Béla Becker (DECAFBAD on the Discord forum), likely supercharged with a generous dose of caffeine :-), suggested a super cool improvement to my center stability design. I LOVE IT. It’s elegant, intuitive, and above all simple. Simple is beautiful. I always prefer the simplest design.
For those who tuned in late, see these posts for reference:
The E-Whammy Update
The E-Whammy Explained: What It Is (and Isn’t)
The E-Whammy: Evolution
Spring-less E-Whammy: Proof of Concept.
The E-Whammy : Center Stability
Here’s the schematic diagram:
The circuit uses two half-wave precision rectifiers, U3 and U4, offset by the user-defined window. See my previous post for context. Unlike my design, this one does not have the undesirable jump, which I had to filter out, when transitioning into the deadband. Essentially, it functions as a parametric crossover distortion circuit.
The “precision diode”, or ideal rectifier as we call it, is something I’ve learned about quite some time ago. When I read your post about the e-whammy, in my mind this was the more obvious solution: the combination of two half-wave opamp rectifiers slightly shifted.
— Béla Becker (DECAFBAD)
The graph shows a simulation focused on the center of operation while tracking a ramp input. The green plot shows the output snapping to 2.5 V when the input (X-axis) falls between 2.4755 V and 2.5245 V.
How does it work? See the graph below:
The upper half-wave rectifier, offset by 1/2 the deadband window (light blue plot), follows the input when the signal is above the window. When the signal is below the window, its output is fixed at 2.5 V + 1/2 the deadband window. The lower half-wave rectifier takes care of the bottom half of the signal. Offset by -1/2 the deadband window (dark blue plot), it follows the input when the signal is below the window. When the signal is above the window, its output is fixed at 2.5 V – 1/2 the deadband window.
Take note that the rectifiers are inverting, and hence the outputs are inverted. The two outputs are then added in U2, which is also inverting. The inverted sum of both rectifiers is shown in the green plot. The crossover between the upper and lower half-wave rectifiers naturally pulls the output to 2.5 V—the center.
Brilliant! Hats-off, Béla!