8

Yes, they have polarity and it has to be right to work- the output needs to be biased positive with respect to the ground terminal. The ground/GND terminal should be common with the case, so you can check polarity with a multimeter. Here, from a Panasonic Datasheet, is a typical arrangement: The two diagrams you show are equivalent, one is just drawn ...


7

That's a crappy circuit. Don't believe everything you find lying around on the internet. For reference, here is your circuit: The 10 kΩ pullup to power from 3 to 9 V should be good enough for most electret microphones. C1 then feeds just the AC part of the microphone voltage to the amplifier stage. That's all fine. The problem is the poorly ...


6

I am a technician at a boutique mic company. I like to build electret mics in my spare time. You can increase sensitivity, gain, and signal to noise ratio by running multiple electrets in PARALLEL-not series. This works because: 1) each capsule has an onboard JFET. When combining noise from multiple FETs, some of it cancels. Two amps= -3dB, four amps= -6dB ...


5

The case of your microphone is probably electrically connected to the flexible membrane inside the microphone, and is responsible for grounding it, while the "ground pin" is only used to provide the return path for the FET preamplifier. In normal operation, both need to be grounded so that there's a complete circuit to drive the gate of the FET. With the ...


5

The eletret microphone requires a dc bias to enable it to function. However, you only need to detect the audio (ac) signal to amplify and feed to a speaker. The capacitor blocks the dc bias, whilst passing the audio signal to the amplifier. There must be an amplifier to generate the required power to drive the speaker. The speaker will have a low impedance, ...


5

The input bias current of the AD8051 might be as high as a couple of micro amps and this doesn't sound much but, through a 1Mohm feedback resistor, this will generate a dc error of 2 volts on the output. Note that with the +input seeing a DC resistance of about 5kohm, the same bias current will produce an error of about 10mV. I would suggest equalizing ...


5

The capacitor is there to block the DC voltage from feeding into the A/D input of the microcontroller. Inside the electret microphone there will be a FET that can conduct current to GND as sound impinges in the capacitive diaphram of the mic. The external resistor provides the bias current for the FET. Variation of the current flow in the FET is also seen ...


5

The LM358 is not exactly low noise. You are using a lot of gain. 48000/180= 266. The amplification applies to noise as well as the signal. The bias resistor for the microphone is rather large. This will also affect how much noise you have. You haven't mentioned the power supply, but you have 5V for the microphone bias. The LM358 can operate on 5V, but ...


4

Generally, okay! The DC gain of each stage is one, so a few mV of offset voltage is of no importance at all. The gain seems a bit on the high side unless it's some kind of hidden microphone. Remember that the V/Pa sensitivity is always quoted for RMS 1 volt, and you'll start to get clipping around 3.2V peak-to-peak. You might want to put an RC filter in ...


4

C4 reduces closed-loop gain at high frequencies. It is a form of dominant pole compensation to fend off the risk of amplifier instability. It shouldn't be necessary with internally compensated op-amps, but it's good to leave a spot on the circuit board for it. As for C2, primarily it is needed for proper biasing. If R6 were connected directly to ground, the ...


4

I'm starting to wonder whether the 1k resistors are too small, as they're smaller than the 2.2k output impedance of the microphone. Those are the output impedance of the microphone. If you look at the mic capsule's datasheet you'll see an equivalent circuit: I don't know why manufacturers always show the FET as a triangle. This is how it's actually ...


4

I think you've misinterpreted the circuit shown on the web page. It applies to any electret. Basically it shorts out only the AC (signal) by using a large capacitor but avoids switching the DC bias voltage which is the source of the pop. When the mic is plugged in C1 experiences a step voltage (from the 5V supply/R2) which brings both terminals of the ...


4

Low frequency noise (~50/60Hz) is mostly caused due to induction of electrical noise into the traces on PCB (or wires, if you're not using a PCB). This is particularly bad with breadboard setups due to the nature of their construction. Since you have figured out that the source of noise inductance is between your microphone and the amplifier, you could try ...


4

You selected a microphone board with automatic-gain. This is exactly the OPPOSITE of what you need. You can not measure the actual audio levels when there is something upstream UN-doing all the audio level changes ("auto-gain"). So first, you must use the proper microphone module that will deliver the actual, honest, un-modified audio levels to you. ...


