potentiometers

[Estebandito]

This question must have been asked/answered a million times already but here it goes: what is the reason my rc oscillator freaks out at the end of the dial? Whenever I build an rc oscillator, the pitch at the very end of the clockwise turn suddenly sounds distorted, almost as if there is a physical reason to do with the potentiometer - is it possible the wiper goes past the carbon trace inside the potentiometer? Or does this have to do with the capacitor vs resistor values? And more importantly, is there a way to prevent this from happening?

[blue hell]

Probably:

At the end the resistance (almost) becomes zero then the R * C time will become zero .. which would mean that the frequency (related to 1/R*C) would become infinite - except that such would require infinte power too .. soo .. it breaks down instead.

You can prevent this indeed. Add a series resistor to the pot ... this will limit the frequecy on the top end and prevents the breakdown. Got to experiment a bit with the (smallest) value still working for you.

[PHOBoS]

If it's a simple RC oscillator using a schmitt trigger (40106, 4093 whith a potentiometer between the input and output
and a capacitor from the input to GND) there always needs to be some minimal resistance otherwise you are shorting
the input and output together. So if you would turn the potentiometer all the way clockwise (assuming that makes the
resistance smaller / frequency higher) there will be a point at which the resistance is too small for it too properly work.
A simple solution for this is to add a resistor in series with the pot.


It could also be a mechanical problem as at the end of its travel the wiper will go from the touching the carbon track to the
contacts you connect to, which can be a little jumpy. You can see that transition on this photo (from The Secret Life of Pots)




edit: I see blue hell beat me to it

[Estebandito]

Thank you, this makes sense to me now. I will keep using my budget potentiometers for now and add series resistors to the feedback loop ofmy oscillators.