Intro
The Tone Stack calculator is designed to help you check out the design and response curves of a variety of tone stacks used in popular guitar amplifiers.

It is intended to be of interest to amplifier technicians, amp modifiers, hobbyists and students.

Key features

Tone stack types: Fender modern, Vox, Marshall, James (passive predecessor to Baxandall), Fender E series, Steve Bench tone stack, and now the Big Muff tone stack used in FX units. Simply click on the appropriate tab to bring up a different schematic.
Components: Values can be altered simply by double-clicking on the component. With potentiometers, the taper can also be altered. The generator source impedance can be altered to give realistic simulation results for both cathode followers and common cathode drivers.
Bass/Mid/Treble: Slide the controls along and see the changes to the tone stack response in real time.
Snapshots: Freeze any trace so it can be overlaid by other traces. Up to a maximum of 12 traces can be frozen in this way. Can sweep the controls to show the range.
File Open/Save: Keep your favourite configurations on disk with this new facility.
Printing: Send the graphical results to your printer for a hard copy.
Other features: Online context sensitive help, variable plot resolutions supported to optimise performance.

more at: http://www.duncanamps.com/tsc/index.html