3

Note that in this case you actually have 2 kΩ bias, not 1 kΩ. That is because the bias resistor is split on both sides of the mic, probably hoping for most of the noise pickup to be common mode, which the amp looks like it is designed to reject. The outer (argh, use component designators already!) 1 kΩ resistors are for filtering the ...


3

Let's start with the electret microphone basics. The actual microphone is formed by a (very very) thin sheet of mylar film that is charged. This is connected to the metal body of the electret capsule but insulated from the pick-up plate. The mylar film and the pick-up plate form a capacitor. The charge on the mylar film produces a voltage difference between ...


3

Hope I haven't missed anything. Well possibly I did - David Kessner reminded me that answers sometimes have to go the extra mile because they may be read by a person who has R6 (10k pot e.g.) tied to a midrail point and therefore doesn't need C2 to make the circuit function correctly. Under these circumstances C1 becomes the dominant component to block low ...


3

Negative Feedback It gives you: better linearity lower gain even lower output impedance opportunity for frequency-dependent gain As shown, you get DC feedback via R1+R2. But R1/C1 forms a low pass filter for signals coming from the collector and going to the base. Less negative feedback means less reduction in gain for high frerquencies. Cancel out all ...


3

Get off you idea of "WITHOUT any special parts". An electret microphone will output a low level analog signal when some bias current is applied to the part via a resistor from a supply voltage. That low level signal then needs to be amplified to some level that is compatible with the analog to digital converter that will be used to produce the 1's and 0's ...


3

A typical digital microphone circuit is produced of a few parts. Power, Microphone + Analog Pre-amp, a Analog to Digital Converter, and the Microcontroller/Receiver. Often the ADC and Controller are one piece. The Preamp can be as well. For example, the OVC3860 Bluetooth Audio IC is an all in one IC that provides Mic power, pre-amp and ADC, as well as ...


3

You are running a gain of 40 dB. Any noise that is present at the input will be amplified by 100x. There are several possible places where the noise might enter the circuit but the most likely spot is the bias resistor. There are a couple of things that you can try. 1) Move the bias resistor power lead from Vcc to ground. Although the mic won't work, ...


3

Well, with a bias resistor (aka load resistor) of 2k2 (as specified in the data sheet picture in the question), the sensitivity figure (-42 dBV/Pa) means that at a sound pressure level of 94 dB (1 pascal), the output voltage of the microphone is -42 dBV or 7.94 mV RMS when the sound is 1 kHz. With a 10 uF coupling capacitor and a 20 kohm load, the low ...


3

You have the wrong thing, first off The automatic gain control (AGC) on your existing microphone-board is not what you want here -- a sound level detector is going to get thrown off by the action of the AGC loop changing the gain all over the place as it tries to maintain a constant output level (what else would you expect from an AGC loop?). You might as ...


3

Check to see if C2 is microphonic by listening while tapping directly on C2. If this is the problem, it can be fixed by replacing C2 with a Mylar capacitor. Ceramic capacitors are often microphonic. I don't expect the aluminum electrolytic to be microphonic, but it is worth checking. It could be that the effective series resistance (ESR) of C1 is too high. ...


3

You could also try adding a smaller-value capacitor across (in parallel with) the large 100uF capacitor. That would better attenuate high frequency sound that was still leaking through. It is impossible to imagine that "blow into the mic or tap it hard" could "sound like high pitch feedback". You may not be using the terminology in the common meanings. An ...


3

The audio detector you have chosen is IMO not viable for your project needs. The KY-038 is a very simple sensor and from it's schematic (shown below) you can see that the gain is adjustable but with no pre-amplification to the analog output. The potentiometer in the main adjusts the threshold for the level detector, though it also has a gain effect for the ...


3

You have several problems if you want to power your amplifier and filter through just the bias for the electret microphone. Voltage. You've already mentioned this. There's only a couple of volts available as bias for the microphone on your cellphone. There are amplifiers that can operate on just a couple of volts, but they are rarer and more expensive ...


3

On this Wikipedia page it is explained how an Electret microphone works. What you call the "microphone" is actually the microphone diaphragm itself and a JFET. The JFET is needed to amplify the small signal from the microphone diaphragm such that it can be used. Without the JFET the signal would simply be too weak and the microphone would not be useful. To ...


3

If you are concerned with linearity of voltage response to membrane displacement, the response is linear. Instead of reconstructing the math myself, here is the explanation from openmusiclabs.com: As one can see, the response is linear, which is why electret (and condenser) mikes are the best. The "flatness" of frequency response over the range of acoustic ...


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