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how to design a low noise pre amp using IC uA741?

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xeon89

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Can anyone tell me how to design a low noise pre amplifier using IC uA741?? It can be multiple stage... Thanks.=)
 
forget it....a ua741 is definitely not low noise...if you are using it for audio applications,try the OPA134 or OPA2134 dual op amp,from Burr Brown... they are premium op amps for use in hi fi audio equipment....

if its not for audio applications, you can use TLO71 or TLO72 dual opamp ...they are FET op amps with very low noise.

if you still want to use the 741 op amp, there are plenty of 741 tutorials on the net...just google for them

cheers,
deepak
 

xeon89

New Member
thanks deepak.. that is why i am asking .. i know uA741 is an very old op amp and will produce a lot of noise.. so is there any ways to make it less noise?? maybe building it in few stages pre amp??
 

Nigel Goodwin

Super Moderator
Most Helpful Member
thanks deepak.. that is why i am asking .. i know uA741 is an very old op amp and will produce a lot of noise.. so is there any ways to make it less noise?? maybe building it in few stages pre amp??
If you're building a separate preamp in front of it, why add the 741 at all?.

Use a decent opamp to start with.
 
yes xeon,...im afraid mneary and Nigel are right...a 741 is quite useless in todays applications...its much better if you substitute it with a better opamp.

anyways, no harm in trying...go ahead and try it with a 741, and then substitute the other opamps and see...you will understand why a 741 is a bad choice...

cheers,
deepak
 

audioguru

Well-Known Member
Most Helpful Member
The transistor preamp is low noise and pretty good quality but it has a low input impedance. What are you amplifying?

What do you want to switch with a transistor?
 

xeon89

New Member
Hi audioguru , i am amplifying a audio signal with 200mVp-p at 1kHz .. it will be used as a music wave and be amplify using a audio amp TDA7052.

i will like to have a choice of voice(filter the audio signal with a band pass filter), music ( non-filtered signal) or mute mode. This will be done using a transistor switching circuit which will receive a 2 bit signal that is stimulated by SPDT switches. The power supply will be 5V.

Thanks in advanced...=)
 
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audioguru

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Most Helpful Member
The 741 opamp has performance that is poor for music.

Why filter voices with a bandpass filter? FM radio and TV announcers and commercials don't filter voices to sound like a muffled telephone. The important consonants sounds in speech reach up to 14kHz.

Use a TDA7052A power amplifier instead of a TDA7052 bacause it has a DC volume control that can be used to mute the audio.
 

bountyhunter

Well-Known Member
Hi audioguru , i am amplifying a audio signal with 200mVp-p at 1kHz .. it will be used as a music wave and be amplify using a audio amp TDA7052.
At that level, you don't need a very low noise op amp like you do for a microphone or phone pre amp. You could just use any decent op amp with adequate slew rate like an LF-356 or TL-084 or many others.
 

audioguru

Well-Known Member
Most Helpful Member
What is the preamp for?
The TDA7052 has a gain of 60 to 80. Then its output with a 200mV input will try to be 16V RMS which is 45.2v p-p. Its max supply voltage is only 18V and it is spec'd with a 6V supply.
 

xeon89

New Member
the preamp is to stablize the input... but gathering all the info here.. i can conclude that my signal is rather big enough.. so an op amp will already stabillize the signal right?? how about the transistor as a switch part?? can anyone teach me?? thanks..=)
 

audioguru

Well-Known Member
Most Helpful Member
the preamp is to stablize the input... but gathering all the info here.. i can conclude that my signal is rather big enough.. so an op amp will already stabilize the signal right??
We don't know what you mean when you say "stabilize the output". Your 200mV signal is big enough to feed directly into a TDA7052A power amplifier.

how about the transistor as a switch part?? can anyone teach me?? thanks..=)
What will the switch do? If you want to mute the audio then use the DC volume control function built into the TDA7052A amplifier. It mutes with an attenuation of 80dB.
 

ajitjaison

New Member
to audio guru

the circuit given by you for electronic stethoscope is pretty good. but it had some problems related with the audio power amplifier. we had to change that part. any way our project was a sucess . thank you.
 
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