I’m using a switched-mode power adapter/supply (SMPS) and hear a high pitch “whine”, why is that?
Some of these SMPS adapters are noisier than others, especially those that aren’t from a reputable or brand-name MI manufacturer. Another reason could be that you’re trying to run to many devices from a single adapter. Though many of them have a high current output and tout being able to power many devices, doing so can result in the development and/ or increase of noise, for some reason. If this is happening, we recommend either trying another adapter, or better yet - using a universal pedalboard power supply with enough isolated outputs to power every device on your pedalboard individually; better power = less noise = more tone!