Info from Home-Wrecker:
The Dr. Q project by JD Sleep was the first non-fuzz effect I built. It was also, at the time, the most complex circuit I had undertaken. Despite reading the many improvements to the design offered by the Dr. Quack (designed by Jack Orman) I still chose the Dr. Q, deeming the Dr. Quack even more complicated. The Dr. Quack circuit actually isn't that much more complicated than the Dr. Q, but it looked like it would be on my preferred medium of perfboard.
The Nurse Quacky is the result of suggested mods by Mark Hammer, the aforementioned improvements by Jack Orman as found in the Dr. Quack, and my own dissatisfaction with the Dr. Q's shortcomings. The Nurse Quacky is not intended as a competitor or successor to the Dr. Quack (hence the demoted title). The Nurse Quacky is simply my personal version of the Dr. Q circuit. Additionally, the mods I implemented can be transferred to the Dr. Quack with ease.
-The .01uF cap (preceeding the 3.3M resistor) lessens the bass sensitivity of the envelope follower, and was suggested by Mark Hammer. It can be raised to .022uF (original Dr. Q value is .047uF)
-The 3.3M gain resistor, raised from 2.2M in the original, results in a stronger envelope signal. (Mark Hammer)
-The Attack control (the 51 ohm resistor and 1k pot) replaces a fixed 100 ohm resistor in the original. Also, the 10uF cap has been increased to 22uF for ripple-free decay. (Mark Hammer)
-The circuit is hard-wired in the Bass setting of the Dr. Q switch. The Normal position never sounded good to me.
-The .047uF output cap has been increased to .1uF.
-The two .0047uF caps can be socketed. Larger values (.0056 or .0068) will move the sweep range lower in frequency. Additionally, the transistor and op-amp should be socketed as well.