Dilshan R Jayakody’s Web Log

For some time, hobbyists have relied on dedicated sound generator ICs, such as the UM3561 , UM3562 to build compact alarm and siren circuits. Unfortunately, this device is becoming increasingly difficult to find in the market. The manufacturer of the chip, United Microelectronics Corporation (UMC), is still around. However, they are no longer producing the UM3561 or UM3562. As part of a fun experiment, I decided to design a replacement circuit using only discrete transistors and passive components. This avoids the need for specialized ICs altogether. The result is a simple yet effective transistor-based siren. It can reproduce the familiar rising and falling alarm effects typically associated with police cars, fire trucks, or ambulances. Finished prototype of the electronic siren. The design philosophy behind this project was straightforward: recreate the functionality of the classic two-timer based siren circuit ( NE556 / NE555 pair), but instead of timers or sound generator ICs, u...

TC-252 is 3-speed reel to reel player manufactured by Sony in around 1970 – 1972. This is transistor based tape player with 4W × 2 audio output power, sound-on-sound, and sound-with-sound recording features. The TC-252 which we got to restore had many problems. The major problem is someone alters the circuit in that recorder and attach LA4440 power amplifier into the circuit. Apart from that, the motor speed of that recorder also starts to decrease after 10min of continues playback. Other than above two major problems it had some mechanical problems in playback position and all the potentiometers in the front panel are damaged beyond repair. TC-252 main PCB after restoration. As a first step of the restoration, we remove the LA4440 module attached into that recorder and rewire the player with original wiring layouts. After rewiring we check all the transistors in that player and find out that the couple of 2SC634 transistors are damaged in that player. Because 2SC634 is not a...