Yes. But + to the ground if you have bipolar supplies.
Yes. as long as the combined input of 10 keys ( I only have 5 on each hand) doesn't over voltage the amp, and the impedance the amp has to drive is so far unknown, otherwise only one amp
You could run them off a 4.5V wall wart all in parallel, Operating off batteries I dont think the current will be an issue
This will need couple of diodes to drop the voltage,
Add as many R1 as needed. Since the output is low impedance the value is not very critical 10K will do. Set the gain with R2 The other resistors are to set the operating point to 1/2 V for single supply, not needed with dual supply. Is this a Hammond Rotary?
Most machines look for a disc when the tray closes If you can see the lens watch what it does Usually the lens will attempt focus lock (goes up and down). The usual no of attempts is 3
Yep. But there is still the use of gates to achieve the final result. I have scribbled down a solution that takes into account available parts (minimised) and I would like to see the solution