Circuit Project Electronic

Three-Level VU meter using LM339
Thursday, November 20th, 2008





This circuit is intended to indicate the power output level of any audio amplifier. It is simple, portable, and displays three power levels that can be set to any desired value. For a standard HiFi stereo power amplifier like the 25W MosFet Audio Amplifier described in these pages, the power output values suggested are as [...]

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Six-LED Bar VU meter
Thursday, November 20th, 2008





This device, connected to the loudspeaker output of an audio amplifier, will indicate the instantaneous output power delivered to the loudspeaker(s) by means of six LEDs illuminating one after another by voltage values increasing little by little, providing the visual impression of a luminous bar or column, increasing and decreasing in height following the increase [...]

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Precision Audio Millivoltmeter using CA3140
Thursday, November 20th, 2008





Notes:
* Connect J2 and J3 to an Avo-meter set to 50µA range:
* Switching SW2 the four input ranges will be multiplied by 5
* Total fsd ranges are: 10mV, 50mV, 100mV, 500mV, 1V, 5V, 10V, 50V
* Set R11 to read 1V in the 1V range, with a sine wave input of 1V @ 1KHz
* Compare the [...]

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