audio preamp buffer - with variable gain

with variable gain The design for the circuit here was created when problems arose with the matching of some output stages with a preamp. In effect, the circuit is simply what the title suggests, a buffer between an audio preamplifier and an output stage. It does have the added facility however, of being able to drive more than one output amplifier simultaneously. The preamp load is standard at 100 pF in parallel with 47 k. To be fully versatile it was considered that the opamp used must be capable of driving similar loads at a level of 10 V without a problem. The LF 356 shown here can manage this. The amplification factor is adjustable between 1 and 5 with the aid of the preset potentiometer in the feedback loop of the opamps. These also serve to balance the output levels of the two buffer stages. If required, the balancing can be achieved very easily by means of a 50 Hz signal source and an ordinary multimeter. The 50 Hz is applied to both inputs of the buffer circuit and one pr...