correct testing methodology of electrical parameters of a microphone preamplifier

Thread Starter

nickandreas

Joined Dec 5, 2016
4
hello , i have been searching for the correct testing methodologies of the electrical parameters of a microphone preamplfier board on the internet for a while now and i have not come across any reliable answer for testing noise ,input and output impedance, distortion and current intake. can anyone guide me on how to test my microphone preamplifier board for these electrical parameters?
 

Alec_t

Joined Sep 17, 2013
14,280
Welcome to AAC!
What measuring equipment do you have available? Quantitative noise and distortion tests would require specialised equipment, but impedance and current measurements would be possible with commonly available kit.
 

Thread Starter

nickandreas

Joined Dec 5, 2016
4
Welcome to AAC!
What measuring equipment do you have available? Quantitative noise and distortion tests would require specialised equipment, but impedance and current measurements would be possible with commonly available kit.
i can use an oscilloscope and a digital multimeter.
 

#12

Joined Nov 30, 2010
18,224
You are seriously not equipped for this.
Let's see, low distortion frequency generator, distortion meter, low noise amplifier, maybe a spectrum analyzer...

Audio amps aren't all that exotic that you need a full blown testing laboratory to buy a $10 kit.
 

#12

Joined Nov 30, 2010
18,224
So, what's your goal? Trying to design a laboratory quality microphone to test professional audio equipment?
 

Kermit2

Joined Feb 5, 2010
4,162
Did you switch to decaf #12?
:)

Be nice to know what operational specs CAN be discerned with reg. Tech gear.

If ....That is.

Hmmm.... (Kermit taps foot and glances at watch)
 

#12

Joined Nov 30, 2010
18,224
Did you switch to decaf #12?
Am I nicer than usual today?:rolleyes::p

With nothing but a DMM and a scope, you can just about see if it's working.
Anything after that requires an input generator and an output analyzer.
I can do a frequency response sweep with a signal generator and a 'scope, but measuring distortion is a whole different game, and measuring inherent noise starts with some really good, low noise amplifiers. Your equipment must be better than what you're measuring or you'll just be measuring your equipment. It's so doggone easy to do good quality audio designs that you immediately get hit with needing top quality equipment to measure with.
 

ronv

Joined Nov 12, 2008
3,770
hello , i have been searching for the correct testing methodologies of the electrical parameters of a microphone preamplfier board on the internet for a while now and i have not come across any reliable answer for testing noise ,input and output impedance, distortion and current intake. can anyone guide me on how to test my microphone preamplifier board for these electrical parameters?
If your goal is to understand it's typical operation you can simulate it. If you need to actually test it you need more "stuff."
 
If your after resistive input and output Z. you can put a Potentiometer in series and adjust the signal so it's 1/2 the size with no pot. Measure the POT and you get the resistive impeadance.

The range of current may determine the method, or the equipment. Feedback ammeters (Very little voltage drop) are available or you can make one.

Frequency response of the board is a lot easier than the system.

Audio distortion analyzers don't come cheap.
 

Kermit2

Joined Feb 5, 2010
4,162
The human ear is the cheapest analysis you can get, and with practice listening for the right things can do very good even compared to expensive equipment.
Some amount of noise in the silence is to be expected, but somewhere around -60 dbm the human ear can no longer detect the sound in the background of program material. It is still there and can be heard if you turn up the amp during a quiet period, but the program material will be much to loud at the settings needed to hear the noise floor.
So advertising that claims this or that amplifier is better because of some specific response curve or noise level number is just a bunch of noise itself.

It comes down to the ear of a human.
Which amplifier "sounds best" to you. Marketing double talk has confused people about such things.
 

Thread Starter

nickandreas

Joined Dec 5, 2016
4
So, what's your goal? Trying to design a laboratory quality microphone to test professional audio equipment?
My goal is to check 2 electrical parameters (such as noise ,input and output impedance, distortion, frequency response and current intake ) of my microphone preamplifier (which is my professor's design) and actually understand my findings . i can use my university's lab for this tests but i cant find any resourceful methodologies anywhere and i was hoping someone could guide me on how to perform the tests and the equipment needed for them
 
I gave you easily how to do resistive impeadance with a potentiometer.

Reactive, would be a little harder, but not that hard. Look up osciloscope probe compensation. With a square wave in, you may have output a non-square waveform. With a RC network divider after the input signal, adjust for a square wave and back out C indirectly.

Once you have a compensated square wave input, look at the output. Again adjust an RC divider so the output is square. Back out C.

The result may be frequency dependent.
 
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