I am a college level electrical physics student (and so I do not have a lot of knowledge on the topic of electronics) and I am in the midst of writing a report on a project that was done throughout this session.

The project was the conception of a synthesizer, which I did pretty much by myself (I used some videos, manuals and other as sources). I ended up being able to build a functionnal synthetiser on a breadboard, and everything was working fine.

Now that I am writing the report, the teacher asked me to provide a functionnal simulation for the circuit, and so I tried doing just that.
At first, I used [falstad][1], and was not able to create a functionnal simulation, for some reason the software did not specify (so I have no clue why the falstad simulation does not work). Next, I tried using [tinkercad][2], and again, it didn't work. This time though, the software provided me with an explanation as to why the simulation didn't work, but I wasn't able to make sense of it.

Hence why I am here, asking for help in order to make a working simulation of the circuit. I want to know if I am simply making a stupid mistake or if it's actually a circuit that is hard to simulate using those software (In which case I will simply report to my teacher that simulating the circuit was impossible).

Here is the circuit diagram, made in falstab (the first simulation that ended up not working
[![Here is the circuit diagram, made in falstab (the first simulation that ended up not working)][3]][3] 

Here is the tinkercad simulation that also doesn't work
[Link to the tinkercad simulation][4]
[![Here is the tinkercad simulation that also doesn't work][5]][5]

Here is the actual working circuit, built on a breadboard
[![Here is the actual working circuit, built on a breadboard][6]][6]
The wires that are not connected to anything are:
 - 1 red and black for power supply
 - 1 red and black for the speaker 
 - one black for the oscilloscope probe used
 - 2 green (on the keyboard) to plug in the keyboard.
The electrical components used are
 - CD40106B CMOS Hex Schmitt-Trigger Inverters
 - 2N3904 BPJ NPN transistor
 - IRF510 nMOSFET transistor (I think that this is the full name?)
 - The speaker's label was erased but I know that it's a 100W with 8 Ohm entry impedence.
 - 10k Ohm potentiometer for the volume
 - A 5W 50 ohm resistor (supports higher currents)

For the values of other parts, I think I've written everything on the circuit diagram.
I didn't put all of the potentiometers from the keyboard since I don't know the exact value; they are tuned for a specific note. They vary from 1k to 20k.

As can be seen on the tinkercad simulation, there are also (ideally) a few oscilloscope screen that I would like to show. This is what they look like when I use the physical oscilloscope with the breadboard circuit:
[![Oscilloscope out][7]][7]
Oscilloscope out

[![transistor base out][8]][8]
transistor base out

[![transistor out (collector)][9]][9]
transistor out (collector)

[![After capacitor wave delay][10]][10]
After capacitor wave delay

[![MOSFET out][11]][11]
MOSFET out, what plays into the speaker.


  [1]: https://www.falstad.com/
  [2]: https://www.tinkercad.com/
  [3]: https://i.sstatic.net/U1awXoED.png
  [4]: https://www.tinkercad.com/things/k1Ky81X0nQC-copy-of-functionnal-synth/editel?sharecode=-3fixhWhJ2VYvrzhNM7kW4vpCx13pcn169tg2e1EQlU
  [5]: https://i.sstatic.net/KMuxFbGy.png
  [6]: https://i.sstatic.net/8MSC6sFT.png
  [7]: https://i.sstatic.net/6rqQq3BM.png
  [8]: https://i.sstatic.net/6bwJqRBM.png
  [9]: https://i.sstatic.net/jtpgnzXF.png
  [10]: https://i.sstatic.net/Z4ZhuLYm.png
  [11]: https://i.sstatic.net/pB6zMVYf.png