Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

March 28, 2024, 01:26:18 PM

Login with username, password and session length

Recent Posts

 

measuring input impedance of my amp

Started by duclon, June 15, 2007, 08:22:42 PM

Previous topic - Next topic

duclon

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

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.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

teemuk

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

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

Quote from: duclon on June 19, 2007, 04:03:04 PM
if i hook up my instrument to my amp and like the sound then go with it.  :)
Mike


Bingo, thats what its all about.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com