Audio Output Level Indicator


Posted on Feb 7, 2014

This unit is designed for monitoring the audio output level across a loudspeaker when carrying out alignment of radios. As no great precision is required, a simple passive circuit arrangement has been used. The circuit is a voltage-doubling rectifier driving a panel meter. The input signal is AC coupled via C1. D1 holds the signal so that the nega


Audio Output Level Indicator
Click here to download the full size of the above Circuit.

tive peaks are at ground potential. The mean level is above ground, so the polarity of C1 is important. The peak level is rectified by D2 and stored in reservoir capacitor C2. The value of R1 has been selected to give the required calibration with a 250uA meter movement. If a 100uA is used, the alternative component values should be used. The prototype was constructed using a small piece of plain matrix board. Tag strip or stripboard could be used if preferred. A PCB would be overkill for such a simple design! The meter used on the prototype was a low cost ( £3. 20) 250uA signal strength meter obtained from Maplin (Order Code LB80B). This is marked "SIGNAL" and has an arbitrary scale marked 0 to 5, making it ideal for the purpose. A higher quality meter could be used, but this would offer no real advantage. The input may be bought in via a length of two-core speaker cable. The free end may be fitted with a pair of small crocodile clips for easy connection to the speaker tags in the radio being aligned. The unit is designed for connection across a loudspeaker. If you wish to disconnect the loudspeaker because of the annoying noise, replace it with a suitable wirewound resistor. Two people have contacted me regarding the availability of the OA47 germanium diodes. These are listed in the current Maplin catalogue (Order Code QH70M, price 49p each). I followed your online article using 10uF for C1, 2. 2uF for C2, silicon diodes...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Telephone Visual Ring Indicator
    Simple Mobile Phone Battery Charger
    LED Lamp Dimmer Circuit Schematic Diagram
    Low-Noise Microphone Amplifier (OP270E)
    Time Domain Reflectometer (TDR)
    SCR Phase Control Speed Control/Dimmer
    Tesla Switch
    MM36SB020 two-wire wiring diagram
    12kHz IF signal generator circuit diagram



    Top