Among the most popular control circuit found in an audio system is tone control. The tone control is used to modify the tonal characteristic of the signal chain i.e. it enables the listener to alter the tonal quality of the sound being reproduced. The effect of tone control has on the frequency response of the equipment and their purpose is to help remedy shortcomings in the source program material, the receiver or transducer, or in the loudspeaker and the listening room combination.
These are either of the passive types, of which a typical circuit layout is shown in Fig. 1, or are constructed as part of the negative feedback loop around a gain block, using the general design due to Baxandall. Typical circuit layouts for active tone control are shown in Figs. 2-5.
PARTS LIST FOR FIG.1 PASSIVE TONE CONTROL
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 = 15 KΩ
R2 = 2.2 KΩ R3 = 22 KΩ VR1, VR2 = 100 KΩ |
| Capacitors |
| C1, C6 = 10 µF/12V (Electrolytic Capacitor)
C2 = 0.022 µF C3 = 0.22 µF C4 = 0.001 µF C5 = 0.01 µF |
PARTS LIST FOR FIG.2 ACTIVE TONE CONTROL USING SINGLE TRANSISTOR
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1, R2, R4 = 10 KΩ
R3 = 5.6 KΩ R5 = 220 KΩ R6 = 33 KΩ R7 = 4.7 KΩ R8 = 1 KΩ VR1, VR2 = 100 KΩ |
| Capacitors |
| C1, C5, C7, C9 = 10 µF/12V (Electrolytic Capacitor)
C2, C6 = 0.0033 µF (Ceramic Disc) C3, C4 = 0.033 µF (Ceramic Disc) C8 = 47 µF/6V (Electrolytic Capacitor) |
| Semiconductor |
| T1 = BC148 |
PARTS LIST FOR FIG.3 ACTIVE TONE CONTROL USING LM387
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 – R4 = 10 KΩ
R5 = 680 Ω R6 = 180 KΩ R7 = 1 MΩ VR1, VR2 = 100 KΩ |
| Capacitors |
| C1, C7, C10 = 10 µF/12V (Electrolytic Capacitor)
C2, C5 = 0.0033 µF (Ceramic Disc) C3, C4, C6 = 0.033 µF (Ceramic Disc) C8, C9 = 0.1 µF (Ceramic Disc) |
| Semiconductor |
| IC1 = LM 387 |
PARTS LIST FOR FIG.4 ACTIVE TONE CONTROL USING LM349
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 – R4 = 10 KΩ
R5 = 1 KΩ VR1, VR2 = 100 KΩ |
| Capacitors |
| C1, C4 = 0.0033 µF (Ceramic Disc)
C2, C3, C5 = 0.033 µF (Ceramic Disc) C6, C7 = 0.1 µF (Ceramic Disc) |
| Semiconductor |
| IC1 = LM 349 |
PARTS LIST FOR FIG.5 ACTIVE TONE CONTROL USING LM741 OR LM348
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1, R3 = 10 KΩ
R2, R4, R5 = 15 KΩ VR1, VR2 = 100 KΩ |
| Capacitors |
| C1 = 0.047 µF (Ceramic Disc)
C2 = 1 Kpf (Ceramic Disc) C3, C4 = 0.1 µF (Ceramic Disc) |
| Semiconductor |
| IC1 = LM 741 OR LM 348 |