Mic newbie question - testing a mic amp for linearity and distortion?

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shaggy

Well-known member
Joined
Jul 28, 2010
Messages
127
Location
California USA
I've tested power amplifiers while driving a dummy load in place of a loudspeaker; and preamps, similarly with an appropriate load, the inputs in either case being fed a low distortion signal to which the resulting output is compared (as to frequency response, THD, etc).

My question is, can one test the linearity/distortion characteristics etc of a mic's preamp/impedance converter in a similar way - that is, without the transducer - by substituting ...something... for the capsule, applying a very (very) low-level signal across it, and testing the output?

Am I off-track here...how does one normally do this test? Obviously I mean to take the non-linearity of the capsule out of the equation in order to find out the frequency response and distortion characteristics of the electronics alone.

Thanks for any feedback!
Dave
 
OK, I feel like an idiot now. Of course a condenser capsule isn't an AC generator, but the variable element in a bridge circuit. So you'd still need some kind of variable capacitance in place of the capsule, but (for my test scenario) one that was electrically, rather than acoustically coupled to the signal generator.

Or you could just use a known 'flat' condenser capsule...but you'd still need an anechoic chamber, which was what I was tying to get around in the first place...

So, just my uninitiated/half-asleep thoughts...probably wasting my time and sounding like a total noob. I suspect most people don't worry about this simply because the poor linearity of a typical mic capsule makes amplifier performance almost a moot point. But if I build an amplifier, I want to know how it performs.

Any thoughts?

Dave



 
Actually you simply inject the signal through a small capacitor with it's value near the actual capacitance of the capsule e.g. 50 to 100 pF.
 
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