Jim Marshall crafted guitar amplifier masterpieces without the assistance of computers, software or the Internet... In 1963 "graphical methods" meant drawing Bode plots with a pencil and ruler... Times have changed. ● Master the basics ● Design your amp ● Know it works Amp Design for the 21st Century

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What does this calculator do?

guitar amp grid-stopper resistor circuit

The grid stopper resistor RGS blocks radio frequencies while allowing audio signals to pass. This keeps the amplifier from becoming a radio receiver and prevents the stage from breaking into parasitic oscillation. Large values can be used to attenuate treble and improve the dynamics of overdrive.

The frequency response for a given resistor value depends on the output impedance that drives it, the inter-electrode capacitances of the tube, and the voltage gain that it achieves. The calculator plots gain versus frequency based on these factors.