[HBQRP] Who's an op amp expert?

[Dale Botkin]

I know we tend to pull out the old standards (LM386, 741, 555, etc) but 
there are a TON of new generation, low voltage, ultra low power chips 
out there.  You can thank the explosion of MP3 players, cell phones, XM, 
GPS and various other battery powered portable electronics.

In the MK-1, I used an LM386 audio amp.  It's tried and true, works 
great, but I had to add an 8V regulator just for it (couldn't depend on 
a specific input voltage).  When designing a new keyer recently, I 
really wanted something suitable for battery power, and if I could use 
it with headphones -- bonus.  I found the TPA711.  Perfect for battery 
power - 2.5 to 5.5V supply.  You can drive an 8 Ohm speaker quite well 
on a couple of AA cells, and it's designed to switch from "bridge-tied 
load" (push-pull) to single-ended when you plug in headphones.  Amazing 
little amp.  It's not even that new; the data sheet is dated 1992, last 
updated in 2002!

OK, so it's SMT only.  Still...  what a great little audio amplifier for 
a portable rig.

73,
Dale - N0XAS


On 2/18/2014 9:29 PM, Rick Bennett wrote:
> That all makes perfect sense, the bias should be right in the middle of the supply voltage for this application.  Interesting little op amp that can work at such a low voltage.  Most of my op amp trials have been using a 12 volt supply.  Thanks, I learned something!
>
>
> Rick
>