Guitar output signal. How to measure it with a voltmemter?

[Zappacat]

How do I measure the output signal strength of my guitar?  Can I do this with a voltmeter?  I'm trying to start my first SS guitar amp and I'm trying to trace the signal levels from the guitar to the final output stage.  This may sound like a stupid question for someone building their won amp but I'm stuck at square one.  Any help greatly appreciated.

[Enzo]

If you just want to find the signal levels through the amp, apply a sine wave and use your AC volt meter.  If you have a "true RMS" meter great.  I find that my basic FLuke meters read AC pretty well up to at least 1kHz.  Certainly at 40Hz it is OK.

Now that tells you little about tone or frequency response, but your question was about levels.

The use of a steady test tone yields consistent results.   It is darn difficult to get steady test levels from a guitar.

A scope is a natural for this, you can look at the vertical range of the signal and frequency doesn;t much matter.

Your guitar amp is not hifi, it is not flat in response, so the note or frequency of your test signal makes a difference in signal level.

[J M Fahey]

Hi Zappacat.
Most general purpose multimeters aren't sensitive enough to measure such low voltages, unless they have a 200 mV AC full scale range.
If you have one of the latter, hook one to a plug, plug it into your guitar with all controls "open" and play.
You'll measure around 200mV on full chords, and 10 to 50 mV picking single strings.
Measurements vary wildly with different pickups, strings, mics, whether you use a pick or not, and even how tired, bored, or excited you are.
If not possible, design considering your guitar a 50 to 100 mV generator (with occasional 500/800 mV bursts) and you won't be far off.
I've drawn  some schematics for you, about a step-by-step build, from the simplest LM386 project, to an LM3886 50W amplifier, driven by said LM386 used as a preamp/distortion. A 2 Knob 2 switch amp usable in jams and gigs.
After you build and test it, it's relatively simple to embellish it with different preamps, tone controls, effects, whatever , but you start with something always usable.
I'll scan and post it in the other post.
Good luck.
Juan Manuel Fahey

[Zappacat]

Hi Zappacat.
Most general purpose multimeters aren't sensitive enough to measure such low voltages, unless they have a 200 mV AC full scale range.
If you have one of the latter, hook one to a plug, plug it into your guitar with all controls "open" and play.
You'll measure around 200mV on full chords, and 10 to 50 mV picking single strings.
Measurements vary wildly with different pickups, strings, mics, whether you use a pick or not, and even how tired, bored, or excited you are.
If not possible, design considering your guitar a 50 to 100 mV generator (with occasional 500/800 mV bursts) and you won't be far off.
I've drawn  some schematics for you, about a step-by-step build, from the simplest LM386 project, to an LM3886 50W amplifier, driven by said LM386 used as a preamp/distortion. A 2 Knob 2 switch amp usable in jams and gigs.
After you build and test it, it's relatively simple to embellish it with different preamps, tone controls, effects, whatever , but you start with something always usable.
I'll scan and post it in the other post.
Good luck.
Juan Manuel Fahey

Thanks to both you and Enzo for your help.  I can't tell you both how much I appreciate you guys answering my "beavis and butthead" questions.  I was really looking for the voltage range to be expected(from the guitar signal out) at this point of the design and understanding phase.  From that point on I want to work out(mathematically) what the signal level would be as it moves upwards through the gain stages of the preamp -> power amp -> speakers.  Since I don't have a lot of advanced electronic analysis hardware I really needed to know the expected voltage envelope that is coming from a typical guitar output to reference as a starting point for later calculations. Based on what you've said I'll expect it to be anywhere from 50mv to 800mv.  I'm looking forward to see those schematics.  I'll post my build when I'm done in a coherent format so it might help someone else in the future.

Just one more thing, if I had an oscilloscope and everything I needed to plug a 1/4 inch jack into my guitar, what measurements would I actually get out of it?  I realize there is a waveform and voltage but what else is there?  I think I'm missing something really fundamental here and I'm lost.  What is the waveform a product of?

Thanks again guys!

[J M Fahey]

Well, a waveform as seen on an oscilloscope has *a lot* of information, but of course you must learn how to read it .
You see the voltage better than any voltmeter, the note harmonics, buzz, hum, any intrference, in an amp or preamp whether it clips, blocks, oscillates, instability, frequency, the works.
It´s all there.
As of the guitar signal levels, design your preamp to be able to amplify a 50mV signal, but not to clip with an 800/900 mV one, that's about it.
Even shorter: in a +/-15V powered op amp , design with no more than 20x gain , or no more than 10x if you use very powerful pickups and/or are heavy handed.
Study the input stage of many commercial SS guitar amp and you'll see.