“Making an AC Bias Tape Recorder(Cassette Recorder) To record new audio tracks on Magnetic Tape.
Introduction
Hello everyone! in my previous tutorial, I showed you how you can make an AC Bias Tape recorder or Cassette recorder. So You can record your favourite songs on old audio cassettes(Magnetic Tape). But in that tutorial to make the necessary circuits(Recording amplifier, Recording Equalizer, Playback Equalizer, Bias Oscillator and Motor speed Controller) for recording, I have used some Integrated circuits aka ICs( such as LM358, LA3210 and LA3161). So it may be difficult to understand and create your own circuits for absolute beginners. But here you don’t need to be sad if you was unable to understand and build that circuits because in this tutorial I am going to use only Bipolar junction Transistors(BJTs) for making the same circuits. Some viewers has also complained that they was unable to get the bias oscillator and requested to make a simpler version of the bias oscillator circuit that does not require a bias coil. So here I am going to make a very simple and effective bias oscillator circuit without a bias coil and operating frequency of 50KHz. So let’s get started.
List of Required Components
- Transistors(BC549C, BD139, BD140)
- Diode(1N4007)
- Resistors(1k, 2.2k, )
- Capacitors(10UF/63V, 4.7UF, 100PF, 6.8NF, 3.3NF, 2.2NF, 470UF/16V, 220UF/16V)
- Playback/Record head(Stereo)
- Erase Head
- Loudspeaker(4 Ohm and 5W)
- Audio Cassette(C 60)
- SMPS(12V, 2A)
- Lead acid battery(12V)
- Lab bench power supply
- Cassette Mechanism(With motor, capstan, pinch roller, fly wheel, spool and clutch)
- Jumper Wires(m-t-m)
- Breadboard
- Alligator wires
- Main lead
- Potentiometers(10k, 100k and 20k)
- 3.5mm audio cable
Tools
- Soldering Iron
- Soldering Flux
- Soldering wire
- Ribbon wire
Theory
Making the Playback Pre amplifierCircuit
The BC549 or BC109 has been chosen for the input stage because it is particularly suitable for use in audio input stages where low noise is essential. Its collector is directly connected to the base of Q2 ; its emitter is connected via an RC network to the collector of Q2. This RC network provides a path for negative feedback by means of which equalization is effected. The frequency response curves on playback are shown in Fig. 53. A D.C. feedback path is also provided from the emitter of Q2 to the base of Q1. The D.C. feedback along this path stabilizes the working points of Q1 and Q2.”