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Power amplifier volume knob question

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Ital-Rolando:
I remember, not sure where I heard this, that the knob of a power amplifier (for live sound uses) can be thought just like a water tap, because the level inside the circuitry it always running at full, just like the water pressure in our houses.
I must say that, even I do not have any clues, it makes sense to to me and I’ve accepted it.
Could anyone get more in depth about it?

Thank you

Steve-White:
Think of it as a gain control and not a volume knob.  It's purpose is to set the input sensitivity of the amplifier to the incoming signal level in the system.  High signal level, low gain is needed.  Low signal level, higher gain is needed to drive the amp to full power.

This is a car audio site, but a decent explanation:  https://www.extremeaudio.org/what-is-a-gain-control/

Paul G. OBrien:

--- Quote from: Ital-Rolando on November 16, 2021, 03:05:09 AM ---I remember, not sure where I heard this, that the knob of a power amplifier (for live sound uses) can be thought just like a water tap, because the level inside the circuitry it always running at full, just like the water pressure in our houses.
--- End quote ---

Nope it doesn't work like that at all, the volume control does NOT limit the amplifier output it just changes the amount of input signal level need for full output.

John Roberts {JR}:

--- Quote from: Ital-Rolando on November 16, 2021, 03:05:09 AM ---I remember, not sure where I heard this, that the knob of a power amplifier (for live sound uses) can be thought just like a water tap, because the level inside the circuitry it always running at full, just like the water pressure in our houses.
I must say that, even I do not have any clues, it makes sense to to me and I’ve accepted it.
Could anyone get more in depth about it?

Thank you

--- End quote ---
That is an awkward analogy I won't try to fix it.

Perhaps the relationship that analogy was trying to explain is that power amps are typically designed to run at high nominal gain, because that is more stable and resists oscillation from random irregular loads.

BUT to accommodate integrating into systems requiring less than full gain, most amplifiers incorporate an input attenuator to pad down the signal input. The combination of this input attenuator followed by high fixed gain, behaves like a variable gain amplifier to the user. 

Don't overthink this, the inner workings are mainly of interest to amplifier designers.

JR       

Ital-Rolando:

--- Quote from: John Roberts {JR} on November 16, 2021, 10:00:31 AM ---That is an awkward analogy I won't try to fix it.

Perhaps the relationship that analogy was trying to explain is that power amps are typically designed to run at high nominal gain, because that is more stable and resists oscillation from random irregular loads.

BUT to accommodate integrating into systems requiring less than full gain, most amplifiers incorporate an input attenuator to pad down the signal input. The combination of this input attenuator followed by high fixed gain, behaves like a variable gain amplifier to the user. 

Don't overthink this, the inner workings are mainly of interest to amplifier designers.


JR       

--- End quote ---

Thanks John, Paul and Steve.

I had not doubted this analogy up to now also because in many power amplifiers, (i.e. QSC GX5), the knobs are graduated from minus infinity to 0, therefore confirming that the power of the signal inside the amp is always running at full, and you can just limit its full output with the knobs.
What you wrote John, is the closest description to what I have read and has remained in my mind.
I also agree with what Paul and Steve wrote, I have probably just added and accepted a familiar analogy.

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