My amplifier doesn't work very well [2N3904][collector feedback bias][capacitor mic]

Thread Starter

booboo

Joined Apr 25, 2015
168
The circuit in your posted #73, you can adjust the R2 to adjust the sensitive, you can also adjust the R3, but you only can adjust a little bit range.

Op-Amp Microphone Preamp, using the specific IC is better, but you also can using LM358 to do the experiment.
No, the circuit in post #43.

I have used a non-inverting amplifier but didn't work (+ an potentiometer to change the gain). are you sure about the circuit you posted?
I need to clarify objectives. What is the voltage? What a load? Battery power or not? Whether the economy?
Hey dude! how you doing!;)
Voltage 3-9v
if we assume the load is my speaker then an 8ohm speaker.
more probably yes. the supply is battery.
 

Thread Starter

booboo

Joined Apr 25, 2015
168
There are a couple schemes for supply voltage 9 volts:View attachment 97379
Thanks for schematic. today I was seeing the schematic of Sony Ericsson s302. I mean this mobile phone:



And for audio part, I saw this:



Most probably for good quality they use differential amplifier. the output of this circuit goes to two pin of an IC. look:



What's your opinion about differential amplifier? Also I saw this on internet:



from here. I wired it up with an LM358 but didn't work.
 

Bordodynov

Joined May 20, 2015
3,177
Since the operational amplifier circuit 358 will work but will be above the noise level. The spectral density of the noise 55nV/Hz^0.5 (F=[10,20kHz] Vinoise=8uV). Resistor 1kOhm - 4nV/Hz^0.5.
 

ScottWang

Joined Aug 23, 2012
7,397
No, the circuit in post #43.

I have used a non-inverting amplifier but didn't work (+ an potentiometer to change the gain). are you sure about the circuit you posted?
The circuit on the bottom of the page that I linked in posted #66, that is a small power amplifier and it used TL431, that is matched what you want, but you still need to build a preamp for the mic, the preamp used to amplifying the small signal from mic, and the power amplifier used to amplifying the higher signal from the preamp.

The source of circuit.

You can using the circuit that you posted in #73 to be the preamp and adjust the values of R2, R3 as I suggested.


I'm not sure why you insist to used TL431 to amplifying the signal, are you just want to do the experiment to know more about the TL431?
 

Thread Starter

booboo

Joined Apr 25, 2015
168
Since the operational amplifier circuit 358 will work but will be above the noise level. The spectral density of the noise 55nV/Hz^0.5 (F=[10,20kHz] Vinoise=8uV). Resistor 1kOhm - 4nV/Hz^0.5.
Do you have any idea for it?(make it to work)
The circuit on the bottom of the page that I linked in posted #66, that is a small power amplifier and it used TL431, that is matched what you want, but you still need to build a preamp for the mic, the preamp used to amplifying the small signal from mic, and the power amplifier used to amplifying the higher signal from the preamp.

The source of circuit.

You can using the circuit that you posted in #73 to be the preamp and adjust the values of R2, R3 as I suggested.


I'm not sure why you insist to used TL431 to amplifying the signal, are you just want to do the experiment to know more about the TL431?
No, if I'm insisting on TL431 that's just because it's cheap and has a high gain. ok, I'm going to make that pre-amp circuit and apply your suggestion on my circuit.
 

Bordodynov

Joined May 20, 2015
3,177
Who is your target. Purpose of the amplifier. Supply voltage. The load of the amplifier. One of the three options.
1. This is the preamplifier. Load power amplifier.
2. This 32 ohm headphones.
3. This speaker 8 ohms.
Level signals. What a source of electrical signal:
1. Condenser microphone.
2. Electrodynamic microphone.
3. Surrogate source (speaker, loudspeaker with transformer).
From all this it depends heavily on the amplifier circuitry. It can be a very long time to discuss the various schemes, but without a particular purpose it can take a long time! Or is your goal to talk with experienced people and increase their erudition without difficulty?
See:
Am4.png
 
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Thread Starter

booboo

Joined Apr 25, 2015
168
What is your target? Purpose of the amplifier. Supply voltage. The load of the amplifier. One of the three options.
1. This is the preamplifier. Load power amplifier.
2. This 32 ohm headphones.
3. This speaker 8 ohms.
Level signals. What source of electrical signal:
1. Condenser microphone.
2. Electrodynamic microphone.
3. Surrogate source (speaker, loudspeaker with transformer).
Due to these options, it depends heavily on the amplifier circuitry. It can be a very long time to discuss the various schemes, but without a particular purpose it can take a long time! Or is your goal to talk with experienced people and increase your erudition without bothering yourself?
See:
View attachment 97388
I want to use my circuit for a simple RF transmitter. kinda like a spy transmitter to eavesdrop.:D (I'm just kidding. ignore it :p).
Nowadays working with amplifiers and learning how to design them is very important especially audio amplifiers. e.g. connecting an electret microphone to micro-controller for DSP purposes and so on. there are tons of reasons why to learn designing an audio amplifier.
 

Thread Starter

booboo

Joined Apr 25, 2015
168
Thanks. I connected it to Vcc with a 10kohm and now it's working. but there is too much noise at output. a sound like BeeZeeZeeZee... like the sound of a Moped.:D I used a 10uf cap for bypass(pin number 7 of LM386) but didn't work. how to remove the noise? any idea, suggestion,...
 

Bordodynov

Joined May 20, 2015
3,177
It is wrong to place the microphone close to the speaker on. The distance between them is small! Effective acoustic feedback. I encountered such a problem in the design of sensitive amplifiers. One solution is to use a stereo phones. They face each other and act in opposition. This allows a greater amplification.
 
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Bordodynov

Joined May 20, 2015
3,177
If you want to reduce the sensitivity to the sound, you can reduce value of the load resistor of the microphone. For example, instead of 10kohms put 3.3kohms. This is almost three desensitize.
 
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