The Warpfield Resonant Drive is an adaptation the incredibly rare Pearl Warp Sound, also sold under the Vorg brand name.
The Warp Sound was a generally unnoticed pedal when it came out in the mid-1970s. A few decades later, though, Kevin Shields of My Bloody Valentine was seen with one on his pedalboard that he had marked “Sometimes” (the eighth track on their classic album Loveless), and the MBV association has since caused them to sell for upwards of $500—if you can find one.
At its heart, the Warp Sound is a static resonant low-pass filter with adjustable frequency, sort of like a cocked wah. This is combined with a fuzzy, rough-around-the-edges distortion to create some really interesting textures. It’s not going to be your main drive pedal, but it’s a great tool to have in your arsenal.
The original Warp Sound only had two knobs on the outside, with the distortion trimmer set internally. The Warpfield puts the distortion control as an external knob. Many people like to leave the distortion all the way up, but you can be the judge.
The Warpfield is a direct adaptation of the Warp Sound. Other than the relocation of the Distortion control, the only other change was to make it true bypass (the original was buffered). You’ll notice a vestigial resistor and capacitor coming off of IC1. These were part of the buffer circuit, but since the signal does pass through them in effect mode forming a very slight filter, they were left in.