Brian O’Brien of Weston, MA, called with a solution to problems with LOAD. None of 3 recommended brands of tape recorder worked well on his ZX80, so he put a 0.1 uF capacitor in series with the input on the ear line and a 1k resistor across the input (this might change with the tape recorder).
All 3 recorders now work. Brian added that most tape recorders put out 20-200 Hz noise, and he didn’t think the ZX80’s low-frequency filter was adequate. He also suggests that readers try using a 5k variable resistor and changing values until they get one that works well.
Brian also suggests using an external regulated DC power supply to run the recorder. Most small recorders that operate on batteries will run from a 5-volt regulated supply. Because the recorders we checked drew less than 400 mA, a 5V, 0.5 A supply would suffice. This eliminates an alternate path for motor noise to reach the ZX80.