Re: notebook headphone output - how to amplify?

I would suggest you to "invest" in an USB audio interface, it's so cheap currently, like this one:

http://www.highlite.nl/silver.econtent/...ces/ds_cv1

For less than 40 euros (+VAT) you'll probably get a better signal/noise ratio and you'll get a phono & line input for free ! ;-)

Re: notebook headphone output - how to amplify?

The mixer inputs have an impedance of 10K, which is a far easier load for the notebook than the 32 ohm headphones.    There is no guarantee that the sound you hear with the headphones plugged into the notebook is the "right" sound, just because you prefer it - it is possible that the sound you hear from the mixer is actually more accurate.  If the headphones have an impedance that varies substantially with frequency, and the notebook has an appreciably different output impedance to the mixer's headphone output, that could cause a difference in frequency response, and hence a difference in tone. The mixer has an output impedance of 100 ohms, but I do not know the output impedance of the notebook.  (FYI: I have measured my own notebook at 69 ohms)

It could be something to do with the low output level of the notebook I suppose, although the mixer has some inputs with adjustable input gain.

What make/model of headphones are you using? (and are you using the same headphones with the notebook and the mixer? I assume so)

Which inputs are you using on the mixer, and are the EQ controls all centered? (I know this is a silly question, but I want to make sure, that's all ;^)

Can you get the input peak level indicators to flash?

Do you hear much background hiss and/or hum when you are using the mixer?

You might want to burn a CD with a recording of Pianoteq, and connect a CD  player up to the mixer, and see if that improves  the fidelity.  You could also copy the recording to an iPod, and see how that sounds with your headphones.  iPods have a very low output impedance (which is good), and will be very well matched to your 32 ohm headphones.

Greg.

Last edited by skip (13-02-2012 10:35)

Re: notebook headphone output - how to amplify?

Luc Henrion wrote:

I would suggest you to "invest" in an USB audio interface, it's so cheap currently, like this one:

http://www.highlite.nl/silver.econtent/...ces/ds_cv1

For less than 40 euros (+VAT) you'll probably get a better signal/noise ratio and you'll get a phono & line input for free ! ;-)

This is what you should do. Forget about built-in headphone outputs on a laptop. Get a real audio interface.

Hard work and guts!

Re: notebook headphone output - how to amplify?

Just btw, the notebook's output level may not be all that low. My own notebook has about the same level as my M-Audio Fast Track Ultra USB interface - about 1V RMS. (this is about half the level of a typical component CD player, which is 2V RMS = 5.6V peak-to-peak, which matches the level given in that article)

Neither my notebook or my USB interface can drive high impedance headphones loudly, especially with solo piano.  My USB interface has a lower (better) headphone amp output impedance - 2.5 ohms measured cf 69 ohms measured for my notebook, as I mentioned.

For driving this Yamaha mixer, my notebook would be very similar to my USB interface, IMHO.

Greg.

Last edited by skip (13-02-2012 13:51)

Re: notebook headphone output - how to amplify?

just out of curiosity: did you use the input 7/8 on the Yamaha or one of the 3/4 - 5/6 ? On the input 7/8 you don't have any control of the input level (it's fixed to -10dB) ... try input 3/4 or 5/6 (+10 to -34)

Re: notebook headphone output - how to amplify?

Wow, lots of useful informations, thank you all.

@jcfelice88keys
Nice link to beavis, thanks. Transformers or JFETs, hm, I guess I would prefer OPA today for linear audio.

@Luc Henrion
USB audio interface is not an option for me at the moment, thanks. I have excellent latency out-of-the box with onboard sound on that HP 635 notebook. I already have a highly tuned eeePC with USB-soundcard Behringer UCA222, which I use exclusivly as "sound-engine". I was hard work, but it has good latency after many tweaks and there are two describing threads in this forum (netbook thread and zero latency thread iirc). Those tweaks were on kernel 2.6x and may not work the same on kernel 3.2 eventually. Another reason is, I'd like to use the HP 635 for other, more standard purposes and keep the setup straight-forward this time.

@skip

skip wrote:

There is no guarantee that the sound you hear with the headphones plugged into the notebook is the "right" sound, just because you prefer it - it is possible that the sound you hear from the mixer is actually more accurate.

