Yamaha DX7 Technical Analysis
I was under the impression that, despite the name, the Yamaha FM synths didn't actually use frequency Modulation but rather phase modulation. With Frequency modulation you can't have an operator feed back on its self.If you take a DX7 patch and implement it on something like the PreenFM2 or PreenFM3 (which uses actual FM), any algorithm  with more than a few operators is going to sound quite different.I still love the old Yamaha FM synths though, the lo-fi-ness of the DACs are so musical/magical.Here's a IDM track I made with just the Yamaha TX81z 4op FM synth. 
https://soundcloud.com/cassilda_and_carcosa/ontologies-tape-...