[AMRadio] re: Apache audio not good

[John Coleman]

Good Point:
	Negative feedback is a real good idea and I have found a few good points to
follow.

1.  Don't over do it.
    Make the Class A stages as distortionless
    as posible without feed back other than
    unbypassed cathode resistors.

2.  Don't try to include too
    many stages in the loop.

3.  Power stages with unconstant loads
    such as (DRIVERS for Class B)
    need it the most.

4.  Using the feedback points for in and out,
    sweep the amp first for frequency responce
    and make a graph.

5.  Sweep again for phase shifts
    and make a graph on transparence paper:

6.  Overlay the graphs.

7. Designe your feed back divider circuit
   for the same responce curves,
   or as close as you can get.

These or just some of my findings
and guides and certainly not writen in stone.

Good Luck, John, WA5BXO


-----Original Message-----
From: amradio-admin at mailman.qth.net
[mailto:amradio-admin at mailman.qth.net]On Behalf Of Gary Schafer
Sent: Monday, April 15, 2002 9:58 AM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] re: Apache audio not good


With a feedback circuit it is best to limit the frequency response at the
high
and low end of the feedback loop. This limits the amount of phase shift in
the
feedback circuit that can cause oscillation.

73
Gary  K4FMX


AA8TV at aol.com wrote:

> Hi Russ,
>
> One trick I used on the negative feedback circuit for my DX-100 was to do
the
> voltage dividing first, and then de-couple the dc with a cap. This way the
> cap is a 50 volt part rather than a 1000 volt part. You can use a 100uf
50v
> electrolytic if you want to, it's easy on the pocket, and physically
small. A
> 100uf plus cap also helps in adding feedback on the low audio frequencies.
> The Apache uses the same mod iron as the DX-100. They both have a 500 ohm
tap
> to use for the negative feedback. I'll bet this would work in the apache
as
> well.
>
> 73, Ed
> AA8TV
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