I have been working on small projects recently like the clock and other broken odds and ends.
One project is an Echo dot second gen speaker dock. It started getting a popping noise on the speakers when there wasn’t any input. Finally the dot started to reboot. I figured it would be a power issue. It had six 220 uf electrolytic caps and a 470 uf one. I just happen to have a kit of caps so I changed them all out even though they tested ok with a cap meter. The problem seemed to happen after a warmup period so even if the caps tested OK they might be breaking down under a load. Nope, that was not the problem. I could watch the power rail bounce between 5 and 4.3 vdc but could not identify the PS section due to everything being SMD. There was a buck converter downstream but it had about 8 vdc going into it which was also bouncing with the input voltage. I put a current/voltage meter on several USB wall plugs and it was only drawing about 300 ma. I tried to find the different sections following the power rails but they went back and forth across the PCB. Enough time to not find anything concrete so I found a 15 watt per channel amp on Amazon for about $2.50. The one in the dock claims to be 10 watts/channel but I doubt it. The speakers are really cheap.
So when the amp comes in, I will also add a Bluetooth module to the mix and the speaker can do double duty. I will omit the 3.5 mm audio input that is available on the existing unit. It will go into the bathroom for noise during the weekly cleanup!
Well the project was a lot of fun and I learned a lot about the state of new audio amp behaviors.
This is the audio amp I ended up using. It has very good specs for the price. It sounds amazing! I have plans to use it on some other projects.
I purchased these Bluetooth modules awhile ago and are very versatile power wise.
I used a 12VDC power source for the amp and needed 5VDC for the Echo and BT. This is what I used for the 5VDC supply. It is again very versatile and robust.
With everything wired up, I powered up the speaker to be greeted with a horrible whine and static! Removing power to each component, I realized that there was a ground loop from the audio amp to the Echo and BT adaptor. I tried to power the Echo on its own USB power but the sound quality through the 3.5mm audio jack was horrible. Back to the drawing board. After refreshing my knowledge of audio filters (60’s and 70’s cars were horribly notorious for audio noise when adding aftermarket stereos. The worst one I made workable was a '57 VW bug with a 6 VDC system and a 12 VDC converter!) I found this transformer based isolator.
I gave up on trying to integrate the Echo back into the base and ended up sending the audio over BT while on its own PS.
The speaker is now only BT but sounds better than ever. It could use some cosmetic help with the external wiring but not a deal breaker.
The whole experience made me appreciate the engineering that went into the original amp/power supply and remind me on how much your forget when you do not use certain skills.