Input grid resistor

[Vlada]

Hi guys, I am building high gain tube preamp and was wondering about V1a grid resistor. Some say lowering this resistor can reduce hiss while others claim that this can lead to overloading input when using overdirve pedals. I am thinking of using 10k resistor with capacitor from tube grid to ground to get the same cutof as with 68k resistor. Are there any other thing to consider? And should I wory about input overloading?

[kagliostro]

Not very much to say (from my part)

only to remember that a high W rated resistor has the tendency to insert less noise

and ... use a metal film resistor instead of a carbon composition resistor

this will result in less nois at same resistence values

BTW, Mesa, in some amp, didn't used a resistor, they used a ferrite bead, no resistance added and no noise

Franco

[PRR]

> overloading input when using overdrive pedals

Um, so it distorts when you use distortion pedals?

The experiment costs pennies. Just try it.

[pdf64]

Tube guitar amps typically use input grid leak resistors and input mixer / grid stopper resistors.
Ok, from the context it’s apparent that this thread is in regard of the grid stopper, but it’s always best to try to avoid folk having to assume relevant info.
To be clear, it’s essential for tubes to have a dc path between their control grid and cathode, with the max resistance of that dc path usually being specified in the tube info.

[d95err]

Merlin has a good article on the subject:
http://www.valvewizard.co.uk/gridstopper.html

I use his duggestion with a low value input resistor and a capacitor. Works fine and does reduce hiss a bit.