Hi Sammy, I am sorry for your experience and I understand your frustration. In the Arduino Board the ADCs/DACs always introduce a small level of noise, there are several threads in the Arduino forums talking about it.
In my experience, the power supply makes a big difference in the background hiss, some USB chargers have a nice sound (old iPod models), and some others are a bit more noisy. But you write before that you did not find a big difference between your models.
There is a topic about it for more details:
electrosmash.com/forum/hardware-pedalshield/26-powering-arduino-due
I always use original Arduino boards, I use some cheap clones in the past and I did not have a good experiences with them so I stop using them (I teared away the connectors after few uses). It might be some differences in the decoupling that can affect the sound.
The best practice to minimize the output hiss is to keep the output level always to the maximum (or almost maximum volume). Doing that the signal to noise ratio improves a lot.
Arduino is a great platform to learn about digital signal processing, and it intuitive because you can code all in C, but it has some limitations.4
With the sinusoidal sketch if you keep the output level maxed, the hiss should be inaudible, I am trying to think what other things you can try:
- Try to keep the amplifier gain not very high, amps are prone to emphasize oscillations.
- Check the connection between the shield and arduino, some people cut the pin headers using a wire cutter 2 or 3mm, reducing the path of the signal between boards, but the improvement is very light.
- Try to see if you can find a better mini usb power supply.
- Some Arduino boards sound better if they are in a certain position or location, over the carpet, on your hand, on a table... some areas are better for elector-magnetic interference.
If you have any tweak to improve the design or you have some idea let us know, this is an open source project and we always look for improvement.
I hope this helps.