I’m glad your build went well, but i’m sorry about the ac hum. If everything works well with your bench supply, then there must be an issue with your radio shack power supply. Try a different power supply or a battery to see how it goes. Possibly the filter cap(s) may be old/dried out in your ratio shack supply. You could check the ac ripple under load from your supply with your voltmeter.
Thanks for the suggestions. We are currently in the process of designing the Macchiato MKII which will have several improved features. I”ll take your suggestions into consideration when we make the assembly manual for it.
Thanks and good luck.
-Brach