Good point. If there is "sounding", it is more likely the impedance interaction between headphone-output and headphone, than the interaction of headphone-output with a typical line-input. To make the comparison more fair, I plugged the headphone (audio-technica ATH-M40fs) now into headphone-out of the notebook directly and after that into the headphone-out of the Yamaha mixer. It is not as far away, as it was yesterday (?!). The direct headphone-connection is a little brighter, but as you said - "sounding" is more likely happening with this direct connection. All controls were neutral and no hiss nor hum. Important is to adjust the headphone level to max in the software-mixer. It is not impossible, that it was not fullscale yesterday, sorry if that happened!

skip wrote:

Just btw, the notebook's output level may not be all that low.

I will measure it when I have more time. It would be interesting, if those energy efficient APU notebooks use low voltage for sound output, though I don't think so.

Luc Henrion wrote:

just out of curiosity: did you use the input 7/8 on the Yamaha or one of the 3/4 - 5/6 ? On the input 7/8 you don't have any control of the input level (it's fixed to -10dB) ... try input 3/4 or 5/6 (+10 to -34)

Normally I use 7/8, because it is the best sounding input. Yesterday I tried also the 5/6 with its additional input gain control but it was no big difference soundwise. Something else went wrong, as I guess above. For a while I was connected with my keyboard combos and you all know, how big the contrast between headphone and loudspeakers can be

With output level full scale on the notebook, I can use 7/8 ok. Another interesting measurement would be the output-impedance of that notebook. Maybe a little sound degradation is possible if it should be exceptionally higher than average 120 Ohm. A workaround could be just to use the treble controls on the mixing console or the keyboard amps

Thanks for reading english, not my world
- groovy

Re: notebook headphone output - how to amplify?

Just btw, the ATH-M40fs appear to have an impedance of 60 ohms, not 32 ohms:
http://www.audio-technica.com/cms/headp...index.html
(what made you think it was 32 ohms?)

Greg.

Re: notebook headphone output - how to amplify?

Hi,
who thought, the Audio-Technica has 32 Ohm?

- groovy

Re: notebook headphone output - how to amplify?

Groovy,
I thought you had said you were using 32 ohm headphones, in your very first post. In fact, I could have sworn that I had seen 32 ohms. However, I see that you simply said "low impedance", so I must have somehow converted that to 32 ohms! I apologise.

60 ohms isn't particularly low by today's standards IMHO. It might be low compared to 300 ohms, but today, folks seem to usually mean 32 ohms or less when they say "low impedance".

Anyhow, I haven't found an impedance vs frequency plot for your headphones yet.

I'll measure the output level & impedance of my Toshiba NB300 netbook, just out of curiousity.

Greg.

Re: notebook headphone output - how to amplify?

I've measured my Toshiba NB300 netbook.(codec chip is a "Realtek High Definition Audio")  When I plug something in, it pops up a message asking what type of device has been plugged in - headphones, or line-out.  I was very pleasantly surprised to find that this actually DOES something!! The output level is 1.3V RMS in both cases, however it changes the output impedance depending on the which mode it is in. For headphones, the output impedance is 50 ohms, and for line out, it is rougly 170 to 180 ohms. (I took two measurements with two different load resistance, and got two different results. I always do this to see how closely the the output represents an ideal voltage source behind a constant resistance.)

@Groovy: if you don't have this pop-up, you might want to check whether you can manually configure the output mode.  I doubt whether this setting will make any audible difference when connected to the mixer, but it might make a difference when driving headphones directly.

I'm not 100% sure, but I believe that there are at least two reasons for a higher output impedance in line-out mode:
a) For short circuit protection
b) To lessen the risk of instability in the output driver due to cable capacitance.

Greg.

Last edited by skip (14-02-2012 15:54)

Re: notebook headphone output - how to amplify?

Hello skip,

very interesting in deed, I didn't know, that laptop outputs can do impedance switching.

I also tried to measure the output impedance of my HP 635 with a Digital Multimeter. Without any load I measure 1 V at the headphone jack (with 400 Hz sine generated fullscale in a wave editor (audacity) and with all headphone-, PCM- and master-fader maximum in kmix)

With a load of 100 Ohm resistor in both channels the voltage drops to around 0,8 V, which gives with the voltage-divider formula Rl/Ri=Ul/U0 an output impedance Ri of 120 Ohm for headphone-output.

That is low enough to be no problem for common line inputs with 22k-47kOhm or 10kOhm like my Yamaha mixer. But it is also not a very strong signal, which is 2V normally with line outputs.

