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Old 8th January, 2002, 12:17 PM
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Media forte - soundcard prob

Can this soundcard drive headphones directly thru the "line out" jack. Or is amplifier needed

I have used several sound cards thru the years, all of them can deliver acceptable sound to headphones thru the line out jack.

This unit is in my coworkers workstation and is sounds very veek without bass and distortion. Sounds just like the sound card cannot deliver enough current to drive the headset

Any ideas guys?http://www.mediaforte.com.sg/product..._pcs/index.htm
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Old 8th January, 2002, 04:49 PM
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Quote:
"Theatre X-Treme 5.1 is simply the most cost-effective xtreme Solution for the Xtreme Sounds of today's audio requirements."


I fear companies that use words like "Cost effective... solution" to sell their product.

I think your diagnosis was correct, it's poor hardware causing the lineout to be weak.
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Old 8th January, 2002, 06:39 PM
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I have noticed that the souncards are mot as powerful as they once were, I think they just assume your going to use amplified speakers with a decent sound card
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Old 8th January, 2002, 06:45 PM
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im glad soundcards arent too powerful anymore...... i got a amplifier and hi fi speakers plugged into mine, dont wanna blow hte amp!
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Old 8th January, 2002, 08:40 PM
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Quote:
Originally posted by Pinky
I think your diagnosis was correct, it's poor hardware causing the lineout to be weak. [/B]
Careful here! Lineout has never been designed to drive headphones. It's designed to drive loads like the input of a power amplifier, which present many thousands times the resistance of headphones.

Typically lineout is meant to drive a load in the area of 20,000 Ohm. Your headphones are typically around the 32 Ohm mark. If it says lineout, generally it means it. If it says headphone out, then it means that instead. A few sound cards have jumpers to select between the noisy headphone amp, and the lower level lineout. If you can power your headphones from your lineout, then be glad that your soundcard is so far out of spec!

Also, not including the power amp on the output of the soundcard generally improves it's quality, as the power amp is normally cheap enough to produce most of the white noise (hiss) from the sound card. Personally, I'm glad of this!

AidanII
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Old 8th January, 2002, 10:21 PM
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Again, good points Aidan... I think this matters little since windows has a volume control

perhaps over time either the headphones or card will suffer some ill-fate from running a device out of spec...

I still think that low-level line out is indicative of poorer hardware, however, since line volume is still critical even at a higher/lower impedance...

hell, maybe I should just ask you to explain further
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Old 8th January, 2002, 11:21 PM
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I figured you might... I covered all this once upon a time, on another planet, in another lifetime...

The thing that everyone calls Line Out is actually has a defined standard. Well, ok, it has two standards, but you're unlikely to come across the second one.

The (consumer) line level specification is designed to provide a signal level of -10dBu (~0.7V) into 10KOhms of impedence. Thus, if you attached a 10KOhm resistor to the output of your soundcard, and got it to produce a 1KHz sinewave at 0dB FS(Full Scale), then you should see a signal at 0.7V.

Anything above or below this figure is basically miscalibrated. A higher impedence shouldn't make much difference, other than making the equipment more sensitive to noise. A lower impedence provides a heavier load and brings the voltage down, but decreases the noise levels. The whole line level thing requires the output to have a certain impedence, and the input to have a different impedence.

The professional line level is designed to provide +4dBu(~1.5v) into a 600ohm load, normally balanced. Connecting professional equipment to consumer equipment requires either an amplifier (consumer->pro) or an attenuator (pro->consumer).

Speaker level is +10dBu (~5v) and higher into 4ohms or so. Headphone level is pretty similar to low power speaker levels...

AidanII

Yeah, I had to learn this stuff when I was an audio engineer..
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Old 9th January, 2002, 01:24 AM
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Quote:
Originally posted by AidanII
Yeah, I had to learn this stuff when I was an audio engineer..
lol I thank you for taking the time to explain it

I gave up in electronics 101 years ago... have the foundation but never actually got to the point of applying any of it or working with that knowledge abstractly/intelligently. You obviously had to know this, as will I once I decide to work deeper into music and integrating musical equipment.

I'd say I understood 2/3 of your explanation. In lamen's terms you're saying the headphone's impedance causes the signal to actually be greater since the expected resistence is in the thousands when the headphones are at 32ohms?? So then it would be possible to "blow" the headphones since the resistence is less than expected...

