Input impedance

January 25, 2017
 by Paul McGowan

Every electronic product with an input has an impedance, though I suspect few of us pay much attention to it.

Understanding input impedance is valuable for those connecting equipment or making purchasing decisions.

Input impedance is defined by Wikipedia as, "... the measure of the opposition to current flow (impedance), both static (resistance) and dynamic (reactance), into the load network being connected that is external to the electrical source."

What a lot of gobbledygook. Let me see if I can put it in more understandable terms.

Input impedance determines how easy or hard the source equipment works to supply music. The lower the number, the harder it works.

Over the next couple of days we'll look at some of the use cases and what they mean.

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4 comments on “Input impedance”

  1. Good topic!

    Opinions about the "match" of impedances between amplifiers and pre-amps, the latter, both active and passive, would be useful.

    PS Audio 6.0 comes into my head, or any other of those that are currently sold in the market.

    Is it possible to get used to the coloration presented by the vast majority of the active pre-amps that makes us say that they sound better than the passive ones, although they have greater distortion than the latter?

    There is no "wire with gain" as we all know

    1. I have 3 different pre-amps that work their best within fairly narrow setting for their volume control. One says a medium setting in the manual, and one a high setting in the manual. So, the imput impedance of the power amp combined with preferred listening volumes have to be factored in. One pre-amp I used to have needed to have the volume set so low for acceptable listening levels that it sounded terrible with my best power amps that have an input impedance on the low side. In fact, with low input impedances current transients become more of an issue as well, so some pre-amps may not have decent line drivers at all for this situation. It is a pity that there is no standard for input impedance of power amplifiers.

      1. I have always wondered why home audio amplifier manufacturers have not agreed to standardize the input impedance figure. In professional audio the standard is 600 Ohms.

        It does not say in your post whether your preamplifiers are active or passive.

        I reiterate that it is a good topic for us, the users

        1. "In professional audio the standard is 600 Ohms".

          Most professional audio is no longer using 600 ohms.
          They have gone to a much higher input impedance but kept the the same 600 ohm scale for measuring levels.
          They now measure levels in dBu rather than dBm.

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