Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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Now it is clear that you are confused.

Posted by Al Sekela (A) on March 22, 2007 at 10:59:08

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.

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Kimber Kable

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