Home |
Search |
Today's Posts |
#1
|
|||
|
|||
gain adjustment in an amplifier utilizing NFB
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. |
#2
|
|||
|
|||
"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. |
#3
|
|||
|
|||
"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. That seems to be pretty much the standard way to do things. 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? Yes, global NFB is not very suitable for the purpose of controlling gain over a wide range. For example, you can't reduce the gain of something to zero with a typical NFB loop. The best you can do is reduce the gain to unity. In a typical power amp that means that you are limited to about 30 dB gain control range. Furthermore, the world is full of perfectly servicable amplifiers that are not stable over a wide range of NFB settings. Obtaining very low amounts of gain with good stability can be hard to do. High gain is generally easier,but to have a working gain control you need both. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Jeff Rowland 8TI-HC ( High Current Version) Power Amplifier | Marketplace | |||
Lexicon Omega gain adjustment | Pro Audio | |||
List of NOS mostly tubes | Vacuum Tubes | |||
Mechanic blames amplifier for alternator failing?? Help>>>>>>>>>>> | Car Audio | |||
FS: SOUNDSTREAM CLOSEOUTS AND MORE!! | Car Audio |