Simple Products Details

The Bluetooth Receiver Modules

The AS21 and TB21 are actually specific models of pre-assembled amplifier boards (usually from the brand Wuzhi Audio) rather than just raw chips.

• ZK-AS21: This is a powerhouse for 2.1 systems.
• Channels: 2.1 (Left + Right + Subwoofer).
• Power: Usually around 220W total ($50\text{W} \times 2$ for highs + $100\text{W}$ for the sub).
• Best for: A "Boombox" setup where you want dedicated bass.
• ZK-TB21: The "little brother" to the AS21.
• Channels: 2.1.
• Power: Around 150W total ($50\text{W} \times 2 + 100\text{W}$). It uses the TPA3116D2 chip, which is legendary for being efficient and clean.

The A158 (PAM8403)

The A158 usually refers to a specific small-form-factor board using the PAM8403 chip.

• Type: Class D Digital Amplifier.
• Power: $3\text{W} + 3\text{W}$.
• Voltage: Runs on 5V (perfect for USB power or a single Lithium battery).
• Best for: Ultra-portable projects or desktop "fidget" speakers.

The 3-inch Speaker Factor

A 3-inch driver is a "sweet spot" size. It’s large enough to move some air for decent sound but small enough to keep the enclosure portable.

• For AS21/TB21: You would use two 3-inch speakers for your Mid/Highs and a larger 4 or 5-inch speaker for the Subwoofer channel.
• For A158: A 3-inch full-range speaker is perfect. Since the A158 only puts out 3W, look for a speaker with high sensitivity so it sounds louder with less power.

Comparison Table

Quick Tips for Your Build:

1. Power Supply is Key: If you use a TB21 or AS21, don't skimp on the power brick. A 24V 5A supply will make a world of difference in bass punch compared to a 12V supply.
2. Enclosure: Even the best 3-inch speaker will sound "thin" without a box. Use MDF or thick plastic and seal the edges to prevent air leaks.
3. Ground Loop: If you hear a "hum" or "buzzing" when Bluetooth is connected, it’s often a ground loop. Using a dedicated isolated power module for the Bluetooth side can fix this.