Adjusting RC Oscillator Circuit Frequency Problem

Hello guys,
Recently I am working on RC oscillator circuit based on it, but I had problems with adjusting frequency. I can adjust frequency but it effects amplitude too (amplitude is changing while adjusting frequency), how can i separate these two variables ? I mean, when I am adjusting frequency, I want to amplitude remains same, and also for amplitude too. By the way I am using this circuit : (Ignore the opamp circuit, it is converting sinusoidal wave into square wave.)

Anyone has ideas of it? Thank you in advance.

The usual answer is a light bulb or thermistor to control the amplitude. A google search for

“oscillator with constant output amplitude” turns up this

among other references.