Wednesday, March 22, 2023

But Does It Amplify Audio?

I've finished building the first stage of my Elenco AM/FM radio kit, which is an audio amplifier. The build instructions now recommend a series of tests using a multi-meter, audio generator and oscilloscope. While I'm all for doing these formal tests, I couldn't help but take a detour and try my own more casual experiment.

Here's my thinking: if I've built an audio amplifier, doesn't that mean it should amplify audio? That is, if it I take an audio signal from my cellphone's headphone jack, shouldn't I be able to hear it over the speaker? I really wanted to find out.

I picked up a set of these audio jack adapters that allow you to connect arbitrary wires to any 3.5mm headphone jack. Using a bit of hookup wire and some alligator clips, I connected one lead of the headphone cable to ground , and the other lead to the audio amplifier's input.

On my cell phone, I switched over to YouTube and hit play on a video. I then cautiously turned on the radio, increasing the volume every so slightly. And....

Success! I could hear the cellphone's video playing through the radio's audio amplifier. Whoo! I'm #1, I'm #1!

To anyone with even a bit of electronics experience, I'm sure you're shaking you're head. I'm using an audio amplifier to amplify audio; of course it works. And technically, I didn't even build the audio amplifier. All I did was wire in an audio amplifier chip (an LM386N) to a speaker with a few resistors and capacitors to help it out.  But still, to have my mental model match up to hardware I've personally built was quite a rush!

Next up: I'll get a bit more technical and the measure gain of the amplifier I've built. This is fun!

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