I was hoping to be able to do one post a week, so far that isn't happening. Works been crazy busy but I love what I do so I am more than happy to do it.
Anyway....
I am working on a side project and thought this would make a good how to. Most of the electronics projects that I do are focused on audio and this one is no different. This is a small three channel mixer going made with a LM368 amplifier. (data sheet:
http://www.ti.com/lit/ds/symlink/lm386.pdf )
This particular setup is to mix three microphones (the cheap kind you get at radio shack etc) into one output. This output can drive a small speaker or be used as a source to some other device.
Starting with the stereo jacks ( I didn't feel like looking for mono ones in Eagle), the signal goes into a pot that is used for adjusting the level of the incoming signal. The cap (C49,C56,C50) is there to block any DC coming from the source.
As its used here the LM386 has a gain of 200, if you get rid of C46 and C48 the gain will end up being 20. With the lower gain it would be more suited for higher level signal devices like an MP3 player.
The 250uf cap (C47) is there to block the output DC coming from the LM386 since it is biased at 1/2 of Vin on the output. DC on the audio signal path is usually a bad thing.
If you get creative you could set this up as a stereo mixer. You would just need to copy the everything after the jack and use the right channel on the other side. This could also make a very useful portable headphone amp.
That is pretty much it, not much to it really. The setup here for the LM386 is taken straight from the data sheet as a reference design. There are some others included as well. If you have any questions please ask or if you would like to see something else let me know.
(be careful though, you do not want to over drive the what ever you are using after this....you have been warned and I take no responsibility if you let the magic smoke out).
