Loudspeaker as a Microphone

This circuits allows you to use a cheap loudspeaker as a microphone. Sound waves reaching the speaker cone cause fluctuations in the voice coil. The voice coil moving in the speakers magnetic field will produce a small electrical signal.

The circuit is designed to be used with an operating voltage between 6 and 12 volts dc. The first transistor operates in common base mode. This has the advantage of matching the low input impedance of the speaker to the common base stage, and secondly has a high voltage gain. The second stage is direct coupled and operates in emitter follower. Voltage gain is slightly less than unity, but output impedance is low, and will drive long cables.

Speech quality is not as good compared to an ordinary or ECM microphone, but quite acceptable results can be obtained. Speaker cones with diameters of 1 inch to 3 inches may be used. Speaker impedance may be 4 ohm to 64 ohm. The 8.2 ohm resistor value may be changed to match the actual speakers own impedance.

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One Chip AM/FM Radio with Audio Power Amplifier

Description: The integrated circuit TDA1083 includes, with exception of the FM front end, a complete AM-/FM-radio-circuit with audio power amplifier. An internal Z-diode stabilizes the supply voltage at VS 13 V, which allows with the aid of a resistor and a rectifier, the circuit to be driven by a higher external supply voltage. Features: Large supply voltage range VS = 3 to 12 V High AM-Sensitivity Limiting threshold voltage Vi = 50 V Audio output power P0 = 0.7 W AFC-connection for VHF-tuner AM-FM switching without high frequency voltages Applications: AM-/FM- and audio-amplifier Circuit Diagram: Circuit diagram for One Chip AM/FM Radio with Audio Power Amplifier Datasheet for TDA1083: Download

2 x 15 W stereo Bridge Tied Load (BTL) audio amplifier

General description: The TDA8946J is a dual-channel audio power amplifier with an output power of 2 × 15 W at an 8 Ω load and a 18 V supply. The circuit contains two Bridge Tied Load (BTL) amplifiers with an all-NPN output stage and standby/mute logic. The TDA8946J comes in a 17-pin DIL-bent-SIL (DBS) power package. The TDA8946J is printed-circuit board (PCB) compatible with all other types in the TDA894x family. One PCB footprint accommodates both the mono and the stereo products. Features: Few external components Fixed gain Standby and mute mode No on/off switching plops Low standby current High supply voltage ripple rejection Outputs short-circuit protected to ground, supply and across the load Thermally protected Printed-circuit board compatible Circuit Diagram: Circuit Diagram for 2 x 15 W stereo Bridge Tied Load (BTL) audio amplifier PCB layout: PCB layout TDA8946 Datasheet for TDA8946J: Download

200W Hybrid Audio Amplifier Circuit

200W Hybrid Audio Amplifier Circuit - c onnecting two TDA2030 thru cheap power transistors we can create a amplifier wich can deliver a higher power. With the components value from the schematic the total amplifier gain is 32 dB. The speaker can be 2 ohm instead of 4 ohm if we use the TIP transistors. TDA 2030 is produced by SGS Ates and is a complete audio amplifier. AB class of the final amplifier cand deliver up to 14W on 4 ohm at a +-14V power supply. With a proper designed power supply this audio amplifier can output 200W. Active components: IC1, Ic2 TDA 2030 T1, T3 = BD 250, TIP 36 T2,T4 = BD 249, TIP 35 D1 … D4 = 1N4001 200W Hybrid Audio Amplifier Circuit

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