1.5 Hour Lamp Fader Sunset Lamp Circuit Diagram

Circuit Diagram

This diagram illustrates a crystal radio system incorporating an audio amplifier, exhibiting considerable sensitivity and capable of picking up numerous powerful stations within the Los Angeles metropolitan area. A minimal antenna length of 15 feet is sufficient, though extended antenna lengths will amplify the signal strength but may compromise selectivity, potentially leading to overlapping audio from nearby stations. Connecting the wire antenna to one of the coil’s taps instead of the junction between the capacitor and coil can enhance selectivity. Grounding is necessary; a simple connection, such as resting headphone leads on a concrete surface like a slab, proved adequate for receiving local news broadcasts from KNX 1070. The inductor was constructed with 200 turns of #28 enameled copper wire wound around a 7/8 diameter, 4 inch length of PVC pipe, generating approximately 220 uH. The inductor featured taps spaced every 20 turns to enable optimal diode and antenna connections, with the most effective configuration found at 60 turns originating from the antenna end for the diode. A germanium diode (1N34A type) is recommended for superior performance, although silicon diodes will operate effectively if the signal strength is sufficient. The carrier frequency is eliminated from the rectified signal at the diode's cathode by the 300 pF capacitor, and the audio frequency is permitted passage to the non-inverting input of the first operational amplifier, functioning as a high-impedance buffer stage. The second operational amplifier stage increases the voltage level approximately 50 times and is DC-coupled to the first through the 10K resistor. Precise matching of the 100K and 1 Meg resistors (1%) may necessitate the utilization of closely matched values or the incorporation of a capacitor in series with the 10K resistor to maintain the DC voltage at the transistor emitter between 3 and 6 volts. Alternatively, reducing the overall gain via a smaller feedback resistor (470K) presents a viable solution. High impedance headphones are expected to perform optimally, although standard Walkman stereo headphones can also be utilized. The circuit draws approximately 10 mA from a 9-volt power source. Germanium diodes (1N34A type) can be obtained from Radio Shack, #276-1123.

Operational Amplifiers

Operational amplifiers (op-amps) play a crucial role in this circuit as high-impedance buffer stages. Their primary function is to isolate subsequent stages from the load impedance, preserving signal integrity. These amplifiers are characterized by their ability to amplify weak signals without significantly affecting the source impedance. They are essential in maintaining the fidelity of the audio signal as it progresses through the amplification chain. The use of op-amps ensures minimal loading of the preceding components, contributing to a robust and reliable audio amplification system. Their inherent characteristics enhance the overall performance of the crystal radio.