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Old 19th April 2013, 07:07 AM   #1
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Default Mixer + LM3386 amplifier

Say I want an amplifier that is able to mix 2 audio streams.

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1. Would this work? Am I missing something?

2. I suppose the 500k ohms R5 would make the amp susceptible to hum?

3. Am I getting an overall gain of 10x?

4. Is there a better solution?

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Old 19th April 2013, 11:56 AM   #2
JMFahey is offline JMFahey  Argentina
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Location: Buenos Aires - Argentina
Sorry but;
1) you need to add input and feedback resistors to both Op Amps.
Read something about Op Amps, specially inverting Op Amps.
2) no, it's connected between 2 low impedance points which are physically very close.
3) your Op Amps have a gain of "0" , so ..... no.
And you are using the LM3886 in a very crude way.
It *might* work ... but that's not the point.
Use the datasheet example.
4) yes, of course.
Read a little more and you'll do it on your own
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Old 19th April 2013, 02:39 PM   #3
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Thank you.

1. Ok regarding the input resistor and the on the OPA2107. For the LM3886 I suppose the R1 and R3 can not be counted as the input resistor?

2 Ahh, good to know. I intend to place the OPA2107 at the volume pot and the rest can stay with the LM3886.

3. For the OPA2107, I intend it to have a gain of 1 and followed the datasheet example. But I suppose the correct way is to include gain setting resistor at 1:1 ratio? For the LM3886, I suppose R1-R5 doesn't work as gain setting resistor? Which to my understanding, is a voltage divider from the output to ground?

4. I knew it.
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