The author mentions that some programs have made sound with the TRS-80 by using tight timing loops that access the bus(es), which create a lot of RFI that can be received by a nearby AM radio tuned off-station. The software loops can be timed to produce musical notes that will be heard (along with much static) on the radio. Looks like he used the cassette outputs directly for sound in this case.
I never owned a desktop TRS-80, but I repaired one once after a friend of mine inadvertently put 120VAC on the internal 5V power bus. About 1/3 of the chips were blown.
He told me how he blew it up: The Condor power supply he was using to provide +/- 12VDC needed for the RS-232 EIA voltages to drive his modem had the input (line voltage) present on a the same terminal strip with the +/- 12VDC output terminals. After a few beers, he had dropped some metal object (bottle opener?) and it momentarily bridged the 120VAC and one of the 12VDC outputs. The line voltage found its way through one of the 1488/1489 EIA converters, and onto the 5VDC bus. That was enough to let the "magic smoke" out of about a third of the chips.
I noticed that the video link on his web page was not a hyperlink. His video is here: https://www.youtube.com/shorts/JD9sXwgHMfc
I never owned a desktop TRS-80, but I repaired one once after a friend of mine inadvertently put 120VAC on the internal 5V power bus. About 1/3 of the chips were blown.
He told me how he blew it up: The Condor power supply he was using to provide +/- 12VDC needed for the RS-232 EIA voltages to drive his modem had the input (line voltage) present on a the same terminal strip with the +/- 12VDC output terminals. After a few beers, he had dropped some metal object (bottle opener?) and it momentarily bridged the 120VAC and one of the 12VDC outputs. The line voltage found its way through one of the 1488/1489 EIA converters, and onto the 5VDC bus. That was enough to let the "magic smoke" out of about a third of the chips.
https://en.wikipedia.org/wiki/Magic_smoke
I do still have a TRS-80 Model 100 in a closet somewhere.
https://en.wikipedia.org/wiki/TRS-80_Model_100