Preamp with Volume Control using BC148 and BC149

Here is a preamplifier circuit with volume control for use with Class A power amplifiers. This preamplifier uses the BC149 and BC148 transistors, which are often available in old stock. As you can see, this circuit has a selector switch for selecting the inputs and there is also RIAA equalization circuit for record players and turntables. If you are a tape user, then there are also equalization options for two types of tape speeds. In this circuit, the transistors form a directly coupled pair, with the base voltage of the first transistor being derived from the emitter of the second transistor. The equalization is obtained by feedback from the collector of the second transistor to the emitter of the first. The input sensitivity at 1 kHz for an output of 60 mV is as follows:

• Ceramic pick-up 130 mV
• Magnetic pick-up 3 mV
• Tape head (7.5-inches/second) 5 mV

This Article Continues...