Low noise 1W amp

"Fonz"

** What is the signal source being used ?

There should be no audible hiss with the input to the LM386 disconnected & grounded.

What are the headphones - ie make model and impedance.

....... Phil

I

me),

This might be a case of too much gain in later stages and too little up front. Assuming that your first amp has a fixed noise output, then the lower your subsequent stage gain, the lower your output noise. If you knock the gain of the final amp down as far as you can and bump it up on the preamp, you should see an improvement. For me in the past, that approach has made the difference between intolerable and excellent.

I

me),

I haven't done any detailed comparisons, but admit to being a big fan of the TDA2822 over the venerable LM386. It's stereo not mono, draws little current and is better behaved than the 386. I'd never use a 386 again and wonder why so many projects still specify it.

My last use of one was to put one into an AM/FM stereo tuner to make it a receiver. Made a loop antenna (25cm diameter), put a switch on the back to extend coverage up to 1850 kHz and it works a treat on both local and interstate stations. The dial lights dim when the volume is cranked to the max, but it still provides a roomful of sound at lower settings before the onset of distortion.

Peter

There are many ways to skin the simple power amplifier cat. If I were doing it I would first use a low-noise op amp which would drive it's own output from rail to rail. Assuming that this gives the proper voltage swing, it is only necessary to buffer the signal to get some current-gain. You could use a power amp chip like the Lm386 at a low gain (-1V/V) or in my case being a transistor man, I would use some 2N2222A and 2N2907A transistors to provide the muscle.

Many years ago the military got fed up with all of the different transistors and told the industry to build a general purpose NPN and PNP to do everything. The result was the NPN 2N2222A and the PNP

2N2907A. These transistors have specified current gain from 10uA or so right up to 0.25A and are quite robust. It may look tacky but there is nothing wrong with a few of these in parallel to get the desired output current and power-handling level. I would sprinkle some 10-ohm resistors around to be sure the transistors share the current OK. and also are short-circuit proof. Finally, for the best fidelity, the op amp feedback is taken from the transistor-buffer output so that the transistor buffer is inside the feedback loop, such that the 1W output signal is a perfect, very quiet, replica of the input signal.

Charles Gilbert Consultant

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Charles Gilbert NonDigital.Netfirms.com