Baxandall tone control
Bass and treble pots sit inside the feedback network of an inverting amplifier. At low frequencies the bass capacitors open up and only the bass pot matters; at high frequencies the treble capacitors take over. In the middle both are flat, gain −1.
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How it works
With both pots centred the network is symmetric: gain = −1 (0 dB) at mid frequencies.
Bass turnover ≈ 1 ÷ (2π·R_pot·C1) = 34 Hz shelving to ±(R_pot ÷ R1) ≈ ±20 dB; treble turnover ≈ 7.2 kHz.
Try it on the bench
- Turn Bass fully one way and run the Bode plot.
- Set V_in to 50 Hz and turn Bass: the output swings by up to ±15 dB.
Parts on the bench
- 2 × Bench power supply
- AC source
- NE5532 low-noise op-amp
- 3 × Resistor
- 2 × Potentiometer
- 4 × Film capacitor
In the course
Electronics Engineering, module “Filters and frequency response”.