Hello NFARL members! Lee, N4WYE, here. As many of you know, there’s nothing quite like the satisfaction of rescuing a piece of gear and getting it back into top shape. I recently had a little adventure with a pair of Monoprice Pro Audio Series Model 605300 powered speakers that I picked up. They're excellent speakers, and they truly made my home computer setup sound professional, even making my Hermes Lite SDR transceiver sing.
The Fryer, Not the Amplifier
The only snag? One channel was completely inoperative. Since I've shed my bench full of test equipment over the years, I called on my good friend Dave, KO4USA, for some troubleshooting help. We expected a simple fix, but what we found was startling! The original Class AB analog amplifier/power supply had enough power dissipation to literally cook the connector and the printed circuit board. Talk about thermal runaway!
Dave worked his magic and was able to repair the amplifier by replacing an operational preamplifier IC. I was careful to turn the speakers off every night to try and prevent another burnout.
But as Murphy’s Law often dictates in electronics, it failed again after only three weeks.
Out with the Old, In with the Digital!
That was the last straw. It was time to pull out that failure-prone Class AB analog amplifier and replace it with something far more robust and efficient: a Class D digital amplifier.
For those who love efficiency (and who among us hams doesn’t?), Class D amps are the way to go. They run at an impressive 90% efficiency and generate significantly less heat —meaning no more fried connectors!
I quickly sourced the perfect little Class D stereo amplifier. It offers 80 Watts of power and operates on 12-24VDC, all for under ten dollars! Plus, it came with handy gain, bass, and treble controls.
Victory is Sweet and Cool
The result? The unit now runs much cooler, and because it draws so little power, I just leave it on all the time. The best part, though, is the sound! It’s rich in tone, crystal clear, and has plenty of power.
This project was a great reminder that sometimes, the easiest and most modern solution is the best one. Digital wins again!
Got a piece of gear you’ve rescued or digitized? I'd love to hear about it!
73,
