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What is the minimum difference between output impedance and load impedance required so as to...

post #1 of 15
Thread Starter 

Hi Guys,

 

Posting here since you guys are the smartest bunch we have here on these boards.

 

My Essence STX has an output impedance of 10ohms on the HP output. Not great I know.

 

With 32ohm cans like Denon's and Grado's, I get some sibilance issues and I believe it also affects bass frequencies (as in, you get less of it).

 

So I'm wondering what the minimum difference between the output and load (in ohms) is required so as not to have any issues.

 

Any help/educating you can do in regards to this would be very much appreciated. :beerchug:

 

Edit: Answered my own question with a better phrased google search. In short, you want the headphone impedance to be 8x the output impedance.

 

So I guess a follow-up question would be, is it possible to make an adapter to lower the output impedance of a soundcard? Specifically, the STX?


Edited by Bojamijams - 9/11/13 at 9:02pm
post #2 of 15

Lately I just plug my O2 into the STX's RCA output, for listening to music or 2-channel videos.

Plug my 40-Ohm ATH-A900Xs into the O2.

 

There is the PAV2V headphone amplifier for around $60, but not sure on it's impedance.

post #3 of 15
Quote:
Originally Posted by Bojamijams View Post
 

With 32ohm cans like Denon's and Grado's, I get some sibilance issues and I believe it also affects bass frequencies (as in, you get less of it).

 

So I'm wondering what the minimum difference between the output and load (in ohms) is required so as not to have any issues.

 

 

To be blunt, most of the issues you describe are simply due to the nature of your headphones. 

 

Dont be surprised when you obtain an amp with 1ohm Zo only to find your headphones still soound like they do. 

 

On that note, There is no real rule. Quite a few people prefer grados when driven from an amp with a bit of output impedance, certainly more than 4 ohms... 

 

While it is nice to have an (one) amp with 0.0001ohm output impedance in your stables, its not worth the effort to have more than that, and only barely worth it for the first. 

post #4 of 15

Yep.  Grados don't like low output impedance amps. ;)

post #5 of 15
Thread Starter 

Problem is, I want to keep using the HP out part of my sound card as that is the only one that Dolby Headphone works for.  I suppose I could double amp but that would introduce other issues and I don't know if the original ones would go away either.  

 

Let's say I do double amp (obviously noise floor increases), and the output impedance of the 2nd amp is <2 ohms, (1st amp is 10), would that be all that is required to match up the 48ohm headphone better? I remember reading something about input impedance into an amp having to be 47kohm but I don't know if that applies in this case? 

 

Alternatively, I need something like this faux impedance decreasing adapter mentioned here http://www.head-fi.org/t/601669/impedance-adapters-cables-explained-listed but unfortunately don't have the skills to build one. 

post #6 of 15
Quote:
Originally Posted by Bojamijams View Post
 

Problem is, I want to keep using the HP out part of my sound card as that is the only one that Dolby Headphone works for.

Maybe sell off the Essence STX and get the Xonar DX or D1 sound card (used $60) and also get an external headphone amplifier, like the Schiit Magni, $99. The Magni has an output impedance of less then 1-Ohm.

 

What model Denon and Grado headphones do you have?

post #7 of 15
Quote:
Originally Posted by Bojamijams View Post
 

Problem is, I want to keep using the HP out part of my sound card as that is the only one that Dolby Headphone works for.  I suppose I could double amp but that would introduce other issues and I don't know if the original ones would go away either. 

Sorry.  That statement puts your question in a different category.

post #8 of 15
Quote:
Originally Posted by PurpleAngel View Post
 

Maybe sell off the Essence STX and get the Xonar DX or D1 sound card (used $60) and also get an external headphone amplifier, like the Schiit Magni, $99. The Magni has an output impedance of less then 1-Ohm.

 

Considering that you'd make a loss selling the STX and buying the DX or D1, this doesn't seem like a good idea to me. Especially as it is a definite downgrade in paper specifications anyway.

 

Sure, you can buy a headphone amp if you feel that you have a problem with the output impedance on the STX, but 10 ohms is pretty good. Have you actually tried a comparison with a lower output impedance rig to confirm that that is what is the cause of your perceived problem? If you discover that you can hear an improvement then an amp is probably the way to go, although you could consider switching to some higher impedance phones, $99 plus your existing phones should put you in a pretty good range and 64 ohms is well enough above the STX's 10 that any problems are unlikely to be output-input impedance related. The headphone amp chip on the soundcard (TPA6120A) is very good, very highly regarded (ask jcx), although as with everything, there are always a few people who will not have it, although many of these are anti-solid-state anyway.

 

The STX can be modified to give a lower output impedance by replacing 2 resistors with chip inductors, but considering the potential for damaging the soundcard, it's not a procedure I'd recommend to anyone other who doesn't have a lot of experience, particularly of soldering 1206 style SMT parts.

 

w

post #9 of 15
Thread Starter 
Quote:
Originally Posted by wakibaki View Post

 

Have you actually tried a comparison with a lower output impedance rig to confirm that that is what is the cause of your perceived problem? 

