Variable input loading - how to?

[bufferz]

I noticed on the empress buffer+ there is a feature to adjust the input impeadance from 20k - 1M. Could someone explain how this is done, I know that a pot is just a variable resisior but how do you think this is implemented and how do they adjust the range from 20k as minimum ( I suspect this will be enough to avoid popping issues?)

I am a visual learner so any links to topics where this concept is llustrated would be much appreciated.

Cheers

[CynicalMan]

Their website says 10k - 1M, but I'll bet it's just a 1M trimpot in series with a 10k resistor. The extra 10k is almost certainly within the tolerance of the trimpot, so it makes sense to just say 1MΩ instead of 1010kΩ.

[Lurco]

Completely different, and more complex, but definitely interesting: http://www.diystompboxes.com/smfforum/index.php?topic=39559.msg282433#msg282433

[bufferz]

so is this 1m pot to 10k resistor taking the place of the (anti-popping) input resitsor to ground or the resistor coming from  VREF 4.5 V?

[slacker]

It's placed between the guitar and whatever circuit you want to change the input impedance/loading of, so if you wanted to add it to an existing circuit it would replace the pull down (anti pop) resistor. The guitar sees the resistor to ground or vref after the input cap in parallel with the pull down resistor so changing either of those resistances does change the input impedance. However, the resistor after the input cap forms a high pass filter with the input cap, so changing it may cut some lows as well as changing the loading.

[bufferz]

It's placed between the guitar and whatever circuit you want to change the input impedance/loading of, so if you wanted to add it to an existing circuit it would replace the pull down (anti pop) resistor. The guitar sees the resistor to ground or vref after the input cap in parallel with the pull down resistor so changing either of those resistances does change the input impedance. However, the resistor after the input cap forms a high pass filter with the input cap, so changing it may cut some lows as well as changing the loading.

thanks!

[Gus]

A link to check.   Note what happens in the graphs.
http://www.diystompboxes.com/smfforum/index.php?topic=99139.0