The sound seems higher in treble and lower in bass than what I hear in the few videos of real 280-ZZZAP machines I can find...
Remember this, from back at the end of May? Turns out the problem was that I had missed a diode in the internal netlist for the MC3340. Or rather, noted it and deliberately omitted it
, thinking that it didn't make any difference in the sound. Well, that turned out to be very wrong. The engine sound is now much more "growly", sounding quite close to real machines.
Motorola's MC3340 chip schematics, while certainly helpful (without them full 280-ZZZAP sound would be nearly impossible to figure out) have also been sources of confusion. Late ones (1990s) have resistor values, early ones (1970s) don't. Late ones miss an internal connection that early ones include: a crossover gets a dot in the early ones and no dot in the late ones. And late ones have one internal diode while early ones have three. It turns out those two extra diodes matter. (It would have been less confusing if Motorola had left all diodes off the late schematics—at least you could say, "oh, they just left out their diodes". Leaving out some
diodes and not others makes you think the omitted diodes are supposed to be irrelevant or something.)
Anyway, the fix has been made and incorporated in master.