Hi,
i readed your post, found some samples online and tried, it sound similar,probably witout reverb is better, giveit a try, hope it helps ;)

the samples are from here: http://www.freesound.org/tagsViewSingle.php?id=1055

if you have better samples i'll try to do a better instrument ;)

Interesting! Where did you find the samples? I can't seem to track them down myself. ^^

Alternatively, I suppose I could probably use FamiTracker to generate the C pitches that it looks like ThumbJam uses for its instrument samples and just work them all into a set or several… : )

i found the samples in the link sended before. the sounds i used is: from 01_ProgressiveSID_C1.wav to 06_ProgressiveSID_C6.wav

yes, you can use any program you want for the samples, and you can export not only the c but how many samples you want. and, more sample you use, better the instrument sounds, especially for natural instruments recorded :)

That instrument posted above has some metadata corruption that actually caused crashes in the app. I've taken the samples, properly looped them and made a new instrument from them.