Tone stack question.

[pinkphiloyd]

Okay. In the last 48 hours or so, it's become painfully obvious to me that I know less about tone stacks/controls than I do any other part of an amplifier. I understand they're just various combinations of hi and low pass filters, but that's about the extent of it. So I've been trying to do some reading. My immediate question is this. What's the purpose of the resistor I've circled in red here? I'm guessing it effects the mid boost frequencies, maybe? But in my brain simply bypassing the second cap would have pretty much the same effect simply by allowing a lower range of frequencies to pass. More capacitance=lower frequencies. So clearly I'm missing something.

[martin manning]

It's main purpose is to prevent a pop in the speaker when the switch is thrown. This set-up is just a dual value treble cap, where opening the switch connects the 0.002uF in series with the 1000pF to make 666pF.

[RockinRocket]

Whats the name of this tonestack? And what amps is it used in?

[martin manning]

It looks to be a hybrid of Dumble tone stacks.

[pinkphiloyd]

It's main purpose is to prevent a pop in the speaker when the switch is thrown. This set-up is just a dual value treble cap, where opening the switch connects the 0.002uF in series with the 1000pF to make 666pF.

Okay, so just as I suspected, then. As soon as I read your explanation about the popping, I felt like an idiot for not seeing it.

Yea, schem is from the JM sig found in the Dumble section.

[wattsup]

So the 2M2 resistor has no affect on the tone?

[pinkphiloyd]

So the 2M2 resistor has no affect on the tone?

I'm going out on a limb with this one, but I'm guessing no. It seems to me like it might form part of a high pass filter with the coupling cap in front of it, but even if that's the case, this one is passing everything above ~36 Hz, well below anything practical for a guitar amp.

Again, take any and everything I say with a grain of salt until somebody else with a more respectable pedigree comes along to confirm it.

[Garthhog]

I don't know what you want for a pedigree, but the 2M2 resistors is too large to have any discernible effect on the tone other than a parasitic effect. It may contribute to hiss due to it's large value and proximity to the audio path.

[pinkphiloyd]

I don't know what you want for a pedigree, but the 2M2 resistors is too large to have any discernible effect on the tone other than a parasitic effect. It may contribute to hiss due to it's large value and proximity to the audio path.

Yea, that makes sense as well.

[ValvElectric]

The more I learn about amp building, the more frequently I seem to find myself in similar situations.
If you haven't read this already, I think this article provides a simple explanation and really helped my initial understanding of the tonestack and it's basic functions.
http://pickroar.com/1003/the-tone-stack ... or-humans/