Moving the control in one direction simultaneously boosts
the treble and cuts the bass until about 5.5 dB of boost and
23 dB of cut are obtained. Moving the control in the other
direction boosts the bass and cuts the treble in an identical
fashion. Figure 2 shows the typical curves obtained from 20
Hz to 20 kHz with a 1-kHz center frequency, for the lower half
and upper half of the control range, respectively.
Naturally, for stereo, the circuit would be duplicated and VR1 substituted with a dual, ganged component. Since the circuit is purely passive, it is easy to insert in the signal chain. However, it must be preceded by a low impedance (below 100 Ω) and followed by a high impedance (more than 250 kΩ) for best results. Under these circumstances, insertion loss (at center) approaches 6 dB.
Since this is a purely passive circuit, all component values may be scaled without affecting the ac transfer function. With lower resistor values (and higher capacitor values), the signal-to-noise ratio improves, but the circuit requires a lower impedance to drive it. The values shown represent a good compromise. Overall signal-to-noise ratio in a 20-kHz bandwidth is about –113 dB referenced to 1 V rms with the control in the center position.