- groovy

P.S. "low impedance" is relative, you're right, I should have been more exactley. My reference was my Sennheiser headphone, which has 600 Ohm and compared to that my Audio-Technica with 60 Ohm is on the low side

Re: notebook headphone output - how to amplify?

My Asus netbook has a low output. I use a small Fiio E5 headphone amplifier to boost the signal. $20-30 US last time I looked.

Michael

Re: notebook headphone output - how to amplify?

I used 150Hz. 400Hz is right on the edge of the frequency response of my multimeter. (did you check the specs of your meter?)

Anyway, assuming your meter is correctly reading at 400Hz, your internal resistance is actually 25 ohms.   Check: Vout = Rl/(Rl+Ri)*Vint = 100/(100+25)*1 = 0.8V RMS = correct. ;^)

I agree that even if your output impedance was 120 ohms, that would have been fine for the line inputs of the mixer. 

How long is the cable that you are using between the laptop and the mixer? Keep it as short as possible, anyhow.

Yes, 60 ohms is definitely "low" compared to 600 ohms!!!

1V RMS is not too bad. As I said, my USB interface has this level as well.  I really do not think this will be a problem, unless your mixer has a lousy signal-to-noise ratio.

Greg.

Last edited by skip (14-02-2012 21:31)

Re: notebook headphone output - how to amplify?

Ah, thanks for correcting me, skip! My mistake was Rl/Ri, the correct term is of course Rl/(Rl+Ri). 25 Ohms output-impedance is good news, compatible with more headphones I guess. My DMM is specified with 40Hz - 400Hz for AC and I checked in the past, that I can trust it at 400Hz. The audio-cable from laptop to mixer is just around 1 m, which should have no influence (unless it's broken).

- groovy

Re: notebook headphone output - how to amplify?

Given that your laptop's output impedance is better than the mixer (25 vs 100), that might make a difference, but I suspect you'd mostly notice it in the bass, if it's going to make an audible difference at all. If it's important to be able to use headphones with the mixer, it might be worth trying a headphone amp on the output of the mixer, to see if it makes any difference. (but do you even notice a difference any more? You don't seem so sure now)   

FiiO seem to have really good value stuff.  Here's a technical review of the E5 that Michael mentioned: http://nwavguy.blogspot.com.au/2011/03/...e-amp.html
Points to note:
a) it seems to be designed for low output portable devices, because it has a maximum input level of 760mV RMS.
b) it is more suited to low impedance headphones, because it has a rather low maximum output level of 1.3V RMS.
c) It has a very good (low) output impedance of 0.7 ohms. 

For high impedance headphones, their E9 would be more appropriate, although unfortunately it's 10 ohm output impedance may be a problem with some low impedance headphones. (especially some in-ear monitors, I have read)

Note that it is not always correct to aim for the lowest possible output impedance. For one example, Beyerdynamic seem to optimise their headphones for use with a 120 ohm output impedance (120 ohms is a standard), and this is backed up by the fact that their own A1 headphone amp has an output impedance of 100 ohms. (close enough to 120 - not sure why they used 100 instead of 120 though) It's a bit of a murky area. When in doubt, contact the headphone manufacturer and ask them.

Greg.

Last edited by skip (14-02-2012 23:04)

Re: notebook headphone output - how to amplify?

Before buying a headphone amp, perhaps you could try adding 75 ohms of impedance in series with the laptop output, to bring the total output impedance up to 100 ohms, to match the output impedance of the mixer. See whether it makes the sound closer to the sound from the mixer, just as an experiment. (this will drop the maximum volume, it's important to make tonal comparisons at the same volume) 

Or just use the tone controls and move on, as you said.

Greg.

Last edited by skip (15-02-2012 02:59)

Re: notebook headphone output - how to amplify?

skip wrote:

Before buying a headphone amp, perhaps you could try adding 75 ohms of impedance in series with the laptop output, to bring the total output impedance up to 100 ohms, to match the output impedance of the mixer. See whether it makes the sound closer to the sound from the mixer, just as an experiment. (this will drop the maximum volume, it's important to make tonal comparisons at the same volume)

Crazy, that's it! The difference between 25 Ohm output-impedance of the notebook and the 100 Ohm of the Yamaha mixer determines the tonal characteristic with this headphone Audio-Technica ATH-M40fs! Never thought, headphones are so picky with the headphone-output.

