An Audio Amplifier for the Bookshelf Speaker Project
When looking for an inexpensive audio amplifier to power your DIY Speaker project or Speaker Kit, TPA3116D2 & Co. based amplifier boards are easy to find.
And they certainly get the job done from an amplifier point of view, and are fairly cheap. The problem you likely will run into, however, is noise. When your system has a constant humming sound (especially noticeable at low volume or when the audio source is muted), you have a noise issue. The source can be manifold: The AC/DC power adapter, the audio source (FM radio or Bluetooth module), or the amplifier itself. That’s why Class D Amplifiers have not the best reputation when it comes to audio quality…
Common troubleshooting actions include isolated (DC/DC) power supplies, adding LC filters / Ferrite beads for decoupling of the power and audio signals, and using isolation audio transformers to break possible ground loops. The latter – using isolation audio transformers – will most likely help the most. But every system is different, and here we focus on the amplifier.
The Amplifier
While all these actions can help to mitigate the existing noise, depending on what causes it, changing the amplifier used and reduce the noise introduced to the system tremendously in the first place!
In 2018, Infineon Technologies acquired Merus Audio, a Copenhagen, Denmark based startup company. With the acquisition, Infineon inherited Merus’ audio amplifier line.
The announcement reads:
“With the announcement of a new category brand MERUS™, we welcome a new product family to the class D audio amplifier portfolio! MERUS™ integrated multilevel class D audio amplifier ICs, based on the multilevel switching technology, support a supply voltage range of 4-26 V. With a considerably low input power consumption and high power output in a small form factor, these devices do not compromise the produced sound quality.”
The proprietary multilevel switching technology promises to be very ‘smooth’ and to reduce noise significantly. Let’s give it a try!
The Custom Audio Amplifier Board
There are reference boards available, but in order to integrate volume control and a power switch (through a Bourns stereo audio potentiometer), we spun our own board based on the reference design:
TPA3116D2 out – MA12070 in , and… the difference was like day and night.
- The audio noise coming from the amplifier was not noticeable anymore
- The board is tiny (45mm x 50 mm)
- No bulky heatsink needed
- The power consumption is very low and scales with the load (volume)
The Finished Project
This Merus amplifier board is used in this project and is actually quite powerful: Bookshelf Speaker with FM Radio and Bluetooth audio
