Geeetech MP3 Shield with TPA3116 powered 2*100w amp - will it blow up?

Hi there,

I’m wondering if anyone might be able to answer what is hopefully a relatively simple question please?

I have a project (a fully functional BB8 droid) which is using (amongst other things) an Arduino Uno with a Geeetech MP3 shield, and a cheap 100w amp to power a speaker.


Similar MP3 Shield

Reading up on the MP3 shield there are warnings floating around about using it to power an ‘external’ amplifier, because of the risk of a ground loop. My Project only uses one power source (12v battery) to power everything, including the Arduino (via a voltage regulator set to 9v) and amplifier (which uses 12v), so do I still need to be concerned about amplifier protection? If so, what might my options be please?

Thank you for any help you can provide :slight_smile:

Edit, typical noob move, posted in the wrong forum. Sorry, I’ve reported my post to admin for moving/removal. Doh!

"Star Grounding"

Sometimes those audio shields with headphone outputs use a virtual ground at the headphone output. That’s done so you can get AC out (positive and negative voltage swing) relative to the virtual ground with a single-ended power supply.*

Connecting/shorting the virtual ground to the actual ground at the amplifier can cause “problems”. If the manufacturer of the MP3 shield doesn’t tell you how to deal with a virtual ground, check the datasheet for the chip.

And, any clicks, pops, hum/buzz, loud test-tones, or loud distorted voice/music at 100W can fry most speakers… It’s kind-of “dangerous” to play-around with high power until everything is tested-out and stable. (A 100 W speaker is designed for handle occasional 100W peaks at around 10W average.)

and amplifier (which uses 12v),

You can’t get 100W from 12V. 100W into 4-Ohms requires 20V RMS, which is 28V peak and 56V peak-to-peak. Double that with an 8-Ohm speaker. That requires a power supply slightly higher than 56V for a normal single-ended output or slightly-more than 28V with a bridge output. (High-power car amplifiers have an internal DC-DC voltage booster, to get high power from 12V.)

  • DC blocking capacitors can will allow positive & negative voltage swing relative to the true ground, but it takes relatively large-bulky capacitors to pass the bass frequencies into headphones. (I don’t see a pair of output capacitors on your board.)

Thanks Doug.

I decided to take the plunge and plug it in at a low volume. It seems to work OK with no odd noises :slight_smile: