Hi Rookie,
Ha, ha, I am being a bit mean here :-) Wanted to wait a bit longer but it's 3 am here and I need to get some sleep before get to work tomorrow... so I was hoping I could drag the tension a bit longer but on the other hand catching some sleep is quite good too ;-)
So, the module in my previous post I was mentioning is the Make Noise - Telharmonic. Check out Make Noise's website regarding this module. There are two (how interesting!) manuals as download for this particular module (Telharmonic). The Telharmonic, fair enough and that one on its own is already a very interesting module and has lots of interesting functionalities however there is a kind of hidden mode or special mode, if one presses the "H-lock" button for more than 5 seconds then the Telharmonic changes into the Spiratone music synthesizer module, different functionality within the same module! Now that was a nice surprise when I read that in the manual :-)
So I did that and then it didn't took me long to discover that Shepard Tone is possible with this module. I discovered that already last night but then it was getting to late, so that's why I came up today with this.
I hope this is what you were looking for, have fun with it and kind regards, Garfield.
Edit: Removed typo.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads