[Premium-Rx] Simple clean audio amp

[Tim Shoppa]

Ka9p at aol.com wrote:
> I've finally reached the point of frustration with a couple of radios and 
> would like to add a simple, clean outboard amp to the back of them, something on 
> the order of 2-5 watts into 8 ohms, very good THD specs, at 12 vdc.
>
> Can anyone suggest any source of reasonably priced built or kit amps fit for 
> this purpose?

LM380 and LM384 (Very common NatSemi audio amp IC's for circa 12V power
supplies) are very commonly used. Official THD specs are not impressive
but in the real world they do very nicely. They are DIP packages
(so very easy to homebrew with Radio Shack proto boards)
and deliver 2.5W/5W nominally (with much better THD if you do not go
to the limits).

For typical HF comms I'm personally satisfied with sub-percent THD.

Here's a slightly different question:

Say I've got 3 or 4 receivers, each tuned to sideband voice utility
HF frequencies. I want to be able to monitor these frequencies
but don't want to listen to the audio unless there's a signal
present. This implies some kind of squelching ability. Radios are
not identical but generally have AGC level out or IF out ability
(actual levels vary from radio to radio.) Is there a "common" solution
to this problem? I look at say old WJ price lists and see squelch as
an extra-cost option, but I'm not about to pay those kinds of prices :-).

With some radios I can turn AGC on and turn the RF gain down to the
point where background static isn't objectionable, and then when a
signal comes in the AGC takes over. But... AGC on my WJ-8716's doesn't
work this way! (Is it supposed to? If I turn on AGC I have no manual
RF gain control, and if I turn on RF gain control I have no AGC. This
is different than my other receivers.)

Tim.