Hi swissdoc, I did not notice the AD9833 before, this changes my opinion. I can see two of them for each voice but I don't see the reason to use a Tri/sawtooth/sine generators as clock for the counters. So I think these might actually be used as oscillators, two per…

Hi @swissdoc, are you sure about this? In the picture of the voice circuit in this post I can clearly see 3 LS193 ICs. I don´t see any other purpose for them.