| 摘要 |
PURPOSE:To cancel DC components and to eliminate the occurrence of pop tone, by subtracting outputs of two pairs of differential amplifiers. CONSTITUTION:The first differential amplifier consisting of transistors TRs Q6 and Q7 generates a current corresponding to an input signal, and the output is inputted to a subtracting circuit 1 through a resistance R6. The second differential amplifier consisting of TRs Q8 and Q9 has a current source consisiting of TRs Q10 and Q11. In this current source, resistances R8 and R9 and a variable resistance VR are regulated to make the coolector current of the TR Q11 equal to the collector current of a TR Q5. As the result, DC conditions given to the first and the second differential amplifiers are equal to each other, and therefore, if outputs of both differential amplifiers are inputted to the subtracting circuit 1, DC components are not generated in the output of an operational amplifier A1. |
