Differences between Low and High inputs in theory

[andrius]

Thank you for the explanations, people. When asked, the seller said: "different impedance, that's all". Laney manual was no better too - it said only that High is for single coils and low output humbuckers and Low is for higher output humbuckers; humbuckers may sound muddy with the High input, - but personally to me, they sound muddier with Low and I always imagined that adding higher frequencies kind of helps muddy situation. It's good there is this forum.

[J M Fahey]

Dear hasserl, donīt even remember what this thread was all about, guess a very simple issue got dragged way over what itīs worth by nitpicking, but please be sure that in my answers (which may be right or wrong, that's another issue), "animosity" is *NEVER* a factor.
Sentimentalism is quite useless when addressing Engineering or Physics issues, which is what Electronics problems really are.
If anything I said looks aggressive to you, I ask you yo forgive me, it was definitely not my intention.

[MarkF786]

Sorry, I'm still confused. There seems to have been some disagreement in the beginning. Could someone explain what's going one, using the below schematic of Fender amps?

What impedance does each jack see?

What resistance exists between the jack and the grid on the first tube (and what's its purpose)?

What exactly are the switches doing? It looks like they are muting the jack by grounding the input, but why does one go through the 1M resistor?

I've looked at this so many times and still haven't gotten my head around it. Any help is appreciated.

[J M Fahey]

Plugging into the High input, basically you see 1M to ground.
From your guitar to the tube grid you have 2 x 68K resistors in parallel, around 34K.
They , together with the tube input capacitance, roll off highs, but above audio frequencies, to avoid RF interference, instability, etc.
Plugging into the Low one, you see 2 x 68K to ground, and signal gets attenuated by half.
You still have 34K in series with the grid, which still serves the same purpose.

[MarkF786]

Thanks, JM.

I drew the circuit to show it's equivalent, accounting for the switches and in an easier to read layout, and now I'm following what you're saying. The schematic and explanation at A closer look at the Fetzer Valve also helps to make it more clear (though the 134K should be 136K as Steve noted above). Before I wasn't able to see the resistive divider in the way the circuit is normally drawn.