Although I had not 75 Ohms resistors you suggested, I used my old adapater with 47 Ohm trimmers in row, that I soldered in the past for another experiment. When this resistance is between the notebook and the headphones, the sound degrades similar to what I hear when these headphones are attached to the Yamaha headphone-out. Exaggerated attributes could be then: more muddy, less life, less breath, less natural. (off course I compensated the volume loss by the added 47 Ohms). This effect can't be simulated with treble or bass knob of channel 7/8 the same.

- groovy

Re: notebook headphone output - how to amplify?

Good one!  It's only recently that I learnt of this impedance interaction issue - I really wish I had known about this a lot earlier.  It will be interesting to see whether the real "acid" test passes - using a low impedance headphone amp on the mixer output. (if you actually do try that)

Here are some more links which I think are very informative:
NwAvGuy: Headphone & Amp Impedance
Sound & Vision:Output Impedance: A Show and Tell
Benchmark Media:The "0-Ohm" Headphone Amplifier: The Sonic Advantages of Low-Impedance Headphone Amplifiers

Greg.
EDITED 11-Jan-16 to update link for the Benchmark Media article.

Last edited by skip (11-01-2016 03:57)

Re: notebook headphone output - how to amplify?

Thanks for those interesting links!
Alas I have no headphone-amp, but I made my hifi-amp to it temporarily Better don't try this at home: I connected my headphone with the speaker-output of this amp with 25 Ohms in row to simulate the notebook-headphone-output (impedance- not powerwise!). Soundsource was Pianoteq on this laptop connected with the aux input of this amp. It also sounds better than the 100 Ohm headphone-output of my mixing console. Reducing the 25 Ohm to 0 Ohm even brings up more nuances. I definitely will experiment with a headphone-amp or different headphones on the Yamaha mixer ( which ist specified for 40 Ohm phones beeing "Appropriate Impedance").

Or I leave everything as it was at the beginning, using the notebook-output directly with my 60 Ohm headphone and be happy!

- groovy

Last edited by groovy (16-02-2012 23:52)

Re: notebook headphone output - how to amplify?

Good idea to try the hi-fi amp speaker outputs - power amps have a very low output impedance. 

If it were me, I'd buy a headphone amp for  the mixer, if I had to use the mixer with headphones.  The output impedance is too high for low impedance headphones (including 40 ohm headphones), but the output level is also too low for high impedance headphones. (75mW into 40 ohms = 1.7V RMS loaded, or 2.4V RMS unloaded. I'd prefer to see an unloaded level of at least 3V RMS, preferably even higher)   If  you really don't want to get an amp, perhaps you could buy some headphones for which you know the impedance vs frequency curve, and choose headphones with a relatively flat curve. http://www.headphone.com have the impedance vs frequency graphs for many different models. 

Greg.

Last edited by skip (17-02-2012 02:30)

Re: notebook headphone output - how to amplify?

Sorry, I made a mistake in my previous reply. The unloaded voltage on the mixer headphone output is actually 6V RMS, which is high enough for many high impedance headphones I think. For example, this would translate to 4.5V RMS across the 300 ohm Sennheiser HD650. The HD650 has a sensitivity of 103dB @1V, so that would produce 116dB SPL, and that's very loud.  The damping factor would still not be very good. (3:1, whereas 8:1 or higher is the recommendation)

If it's true that the Beyerdynamic range is optimised for a 100/120 ohm impedance, then I suppose they would be a good match to this mixer.

Greg.

Last edited by skip (17-02-2012 12:04)

Re: notebook headphone output - how to amplify?

skip wrote:

If it were me, I'd buy a headphone amp for  the mixer, if I had to use the mixer with headphones.  The output impedance is too high for low impedance headphones (including 40 ohm headphones), [...]

Just for interest I tried the headphone-amp Millenium HP1 between mixer-headphone-out (100 Ohms) and two different headphones (60 Ohms and 300 Ohms). Indeed it clears things up and the left hand has more definition and detail. The other side of the medal is, that two audio-device in row (mixing-console and headphone-amp) suck tone also,  more than using the headphone with the notebook-headphone-out (25 Ohm) directly. And it is one gadget and power-adaptor more.

