I'm not sure about the original waveform, but it could be a plain saw.
But add a lowpass envelope that goes quite a bit far down, until you only have the fundamental left, and make sure the sound is already a little dull a the beginning of the plucky strum.
Setup a basic 70% sustain and short decaytime to the volume envelope to make it hit a little harder, and increase the release time so you have a consistent fundamental sounding through the performance.
Oh and make the patch monophonic (no glide).
Experiment with Velocity linking on the filter cutoff and perhaps on a volume knob, as you hear each strike on every beat sounds a little different, and not like it's fading away as if it would have been a delay, that is clearly Velocity linking
Then add some light downsampling to the sound.