@kalali
No material difference between 100K or 1000K input resistance. Both are high enough such that any stray micro-amp current could generate a voltage input to the amplifier.
You need to get to 10K or below input impedance to start making a difference. This means the preamp needs to have a stronger drive output - all good stuff as anything that increases the need for a stronger line level signal means less noise as the end result.
Very old gear used 600 Ohm as standard and was immune to the kinds of noise now affecting high impedance gear but that standard actually came from transmission line theory for telegraph wires so it had other issues.
Another solution to noise on input is to go balanced (this means each signal wire to ground should have the same impedance) - this ensures that RF/EM hum/ground loops are affecting both wires equally and cancel out. However even balanced works better 10K and below for noise suppression.
So as a general rule, ultra high input impedance is a bad design if you care about noise. If you wanted to deliberately design an amplifier to detect very low level signal noise then I can guarantee you it would have a very high impedance just like an oscilloscope input.....
No material difference between 100K or 1000K input resistance. Both are high enough such that any stray micro-amp current could generate a voltage input to the amplifier.
You need to get to 10K or below input impedance to start making a difference. This means the preamp needs to have a stronger drive output - all good stuff as anything that increases the need for a stronger line level signal means less noise as the end result.
Very old gear used 600 Ohm as standard and was immune to the kinds of noise now affecting high impedance gear but that standard actually came from transmission line theory for telegraph wires so it had other issues.
Another solution to noise on input is to go balanced (this means each signal wire to ground should have the same impedance) - this ensures that RF/EM hum/ground loops are affecting both wires equally and cancel out. However even balanced works better 10K and below for noise suppression.
So as a general rule, ultra high input impedance is a bad design if you care about noise. If you wanted to deliberately design an amplifier to detect very low level signal noise then I can guarantee you it would have a very high impedance just like an oscilloscope input.....