Sound card line out V into LM3886tf

kgb_m3 · 4th January 2010, 08:57 PM

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?

wwenze · 4th January 2010, 10:40 PM

A voltage divider is good enough, if you're using a volume control you just need one resistor before the potentiometer.

kgb_m3 · 4th January 2010, 11:03 PM

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?

wwenze · 4th January 2010, 11:21 PM

kgb_m3 · 4th January 2010, 11:26 PM

Still kind of confused, I'm looking at chipamp schematic

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?

wwenze · 4th January 2010, 11:36 PM

Quote:

Originally Posted by kgb_m3

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.

kgb_m3 · 5th January 2010, 12:29 AM

^^Thanks for your help mang!

4th January 2010, 08:57 PM	#1
kgb_m3 diyAudio Member Join Date: Dec 2009	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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4th January 2010, 10:40 PM	#2
wwenze diyAudio Member Join Date: Mar 2008	A voltage divider is good enough, if you're using a volume control you just need one resistor before the potentiometer.

4th January 2010, 11:03 PM	#3
kgb_m3 diyAudio Member Join Date: Dec 2009	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?

4th January 2010, 11:21 PM	#4
wwenze diyAudio Member Join Date: Mar 2008

4th January 2010, 11:26 PM	#5
kgb_m3 diyAudio Member Join Date: Dec 2009	Still kind of confused, I'm looking at chipamp schematic 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?

5th January 2010, 12:29 AM	#7
kgb_m3 diyAudio Member Join Date: Dec 2009	^^Thanks for your help mang!

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