Low noise 1W amp

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View


Hi All.
Can anyone out there help me with a low noise 1W amplifier chip/circuit.  I
am currently using an LM386, and a TDA70?? (sorry I haven't got it with me),
with less than ideal reults.  The hiss is driving me nuts, as I'm using
headphones and I high gain setting (between 20 & 200).
Many thanks in advance
Rob
Melbourne.



Re: Low noise 1W amp



"Fonz"
Quoted text here. Click to load it


**  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




Re: Low noise 1W amp



Quoted text here. Click to load it
I
me),
Quoted text here. Click to load it
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.



Re: Low noise 1W amp



Quoted text here. Click to load it
I
me),
Quoted text here. Click to load it

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



Re: Low noise 1W amp


     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


Re: Low noise 1W amp


I posted an answer. If questions, snipped-for-privacy@gmail.com.

Charles Gilbert
NonDigital.Netfirms.com


Site Timeline