This is a design circuit for the level control, buffer and attenuator. This circuit is control using transistor. The buffer stage is used to ensure that the impedance seen by the attenuator is low, regardless of the pot setting. This is the figure of the circuit.
This is a simple form circuit. This arrangement is not as elegant as some others I have seen, but is quite acceptable and introduces little distortion. The loss introduced by this stage is about 0.05dB, which can be considered negligible. The BC559 transistor will need a small heat sink, as it is operating at a current of about 12mA, so dissipation is 140mW. The level control is a single gang linear pot, and as shown, the attenuator provides a passably constant output impedance of 560 Ohms at all output settings. If desired, the output can be calibrated in Volts, with the ranges 3V, 300mV, 30mV and 3mV. Attenuator accuracy is very good, provided 1% resistors are used for all ranges.
