I'm an electronics newbie, but I've had some experience with oscilloscopes in college lab. However, I need to design and wire a simple circuit that can read values from an electret mic. Since the electret mic produces really low voltages, I need to amplify it (a preamplifier).

The problem is, I do not have an oscilloscope and thus no way to know if the circuit works. Is there any way of knowing if the signal is amplified (or present) with a multimeter? I refuse to believe that every hobbyist out there who wants to play with audio signals has access to a DSO.

  • \$\begingroup\$ Do you have a peak or max detect for an AC measurement on your DMM? \$\endgroup\$ – Samuel May 25 '14 at 8:03
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    \$\begingroup\$ For audio work, an old-fashioned analog CRO (cathode-ray oscilloscope) is more than adequate. You can find working units at hamfests (electronics flea markets) or on ebay for $20 or so. Well worth the investment for the things you'll learn using it. \$\endgroup\$ – Dave Tweed May 25 '14 at 10:49
  • \$\begingroup\$ It is not reasonable to have no way of knowing whether or not whatever you are building works. In that case, you just build something that doesn't work. If you cannot tell that it doesn't work, other people probably cannot either. But then, what purpose does it serve? \$\endgroup\$ – Kaz May 25 '14 at 13:30

With a DMM, you should first measure the quiescent DC voltages of your circuit and make sure those are correct.

You might be able to read the amplitude of AC signals in the millivolt range with your DMM but that depends on your DMM.

The problem is, I do not have an oscilloscope and thus no way to know if the circuit works.

It's not true that you have no way to know if the circuit works. You're just not thinking clearly.

For example, you could connect the (AC coupled) output of your preamp to the input of an audio amplifier or the audio / mic input of a sound card on your PC.

Indeed, a sound card can be used, to some extent, as an audio o'scope.

In my previous life as a technician, I sometimes used a signal tracer to quickly determine if a signal was present or not while troubleshooting a circuit.

Here's a video of someone turning a powered computer speaker into a signal tracer.


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