When I first started developing my own TZXduino PCB boards I was struggling to get it working with my Sharp MZ700 computer. Sometimes it worked and others not. I couldn’t put my finger on it, but then I put a scope on the output of the TZXduino device I purchased from the original guy who made them. I noticed a difference while playing around. I thought about this for a while and had read that LM386 needs to operate at 5v-18v and but really needs to operate higher than 6v to minimize drain. Most of the TZXDuino that were in the wild were driving the LM386 ( or AMP module) from the 5v pin on the Arduino thus allowing it to operate from the Arduino USB power. I noticed that with the drain of other components that only 3-4v was coming out of that pin and it occurred to me maybe that is the issue. So I factored that into the design of the PCB. Sometime later I found myself in a similar situation with certain ZX Spectrums. After digging about I found out some older models of the ULA chip can go a little deaf. In my own systems, I was fixing this issue by replacing the ULA. Fast forward and I decided to architect in the fix I had included for my Sharp MZ700 into my main PCB I use for all the other Retro Computers.. I’m calling it the Deaf Computer option. Now I cannot guarantee it will fix all your problems but Wayne over at Retro Robbins offered to test this theory out for me since he had a deaf Spectrum 128K+. Watch the first part of the video and decide for yourself.