Project (Simple Stereo Audio Amplifier)

Discussion in 'The Projects Forum' started by az00025, Nov 17, 2011.

  1. az00025

    Thread Starter New Member

    Nov 17, 2011
    I'm a new member in these forum and I need some help about 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
    >>>>one of the circuit that I built is show below(Op-Amp Audio Amplifier)...

    However the main two problems that I found are:
    1) 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.

    2)Another possible issue is instability. RF oscillation sometimes shows itself as excessive audio noise.
    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..
    <<<Does anyone have a solution for these problems??PLZ>>>..........
  2. Audioguru

    New Member

    Dec 20, 2007
    Hello again but on this website.
    1) The lousy old LM358 low power opamp has horrible crossover distortion and lots of hiss.
    2) With a supply that is only 4.5V that drops to 3V when the battery runs down, the output power is only about 0.06W which is almost nothing.
    3) The high value of the emitter resistors also reduces the output power.

    Why do you have the gain so high?
    Why do you have an opamp for the "ground"?