Thanks, Jim. I am learning something new here every day.
I've been clear for some time on the fundamental conflict between good
linearity (indirectly creating good IMD) and efficiency. With the last couple
of days of discussion added, I now see that there's also a fundamental
challenge in getting good efficiency and good thermal handling, and that the
negative feedback solution isn't necessarily practical for some designs.
The ideal amp would be highly efficient for lower power draw and minimal need
for heat-sinking, have excellent linearity and IMD, use cheap devices, and
support ALC, voice compression, and 100% duty cycle modes. Looks like a square
circle. :-)
73,
Cathy
N5WVR
Jim Thomson <jim.thom@telus.net> wrote:
### NFB = Negative feedback. 3 db of NFB means you also reduce the gain
of the amp by 3 db. On paper, to achieve say a 10 db improvement in IMD, you
require 11 db of NFB.
## 6 db of NFB on a SB-220 means you now require quadruple the drive
power. NFB will work on a SS amp, since the gain is sky high to begin with.
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