Building a radio (Part 3) - noise reduction

So with the code working after part 2 I added the amplifier and speakers. There was nothing complicated here; just running cables between them all and making sure that the amp had some power.

And when I fired everything up, it worked! Sort of. The sound was dominated by a low frequency hum that was annoying after a few seconds and would be unbearable after a few minutes. What to do?

Luckily I’d read something about this on a forum. Someone else had encountered this problem (to be fair, just about everyone probably has) and they solved it with a pair of audio isolation transformers. What are they specifically? No idea, but I know the basic idea of a transformer and thought it had to be worth a go. I found a couple on eBay that matched the specification I’d read about (one per audio channel) and ordered them in. For about £5 it seemed obvious to try.

Audio isolation transformers mounted on a board — The audio isolation setup.

And they work! The dreadful hum is gone! The only drawback is that the didn’t fit well onto the breadboard along with the other components because they had extremely thin wire legs that fitted poorly. So I fired up the soldering iron and installed them first. Here they are with the necessary cabling. Going from bottom to top, there is the audio in from the amplifier then the wires to link the channels to the transformers. There are the transformers themselves and the audio out to the speakers at the top. The longer black wires supply ground connections to each transformer.

Why did I set this up on its own prototyping board? Because I thought it would be useful to have something that was transferrable and could be moved to something else in the future. I want everything to be as modular as possible so I can swap parts out as I learn things (I am hoping to learn things).

Building a radio (Part 3) - noise reduction

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