In my opinion the best solution is to use the low impedance output of the notebook directly, when playing with headphones. If a mixing console is used and the center of your musical environment, a headphone-amp helps when having high-impedance outputs with 100 Ohms. Eventually it is worth not to use the cheapest headphone-amps on the market.

cheers

Last edited by groovy (22-02-2012 19:31)

Re: notebook headphone output - how to amplify?

Did you try the headphone amp connected to the notebook? If so, could you hear any difference between the direct sound of the notebook and the amp?

For the mixer, I would connect the headphone amp to a line out, for the very best fidelity. (I realise you were connecting to the headphone output for diagnostic purposes though)

Just btw, if this review is correct, that amp has an output impedance of 50 ohms, which is worse than your notebook: http://en.audiofanzine.com/headphone-am...15475.html  ;^)
If you haven't already, you might want to measure it's output impedance yourself.

Greg.

Re: notebook headphone output - how to amplify?

Hi,

skip wrote:

Did you try the headphone amp connected to the notebook? If so, could you hear any difference between the direct sound of the notebook and the amp?

I did so now, and yes, it sounds differently with my AudioTechnica. With the Millenium HP-1 it sounds a little darker and slightly more bassier. But take this with a grain of salt, because didn't level it out very exactly, and I'm sure you know that would be very important for A/B-testing. Eventually I repeat it with a level exactly measured. But I'm quite sure about a sound-difference already.

skip wrote:

For the mixer, I would connect the headphone amp to a line out, for the very best fidelity. (I realise you were connecting to the headphone output for diagnostic purposes though)

...both full ack!

skip wrote:

Just btw, if this review is correct, that amp has an output impedance of 50 ohms, which is worse than your notebook: http://en.audiofanzine.com/headphone-am...15475.html  ;^)
If you haven't already, you might want to measure it's output impedance yourself.

You made me curious, so I measured the voltage-drop of the HP-1 also when loaded with a 100 Ohm resistor. Measured open my testsignal was 1V at 400Hz. Loaded with 100 Ohm I found a drop to 0.667V. With the formula this means 50 Ohm output-impedance of the Millenium HP-1 headphone amp. So I can confirm the user-review in your link, thanks. When I bought it, I thought its output-impedance would be nearer at null, because it is advertised to drive low impedances down to 8 Ohm. It would be interesting to know, which headphone-amps have less than 50 Ohm and are not too expensive.

cheers

Re: notebook headphone output - how to amplify?

Yes, well, maybe that HP-1 has the current drive for 8-ohm headphones, but it's possible that the designer wasn't aware of the impedance interaction issue - who knows.

The aforementioned FiiO E5 is a good example of a very cheap amp with a very low output impedance - about $20 with 0.7 ohms impedance.  The E6 is slightly improved. (note that it allows a higher input level before clipping, too).  The E9 has more power & voltage, but has a 10 ohm impedance, which is still low, but not as low. The E9 can be docked with the E7 or E17, which are both combo DAC/amps. The E7 has a lower output impedance, and I presume the E17 does too. (the E17 is very new, and has not been reviewed yet by NwAvGuy).  The E9 would be best suited to high impedance headphones, with the E7/E17 being more suited to low impedance headphones. If I didn't already have a headphone amp, I think I would have bought an E9 and possibly an E7. (but now I'd get the E17). The amp I have is the Musical Fidelity V-Can, which has an output impedance of 5 ohms. It's a bit pricey for what it does IMHO, considering the competition.  It's output drive (~3V RMS) is borderline for solo piano, with my AKG K601 headphones.  I think it's enough for typical music though.

That blogger designed his own amp - the O2. It appears to be a very simple op-amp design, but using good quality components. It has very good specs. (including a very low output impedance) You can build it yourself, or buy it pre-assembled  from JDSLabs.

Greg.

Re: notebook headphone output - how to amplify?

In the meantime I got the FiiO E5 headphone amp for 20 EUR. Thanks for Michael H and yours advice! Its very low output-impedance is really an improvement with all 3 headphones I tested (60, 250 and 300 Ohm). For all kinds of piano sounds over headphones and percussive sounds in general, low output-impedance seems to be very important (if not essential). I'm happy to have learned that with your help.

The DIY project headphone amp Objective2 ("O2") you mentioned is excellent and very well documented. Alas not as simple as I hoped because of its additional power-supply and protection circuits. But I'm intrigued to build the O2 once I can easily purchase a printed circuit board (PCB) around here.

cheers

Last edited by groovy (28-02-2012 12:21)