Rev sets how much of the reverb mixes with the dry signal. Feedback sends the reverberated signal back to the reverb input, from a short tail to self-oscillation. Gain drives only the reverb path. It can add a little compression to the wet sound, or turn that path into a distorted reverb. The low-pass filter sets how much high-frequency content and modulation stay in the decay. Volume sets the overall level at unity, below unity, or slightly past it.

The circuit and the enclosure went through several earlier versions. The low-pass filter was added after recording with those versions, into low-wattage amps at home, and into higher-wattage amps at volume. The current maker photo shows a unit badged version v1.1. Audio jacks and the DC socket sit on the top edge.