Is this a good preamp

[ken3983]

I used some advice and decided not to go with the LM324 as a microphone preamp.Is this a little better and simpler?I want the frequency to cover between 500Hz and 3000Hz.Is there a way I can make it variable in this circuit?

 

[Sebi]

I'm pretty sure, this two-transistor preamp much better as 324 amp. for mic. amplifying. 500....3000Hz is a phone quality, this circuit can work over 40kHz!

 

[ken3983]

How did you calculate the frequency with the parts given?Was it a combination of capacitor/resistor?

Ken

 

[Nigel Goodwin]

How did you calculate the frequency with the parts given?Was it a combination of capacitor/resistor?

There are no real frequency limiting components in the circuit, apart from the coupling capacitors - which will limit the low frequency response, but it will still be nice and low.

So he's not calculated it, he's basically 'guessed' it - and I agree with him, it'll work well into the ultrasonic frequencies.

But it's simple, it's cheap, build one and try it!.

 

[Roff]

What do you want to vary - the gain, or the frequency response?

 

[samcheetah]

So he's not calculated it, he's basically 'guessed' it - and I agree with him, it'll work well into the ultrasonic frequencies

wow!!!!!!! how did he do that??

what were the factors that told u the frequency range?? i know that analog design is a bit like magic but there is always a good logical reason for everything

from my knowledge i know the following things.

both transistors are in the common emitter configuration and class A

both the output and the input is capacitor coupled

the 150K ohm resistor is producing negative feedback

but what do the 100 microfarad 3V capacitor and the 10 microfarad 16V capacitor do??

 

[Nigel Goodwin]

So he's not calculated it, he's basically 'guessed' it - and I agree with him, it'll work well into the ultrasonic frequencies

wow!!!!!!! how did he do that??

Presumably from experience, it's a old tried and tested design, I first saw it in a very old Mullard application note.

what were the factors that told u the frequency range?? i know that analog design is a bit like magic but there is always a good logical reason for everything

from my knowledge i know the following things.

both transistors are in the common emitter configuration and class A

both the output and the input is capacitor coupled

the 150K ohm resistor is producing negative feedback

It gives DC negative feedback only, there's no AC negative feedback in the circuit at all - so you get maximum gain from the amplifier.

but what do the 100 microfarad 3V capacitor and the 10 microfarad 16V capacitor do??

The 3V capacitor prevents AC negative feedback, by decoupling the emitter to ground. The 16V one is just an HT decoupler, it makes the 12V rail and ground the 'same', as far as AC goes - it's an important component in almost every circuit.