microphone preamp and its connection

[riversun]

Hello,

I built this simple microphone preamp for electret mic (design as an attachment).
It works very well recording good quality sound connected from its audio out to minidisk mic input.

But could this simple system also amplify sound to be heard from speakers? I need small microphone to amplify low volume sound from a small fitting place.
I tried connecting its audio out to stereo amplifiers cd input in the back. Only if one blows directly on the mic this sound comes from speakers no any other kind of sound. And if one puts volume up from the stereo distortion noise start. Am I connecting it wrong? Also tried with mixer connected to the stereo amplifier without any result.

What kind of mic preamp should I get and how to connect it?

grateful for any advice or insight,
Riversun

 

[BradtheRad]

Your schematic shows how to get a mic-level signal from your electret mic.
However it is not a pre-amp. The signal needs more amplitude, for it to be strong enough to drive the input of your amplifier.

Right now you have a weak signal. You have to speak loudly before you can hear any sound from the speakers.

Since you've been able to get this far, you should not find it too hard to make a mic pre-amp. It can be based on a transistor, or an op amp.

There are many websites with projects for building such a pre-amp.

 

[riversun]

Thank you for your advice BradtheRad,
so I am planning to make more complicated preamp.
It now looks like to me , it is not possible to do it just having 9 V battery powering it and having the electret mic coming from the speakers.
greetings,
Riversun

 

[BradtheRad]

Hmmm... I see 'capsule, cold, hot'... The schematic has a caption which mentions 'PZM'. This suggests it's for a pressure-zone mic, rather than a plain electret which you probably have.

I believe that is a more complicated schematic than you need.

This pre-amp is what I would try.



Adjust the potentiometer so the collector signal is in the middle of the region between 0 and 9 V.

10 mV is a typical amplitude produced by a microphone. (With a 9V battery it may be greater).

The element has some impedance. I gave it 2200 ohms only because I saw that is the value of the resistor above it.

 

[riversun]

Hello BradtheRad, yes I could try making schema you suggested.
What kind is the transistor in it?
I take the pot is the resistor next to the text.
I'm quite new with these and cannot tell....
greetings,
Riversun

 

[BradtheRad]

What kind is the transistor in it?
I take the pot is the resistor next to the text.

The transistor can be a small-signal general purpose. Inexpensive. Common types are 2N3904, 2N2222.

Yes, the pot is the resistor with an arrow pointing to its middle.

 

[riversun]

Hello BradtheRad! Getting the parts from the electronics shop, I was told the 10 microFarad capacitor that is not polar, does not exist!
Could it be 1microFarad or use 10microFarad with polarity? But which side is plus and which minus in this case?
greetings!

 

[BradtheRad]

Hello BradtheRad! Getting the parts from the electronics shop, I was told the 10 microFarad capacitor that is not polar, does not exist!
Could it be 1microFarad or use 10microFarad with polarity? But which side is plus and which minus in this case?
greetings!

A voltmeter will tell you where is the more positive polarity in the circuit.

Whenever you need a non-polarized capacitor, you can create an equivalent by connecting two polarized capacitors back-to-back.

There is a slim chance you do not need the capacitor at all, if you are able to adjust volt levels to be equal across the wires where it normally would go. We usually see schematics with the capacitor included, however.