I've never owned or used a multimeter before and was wondering if I need to buy an adapter of sorts to measure voltage coming from a 3.5mm (1/8") patch cable. The voltages are coming from my modular synthesizer.

Thanks and apologies for the novice question.

 

That meter will be handy for many things, but not to characterize the time varying voltage out of a synthesizer. The meter does not respond fast enough to track the signal.

To visualize your synthesizer output, an oscilloscope is the thing to use. Follow this thread - http://forum.allaboutcircuits.com/showthread.php?t=35175 - to get freeware that lets you use your sound card as an audio oscilloscope (your monitor is the display).

 

I tried mesuring voltage coming from a headphone TRS connector once, the volmeter doesn't pick any stable voltage from there, it varies a lot, and not "a lot" like going up or down, it's actually a frecuency. It has to do with digital-to-analog signal conversion. It's like trying to measure the frequency of sound with a voltmeter.

 

I've never owned or used a multimeter before and was wondering if I need to buy an adapter of sorts to measure voltage coming from a 3.5mm (1/8") patch cable. The voltages are coming from my modular synthesizer.

The answer is yes, you'll need an adapter. It would be straightforward to make one from a plug, some wire, and two 4 mm banana plugs. These can be found at a store like Radio Shack.

You don't say why you want to measure the signal. There are nuances involved, as beenthere alluded to. If the synthesizer is putting out a sine wave within the bandwidth of your multimeter, then you can meaningfully measure the output. If your multimeter is RMS responding, then it doesn't have to be a sine wave. But few multimeters have a 50-100 kHz bandwidth, which is about what you'd want to get accurate RMS readings up to around 20 kHz.

If you tell us what it is you're trying to do, you'll get better advice.

An oscilloscope is a much better tool to examine the output and even inexpensive scopes should be able to deal with the output, assuming it's in the audio range of frequencies.

 

I should have been more specific. I'm going to build a sequencer for my modular synth. I would like to see what kind of voltages my current sequencer sends.

It's not a vco, so it's not generating audio frequencies. It sends control voltages that trigger vco's and gates that trigger envelopes. My goal is to find out the voltages being sent from the sequencer. In particular, I want to know what voltage the gates are being triggered at. I've read 3v, 5v and a range of voltages. I'd like to know for sure. An oscilloscope is out of my price range at the moment, but is on the wishlist. As far as I know, sequencers generate regular voltages.

 

Unless you have some special knowledge about the circuit's output, the only tool appropriate for this is an oscilloscope. If you don't have one, maybe you can barter with someone to trade for some time on one. There's also the approach of using the sound card on a computer with some software to make a poor man's oscilloscope.