"MZ" wrote in message
...
Some amplifiers I've encountered have what amounts to a gain adjustment
that
consists of nothing more than a voltage divider at the input, oftentimes
followed by an op amp buffer, etc. Basically, the gain adjustment is done
prior to the input stage of the amplifier.

Some amps that utilize global NFB have a voltage gain that's defined
solely
by the value of one resistor (per channel). Why introduce the added
components associated with the input circuit I described if that resistor
could be replaced with a potentiometer? Is there something that makes
that
resistor unsuitable for gain adjustment? Somehow more prone to noise?
Thanks.

PS - I'm not looking to modify or construct an amp in this fashion; I'm
curious more than anything else.

Sometimes gain is adjusted by changing the feedback, but amplifiers are
often optimized for a specific gain/feedback, and changing the feedback
makes the overall performance sub-optimal. Furthermore, it is usually
advisable to keep feedback wiring as short and straight as possible, which
is made more difficult with a variable resistor in the circuit. A simple
adjustable voltage divider (potentiometer) that is responsible for just one
purpose (variable gain control) is usually more reliable.