This is a simple multi-phase chorus made using PT2399s. Multi-phase choruses are choruses with more than one voice, with each voice using a different phase of the LFO signal, such as the Boss Dimension C. They sound more deep than single-voice choruses, and they don't sound as annoyingly wobbly at high depth settings. This chorus uses two voices, with the LFO signals for each 180° out of phase with one another.
The fact that there are two swept PT2399 delays means that there's flanging going an as well as chorusing. As the sweeps approach one another on higher depths, you get a subtle flanging sound. This is more prominent using the Dry On/Off mod (see below). Although I avoided it here, there's also potential for through-zero flanging, which can be achieved by adjusting R2 or R5.
Here are schematics showing possible mods. Note that the stereo mod hasn't been tested yet.
The modded version has two added switches. The Dry switch selects whether the dry signal is mixed in or not. The Voice switch chooses between 1 and 2 voices. Between these two switches, you can get vibrato, normal 1-voice chorus, 2-voice chorus, or light flanging.
This version adds a switch that should select between Mono use (with the dry signal in Output B), and Stereo chorusing, with one voice and the dry signal going to each channel.