I thought the LM386 was an audio amp (not to DC), but had a try anyway
with a 5Hz squarewave. Distortion was pretty bad. Also, regardless of
frequency, I only get 1V swing out with 6V in. It is supposed to have
a built-in gain of 20. This I don't understand.

Getting back to my original post. Is it possible to have a single op
amp design that will cover the variation in supply voltage and load
described?

Thanks for any advice.

Trevor Morton



On Thu, 22 Mar 2007 23:46:38 GMT, Rich Grise wrote:

On Thu, 22 Mar 2007 21:35:33 +1100, Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

You've just described the National LM386, as if you'd copied that off
the data sheet:
http://www.national.com/ds/LM/LM386.pdf

Have Fun!
Rich