I had a cassette recorder that used a transistor for AGC but only for very low mic levels and the distortion was not too bad.
I tried a photo-Jfet that claimed "low distortion" in a Wien Bridge oscillator but it had distortion too high. Then I tried a dual one so that the second photo-Jfet tried to cancel the distortion of the AGC one and the distortion was better but was still too high.
I tried a photo-Jfet that claimed "low distortion" in a Wien Bridge oscillator but it had distortion too high. Then I tried a dual one so that the second photo-Jfet tried to cancel the distortion of the AGC one and the distortion was better but was still too high.