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In Reply to: Re: Well, then you made a false connection... posted by theaudiohobby on March 22, 2007 at 09:31:54:
Your garbled post left room for doubt which you have now removed."...it is self-evident that feedback does not affect the input impedance but input impedance affects the amplifier's linearity, because the amplifier becomes more sensitive to the preceeding components output impedance and its connecting cable."
This is simply wrong. The amplifier neither knows nor cares about the upstream component's ouput impedance, or the connecting cable's electrical properties. It responds to the voltage present at its input terminal. Amplifier linearity is an internal property of the amplifier as connected to its load impedance.
The amplifier's input impedance determines the relationship of input current to the input voltage. It is the upstream component's output impedance that determines whether the input voltage suffers distortion from the current requirement. Similarly, it is the upstream component's output impedance that determines whether cable dielectric properties will seriously affect distortion of the input voltage to the amplifier.
It is important to know the amplifier's input impedance in order to select a compatible source component. An amplifier with a low input impedance will burden a source with a high output impedance, such as a plate-loaded triode stage as found in some BAT gear. The resulting sound will be less satisfactory, but that is because the source component was not a good match to the amplifier, not because the amplifier is somehow more nonlinear.
Follow Ups:
The resulting sound will be less satisfactory, but that is because the source component was not a good match to the amplifier, not because the amplifier is somehow more nonlinearYou are obviously a lot more confused that I am, I clearly stated in a preceeding post on this thread that I was interested in "frequency non-linearity as a result of high output impedance and/or low input impedance."
Frequency nonlinearity is affected by the input and output impedances under specific circumstances not as a result of the amplifier's inherent nonlinearity (I never stated otherwise) but as result of intereaction between the amplfier in question and other devices, so your text is convoluted and rather pointless in respect of the original point.
If the input impedance is low wrt the output impedance of the preceeding, the voltage developed across the inputs may be less than optimal as the preceeding component struggles to source enough current (i.e. what you refer to as overloading) to permit sufficient voltage across the amplifier inputs to enable optimal peformance of the amplifier. Nevertheless, Even if the preceeding device sources sufficient current to permit sufficient voltage across the amplifier inputs, there will still be modifications to the amplfier's frequency response as result of impedance interaction between both devices owing to Ohm's law.
"Nevertheless, Even if the preceeding device sources sufficient current to permit sufficient voltage across the amplifier inputs, there will still be modifications to the amplfier's frequency response as result of impedance interaction between both devices owing to Ohm's law."Wrong.
it is not wrong, if you disagree, state your reasons.
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