Home › Forums › temp › Using PC for audio source – Is earphone jack sufficient? › Using PC for audio source – Is earphone jack sufficient?
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The bottom line answer is yes, the earphone jack is just as good as a line-out jack.
Unless you own a high end “multi-media” computer, you likely don’t have a “sound card”. Your audio is handled by an audio chip on the motherboard, which is compliant with the INTEL AC’97 or HD Audio standards. My 5 year old computer has a Realtek AC’97-compliant audio chip.
There are a dozen or more manufacturers of audio chips that may be in your computer. In Windows XP, you can find your chip manufacturer by clicking Programs -> Accessories -> System Tools -> System Information -> Components -> Sound Device. Then search the web for a datasheet that matches what you see.
Your chip will most likely be compliant with the AC’7 spec http://download.intel.com/support/motherboards/desktop/sb/ac97_r23.pdf spec, but if it is new, it may comply with the INTEL HD Audio spec. For AC’97, here is the pertinent information:
– Headphone output:
– Full scale output = 1.41 Vrms.
– Load impedance = 32 ohms
– Level controlled by master volume control
– Line output:
– Full scale output = 1.0 Vrms.
– Load impedance = 10k ohms
– Level NOT controlled by master volume control
The outputs are fed by op amps inside the chip. Op amps have an ideal output impedance of 0 ohms, but real implementations have a little higher output impedance. A series resistor is usually added at the output mainly to prevent destruction if the output is shorted to ground. The Realtek ALC201 datasheet shows the output impedances as follows:
– Headphone output: 10 ohms
– Line output: 200 ohms
The difference is insignificant for feeding typical AM transmitters which have an input impedance of 10k ohms minimum.
Searching the web for computer audio “static” returns a ton of hits. The consensus seems to be that the software drivers are to blame, not the computer analog audio output scheme.
Here is a VERY important thing to consider if you are using a mono transmitter. Don’t select any advanced audio functions like stereo-wide or surround sound or whatever in your sound setup. These modes add phase shifting between the two stereo channels. When you mix the two channels to mono, the phase shifting will cause weird and undesirable reinforcements and cancellations.
Another important thing to watch out for when using a headphone output. The level is controlled by the Master Volume Control. Be absolutely sure the master volume is set to MAXIMUM. This will give you the highest audio level and the highest margin above the noise floor of the computer audio circuit.