Balance Indicator

4 If your amplifier is fitted with two balance controls (as, for instance, the Elektor Electronics Preamplifier for Purists - Ref. 1), it actually offers you a balance control and a level control. A drawback of this is that it is quite difficult to set the balance prop- erly. This may be obviated, how- ever, by replacing the two mono potentiometers by stereo ver- sions, P1 and P2 in the diagram. One half of the pair, P1a and P2a, assumes the tasks of the removed components. The other half is connected in a bridge cir- cuit. The voltage between the wipers of the potentiometers is then a measure of the balance between the two channels. The lower the potential, the better the balance. If you are interested in knowing the degree of unbalance, connect a centre-zero moving coil meter with a bias resistor between A and B. With this arrangement, zener diodes Dl and D2 may be omitted: they are <20mA necessary only with the LED indi- cator shown in the diagram to prevent the input voltage...