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Power amplifier volume knob question

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Luke Geis:
To re-iterate, the knob has nothing to do with the power output of the amplifier. If you turn the knob down to -40 ( or whatever its lowest setting is that is not full off ), you would have to drive the amplifier with that much more signal ( from the mixer ) to achieve the same level from the amplifier. The amplifier is a fixed gain device, if there is X level actually getting to the amplification stage, it will produce X output regardless of the input volume knob setting. All that knob does is act as another volume knob.

Ital-Rolando:

--- Quote from: Luke Geis on November 16, 2021, 10:18:54 PM --- The amplifier is a fixed gain device, if there is X level actually getting to the amplification stage, it will produce X output regardless of the input volume knob setting. All that knob does is act as another volume knob.

--- End quote ---

Thanks Luke, that's exactly the definition that clarifies my ideas.

Ivan Beaver:

--- Quote from: Luke Geis on November 16, 2021, 10:18:54 PM ---To re-iterate, the knob has nothing to do with the power output of the amplifier. If you turn the knob down to -40 ( or whatever its lowest setting is that is not full off ), you would have to drive the amplifier with that much more signal ( from the mixer ) to achieve the same level from the amplifier. The amplifier is a fixed gain device, if there is X level actually getting to the amplification stage, it will produce X output regardless of the input volume knob setting. All that knob does is act as another volume knob.

--- End quote ---
Not exactly.

The amplifier (actually a voltage amplifier, NOT a power amplifier (they actually LOSE power)-but that is a different argument), has a rated gain (from input to output) of a certain amount of dB.

That is ONLY true when the level control is at maximum (turned all the way up).

Whenever you turn it down, the gain of the amplifier also goes down.  SO it takes a stronger input drive level in order to have the same output voltage (wattage into a particular load).

It is also possible on many "amplifiers" to NOT be able to get the rated output if you turn the level down below a certain point, no matter how hard you drive it.

This is because the power supply voltages on the input stage are limited.  They will often clip the signal when driven hard, even if the actual output is well below rated power.

So you cannot turn it down to -40 and still get full output.  The idea is solid, but the actual implementation will simply not allow it (in most cases).

Miguel Dahl:
I don't know if this is of any help. But when using a Yammie on the "the usual monitor amps". I can either turn down the aux master outputs, to operate the aux-sends from the channels at a normal  -10 to 0 dB level send for monitors, or just turn down the attenuation knobs on the amps without turning down the aux masters. It will be equally loud, but with less hiss through the wedges due to internal hiss from the amps when they are wide open.

Chris Grimshaw:
If the input attenuators are adjusting the volume of the hiss, chances are the hiss is further upstream.

Chris

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