Biasing an electret microphone?

[boylesg]

I have looked on the web and all I have come up with is hopelessly conflicting information on this.

One examples uses a series 10k resistor from a 3V power supply.

Another uses a voltage divider of 3.3k and 5.6k with 9V power supply and no series resistor.

Another uses a 2.2k series resistor from a 12V power supply.

I want to use a 12V power supply so how should I bias my electret?

 

[frankrose]

Connect a potmeter in series, like 20kOhm, decrease its value and set voltage at the common point to 6V, then you will know how much should be your resistor value. The half supply voltage is a good thumb rule, but I am not sure it cannot damage the JFET device inside, you should know how much is the max. voltage. Probably it can tolerate this voltage, it is not too high.

Hmm.. In some specifications the max. voltage level is 10V. If your device has 10V max. voltage use a divider rather.

 

[Audioguru]

The datasheet of an electret mic shows a working voltage of a few volts and a current of about 0.5mA. Its output impedance is listed at about 2.2k ohms. Then if you power it from 2.2V the resistor to give it 0.5mA will be 2.2k ohms and will cut its signal in half. Its voltage will be only 1.1V and will cause severe distortion with medium to loud sounds.
If a 10k resistor feeds it from 9V then its output level will only barely be reduced, it will have 4V across the mic and produce no distortion with fairly loud sounds.

 

[c_mitra]

Another uses a 2.2k series resistor from a 12V power supply...

As Audioguru rightly says, you will need a current around 0.5mA (perhaps it will work even with 0.1mA- that means the mike will work till the battery- mostly a button cell- nearly dies) but if you are using a phantom supply of 12V, you will need a series resistance of 47K or 56K but see that your preamplifier can take it. Also higher voltages and larger resistors will give you more noise and therefore it is better to have a voltage divider to get around 3V or so. 10K series resistor with a 3V supply will work fine. You can even use a zener to get around 3V from 12V.

 

[boylesg]

Well I have an electret microphone (6050 I think) soldered into a ShortCircuits Pre-Champ Pre-Amplifier with 12VDC supply.

9V is on the + pin of the electret.

If I short the electret pins with a 5.6V zener diode then I no longer get audio output on my earphones.

 

[KlausST]

Hi,

That´s expectable.
The zener draws down the 9V to about 5.6V and thus shorts the audio signals.

Klaus

 

[Audioguru]

Shorting the output signal of an electret mic with a 9V power supply also kills the signal from it. The electret mic must be biased with a current, not a voltage but its voltage must be a few volts. Feed it 0.5mA though a 10k resistor connected to filtered 8V. Then the voltage across the 10k resistor is 0.5mA x 10k= 5V and the remaining 3V is across the mic. The 10k resistor loads down the signal only a little.

 

[c_mitra]

If I short the electret pins with a 5.6V zener diode then I no longer get audio output on my earphones. ...

Electret microphones are similar to capacitor microphones.

The current through the sensor varies with the sound pressure.

This current is converted to a voltage using a simple resistor.

This resistor is key to the proper functioning of the microphone. The sensor is basically a current device.

If you short the output with a zener, the current to voltage converter (the resistor) is defeated.

 

[boylesg]

Electret microphones are similar to capacitor microphones.

The current through the sensor varies with the sound pressure.

This current is converted to a voltage using a simple resistor.

This resistor is key to the proper functioning of the microphone. The sensor is basically a current device.

If you short the output with a zener, the current to voltage converter (the resistor) is defeated.

I tried the zener because someone mentioned that the voltage at the electret should be about 6V, whereas I measured 9V.

 

[boylesg]

My electret is probably a 6050. I got it from ebay and this type seems to be the most common device. Didin't pay much attention to its details at the time because I thought all electrets were much the same.

A 6050 datasheet I looked up says its max voltage is 10V.

 

[c_mitra]

A 6050 datasheet I looked up says its max voltage is 10V.

The circuit diagram is also given in the datasheet; they are most commonly used with a button cell. For example, 1 single LR44 (or equivalent) shall last for several hours.

The standard operating voltage is mentioned as 2V; perhaps a Li button cell may be more suitable. Use the lowest usable voltage because higher voltages produce higher noise.

 

[Audioguru]

The datasheet for the electret mic shows that its sensitivity (and overload level) are reduced when the voltage across the mic is reduced from 2V to 1.5V. it shows RL as 2.2k ohms, Then the 0.5mA mic current in the resistor produces (0.5mA x 2.2k=) 1.1V across the resistor so the supply feeding the 2.2k resistor should be 3.1V minimum. I would use a 5.6k resistor with a well-filtered 5V supply.