In the case of the original question and my original response, a low output level would still be indicative of something being wrong with the soundcard, right?
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Old 9th January, 2002, 08:51 AM
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Quote:
Originally posted by AidanII


Careful here! Lineout has never been designed to drive headphones. It's designed to drive loads like the input of a power amplifier, which present many thousands times the resistance of headphones.

Typically lineout is meant to drive a load in the area of 20,000 Ohm. Your headphones are typically around the 32 Ohm mark. If it says lineout, generally it means it. If it says headphone out, then it means that instead. A few sound cards have jumpers to select between the noisy headphone amp, and the lower level lineout. If you can power your headphones from your lineout, then be glad that your soundcard is so far out of spec!

Also, not including the power amp on the output of the soundcard generally improves it's quality, as the power amp is normally cheap enough to produce most of the white noise (hiss) from the sound card. Personally, I'm glad of this!

AidanII
Thank you all for your input guys!!

You are right AidanII the "typical" soundcard has much less internal resistance than the audio standard line out. Thank god for that! I have actually never bothered to even think about what standard the pc based audio is using. Anyway this mediaforte card has "high" impedance output, thats for sure! Still I doubt it has 20Kohm cause it could "almost" drive the headset

The solution: the dude got himself a small pair of speakers with headphone jack outlet. So much for good sound
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Old 9th January, 2002, 01:52 PM
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Quote:
Originally posted by Pinky
I'd say I understood 2/3 of your explanation. In lamen's terms you're saying the headphone's impedance causes the signal to actually be greater since the expected resistence is in the thousands when the headphones are at 32ohms?? So then it would be possible to "blow" the headphones since the resistence is less than expected...
Not quite. The amplifier on the soundcard is expecting a certain resistance (well, a range of resistances really.). It has it's own output resistance as well.

When everything is right, then the right voltages will appear across the load (whatever you plugged into the soundcard).

If the load resistance is too small, then the amplifier will struggle to overcome it's own internal resistances, and as a result the voltage across the load will be smaller than expected.

Lets say that the amplifier has a resistance of 320 Ohms, and the load has a resistance of 20,000 Ohms. The amplifier tries to output a voltage of a volt.. What happens is that 1v has to appear across a total of 22320 Ohms, giving a total current of 0.044mA (Ohms law). Of that one volt, 0.014V of it disappears across the amplifiers internal resistance, leaving 0.986V to appear across the load.

Someone plugs their headphones in.... The headphones have a resistance of 32 Ohms, and the amp still has a resistance of 320 Ohms. That 1v now appears across 352 Ohms of resistance total, allowing a current of 2.8mA to flow. Of that one volt, 0.9V of it disappears across the amplifiers internal resistance, leaving 0.1V to appear across the headphones!

End result: You don't hear much in the headphones, and the amplifier gets warm. Not warm enough to kill it though, as the wattage is too small to generate much heat.

AidanII
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Old 9th January, 2002, 01:53 PM
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Quote:
Originally posted by Eriksson
Anyway this mediaforte card has "high" impedance output, thats for sure! Still I doubt it has 20Kohm cause it could "almost" drive the headset

The solution: the dude got himself a small pair of speakers with headphone jack outlet. So much for good sound
The solution was definately the better idea.

The output from the soundcard wouldn't have 20K of resistance - that's what it's expecting to see. It wouldn't surprise me if the output had a resistance measured in the hundreds of ohms though.

AidanII
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Old 9th January, 2002, 06:26 PM
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Quote:
Originally posted by AidanII
Someone plugs their headphones in.... The headphones have a resistance of 32 Ohms, and the amp still has a resistance of 320 Ohms. That 1v now appears across 352 Ohms of resistance total, allowing a current of 2.8mA to flow. Of that one volt, 0.9V of it disappears across the amplifiers internal resistance, leaving 0.1V to appear across the headphones!

End result: You don't hear much in the headphones, and the amplifier gets warm. Not warm enough to kill it though, as the wattage is too small to generate much heat.

AidanII
I forgot the math was was working conceptually... not a good idea when playing with numbers

Thanks again, that illustrated it very well for me.
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