Reading Audio Jack Voltages

[Palbert]

Hello All,

I am trying to measure the input voltage coming from my guitar to an effects pedal I've been working on. When I try to read the voltage across the input jack directly (my pedal is bare bones and the jacks are open), it starts out at whatever ambient mV reading then when I connect the leads to each side of the jack, the reading always goes to 0mV. I tried adding a wire to the breadboard where the jack is connected and reading that voltage instead but I get the same response. Am I missing something?

 

[Sceadwian]

What are you using to measure the voltage? A multimeter can not be used to measure complex waveforms such as those from a musical device pickup.

 

[Palbert]

Thats what I was using. I figured I would be able to convert the rms voltage back to peak. Would I have to use a scope then?

 

[Sceadwian]

Even the best RMS meters tend to have a cutoff lower than 1khz, and that's only for sine wave's!

What you think you need to do is overshadowed now by what you're actually trying to do... What is the reason you're trying to measure the voltages from this pickup?

 

[Palbert]

I gotcha. I want to know what the input voltage to my pedal will be so that I can set the gain correctly.

 

[alec_t]

Wikipedia says
"The output voltage of pickups varies between 100 mV rms to over 1 V rms for some of the higher output types. Measurements taken with an Oscilloscope with a hard strum on all 6 guitar strings can produce a larger output voltage swing, typically peak voltages of +/- 5 volts for single coil pickups and +/- 10 volt peaks on dual coil pickups."
It looks as though your pedal will need an input pot which the user can set according to the pickup type.

 

[Palbert]

Nice, thanks. An estimated input voltage will be good enough for now. Thanks again.