I am using the shoot the moon tremolo signal path (and only the part between the IN and the OUT, i.e. the TL72 and attached components) for an optical tremolo project.
I followed exactly this schematic : http://imgur.com/RgvdJem
, but I only built the bottom part : the two rectangles and the Vr part.
The LED modulation is done physically.
The build is done, but when testing I get a lot of noise along the expected sound. The tremolo works, i.e. the output volume is modulated as expected, but I get my input mixed with a lot of noise.
If I replace the LDR with a 220 Ohm resistor, I get strong noise and signal, if I replace it with a 10k resistor, I get a low noise and signal (maybe with less noise). I used these values as they more or less match my LDR behavior.
I double checked everything, my TL072 voltages seems OK to me :
1 - 4,6
2 - 4,6
3 - 4,4
4 - 0
5 - 4,4
Any idea what could be causing that noise ? Maybe this circuit is designed for very low lighting only ?
Thanks for any help, I am not an experienced builder and I don't know how to progress here...