The Lovepedal Provalve. It's been about for a while and indeed preceded the Provalve 2. Here's a description:
And a demo video of the Lovepedal Provalve in action:
Soulsonic reverse engineered one and had this to say:
"Just a single 386. Initial inspection reveals it to be pretty much identical to the Purple Plexi. Switching between A and B just toggles between the two gain controls. And they both function and sound identically, so it's just a way to toggle between two different preset gain levels. It uses FETs to do the switching. It has the Cusack-designed relay switching stuff for the bypass.
The construction is solid enough; except for the jacks - they don't butt up flush against the side of the enclosure, so if you try to tighten down on the nuts, the plastic part of the jack starts to bend out and deform. The nuts were loose when I received it, and they won't stay tight for anything. I wish the battery cable had some strain relief because it looks like something that would break after extended use.
The ground plane on the board does a decent job of keeping out hum, which is good because the metal enclosure is not grounded to the circuit at any point... it may as well be in a plastic enclosure. The box itself has a "lumpy" appearance - like it wasn't cast well. There's no markings on it... so it's neither a Hammond nor an NSC. Looks like the same generic box HBE uses.
The sound is not very good. It does an okay heavy distortion, but in comparison, the Jaw Breaker can get a similar sound, but much much better quality. The worst part - other than the very obvious noise at max gain - is that there is this sputtery static-y sound as the note decays; at any gain setting. Where it could otherwise sound possibly okay at low gain, this bad decay ruins it. The tone control is worthless and just makes it sound muddy. It's obnoxiously loud - I like loud, but I'd prefer not to have to keep the knob all the way down at 9 o'clock.... the extra volume is pretty much wasted."
I don't think he liked it that much....
The circuit is just a Lovepedal Purple Plexi with a switchable gain control.
Theevilone built one up - here's some images of his build:
Here's the freestompboxes.org forum thread for reference: http://www.freestompboxes.org/viewtopic.php?f=7&t=4244