ZN414 Portable AM Receiver Circuit Diagram – Build Your Own!

Notes:

This receiver has been constructed utilizing the prevalent ZN414 integrated circuit. It covers the Amplitude Modulation (AM) band spanning from 550 to 1600 Kilohertz, as indicated in the schematic. For Longwave applications, a different coil must be employed; a coil salvaged from a vintage Medium Wave radio is recommended for convenience. The ZN414 is a frequency-selective receiver, meticulously designed and incorporating numerous Radio Frequency (RF) stages and an AM demodulator. It is susceptible to overloading, and maintaining a precise operating voltage is crucial for optimal performance.

The BC107 functions as a current buffer, while the four 1N4148 diodes furnish a consistent 2.4 volts DC power supply. Combining the 10k potentiometer, which acts as a selectivity control, and the base-emitter voltage drop of the BC107, the operating voltage for the ZN414 can be adjusted dynamically between 0 and 1.8 volts DC. Individuals residing in areas experiencing intense radio interference may require a lower voltage supply; a supply of approximately 1.2 volts was found to produce the best results.

BC107

The BC107 is a general-purpose NPN transistor commonly utilized as a voltage buffer or follower. Its primary function is to provide a low-impedance output, facilitating the amplification of weak signals while minimizing signal distortion. It's a versatile component, frequently found in audio circuits and instrumentation where a stable, low-impedance output is necessary. Its specifications include a collector current of 100mA and a Vceo rating of 40V, making it suitable for a wide range of applications.

1N4148

The 1N4148 is a silicon diode specifically designed for power rectification and switching applications. It’s a standard Schottky diode characterized by its fast switching speed and low forward voltage drop. This makes it well-suited for DC-DC converters, power supplies, and other applications requiring efficient rectification and switching capabilities. Its key characteristics include a typical forward current of 1A and a reverse voltage rating of 40V.

Circuit diagram:

The audio amplifier is constructed around an inverting 741 operational amplifier. Supplemental current enhancement is provided by the BC109 / BC179 complementary transistor pair. The complete audio amplifier exhibits a voltage gain of approximately 15. The audio output of the entire receiver demonstrates excellent quality, notably free from distortion. Further sound samples may be provided at a later date.