That's not entirely true - there's millivolts of DC being produced by the instrument. Whether this is audible is the debatable "cork sniffing" part. I have used both and while the value of the resistor matters most, there is still a slight audible difference between carbon and metal on the input grid. There's also a difference when it is installed right at the pin vs off the input jack, at least in stability/oscillation in high gain preamps. Go ahead and try it!Helmholtz wrote: ↑Tue Oct 01, 2024 2:40 pmAs there's no DC current flowing in the input grid stopper there will only be thermal noise.GlideOn wrote: ↑Wed Sep 18, 2024 12:48 pm An if you want less signal or high content cut, go lower in resistance with the 68ks or use single 10k to 33k resistor, metal film or oxide too as they produce 10% of the thermal noise as carbon ones do which are immensely useful at the very beginning of the amplifying stage.
Thermal or Johnson noise solely depends on resistor value and temperature, meaning that all resistor types will perform the same independent of resistor technology.
Type differences will only show with current (distribution) noise, e.g. with plate resistors.
Yes, there's far more a dramatic difference when used at high voltage junctions (plates, etc) but every little bit helps. I myself like using Metal Oxide from input to V1 and Carbon Film for V2 and beyond. It's also good design principle to use known quieter components towards the input of amplifier whenever possible. Of course if the amp in question is vintage and is working just fine with Carbon Comps throughout, don't fix what isn't broken.
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