The VST plugin described on this page emulates a typical Marshall tonestack. Below, it is explained, how the tonestack was discretized. The resulting algorithm was then used to implement a VST plugin, which can be downloaded for free at the end of this page. The unauthorized use, reproduction, or passing on of individual content items or the complete page is not permitted.
The following figure shows how to get the transfer function from the circuit. The circuit on the very left shows the tonestack. To simplify this circuit, delta-star transform is used two times. Using the impedance of the capacitors Z=1/jwC, one obtains the transfer function F(jw) of the circuit.
To be able to calculate the tonestack recursively, it is necessary to get the z-transform from the transfer function.
The algorithm was finally analyzed in the frequency domain. The frequency- and phase responses of the algorithm are shown in the figures below for different positions of the potentiometers.
Download the 32-bit VST plugin here:
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