LM741 Pre Amplifier help: How to remove such a huge amount of noise at the output ???

Thread Starter

HaseebEngineer

Joined Aug 8, 2013
22
Here is the schematic of what i made so far ... I have an 8ohm speaker .. the output of this amplifier is not that much loud but too much noisy ... I have used several decoupling and bypass capacitor but that didn't work for me :(, instead of making it better it completely remove the sound ... Please help me for how to get a clear sound at the output ... or tell me whats wrong with this circuit ... Thanks alot ... Em Haseeb Khan doing Electrical Engineering ...
 

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GopherT

Joined Nov 23, 2012
8,012
A modern general purpose op amp is supposed to have 600 or more ohms as the load. Your circuit has only 8 ohms. You will get noise and saturation with that.

Remember, a power amp supplies low resistance loads. A pre-amp amplifies things like microphone or guitar signals to a line level (about 1 volt rms) and passes that to a power amp.

You have a pre amp circuit.

Your circuit has a gain of 100x - depending on the power supply, you may be getting saturation if your input signal is too big (more than 0.20 volts peak-to-peak with a 24 volt supply).

Also, the ressitors to your virtual ground for your non-inverting input may be a bit too big. You will get less noise with 10k resistors to Vcc and non-inverting input, then another 10k for non-inverting input to ground. A jfet input op amp like suggested above can handle higher value resistors there (100k).


Finally, I would put the output capacitor after the potentiometer - not before as shown here. The whole feedback loop is floating in your schematic and that can cause some latch-up issues. Put a 1k resistor in series with the potentiometer between the op amp output and the potentiometer) to insure you have at least 1k ohm resistance when volume is all the way up.
 
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Thread Starter

HaseebEngineer

Joined Aug 8, 2013
22
I have a 11v and 1A transformer ... I have made a negative supply using NE555 IC ... so now my positive and negative terminals gives about +-15 volts ... I have set the amplifier to give an output of -9 volts ... the input is i guess 0.336 volts ...
 

Thread Starter

HaseebEngineer

Joined Aug 8, 2013
22
What about this circuit ... I have an input of 0.336v and output gives me -7v all the way up ... but with a lot of noise ... can anyone modify this for me to have almost no noise ... please help
 

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bertus

Joined Apr 5, 2008
20,180
Hello,

As said before, you can NOT drive an 8 Ohm speaker with a LM741.
You will need an LM386 or better to drive an 8 Ohm speaker.

Bertus
 

Thread Starter

HaseebEngineer

Joined Aug 8, 2013
22
Okay thanks for the help .. I'll go buy LM386 tomorrow ... if something went wrong i'll contact you ... can u suggest some best audio amplifiers for i can make a subwoofer system as well ... ?
 

Thread Starter

HaseebEngineer

Joined Aug 8, 2013
22
I have studied about the amplifiers but i just dont know which IC to use to have a perfect and the best loud amplifier ??? I want to make a subwoofer along with left and right speakers ... a loud one without any noise ... can u suggest me a circuit or an IC ? high wattage high voltage with almost no noise ?? ...
 

bertus

Joined Apr 5, 2008
20,180
Hello,

How much power do you want for the left and right channels?
How much power do you want for the sub-woofer channel?
You also will probably need a sound processor for the sub-woofer.

All circuits for these can be found on the projects page of Elliots Sound Products:
http://sound.westhost.com/projects-0.htm

Bertus
 
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