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Author Topic: measuring input impedance of my amp  (Read 2867 times)

duclon

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measuring input impedance of my amp
« on: June 15, 2007, 08:22:42 PM »
Sorry if this has been discussed before but I searched and could not find a definitive answer.
Is there a way to accurately measure the input impedance of the amp I'm building.
I need 1.8 M ohm or a little more for the instrument I'm designing the amp for.
anyone know how using some basic test equipment, multi-meter, oscilloscope?

Mike

joecool85

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Re: measuring input impedance of my amp
« Reply #1 on: June 17, 2007, 01:12:06 PM »
It's easy.  Take a DMM (Digital multi meter) and hook one lead to the positive of the input, and the other to the negative.
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teemuk

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Re: measuring input impedance of my amp
« Reply #2 on: June 17, 2007, 02:31:04 PM »
That method measures only the input resistance. Granted that in most cases that's all one needs to know anyway.

However, true meaning of impedance means that the circuit resistance varies according to frequency. This effect can only be measured by using either constant voltage or constant current source as input. Essentially Z = U/I and if either U or I is known (and the other value measured) Z can be calculated from the results. Note that naturally this must be done at various frequencies.

The method described above is not extremely complex but quite tiresome (and often unneccessary). Therefore it is often easier to stick to the basic methods - like the one given by Joecool85 - just understand it's limitations.

duclon

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Re: measuring input impedance of my amp
« Reply #3 on: June 19, 2007, 04:03:04 PM »
thanks for the reply guys, i think I'm too worried about the impedance. As stated, it might just be unnecessary to go that far. It might be best to just use the best instrument available, my ears. if i hook up my instrument to my amp and like the sound then go with it.  :)
Mike

joecool85

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Re: measuring input impedance of my amp
« Reply #4 on: June 19, 2007, 06:08:02 PM »
if i hook up my instrument to my amp and like the sound then go with it.  :)
Mike


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