Quad Cortex Input impedance explanation

I know there’s a couple topics on the subject in this forum but I’ve been searching for explanation on the input impedance setting of the Quad Cortex. Those available values do not make a lot of sense to me yet as it does not seem to be relatives with guitars output impedance as those values are usually much lower. (i.e. I reed around 7.5K ohm at my Telecaster output). I tried a few settings on the QC and for this same guitar, the 232K ohm setting seems to be the one that sound’s best.

Now where this 232K is coming from and why 1M ohm is the default setting? Where do I measure to get the right reading and make an educated decision instead of guessing?

Not that it’s critical but I like to understand “why” I do things … and yes, you guys can call me a “Nerd” ! :metal: :nerd_face: :metal:

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The input impedance is effectively the input impedance of the “amp” and is not related to the impedance of your pickups. The input impedance of a valve amp is typically 1M ohm, and is set that high to avoid loading your pickups. The amp wants to see a voltage, not a current, and a low impedance would allow current to flow. This would change the characteristics of your pickups, and change the sound (as you have found by trying different values). Some old fuzz pedals have a low input impedance, and need to “see” the impedance of the pickups, which is why they often need to be first in the signal chain. Another pedal between the fuzz and the guitar will change the impedance seen by the fuzz, and it will not produce the intended sound. Lowering the input on the QC or amp will tend to drain off high frequencies, which can be useful to tame the harshness of some bridge pickups. The QC gives you the option of choosing your input impedance, so you can choose the value that sounds best to you.


Ah! This is the answer I was looking for. It is not clear as what this values is related to but it makes sense since the QC is an “Amp”! Thanks for the explanation!