I had on hand some of these 10Pcs XPT8871 5V Mono Channel Digital Audio Lithium Amplifier Board for Arduino (affiliate link) and they were the right size so I'd give them a try.

Since I was aiming for 1W 8ohm speakers, I was wondering what the peak voltage I might see would be:

V = (P * R) ^ 0.5, or (8) ^ 0.5, or 2.83V peak

On the badge there's a choice of 3.3V or 5.0V.

Amp Specs:

Specs from eBay:

• Chip: XPT8871
• Input: DC 5V 1A
• Output power: 5W
• (also a schematic of the board)

Doing some more research I came across this link which corrects and expands on that:

• Input: 2.0V - 5.5V
• 5W (2Ω load) and 3.5W (3Ω load), 3W (4Ω load)
• AB / D switching (Judging by the image of the board, it looks like "Mode" is connected to GND so it's in A/B mode)
• Compatible with LM4871 (although this seems suspect)

There's also a link to the datasheet but it's mostly in Chinese so it's only so helpful.

While the charts in the PDF are in English, they're not numbered, but here's some choice notes:

• For VDD = 3.3V, RL = 8 ohms, THD+N shoots up past 0.4W
• For VDD = 5V, RL = 8 ohms, THD+N shoots up past 1W

If one is to believe it's compatible with the LM4871, the datasheet offers more information, particularly:

• Figure 22 - clipping voltage for 5V is ~0.3V, and for 3.3V is ~0.2V

5V?

At first I tried the 5V source but it was way too noisy and had drop outs - I thought about filtering and adding a cap to get past the drop-outs, but I decided to try the 3V3 source first. I think the issue with 5V is because of the MP3401 Boost circuit, see the description and schematic towards the end of this post.

3.3V?

This worked much better but I could tell I was over-driving the input to the amp and getting distortion. I'll tackle that in the next post.