This is a variation of Valve Wizard's "Engineer's Thumb" circuit. From the builder: R14 was raised from 1K to 2K2 R7 was raised from 10K to 15K R12 was reduced from 1M to 470K.. I know this made the "release" quicker. And the control pots were changed for better control and ranging. LEVEL was changed from 10K-A to 10K-B (Linear) RATIO was changed from 1M-A to 500K-A Velcro on back Price includes shipping to conus. PayPal only.