KTELI ST21 2.1 Digital Power Amplifier Board - Compact 2x100W+200W

In this review the KTELI ST21 is judged as a compact 2.1 channel amplifier board that suits DIY audio builders and compact home theater upgrades; the single biggest reason to buy is its high output-to-size ratio, delivering up to 105W per stereo channel and about 208W to a subwoofer from a 24-30V supply while offering Bluetooth 5.1 connectivity. The board is practical for people who want a powered compact solution with multiple inputs, and the review focuses on real-world compatibility, power needs, and how the board handles different speaker impedances.

Key Features

• 2.1 Channel Output: Provides left and right channels plus a dedicated subwoofer channel so users can build a compact two-speaker plus subwoofer system with clear separation.
• High Power Capability: Delivers up to roughly 105W per stereo channel and up to about 208W to the subwoofer at higher voltages, making it suitable for medium-power home audio setups.
• Wide Voltage Range: Operates from 12-30VDC with a recommended 24-28V, letting installers choose a DC supply that balances available current and desired output.
• Bluetooth 5.1: Built-in Bluetooth with about 15m transmission distance for easy wireless streaming from phones or tablets without extra dongles.
• Multiple Inputs: Supports Bluetooth, AUX, U disk and sound card inputs, which allows connection to legacy sources as well as digital media on a thumb drive.
• TI TPA3221 Amplifier Chips: Uses proven TI power amp ICs for the left and right channels to provide efficient amplification and protection features suited to powered speaker projects.

Who It's For

The ST21 is aimed at hobbyists, builders of compact home theater or desktop speaker systems, and installers who want a single board to drive stereo speakers plus a subwoofer with both wired and wireless inputs. It is especially useful where space is limited but higher subwoofer output is desired.

It is not the best choice for users who need a built-in enclosure, plug-and-play consumer AV receiver features, or those who cannot provide a suitable 24-28V DC supply rated for 10A or more. Also, buyers who require digital room correction, HDMI switching, or network streaming should look elsewhere.

Pros & Cons

Pros

• Generous power output for stereo and sub channels relative to the module's compact footprint.
• Flexible input options and Bluetooth 5.1 make source hookup straightforward for most setups.
• Wide operating voltage gives installers options to tune power versus heat and efficiency.

Cons

• Requires an external DC supply (recommended 24-28V, 10A) and basic wiring skills to install safely.

Specifications

Product type	2.1 channel Bluetooth amplifier board
Channels	Left, Right, Subwoofer (2.1)
Recommended supply	24-28VDC, 10A or greater
Operating voltage range	12-30VDC
Power output (approx)	Left/Right up to 105W@30V 4ohm; Sub up to 208W@30V 2ohm
Bluetooth	Bluetooth 5.1, ~15m range
Amplifier chips	TI TPA3221 (stereo channels)

Our Verdict

The KTELI ST21 board is a solid value for DIYers and compact audio system builders who need robust subwoofer output and flexible inputs without a bulky receiver. It offers impressive power for its size when paired with a proper 24-28VDC supply, and the inclusion of Bluetooth 5.1 and multiple inputs makes it a practical core for a small home theater or powered speaker project.

Frequently Asked Questions

What power supply do I need?
You should use a DC supply within 24-28V and capable of supplying at least 10A for reliable performance and near-maximum output.

What speaker impedances are supported?
The left and right channels support 3-8 ohm speakers up to 100W each; the subwoofer supports 2-8 ohm drivers up to 200W.

Does it have wireless streaming?
Yes, it includes Bluetooth 5.1 with a typical transmission distance of around 15m for wireless audio streaming.