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I was going to build
Amplifier with Gain = 20
Minimum Parts

Fromthis datasheet But I have no Idea how to put the signal on.
I think that the signal is Vin (pin 3)  but that is one cable when a headphone has three cables. I know the red wire is right and the blue is left and the other is comm so I onley need 2. Because there is one input I need to make it one cable. Would this work (I will test what resistor I need with a voltmeter later).
If I am wrong about there olny being one input can someone explane to me how to wire it.

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## 7 Replies

So, which do you want to do? Use a switch to change from left to right (and back again) or combine the signal (convert from stereo to mono)?

I can give you pointers on how to do both. Just let me know which one you are interested in using.

As for the input, yes, pin 3 is the audio input. You would attach the positive wire (the blue or red wire) to pin 3 and the negative wire (common) to ground (pin 4).

Qa

David97 (author)2011-09-20

If I wanted to make the speeker as a middle speeker i was just going to tie the blue and red leads together.

Quercus austrina (author)2011-10-12

Sorry to take so long to reply.

Try this for mono:
------------
Red wire to 300 ohm resistor -
Blue wire to another 300 ohm resistor -
Connect the other ends of both 300 ohm resistors together and feed that to another 300 ohm resistor then attach that to V in at pin 3 as per the schematic. So that is three (3) 300 ohm resistors total.
------------

You want to do this so that you can keep the stereo effect for a stereo amp while combining the left and right for the center channel. It is done for isolation purposes.

You might need a little more gain. If so, use the "Gain=50" schematic and substitute a 10K ohm potentiometer for the 1.2K ohm fixed resistor in the pin1/8 path, connecting the outer lugs to pin 1 and the 10 uF capacitor. Then connect the center lug to the lug at pin 1. Play the music with maximum input and adjust this gain for maximum clear volume or until it matches the other stereo volume, whichever you prefer. You may opt to keep the potentiometer there or you can measure the resistance between the lug at the capacitor and the center lug and use the next lower standard resistor value to replace the potentiometer.

Qa

Re-design (author)2011-09-18

Headphones are stereo.  This amp is mono.  The input to this amp is on pins 2 and 3.  To get stereo you need two of these.

There is a version of this that is stereo built into one chip but I don't remember the number right offhand.

David97 (author)2011-09-18

I know that so I was going to have a switch that changed it from left to right.

iceng (author)2011-09-18

As Re-design points out you need two to tango ( stereo ) and the Gain 20 ckt.

David97 (author)2011-09-18

I am having trobble uploading pics I will post as soon as possable