'Grid Stoppers' for Drip Electronics LA-2A REV10 PCB
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andyfromdenver
Well-known member
Hi Hugo, unless someone more senior disagrees:hugo said:
Grid stoppers act with the input capacitance of the tube to create a very high frequency low pass. They potentially eliminate oscillations and radio interference. Unless the resistor value chosen placed the roll-off in the audible range (no one would desire that) the typical hiss etc. will pass right by the grid stopper.
If a person is looking to minimize noise in a P2P tube build, the historical solutions are several, just to name a few:
Circuit flow- sensitive preamp stage far from noisy power stages.
Component layout- Some true point2point tube gear can sound incredibly quiet even though it looks messy. A tried and true circuitboard layout can be easily as good.
Lead dress- lead length and preamp signal leads being shielded and crossing noise emitters at right angles or with distance.
Tight heater layout- which removes hum
Transformer orientation- to find the flux null so the PT is not picked up in the OT etc.
Metal film resistors-lower noise
Known good tubes-selected for low noise
Shielded transformers- for super bling
hope that helps! my $0.02
I've built over 25 tube "things" now, and just completed my P2P LA2A.
no grid stoppers, and it is extremely quiet, no hum, very slight hiss if output cranked and no signal (aka listening for it at the noise floor)
you may know all this and are asking still and someone may have different input i'm not aware of.
Andy
Hi, thanks for this reply. Hiere is my issu,e which is not a real issue :
I made a P2P pair La-2a, nos nib HA100x, Nos nib A-24, low noise tested new mullards, very very clean dressing. I also made an Opto 6 pair, with sowter and standard electro harmonix tubes. My Opto 6 are dead quiet, full 0 i have -90db on my Daw. My La-2a is about -70db and can jump at -62db.. My two La-2a are maing the same noise, following the same "jumps", and "dead quiet moments". It is only hum..my heaters are solid core ptfe completely at the bottom of the unit for good shielding.. I used CC resistors on both la2a and opto6. I would like to obtain the same signal/noise ratio on my P2P, than on my Opto6s.
I made a P2P pair La-2a, nos nib HA100x, Nos nib A-24, low noise tested new mullards, very very clean dressing. I also made an Opto 6 pair, with sowter and standard electro harmonix tubes. My Opto 6 are dead quiet, full 0 i have -90db on my Daw. My La-2a is about -70db and can jump at -62db.. My two La-2a are maing the same noise, following the same "jumps", and "dead quiet moments". It is only hum..my heaters are solid core ptfe completely at the bottom of the unit for good shielding.. I used CC resistors on both la2a and opto6. I would like to obtain the same signal/noise ratio on my P2P, than on my Opto6s.
andyfromdenver
Well-known member
Interesting! So if it's hum and not hiss, my thoughts center around heaters, AC wiring off the PT, Transformer orientation. But it sounds like you have worked to minimize these in your build.hugo said:
If you want to 100% eliminate heater hum as a problem, you can use a 6V Lantern battery and isolate the heater secondary and run the heaters off the battery, listen for any change. You can also replace the Heater center tap with a 1W or greater 100-200ohm pot, and dial for least hum, need to crank volumes and listen to noise floor, like some pro gear of old.
Lastly, if you used a standup PT like a Hammond, if you can unbolt it and possibly try a 90 degree turn, see if that lessens/removes the hum. However, I would think your shielded OT&IT would eliminate that.
I am super passionate about low noise builds and it just takes a lot of effort sometimes to get there. I feel for ya and wish you success!!!
Andy
*This is a good argument for a well thought out PCB, and I totally understand the appeal, but I know you can get your P2P to the same level!
