Most audio amplifier systems must have preamplifier with many different
characteristics. These include high-gain linear response for magnetic
microphones, low-gain linear response for tuners, and high-gain RIAA
equalization for magnetic phone cartridges.
To meet this broad requirement, most amplifier designers include a single universal preamplifier circuit. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system.
To meet this broad requirement, most amplifier designers include a single universal preamplifier circuit. Basically a high-gain linear amplifier, its characteristics can be altered by switching alternative resistor filter networks into its feedback system.
For example, when the selector switch is set to the Mag phono position,
alternative input sources can be selected by S1-a, and appropriate
linear-response gain control feedback resistors 220K, 470K, and 1M are
now selected by S1-b. Those feedback resistor values are selected
between 10 kilo ohms and 10 megohms to suit individual listener tastes.
Circuit gain will be proportional, to the feedback resistor value.
Universal Preamplifier Circuit Diagram
