Sound card line out V into LM3886tf - diyAudio
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Old 4th January 2010, 08:57 PM   #1
kgb_m3 is offline kgb_m3  United States
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Default Sound card line out V into LM3886tf

I'm in the process of building a custom LM3886 stereo amp that will be getting its line level signal from my PC sound card. According to the sound card it pushes 3v RMS on the output
Auzentech, Inc. X-Fi Forte PCI-Express Soundcard : World First soundcards for Music, HTPC, and Gaming

Input level on the LM3886tf amp says 1v max on the data sheet.

What should I do to avoid feeding 3v into the amp's positive signal input? Also what gain would you guys suggest setting the amp to? I would imagine 20 - 30 should be good considering the sound card acts as a pre-amp. Last thing is debating on the input dc coupling capacitor on the amp itself. My sound card has dc coupling caps on the output so it wouldn't make much sense using one on the input right?
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Old 4th January 2010, 10:40 PM   #2
wwenze is offline wwenze  Singapore
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A voltage divider is good enough, if you're using a volume control you just need one resistor before the potentiometer.
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Old 4th January 2010, 11:03 PM   #3
kgb_m3 is offline kgb_m3  United States
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So I understand it like this,

RCA - - -> potentiometer 25k - - -> resistor 1k - - -> input impedance resistor 22k - - -> amp input

looking at it the pot vertical from rca to ground, middle out to 1k to the top of the 22k that's also vertical to ground and v out to the input of the amp?
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Old 4th January 2010, 11:21 PM   #4
wwenze is offline wwenze  Singapore
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Click the image to open in full size.
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Old 4th January 2010, 11:26 PM   #5
kgb_m3 is offline kgb_m3  United States
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Still kind of confused, I'm looking at chipamp schematic

Click the image to open in full size.

so would I run the 50k resistor into the 25k Pot, then still use the 1k(R1) and the 22k(R2) before the input to pin 10 on the amp?
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Old 4th January 2010, 11:36 PM   #6
wwenze is offline wwenze  Singapore
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Quote:
Originally Posted by kgb_m3 View Post
so would I run the 50k resistor into the 25k Pot, then still use the 1k(R1) and the 22k(R2) before the input to pin 10 on the amp?
Yup.
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Old 5th January 2010, 12:29 AM   #7
kgb_m3 is offline kgb_m3  United States
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^^Thanks for your help mang!
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