This circuit attempts to emulate the nonlinear behavior of a tube power amplifier by exploiting the intrinsic nonlinearity of a BJT long-tailed differential pair instead of using explicit clipping diodes.
The slight mismatch between the collector resistors intentionally introduces a small amount of asymmetry, promoting the generation of even-order harmonics.
The potentiometer acts as a presence control, emphasizing frequencies around 5kHz.
Its output can be fed into a digital processor, such as an STM32-based system, for cabinet impulse-response convolution.
