Lowering noise floor on fender and some Marshall style amps

[Dave H]

One guitar is louder than the other immediately, even if you put the LP in input 2.

If you are using both inputs at the same time it doesn't matter which is used for the LP as they are the same, both crap that is.

[Justin Thomas]

Zackly. But using two separate channels is no issue at all.

Justin

[Leo_Gnardo]

I meant don't use both inputs on the same channel. No issues with using one input from each.

Shelley & I tried every combination, separate channel, same channel, all resulted in that comical gargle tone from the modulation of voice by low pitched bass. Some things are not meant to be.

To support your PA observation, in another band one day our rhythm guitarist showed up without his Vibrolux Reverb, it was in the shop for a repair. So he plugged straight into our Magnatone PA head. Two 4x12 columns with a 60 watt solid state amp built into the base of each, old fashioned hi tech. It didn't interfere with the vocals at rehearsal and he LOVED the sound of his guitar! So - when the band broke up he bought the Magnatone rig - we weren't left with the quandary of selling off the PA. Somewhere out there Peter Bent (real name, no foolin!) might still be twangling his Gibson through that thing. Last I saw him, he was standing on a corner in Harvard Square, Cambridge Mass, still trying to make a living as a musician. Good man - I hope he achieved some level of success.

[Gingertube]

The grid stop resistor is indeed the major source of noise in a high gain amp and reducing the "standard" value from 68K to 10K will help. Then add 470pF to 680pf cap from grod to cathode or grid to 0V to restore the original HF roll off.

BUT
What about the source impedance in the guitar?
A 500K volume pot with knob set at 50% will have a resistance of 250K (assumming a linear pot) and the noise from that will swamp anything generated by the grid stop at the amp input.
Need to run those guitar volume controls at 100% for minimum noise.
That source impedance in the guitar is also going to lower the HF Roll Off frequency from the Miller Capacitance at the input tube grid.
Again run the Guitar Volume Pot at 100% for best HF response.

So is it worth doing?
Yes - but unless you run the guitar volume knob(s) at 100% you won't notice.

Cheers,
Ian

[Chuck H]

And players have been battling this for LITERALLY DECADES! We have guitar preamps, volume pedals, wireless systems and a few mediocre volume pot circuit mods to combat the problem. But the reality is that the interaction between the electric guitar, with the passive pickups we like and the use of volume control has always been a problem. With the exception of players that have been musical enough to find a use for the detrimented tones created by using the guitar volume pot trimmed. But good players can find a musical quality in almost any tone.

JM2C