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Low Voltage Preamplifier by BC549

A low voltage preamplifier optimised for 3 Volt operation.
This is a special low voltage version of my audio preamp. T1′s emitter voltage is biased close to half supply voltage (1.5V) to allow for maximum output voltage swing. Both transistors are direct coupled and have closed loop feedback to aid temperature stability.

Source:http://www.zen22142.zen.co.uk/Circuits/Audio/lvpreamp.htm
Thank you.

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Categories: Pre Amplifier Tags: BC547, Pre Amplifier

Voltage Controlled Switch by BC547

This switch circuit operates when a voltage level which is previously adjusted is applied to the input. Circuit is designed for 24V supply but can be used in a range of 18V-36V. Voltage level which triggers the circuit can be adjusted by P1 potentiometer. A stabilized voltage is applied to this potentiometer through zener diode and Tr5. When the input voltage level exceeds this value TR1 starts conducting and afterwards Tr2, Tr3, Tr4 transistors conduct and relay switches on.

Switch S1 that is connected to relay, carries the signal from Tr3 to Tr1 through R1 and keeps Tr1 conducting.

When the input is short circuited, D1 diode keeps the circuit operating and you can omit it if you want.

Simple microphone preamplifier by BC547

This is a simple microphone preamplifier circuit which you can use between your microphone and stereo amplifier. This circuit amplifier microphone suitable for use with normal home stereo amplifier line/CD/aux/tape inputs. This microphone preamplifier can take both dynamic and electret microphone inputs (preamplifier provides power foe electret microphone elements). The idea of this circuit is to keep the design as simple as possible to be easy to build. That was my goal when I needed a simple external microphone preamplifier for my mixer. The performance of the circuit is nothing superior but can be used with many not so serious projects.