Solution without redstone dust
You can use non-sticky pistons and observers to get a relatively quick transmission.
You would use a non-sticky piston that faces down, one air block, and an observer facing up in a repeating pattern. I tested it against a pillar of observers, this was my setup:
The output at the end will always be a 1-tick redstone pulse, if you want the connection to permanently stay "on" (until switched off), I recommend replacing the last non-sticky piston with a sticky piston and the last observer with a redstone block. This was considerably faster compared to the pillar of observers.
Solution with redstone dust
This is for people who may find this question, but don't mind using redstone dust.
This setup is about as fast with transmitting the signal "on" as the setup above, but it is instantaneous when transmitting the signal "off" and the output will be solid (not a pulse), mirroring the input at the top, do not turn it off before the signal has traveled all the way to the bottom! it basically fixes itself after breaking though when you continue using it