The Signal Tracer RF and audio probe using Lm386 integrated circuit is geared towards maintaining preamplifier, power amplifiers and even RF devices.
As a probe of audio signal and RF, can make maintenance of equipment such as amplifiers, preamplifier, radios, car audio, transmitters, recorders, televisions and more. The basic operation is to follow the audio signal to a point where it is not available or is undergoing any changes that should not occur.
About circuit audio signal and RF follower for bench maintenance
To learn how to use this tool, I suggest you download this PDF of the Newton C. Braga (Portuguese language) – Using test instruments measure.
The operation is simple, in two functions:
RF function: the signal will pass through D2, C4 and R1, which form an AM Demodulator circuit, to detect defects in Radio Frequency circuits, the audio will be demodulated and can be heard on the loudspeaker!
AF function: the signal will stop passing through the Germanium diode D2, so you can hear the audio signal amplifier on the loudspeaker! The capacitor C5 prevents any DC component from going to the device being tested. To control the volume we use a potentiometer of 47K. The overall gain of the Lm386 is set to 200, if you wish you can add a potentiometer in parallel with C3 to gain control of the Lm386. The network formed by C7 / R2, guarantees stability to the Amplifier and avoids RF interference.
To power the circuit we use a 9 Volt battery, so it becomes portable, also a 9 Volt DC power supply can be used.
Circuit diagram of the audio and RF Signal investigator
Suggested printed circuit board for mounting of the circuit
List of material for assembly of the circuit With Lm386
|Resistor’s 1/4 Watt 5%|
|R1||470K – Yellow, Violet, Yellow, Gold|
|R2||10 – Brown, Black, Black, Gold|
|C1,C6||470µF/25V – Electrolytic Capacitor|
|C2||100nF – Ceramic capacitor|
|C3, C5, C8||10µF / 25V – Electrolytic Capacitor|
|C4||270pF – Ceramic capacitor|
|C7||47nF – Polyester or Ceramic Capacitor|
|D1||1N4004 or equivalent – silicon diode rectifier|
|D2||1n34 or equivalent – Germanium Diode|
|IC1||LM386N-1 – Integrated circuit audio amplifier – Dil8|
|IN||Connector for RF or Audio signal input|
|OUT||Connector for speaker|
|DC_9V||Jack to power, connect the external power supply|
|P1||47K – potentiometer|
|BAT||9V Volt battery|
|Solder, wire, PCB, box, test lead, etc..|
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