accurate bass tone control
This accurate bass tone control with A difficult problem in the design of conventional stereo tone controls is obtaining synchronous travel of the potentiometers. Even a slight error in synchrony can cause phase and amplitude differences between the two channels. Moreover, linear potentiometers are often used in such controls, and these give rise to unequal performance by human hearing. Special potentiometers that counter these difficulties are normally hard to obtain in retail shops. A good alternative is a control based on a rotary switch and a discrete potential divider. The problem with this that for good tone control more than six steps are needed, and switches for this are also not readily available. Fortunately, electronic circuits can remove these Elektor 04/07/98 13:04:20
with S1, which means that a +12 selection may be made of ampli+10 fication or attenuation of bass +8 frequencies. The user can choose between attenuation only and extending the range by +6 +4 dividing R9. The control can be +2 bridged by switch S2. d B -0 r To prevent the output imped-2 ance of the circuit having too much effect on the operation of the circuit, the output imped-4 -6 ance must be . 10 .. Resistor -8 R12 protects the circuit against -10 too small a load. -12 At maximum bass amplifica20 50 100 200 500 1k 2k 5k 10k 20k Hzdefault1.at1tion at Uin = 1 V r.m.s., the THD+N <0.001% for a fredifficulties. from Analogue Devices, which quency range of 20 Hz to The analogue selectors used switch noiselessly. Each IC con-20 kHz and and a bandwidth of may be driven by mechanical tains four selectors, so that a 80 kHz. switches, standard logic circuit total of eight are used. The step The circuit draws a current or a microcontroller. The selec-size is 1.25 dB at 20 Hz with a of about 10 mA. tors used in the present circuit maximum of 10 dB.