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Old 11th November 2011, 05:29 PM   #1
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Question Design simple Stereo Audio Amplifier

Does any Know how to design simple Stereo Audio Amplifier(Pre-Amp+Tone Control+Output Stage) by using LM358 op-amp and (8 ohm Speaker) ,the circuit should be working with 4.5V (e.g. 3 AA batteries)...????
I designed several circuits but I got 2 much noise
I really need some help PLZ....one of the circuit that I built is show below(Op-Amp Audio Amplifier)...

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Old 11th November 2011, 07:49 PM   #2
DF96 is offline DF96  England
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Two problems: too much voltage gain (x300), and a noisy signal reference due to thermal noise from the 1M resistors. Assuming a 20kHz bandwidth I calculate 5.4mV of noise at the output, which is likely to be audible.

Another possible issue is instability. RF oscillation sometimes shows itself as excessive audio noise.
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Old 13th November 2011, 11:33 PM   #3
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I'm experimenting this circuit but unfortunately,i'm still facing these problems.... any suggestion with some details to how reduce excessive audio noise....any help, I will appreciate it..

http://www.diyaudio.com/forums/attac...er-circuit.jpg
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Old 30th November 2011, 11:29 PM   #4
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I'm looking for simple volume meter schematic diagram using LED and transistors and 4.5 voltage source to implement it with audio amplifier circuit that shown above ????any suggestion.........
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Old 1st December 2011, 06:07 AM   #5
dangus is offline dangus  Canada
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The easiest level meter is to use an LED driver chip like the LM3915 or LM3916. There are probably others that were more optimized for consumer electronics, but they may be obsolete now that everything is digital. Take a look inside scrap cassette players.
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Old 1st December 2011, 06:41 AM   #6
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All resistors carry <a href="http://www.physics.ucdavis.edu/xdzhu/Physics122_2008/Johnson%20Noise%20Manual_2008.pdf">Johnson noise</a>. The higher the R value, the greater the noise. Your 1M resistors seem to be way high for normal outputs. You might also check the National Semiconductor <a href="http://www.national.com/ds/LM/LM158.pdf">datasheet</a> for your opamp for some ideas.
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Old 1st December 2011, 11:25 AM   #7
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I can not use any LED driver chip like LM3916 or LM3915....just transistors and LEDs
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Old 1st December 2011, 12:38 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by az00025 View Post
I can not use any LED driver chip like LM3916 or LM3915....just transistors and LEDs
why?
Could this be another case of non declaration of student/pupil status?
__________________
regards Andrew T.
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Old 1st December 2011, 03:52 PM   #9
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Because for my experiment there are specifications for using some components,the list of the component that I can use to design the volume meter circuit : Transistors, Resistors,LEDs,Capacitors and AA batteries>4.5 volts.
So if any one can help me and provide schematic diagram I will appreciated..
Many thanks....
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Old 1st December 2011, 06:26 PM   #10
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I got this schematic diagram but I'm not pretty sure what is wrong with it!!!!Please feel free to comment on it...
regards..

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