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Old 30th July 2011, 10:07 PM   #1
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Default little amp, newbie help?

okay, so im gonna go to this lan in october, however, my headset is pretty good at blocking out the sounds around me.

so i came up with this idea.

basicaly, its a box with a little mic, that splices the mic sound into the headphones

so here is what i thought:

mic--preamp--headphoneamp--out

lineout from pc/playstation 3--headphoneamp--out

so three inputs and two outputs, left in right in and mic in, then left out and right out, (with mic on both)

i need to be able to adjust both the lineout volume and the mic volume independently.

heres my problem... how the hell do i do that??
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Old 31st July 2011, 03:00 AM   #2
gootee is offline gootee  United States
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Opamp circuits. There's one called a Summing Amplifier, which you can use to combine the signals from the mic and the line, for each channel. Upstream from those, you could have a buffer amplifier for each input. Somewhere in there, you can have a pot for each input's volume.

Go to National Semiconductor | High-performance Analog and download Application Notes AN-20 and AN-31. They contain schematics of the building-block circuits that you can use.

Remember to add decoupling caps on all of the opamp power pins.

Tom
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Old 31st July 2011, 10:07 PM   #3
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i have no idea what you said, well, i have some.

i googled buffers, and found out there was two kinds, i would think that voltage buffers are the ones i would need.

so i could do something like this:

Click the image to open in full size.
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Old 31st July 2011, 11:30 PM   #4
gootee is offline gootee  United States
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That's pretty-much correct. And each of the summing amplifiers would have an output.

But maybe I misunderstood what you were trying to do. Do you just want to listen to the mic OR the source, but not both at the same time? If so, you don't need to sum anything. You can just use a switch, right?

What does it take to drive those cans of yours? Do you know their impedance?

Download these, anyway:

http://www.national.com/an/AN/AN-20.pdf
http://www.national.com/an/AN/AN-31.pdf
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Old 1st August 2011, 10:21 AM   #5
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well messured with a multimeter they are 36 ohms, but im not sure thats the correct way to messure it,

they are sony MDR-XB700 50 mm driver.

i do want to listen to both the mic and the lineout of the pc at the same time

thanks for the help btw, im not that good at audio
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Old 2nd August 2011, 04:31 AM   #6
gootee is offline gootee  United States
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Try it in LTSpice. It's a free download from linear.com.
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Old 2nd August 2011, 05:06 AM   #7
godfrey is offline godfrey  South Africa
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Maybe you don't need to build anything. I don't know about PS3s but PCs normally gave a Mic input, so you could plug the microphone in there and let your sound-card do the mixing for you. The standard Windows "volume control" software has a mixer that lets you set the levels separately for various inputs etc.
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Old 2nd August 2011, 06:06 AM   #8
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The easiest way of setting up the mixer is to open that annoying windows messenger icon that sits onthe status bar by the clock... inside it you will find and audio wizard... yeah,I know, odd place, but it seems to work best.
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Old 2nd August 2011, 10:50 AM   #9
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well my problem is that i dont have a microphone that goes in via jack, so it doesnt go in to the realtek chip, therefor it cant mix it
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Old 2nd August 2011, 10:55 AM   #10
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btw, how would i go about finding the inductance in LTSpice?
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