how to have an output of 500milli volts dc from 3.5mm audio plug?

Question

Trying to measure output voltage from certain songs but ac voltage goes up and down. How would I accomplish of having a steady voltage to output of 500 milli-volts dc through the audio plug?

Answer 1

Out of the plug? No way. The output stage either has a high pass filter or an output capacitor (effectively the same thing) preventing DC from getting to the plug.

Actually, DC on any audio output is considered an error - and usually, an error that can severely damage the connected components.

If you want to convert audio AC to DC, the rectifier mentioned by bill won't help you very much - a regular silicon rectifier has a voltage drop of about 1.4 Volts, so there won't be anything left from the signal after the rectifier. You'll need an active rectifier, essentially an OpAmp with a diode in the feedback loop.



But going back to your original problem: you said you wanted to measure output voltage from certain songs. For that, you 'll need either an oscilloscope or at least a TRMS multimeter with peak hold functionality. And then you'll have to dig into some maths in order to first define what you mean by 'voltage' when talking about an irregular AC signal - there are at least three commonly used possibilities to choose from: peak, average, RMS. More, if you want specific results.

Answer 2

A steady voltage is DC. The audio is AC. You would have to rectify the audio and filter it. Minimum would be a diode and capacitor. Look up Half Wave Rectifier on the internet. Full wave rectifier would be better still but takes more parts. To get 500 millivolts you would likely need an audio AC voltage of about 750 millivolts AC peak. The actual would depend on what rectifier circuit you use.

Answer 3

No offence intended, but I think you may have misunderstood some equipment instruction/specification. If an amplifier or recording device specifies an input voltage, that will usually be the maximum level it accepts without distortion.

What you need is to adjust levels to get the best result for a clear recording or a good sound. Some gear has VU meters and LED lights showing signal level, which CAN be very helpful, but your ears are more useful than any meter.

Answer 4

Analog audio signals in electrical form are,

by nature and necessity, composed of

a continuously varying AC voltage.



A constant AC voltage would produce a steady tone

(or a combination of steady tones),

not what we would call music or speech.





In order to "measure" an audio voltage,

one must either accept an average of it over a period of time,

or choose a specific instant from it at which to take a reading.



In either case, a broadband AC millivolt meter

or a calibrated oscilloscope (or both) is recommended.