Active speakers with built-in test signals

Sometimes it’s nice to have a tone or sweep generator or even some white noise to test your speakers. SigmaStudio has a good selection of “sources,” even for the ADAU1701, that don’t require a lot of instructions. I’ve never used them before, but I’m finding them very useful for this next round of active speakers that are starting to take shape. This post describes how those built-in test tools are implemented.

The ADAU1466/SSM3582 boards from the ElectrACC Store at AliExpress have quite a few inputs, but I’m only interested in the Bluetooth, SPDIF and analog sources. Once I got all that basic switching straightened out, I added a “Test” button and a new screen to control the sources:

This feature requires some new SigmaStudio “code” for the sources, along with the code that controls the switching. Here is the new section of SigmaStudio code:

The Mute is just an extra white noise generator that is turned off, and the VCO uses the potentiometer on the ADAU1466/SSM3582 board to control the oscillator frequency.

The ESP32C3 code to control the new blocks is fairly easy to write, as it only requires 3 new commands that reuse a lot of existing code. The new commands are: ADAU1466_Source, ADAU1466_Sine, and ADAU1466_Sweep. The VCO and white noise sources don’t require any software control, so they only need to be selected, without any other CPU control. I’m still working on the Sweep code to get a good combination of range, step size and sweep speed, but it’s coming along. These built-in test sources will be a nice feature to incorporate in all future active speaker designs.

On another topic, I had made a throw-away desktop speaker for testing the dipole compensation, using some cheap $1.29 drivers from MPJA. I’ve had to replace all the drivers because those SSM3582 amps have enough power to completely fry the voice coils when the volume is accidently turned up too high. Even though those amps aren’t rated for high output at 8 ohms, I think they will do fine for desktop speakers or the very efficient Martha speakers.

Overall, I’m still impressed with those ADAU1466/SSM3582 boards. For $120 shipped you get a nice ADAU1452/ADAU1466 DSP, plus Bluetooth and analog input that uses a “decent” PCM1808 ADC chip. You also get SPDIF I/O and 8 very high-quality power amps that can provide moderate power at 4 Ohms. With 2 Ohm loads and a 16V supply, they are rated at 50W each. If you can figure out what to do with all of those amps, these boards can be a lot of fun. These boards are an excellent “deal” for the price.

Leave a Reply

Your email address will not be published. Required fields are marked *