This is a quick post to showcase 100W 4 channel AF dummy load which we build to test the output stages of audio power amplifiers. This dummy load use 4, 8Ω 100W wire wound resistors which are available in eBay. In this unit all 4 resistors are mounted on 170mm × 40mm × 60mm high gauge aluminum heat sink.
As you may have heard, the iPhone 7 is ditching the 3.5 mm headphone jack in the name of progress and courage. Whatever your take on that, it leaves the end user out in the cold if — for instance — their preferred headphones still use the old format. Here to save you from an untimely upgrade is YouTuber [Kedar Nimbalkar], who has modified a Bluetooth Smartwatch to incorporate a 3.5 mm jack to allow continued use your current headphones.
After opening up the smartwatch [Nimbalkar] removes the speaker, solders in a 3.5 mm headphone jack and clips out an opening in the watch’s case that maintains the watch’s sleek exterior.
This mod is a bit of a catch-22 — losing out on hearing any notifications from your phone unless your headphones are plugged in and in your ears, and you only get mono audio output using this method; some tinkering with the software might alleviate this issue. However practical this may be for you, workarounds like this one remind us that we can still achieve the functionality we want though innovative expertise. Challenge yourself!
Class D audio amplifier an efficient amplifier by Infineon Technologies, Link here
A Class D audio amplifier is basically a switching amplifier or PWM amplifier. There are a number of different classes of amplifiers. This application note takes a look at the definitions for the main classifications.
An application note from Analog Devices about AD5933, this provides a low cost substitute to expensive test equipment like signal generators, oscilloscope and voltmeters in getting the speaker’s impedance profile. Link here (PDF)
This application note describes a circuit architecture using the AD5933 that allows the system designer to measure the impedance profile of the loudspeaker and integrate this circuitry into the audio signal chain. This offers many benefits. Upon system power-up, for example, the circuitry provides the ability to measure the impedance profile and thus the acoustic properties of the loudspeaker, enabling direct comparison to a factory calibrated profile stored nearby. Any changes in the impedance profile are detected and further diagnostics are carried out, preventing premature damage.
A pretty older application note about the serial audio interface by Cirrus Logic. Link here (PDF)
It may come as a surprise to those trying to make their initial investigation into audio systems design that there is a de-facto standard for transferring audio data within a system. Despite the differing naming conventions used within the industry, these apparently different interfaces are essentially identical. For the sake of simplicity, we will use the term Serial Audio Interface (SAI) in this discussion. The Serial Audio Interface is by far the most common mechanism used to transfer two channels of audio data between devices within a system; for instance, from the analogto-digital converter to the Digital Signal Processor (DSP) and then the digital-to-analog converter.