April 3rd, 2021, 10:08 pm
Low Pass Gain Will match the amplifier’s input sensitivity to the output of the pre-amp source
April 3rd, 2021, 10:49 pm
April 3rd, 2021, 10:53 pm
Cogito wrote:
Dayton Audio explains how "Gain Control' works in their product literature.Low Pass Gain Will match the amplifier’s input sensitivity to the output of the pre-amp source
In essence, the Gain knob reduces the signal voltage by reducing the amp's input impedance.
April 3rd, 2021, 11:21 pm
Roscoe Primrose wrote:Cogito wrote:
Dayton Audio explains how "Gain Control' works in their product literature.Low Pass Gain Will match the amplifier’s input sensitivity to the output of the pre-amp source
In essence, the Gain knob reduces the signal voltage by reducing the amp's input impedance.
I'm not sure how you make the leap from the Dayton quote to your statement....
Roscoe
April 3rd, 2021, 11:30 pm
David McGown wrote:I believe it may be two ways of explaining the same thing. A pot is a voltage divider, the input signal is grounded through the resistive value of the pot, and the wiper is tapping off this resistor at some point that results in a lower signal voltage into the input of the amplifier. The impedance that the amplifier input will see is different depending on wiper setting. If we look at a circuit with a large resistor at the output of the preamp, say 1M, a 100K pot, then the input impedance the amplifier input will see with teh wiper at 100% volume is 1M||100K = 90.09K. However if you set the wiper on the pot to -3dB (50K), then the impedance at the amplifier input is 1M + 50K || 50K = 47.7K. So the impedance at half voltage level (-3dB) is approximately one half of the full voltage impedance. So it is the same. Now, if we are using inductive volume controls, it is a different matter.
Oh, attenuation is negative gain. Although strictly speaking gain does imply some amplification or transformation. A transformer may provide positive AC voltage gain at the expense of negative AC current gain. Obviously, there are impedances involved as well.
David
April 3rd, 2021, 11:37 pm
Cogito wrote:
I am reading the phrase “amplifiers input sensitivity” to mean amp’s input impedance.
If that is the case, of system as a voltage divider network with output impedance of preamp as the first resistor and input impedance of the amp as the second resistor. The difference between these two impedance is huge (something like 200:10000ohms) allowing very little voltage drop. As the impedance of the amp is reduces, the voltage drop increases.
April 3rd, 2021, 11:51 pm
April 4th, 2021, 12:03 am
April 4th, 2021, 1:41 am
April 4th, 2021, 8:05 am
FerdinandII wrote:You need to just forget the concept of impedance when looking at this issue. It is irrelevant.
V=IR
The line level output is (generally) a voltage source.
The line level input is primarily straight resistance.
The only thing that changes when the input resistance of the following stage goes up or down is the amount of current that the (voltage) source device has to put out to maintain it's behavior as a voltage source.