 

w

 

Changing out for another sound card is not really an option as I need Dolby Headphone so I can't just do line out to an external amp. Output needs to be from the headphone output so as to support Dolby Headphone.

 

I haven't tried my future setup yet (STX into Audio-Technica AD700X yet) but the only reason that I'm looking to lower the output impedance is that for a 'proper' setup you need to have load impedance 8x the output impedance. So with the STX's 10ohm output, the 'proper' headphones would start at 80ohms. Anything below that and you start losing some bass frequencies and possibly other issues.

 

Now I know that this setup would work and people do it, but being that we're audiophiles and all :D I'm trying to make it electrically correct. 

post #10 of 15
Quote:
Originally Posted by Bojamijams View Post
 

 

Changing out for another sound card is not really an option as I need Dolby Headphone so I can't just do line out to an external amp. Output needs to be from the headphone output so as to support Dolby Headphone.

 

I haven't tried my future setup yet (STX into Audio-Technica AD700X yet) but the only reason that I'm looking to lower the output impedance is that for a 'proper' setup you need to have load impedance 8x the output impedance. So with the STX's 10ohm output, the 'proper' headphones would start at 80ohms. Anything below that and you start losing some bass frequencies and possibly other issues.

 

Now I know that this setup would work and people do it, but being that we're audiophiles and all :D I'm trying to make it electrically correct.

Just an FYI, but you've been reading some unfounded scuttlebutt.  There is no basis in fact for that statement.

post #11 of 15
Quote:
Originally Posted by Bojamijams View Post
...for a 'proper' setup you need to have load impedance 8x the output impedance. So with the STX's 10ohm output, the 'proper' headphones would start at 80ohms. Anything below that and you start losing some bass frequencies and possibly other issues.

 

 

This is a bit dogmatic. 8x is a rule of thumb. Something you use when you can't be bothered working things out exactly. It's also inaccurate to characterize the situation as '...Anything below that and you start losing some bass frequencies'.

 

Audio transducers, headphones and speaker drivers, have impedances which are not constant over the audio frequencies. Since the voltage output of an amplifier splits between its output impedance and the transducer input impedance, the magnitude of the audio output always varies with frequency. The larger the output impedance of the amplifier, the more pronounced the variations in the response.

 

This doesn't mean that the variation is audible.

 

Here's the impedance of a pair of Shure IEMs, e2c, now unfortunately out of production, but I'm familiar with them, and they make the point..

 

 

You can see that it rises in the bass and in the treble, with a little hump. The rises in the bass and treble mean that the bass and treble (response due to impedance) are more pronounced than the mids (except at the hump @ 4k).

 

Try to relax a bit and take these issues a bit less seriously. Phones with a 64 ohm nominal impedance are unlikely to have a significant audible difference when driven by a 10 ohm output impedance amplifier compared to a 1 ohm one. I wouldn't have made the suggestion if it weren't the case...

 

post #12 of 15
Thread Starter 

Ok, thanks guys.  I'll stop OCDing about the 8x thing :)

post #13 of 15
Quote:
Originally Posted by Bojamijams View Post
 

Ok, thanks guys.  I'll stop OCDing about the 8x thing :)

As the ATH-AD700X is bass light and with the 4 to1 impedance ratio from being plugged into the STX, it might cause a little bloated bass, which might be a benefit.

Sometimes you can find a good price ($150?) on a used ATH-AD900X.

http://www.head-fi.org/t/681450/ad900x

post #14 of 15
Thread Starter 
Quote:
Originally Posted by PurpleAngel View Post
 

As the ATH-AD700X is bass light and with the 4 to1 impedance ratio from being plugged into the STX, it might cause a little bloated bass, which might be a benefit.

Sometimes you can find a good price ($150?) on a used ATH-AD900X.

http://www.head-fi.org/t/681450/ad900x

 

I'm looking for the 700 specifically for it's bigger soundstage and better positioning (to be used in FPS games)

 

But I'm wondering if you could expand slightly on the bloated bass reference.  From my understanding, if the output impedence is too high (as in, not more then 8x or even worse, bigger then load impedence) then bass suffers as the difference acts as a filter.

 

Maybe this only applies in cases where the output impedance is higher then load (this was witnessed when plugging in <40ohm headphones into the Galaxy S4 which had 43ohm output impedance)

post #15 of 15
Quote:
Originally Posted by Bojamijams View Post
 

 

I'm looking for the 700 specifically for it's bigger soundstage and better positioning (to be used in FPS games)

 

But I'm wondering if you could expand slightly on the bloated bass reference.  From my understanding, if the output impedence is too high (as in, not more then 8x or even worse, bigger then load impedence) then bass suffers as the difference acts as a filter.

 

Maybe this only applies in cases where the output impedance is higher then load (this was witnessed when plugging in <40ohm headphones into the Galaxy S4 which had 43ohm output impedance)

I believe "bloated bass" (louder, less detail) is how the bass "suffers", from having a less then 8 times difference.

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