The Saga Continues...

Here's a brief view of the next steps in the Sotabeams Variable Bandwidth Filter use.

This is the very plain-Jane external amplifier circuit that I put together to test the filter using an external speaker as opposed to headphones.

The little LM386 audio amplifier circuit tacked together.

Well, my thoughts on the use of an LM386 as an external audio amplifier are mostly mixed.  The audio is there in terms of amplification.  Most of us who have used the LM386 know that it works as advertised.  The downside is that the audio is poor.  The specs on the LM386 just aren't going to give you the kind of audio you are looking for to follow the output of the Sotabeams variable filter.  You, like me will want to hear some full audio like something close to the audio that you get when using earbuds headphones with the Sotabeams filter direct.

I can say in retrospect that the filter used with decent earbuds is pretty adequate, and the filter works as advertised.  If you want good external speaker audio, then you will need to come up with something a little more elaborate that the LM386-based external audio amp.

Press HERE to see a short video clip of the LM386 audio to an external speaker.

Here is the very simple circuit from the Radio Shack Engineer's Mini-Notebook series by Forrest Mims, III.  I recommend building this circuit just for fun if you are new at playing with circuits and want an almost "no-fail" little project just to have fun.  As hams, we should be building circuits (in my opinion), to keep up our skills and experimentation.

The above circuit is simple and easy to build, and you can use it to amplify low level audio.  It is also fun to build with your kids or grandkids to teach them something practical that will let them say "I did that!"  Below is an improved LM386 circuit that I found at circuitbasics.com   I have not built this circuit yet to test it out.

A possible LM386 circtuit that is designed to have better audio

Obviously, I feel strongly that to use an external amp following an audio filter like the Sotabeams variable filter...well it needs to be a little more "full bodied"than using an LM386.  I would be curious to hear about your ideas for a 9 to 12v small audio add-on filter for the project that could kick out a little stronger audio.

73, Mark 4x1ks