The calculator computes the gain and output impedance of a common plate load mixer. Each input channel controls a separate grid, which affects the plate current through the common plate load resistor RL and cathode resistor RK. The optional cathode bypass capacitor CK increases gain by eliminating negative feedback. If a cathode bypass capacitor is used, the calculator assumes that it is large enough to short the cathode to ground at audio frequencies. (How large is large enough? See our Cathode Bypass Capacitor Calculator.)
As long as the triodes are not overdriven, the inputs are completely independent. Changes in control settings for one channel, for example, do not affect the signal characteristics of the other. Unlike a passive mixer, the circuit also provides substantial gain. Our online article The Gretsch Chet Atkins Active Mixer describes one of the ways that the circuit is used in a guitar amp.
This new approach to guitar amplifier electronics embraces 2018 technology to deliver greater understanding with less math. Computer-based visualization replaces the traditional litany of mathematical formulas. The book's graphing calculators, free on this website, are designed for smartphones and laptops, making them as portable as the book that uses them.
Less Math, Greater Understanding
The book explains the principles of vacuum tube electronics and the design of preamp voltage amplification stages, cathode followers, tone stacks, power amps, phase inverters, negative feedback, and power supplies. An entire chapter is devoted to sculpting the dynamics of overdrive and harmonic distortion.
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