Overview. The line for boost shows a higher impedance than the line for cut. The tone flat line is in between as you might expect. The bass end shows a much wider impedance spread between cut and boost than it does for treble. The highest impedance for treble is mostly less than the lowest impedance for bass. The lines do not merge into a single line as for figure 8.7. They are closest together around 1 kHz but are different because the midrange control is being stepped along with bass and treble.

Specifics for max boost. The line starts out at 35 k ohms at 10 hz. It rises to a peak of 52 k ohms at 85 Hz. It falls to 35 k ohms again at 1 kHz. Starting at 2 kHz it falls more rapidly until it reaches 10 kHz where the value is 15 k ohms. At 20 kHz the value is 14 k Ohms. It reaches a minimum of just below 14 k ohms at 35 kHz. It rises to 15 k ohms again at 100 kHz.

For tone flat. The tone flat line starts out at 155 k ohms at 10 Hz. It does not have a peak. It falls steadily to 85 k ohms at 100 hz then to 45 k ohms at 1 kHz. It passes through 30 k ohms at 7 kHz and falls to 29 k ohms at 10 kHz. It falls to 27 k ohms at 20 kHz and changes little to 100 kHz.

For max cut. The max cut line starts out at 275 k ohms at 10 Hz. Past 20 Hz it falls rapidly passing through 125 k ohms at 100 Hz. It falls less rapidly above 300 Hz passing through 55 k ohms at 1 kHz and 50 k ohms at 2.5 kHz. It passes through 41 k ohms at 10 kHz and 39 k ohms at 20 Khz. It changes little out to 100 kHz.

It should be noted that because the passive part of the circuit is symmetrical The load seen by the feedback amplifier is the mirror image in the impedance axis. That is the lowest impedance is for the cut and the highest impedance is for the boost. End verbal description.
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