ProtoDAC TDA1387 X8 project

[hifinet]

Hello everyone, this is my first post on this forum. Glad to be with you.

A year ago, I built a ProtoDAC:
    Kit sold by Mark on EBay
    + RPI-4B
    + iFi Power supply
    + Roon Bridge renderer
    + No DSP, No Camilla or anything

I am very very pleased with the results, sound quality is great for the money, so a big Thanks to Mark and everyone involved in this great DIY project.

But last month, I started noticing some occasional crispy noise, that seemed to be random, not related to the level of the music being played, and often present at the beginning of a new song - but not always. I was able to isolate the root cause to the ProtoDAC itself after successively playing music without Roon, replacing the microSD card, and replacing the RPI. (I also checked and retouched a few solders without any audible effect.)

Only then did I search this Forum, to find out that others have apparently experienced the same problem, and that odds are the TDA1387x8 is misbehaving. So I ordered 2 new modules from AliExpress... awaiting delivery.

In the mean time, I decided to run some tests on the ProtoDAC, and share the results with you.

I connected an old RPI to the ProtoDAC via GPIO, installed RaspiOS on the RPI and used the ALSA speaker-test utility to generate a 400 Hz sine wave to the I2S interface. I then connected the RCA of the ProtoDAC to the input of my Behringer DAC/ADC and collected the signal into REW wich allowed me to use the scope and capture the following screenshots.

It looks like after a second or so of normal behaviour, some distortion appears, and then the P-P voltage strangely rises, with more distortion being apparent on close-up, and then after some time, PP voltage comes back to its initial value and distortion gradually disappears.

That’s it. I thought I’d share this with you guys. I’m sure some of you are much more competent than me to perhaps comment on this.

The problem is probably with the module. Given the low cost of the modules, it's not worth devoting a lot of time troubleshooting.

Is the noise simultaneously in both channels?

I would do easy, simple things. Reflow the solder to the pins of the module, GPIO power and ground (GPIO 2,4,6). A bad solder joint can show up years later, as moisture and corrosion enter the joint. The bad solder joint could also be in the module itself. Not worth pursuing.

You could isolate the ProtoDAC power supply. Pull ProtoDAC off the RPi GPIO. Use DuPont jumpers for the I2S (12, 35, 40) and ground (6) from the RPi. Use a separate power supply to the 5V/GND pads between the RCA jacks. Standard green screw terminals will fit there or you can solder or clip directly. Double check polarity before powering up.