This is the audio path of the Tremulus Lune with the LFO from the EA tremolo. The LFO is the modded version from GGG with the LED like the BYOC version and a couple of mods I made.
I used the Burr Brown OPA 2134 and it sounds fantastic.
The depth controls the brightness of the LED but not the ratio of bright to dark so it isn't really a depth, it's more like an external volume knob. I really like the sound of the OPA 2134 when it gets a bit gritty. I like fast overdriven tremolo for that rockabilly vibe. To get this I set the trim pot pretty high, even cranked to 50k and use the Depth knob to control how loud or gritty the sound gets.
I used a 5mm Yellow Diffused LED with a photocell that has a light resistance around 2k and dark resistance around a couple of mega ohms. This makes it a bit more of a pulse and sort of sounds like a rotating speaker effect to me. The info above should get you started but you can make your own version with different LED/LDR/photocell combinations. To make a more traditional depth knob, look at the tremulus lune how the pot varies the signal to the LED between the LFO signal and 9V.
I do not have the part number for the photocell.
Youtube clip:
