See? "But an electret mic needs a preamp with a voltage gain of 100 to 400."
Adding one capacitor to an LM386 power amp IC boosts its voltage gain to 200 which is a lot of gain. Then the horrible mic preamp IC you have is not needed.

Would you sketch out a power feed circuit for the mike assuming 9 V power supply?

And what value caps do you suggest for the input and output to/from the LM386?

Thanks.

 

I built this. It works better, but still has some quirks.

VR1 is only effective in about the low 10% of its range; above that, any input seems to overdrive the amp. Rotating the pot through that portion of its range produces some static from the speaker, which stops when the rotation stops. There is no static to be heard during rotation above that range. It's a new Bourns pot, but it's linear, not logarithmic.

The mic sensitivity seems very non-linear. As one moves the mic closer to one's mouth, it seems there is nothing, nothing, nothing, and then suddenly it's loud. The mic is extremely sensitive to breath; in fact, it is louder when one blows into the mic than when one speaks into it. The most effective technique seems to be to hold the mic at a right angle to one's mouth and speak past it as opposed to into it. I know it's just a $1 element, but is that normal?

Comments and suggestions are appreciated.

Thanks.

 

VR1 is only effective in about the low 10% of its range; above that, any input seems to overdrive the amp.

You have the polarity of C1 backwards which causes severe distortion.
Using 2.2uF creates a cutoff frequency of 7.2Hz which is too low. C1 could be a non-polarized 0.33uF (330nF) film capacitor and it will have a cutoff frequency of 48.5Hz.

The LM386 with a 9V supply begins to be overdriven when its output is only 0.45W into 8 ohms which is not much.

Rotating the pot through that portion of its range produces some static from the speaker, which stops when the rotation stops. There is no static to be heard during rotation above that range. It's a new Bourns pot, but it's linear, not logarithmic.

C1 connected backwards puts DC into the pot which causes a static noise when it is turned.
A linear pot has very coarse volume adjustment at the low level end and does almost nothing at the high volume end.

The mic sensitivity seems very non-linear. As one moves the mic closer to one's mouth, it seems there is nothing, nothing, nothing, and then suddenly it's loud.

Distance to a microphone is not linear. It is worse when C1 is backwards.

The mic is extremely sensitive to breath; in fact, it is louder when one blows into the mic than when one speaks into it. The most effective technique seems to be to hold the mic at a right angle to one's mouth and speak past it as opposed to into it. I know it's just a $1 element, but is that normal?

C1 being backwards also causes these problems.

 

You have the polarity of C1 backwards which causes severe distortion.
Using 2.2uF creates a cutoff frequency of 7.2Hz which is too low. C1 could be a non-polarized 0.33uF (330nF) film capacitor and it will have a cutoff frequency of 48.5Hz.

I made this change and there is much improved performance. Still some issues, but about what I expected from the LM386. Thanks for your help.

 

So you had to have Audioguru tell you to do what I told you in the first place.
I saw that one coming.

 

So you had to have Audioguru tell you to do what I told you in the first place.
I saw that one coming.

I am not quite sure what your point is with this post, but if you feel that I ignored your advice, I think you are mistaken. I did everything you told me including this.

C1 needs to be at least 2uF, negative terminal to the mic. 2uF would make the low frequency cutoff 80Hz for that cap. I would also make C2 larger. At 0.1uF, the low frequency cutoff for that cap (with the 10k pot) is 160Hz.

Which turned out to be wrong.

If I am misinterpreting your last post, I apologize.

And in any case, I repeat my thanks for your help. I have no formal training in electronics and am just trying to learn by experimentation.

 

I am not quite sure what your point is with this post, but if you feel that I ignored your advice, I think you are mistaken. I did everything you told me including this.



Which turned out to be wrong.

If I am misinterpreting your last post, I apologize.

And in any case, I repeat my thanks for your help. I have no formal training in electronics and am just trying to learn by experimentation.

In post #6, I said:

you shouldn't need the op amp. You can get gain=200 from the LM386.

I even posted a schematic from the datasheet, as an example of this possibility.
In post #8, I said:

1. The gain of 200 can be had with the LM386 alone.

You replied with:

I know it's not a good design, but it must work; they have sold thousands of them. What I really want is the Nuts and Volts version from December of 2008, but it's more money than I want to spend.

What was wrong with my capacitor recommendations?

EDIT: I guess I'm just old and cranky.

 

What was wrong with my capacitor recommendations?

See post #23.

I don't want to debate this. I respect your knowledge and appreciate your help. If you feel slighted, I am sorry.

 

What was wrong with my capacitor recommendations for your schematic in post #1 where the capacitor feeds an inverting opamp that has a very low input resistance of only 1k so the capacitor value should be large.

Tracecom: "See post #23 where the capacitor feeds a 10k ohm volume control in parallel with the 50k ohms input resistance of an LM386 power amplifier so the capacitor value should be small.

 

Tracecom: "See post #23 where the capacitor feeds a 10k ohm volume control in parallel with the 50k ohms input resistance of an LM386 power amplifier so the capacitor value should be small.

Audioguru, I'm not sure if you are addressing me or tracecom.
Addressing the original design, my points were that C1=100nF into the 1k resistor, plus the mic resistance, would yield a cutoff frequency of ≈1.5kHz, or a little less, depending on the microphone. I recommended at least 2uF.
I also pointed out that C2, at 100nF into 10k (I ignored the 50k input resistance), gave a cutoff frequency of 160Hz. I recommended making it a little larger.
So what was wrong with those recommendations?

 

Audioguru, I'm not sure if you are addressing me or tracecom.
Addressing the original design, my points were that C1=100nF into the 1k resistor, plus the mic resistance, would yield a cutoff frequency of ≈1.5kHz, or a little less, depending on the microphone. I recommended at least 2uF.

Correct and I agree that the coupling capacitor should have a high value of about 2uF.

The OP was commenting that my text is the opposite to your text without knowing that we were talking about 2 completely different circuits.