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Line out vs front panel audio jack - Line out is not amped?

post #1 of 11
Thread Starter 

On my motherboard MSI P67A-C43 (B3) the green line out jack on the back of the motherboard sounds un-amped compared with the front panel audio jack. There is significantly more bass coming from my headphones when connected to the front panel audio jack. All settings are the same across jacks, no EQ. This has happened on a previous motherboard also, it makes sense for the  front panel audio jack to be amped compared to the line out as you would usually plug headphones into the front and speakers into the rear jack.

 

ALC892 is the onboard audio which i assume has a built in AMP that is only connected to the front audio panel...because speakers have thier own amps?

 

Quote:
Hardware Features
  • DACs with 95dB SNR (A-weighting), ADCs with 90dB SNR (A-weighting)
  • Ten DAC channels support 16/20/24-bit PCM format for 7.1 channel sound playback, plus 2 channels of concurrent independent stereo sound output (multiple streaming) through the front panel output
  • Two stereo ADCs support 16/20/24-bit PCM format, multiple stereo recording
  • All DACs supports 44.1k/48k/96k/192kHz sample rate
  • All ADCs supports 44.1k/48k/96k/192kHz sample rate
  • Primary 16/20/24-bit SPDIF-OUT supports 32k/44.1k/48k/88.2k/96k/192kHz sample rate
  • Secondary 16/20/24-bit SPDIF-OUT supports 32k/44.1k/48k/88.2k/96k/192kHz sample rate
  • 16/20/24-bit SPDIF-IN supports 44.1k/48k/96k/192kHz sample rate
  • All analog jacks (port-A to port-G) are stereo input and output re-tasking
  • Port-D/E/F built-in headphone amplifiers
  • Port-B/C/E/F with software selectable boost gain (+10/+20/+30dB) for analog microphone input
  • High-quality analog differential CD input
  • Supports external PCBEEP input and built-in digital BEEP generator
  • Software selectable 2.5V/3.2V/4.0V VREFOUT
  • Up to four channels of microphone array input are supported for AEC/BF applications
  • Three jack detection pins; each designed to detect up to 4 jacks
  • Supports legacy analog mixer architecture
  • Up to two GPIOs (General Purpose Input and Output) for customized applications. GPIO0 and GPIO1 share pin with DMIC-CLK and DMIC-DATA
  • Supports mono and stereo digital microphone interface (pins shared with GPIO0 and GPIO1)
  • Supports anti-pop mode when analog power LDO-IN is on and digital power is off
  • Content Protection for Full Rate lossless DVD Audio, Blu-ray DVD, and HD-DVD audio content playback (with selected versions of WinDVD/PowerDVD/TMT)
  • 1dB per step output volume and input volume control
  • Supports 3.3V digital core power, 1.5V or 3.3V digital I/O power for HD Audio link, and 5.0V analog power
  • Intel low power ECR compliant and power status control for each analog/digital converter and pin widget
  • 48-pin LQFP ‘Green’ package

 

Is this assumption right? if so I am hoping the amp that is obviously powering the front audio jack will be good enough for the Pro 900's I have just purchased.

post #2 of 11

From  Hardware Features,  there must be front and rear amplified jacks:

 

".  Port-D/E/F built-in headphone amplifiers"

 

(The green jack, Line-out, is not  amplified)

 

I could not find any specs related to headphones driving.  Try to find a .pdf of your audio codec, on Google.

Anyway,  you can always get a Fiio amp,  or anyother vendor,  to drive your cans.

post #3 of 11

It is not only the Realtek chip itself that can make the difference between the front/rear outputs, but also its implementation on the motherboard. For example, if the rear jacks use 10 uF coupling capacitors (like it is the case on my motherboard), then the bass will be audibly rolled off with a headphone load, regardless of whether the ALC892 can "amplify" those outputs or not. Generally, it is the front panel that is intended to be used for driving headphones. However, it can also have flaws, like high output impedance (it is 77 Ω with my motherboard, and more than 200 on the rear connectors), or poor grounding that results in audible interference.

post #4 of 11
Thread Starter 
Quote:
Originally Posted by nagual View Post

From  Hardware Features,  there must be front and rear amplified jacks:

 

".  Port-D/E/F built-in headphone amplifiers"

 

(The green jack, Line-out, is not  amplified)

 

I could not find any specs related to headphones driving.  Try to find a .pdf of your audio codec, on Google.

Anyway,  you can always get a Fiio amp,  or anyother vendor,  to drive your cans.

