Posted by
Jim Brown-10 on
Dec 21, 2010; 7:37am
URL: http://elecraft.85.s1.nabble.com/OT-modifying-your-amp-for-lower-drive-requirement-tp5854009p5854944.html
On 12/20/2010 5:28 PM, Phil & Debbie Salas wrote:
> "It's very unlikely any solid-state amplifier uses an input attenuator:
> Transistors and FET's just don't have that much gain."
>
> The Ameritron ALS-600 has about a 15 ohm input impedance. Then they put a
> series 35 ohm resistor for matching and reducing gain.
Actually, input attenuators are fairly common in power amps. It is one
of two good ways to reduce power amp gain to meet the FCC requirement.
Another good method is to use a bit more negative feedback, which has
the added benefit of improving linearity (that is, reducing
distortion/splatter/harmonics) and reducing noise.
As others have noted, most output stages are cleaner if run a bit below
their maximum possible output. While one could safely pick up several
dB of gain by removing the input attenuator, I'd still be careful not to
overdo that, I wouldn't try to reduce the feedback, and I'd run the amp
pretty close to it's published rating.
73, Jim Brown K9YC
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