(01-28-2024, 07:52 PM)hifinet Wrote: You only need the one stacking header between the Q7 and ProtoDAC to prevent 5V from ProtoDAC feeding back to the 3.3V of the Q7 GPIO. Q7 isolates the topside isolated GPIO (J7) from the RPi. That is one of the things it does.
The noise is primarily conducted noise that the RPi is imparting on all of the GPIO lines, power, grounds and I2S, the entire GPIO. Q7 isolates J7 from all this. EMI is much less, orders of magnitude less, IMO.
Yes, I am saying that if you are going to circumvent the isolation of Q7, you might as well save yourself some money and go with MA. MA also has two jumpers so that you don't need to use the stacking header. See the previous posts of @michaelagiles . The solution in that case is to use an RPi that emits less noise. The RPi Zero W would have the least of the current RPi in that regard, since it is single core. In my experience, Zero W is less noisy than RPi 2, which is less noisy than RPi 3.
@hifinet So when you isolate the ProtoDAC from the GPIO (via stacking header with pins 2 & 4 disabled) you are only cutting off the power part of that chain, right? In other words the other isolation benefits of Q7 for the I2S/audio signal should be intact? Or is the 'isolation' benefit of a Q7 entirely hinges on the power flowing through it?