I found the PDF

 

http://www.realtek.com/downloads/downloadsView.aspx?Langid=1&PNid=24&PFid=28&Level=5&Conn=4&ProdID=284&DownTypeID=1&GetDown=false&Downloads=true

 

Scroll down to the bottom where it says ALC892

 

Not sure what I have to look for with regards to amping in there...like a range of specs that certain headphones fit into? :)

 

I just want to know if this codec has a sufficent amping power to drive the pro 900's (It obviously has some kind of amp, low quality or not to drive headphones!) as i wont be getting an amp anytime soon to drive them.


Edited by SIDWULF - 9/21/12 at 9:29am
post #5 of 11
Quote:
Originally Posted by SIDWULF View Post
I just want to know if this codec has a sufficent amping power to drive the pro 900's (It obviously has some kind of amp, low quality or not to drive headphones!) as i wont be getting an amp anytime soon to drive them.

 

If your motherboard has 75 Ω output resistors like mine and as shown in the datasheet, then you may find the power to be lacking somewhat.

post #6 of 11
Thread Starter 
Quote:
Originally Posted by stv014 View Post

 

If your motherboard has 75 Ω output resistors like mine and as shown in the datasheet, then you may find the power to be lacking somewhat.


Does it say that in the ALC892 data sheet? I couldnt find the reference about the output resistors.

post #7 of 11

They are on the schematic diagrams in "Application Circuits". However, other Realtek datasheets suggest 33 Ω resistors for the headphone output, and it may not be the same on all motherboards.

post #8 of 11
Thread Starter 
Quote:
Originally Posted by stv014 View Post

They are on the schematic diagrams in "Application Circuits". However, other Realtek datasheets suggest 33 Ω resistors for the headphone output, and it may not be the same on all motherboards.


Well it has a squiggly line with 75 next to it in the front panel diagram which i guess is the Ohms? How is the Ohms related to the specs of my headphones which are 40 Ohm? Or is that the same thing?

post #9 of 11
Quote:
Originally Posted by SIDWULF View Post


Well it has a squiggly line with 75 next to it in the front panel diagram which i guess is the Ohms? How is the Ohms related to the specs of my headphones which are 40 Ohm? Or is that the same thing?

The output impedance must be =< 1/8 the impedance of headphones,  5 Ohm.

post #10 of 11

Additionally, a high output impedance does also reduce the maximum power available:

- the Realtek chip has a full scale output voltage of 1.2 Vrms unloaded

- with its 2 Ω internal output impedance, the 75 Ω resistors (if any) on the motherboard, and a 41 Ω headphone load, that drops to 1.2 * 41 / (41 + 75 + 2) = 0.417 Vrms, which is comparable to a small portable device like an MP3 player or cell phone

- the Ultrasone Pro900 is not a very efficient headphone, and needs 0.175 Vrms to reach 90 dB SPL (this value is probably subject to some random variation)

- from the above calculated voltage, the maximum sound pressure level these headphones would be capable of is 90 + 20 * log10(0.417 / 0.175) = 97.5 dB; for someone who likes to listen loud, or to highly dynamic music, that might not be enough

post #11 of 11
Thread Starter 
Quote:
Originally Posted by stv014 View Post

Additionally, a high output impedance does also reduce the maximum power available:

- the Realtek chip has a full scale output voltage of 1.2 Vrms unloaded

- with its 2 Ω internal output impedance, the 75 Ω resistors (if any) on the motherboard, and a 41 Ω headphone load, that drops to 1.2 * 41 / (41 + 75 + 2) = 0.417 Vrms, which is comparable to a small portable device like an MP3 player or cell phone

- the Ultrasone Pro900 is not a very efficient headphone, and needs 0.175 Vrms to reach 90 dB SPL (this value is probably subject to some random variation)

- from the above calculated voltage, the maximum sound pressure level these headphones would be capable of is 90 + 20 * log10(0.417 / 0.175) = 97.5 dB; for someone who likes to listen loud, or to highly dynamic music, that might not be enough

i'm learning alot...thanks


So i'm guessing the output is not 2ohm? But you add the internal output impedance and resistors together....so the output impedance of this codec is 77ohm? Really? wow...So I want 5ohms ideally but have 77ohm? hmmm...that dosen't make sense, i have seen posts from around the web saying it's 2ohm output impedance...what motherboard do you have? If it's true that its really 77ohm then what does that mean for sound quality? According to the page posted above if the output impedance does not =< 1/8 the impedance of headphones the bass might become more “boomy” and less controlled, thats it? The loudness dosen't concern me as i listen to below average volume levels.


Edited by SIDWULF - 9/22/12 at 1:09pm
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