Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on December 04, 2021, 10:28:04 am
-
high gain build. what will adding extra grid stoppers do? Ex. add a 33k to V1b and V2a? I already have a 10k on V1a
-
They’ll act to limit the gain bandwidth product. Which may be useful, if the preamp is modded for higher gain, eg bypassed cathode/s.
-
Definitely i bypassed the cathode resistors with caps. The 10k stopper on V1 along with several 470p's in various places has quieted it down but i'd still like to tame it more without losing too much gain
-
In that case it’s worth doing, especially on the 3rd stage grid.
The downside of grid stoppers is the hiss they can add, but the further along the signal chain you go, it becomes much less of an issue (because the subsequent gain is much less).
Anode to cathode caps, 100 to 220pF mounted on the valve socket terminals, are also useful
-
Anode to cathode caps, 100 to 220pF mounted on the valve socket terminals, are also useful
i meant to ask about that. I currently have a 470p from the grid on V1a to ground. Will adding another cap across pins 1 & 3 do anything or interfere with the existing cap to ground from the grid (pin 2)?
-
Rather than interfere, additional filters will increase the high end roll off.
There’s various positive feedback loops that can form though, so rather than piling them on at the input stage, it may be better to spread them out.
So maybe add the anode to cathode cap on to the 2nd stage, and the grid stopper on the 3rd.
-
i like where you're going with this :icon_biggrin: