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Monday 13 June 2011

Bench Amplifier


Description:
A small 325mW amplifier with a voltage gain of 200 that can be used as a bench amplifier, signal tracer or used to amplify the output from personal radios, etc.
Circuit diagram

Notes:
The circuit is based on the National Semiconductor LM386 amplifier. In the diagram above, the LM386 forms a complete non-inverting amplifier with voltage gain of x200.
A datasheet in PDF format can be downloaded from the National Semiconductor website. The IC is available in an 8 pin DIL package and several versions are available; the LM386N-1 which has 325mW output into an 8 ohm load, the Lm386N-3 which has 700mW output and the LM386N-4 which offers 1000mW output. all versions work in this circuit.
The gain of the Lm386 can be controlled by the capacitor across pins 1 and 8. With the 10u cap shown above, voltage gain is 200, omitting this capacitor and the gain of the amplifier is 20.
The IC works from 4 to 12Volts DC, 12Volt being the maximum recommended value. The internal input impedance of the amplifier is 50K, this is shunted with a 22k log potentiometer so input impedance in this circuit will be lower at about 15k. The input is DC coupled so care must be taken not to amplify any DC from the preceeding circuit, otherwise the loudspeaker may be damaged. A coupling capacitor may included in series with the 22k control to prevent this from happening.
The finished circuit.

Low impedance microphone amplifier


Description
The circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones. It will work with stabilized voltages between 6-30VDC. If you don't build the impedance adapter part with T1, you get a micamp for higher impedance microphones. In this case, you should directly connect the signal to C7.
Schematic diagram


Amplifier of acoustic frequencies with preamplifier





Technical characteristics:
Tendency of catering: 15V
Force of expense: 4,2Wrms in the 4W
Minimal signal of entry: 94mVp-p with preamplifier, 0,65Vp-p without the preamplifier.
Circuit diagram


Three-Level Audio Power Indicator


Battery-operated 3 LED display
Simply connect it to loudspeaker output
Circuit diagram


Audio Perimeter Monitor


Circuit diagram

Notes:
Using a single cable such as speaker wire or doorbell cable, this circuit can be remotely positioned, for
example, at the bottom of a garden or garage, and used to detect all sound in that area. The cable can
be buried in a hosepipe or duct and is concealed out of sight. The mic is an ordinary dynamic mic insert
and should be housed in a waterproof enclosure with the rest of the circuit.
The mic output is amplified by the two transistors, the output is fed down the cable via the 220u capacitor.
Here, it has a dual purpose of preventing the DC supply from upsetting the bias of the circuit, and also
allowing the smaller ac audio output to pass down the line. At the power supply, the audio is recovered
by the 10k preset and 220u capacitor. It is used to feed a small audio amplifier (such as the 2watt design)
shown earlier on this site.