Will this circuit work as expected?

[Howlin' Mad Mac]

Here's a tone stack (of sorts) I thought up. My brain tells me it should work but then again I'm getting old & all those years of hops & bong resins have taken their toll. Any thoughts?

Stack.pdf

[Daver]

As drawn it won't work much at all like a tone stack. The 250p cap, 10K and 22K resistors as well as the Cut pot are all at ground potential on one side of each. The Cut will act as a volume. The Punch and Scoop serve to isolate the .022uf cap from ground. That will drop a lot of highs and they won't sound much different from each other. Maybe you didn't draw it like you thought it?
Dave

[Howlin' Mad Mac]

Hmmm... perhaps I should maybe clarify my hopes & dreams here, eh? My thoughts are the pot (cut control) will act like a backwards treble control (brightest at minimum, darkest at maximum) & the SPDT switch select between a very scooped midrange & the "punch" like a Fender tone stack with the mid set to about 6. Does that help at all?

[Howlin' Mad Mac]

Yea, something tells me it's not quite right either but I can't put my finger on what's wrong with it. I've added a second post to clear up exactly what I wish it to do... essentially bass @ full bore, the ability to cut the highs back (as opposed to turning them up) & select between a heavily scooped mid & a standard mid knob set to about 6.

[Chuck H]

What's wrong is that is doesn't reference the cut portion of the signal to ground as most tone stacks do. All you have is a 250k resistor bypassed by a 250p cap to accentuate top end. I'm not going to do the math but it's a lot less profound than if you tank the signal NOT passing through the 250p cap to ground. Thereby accentuating the top end. This is what other tone stacks do.

[Howlin' Mad Mac]

After staring at this awhile last night something came to me & I made several changes. I think this should smooth everything out. Any thoughts?

Stack.pdf

[Chuck H]

You actually have more mid scoop in the "punch" position than in the "scoop" position. Your best bet here is probably to have the 22kR in the punch setting and a direct connection to ground in the scoop setting. You still have just 350k of resistance differentiating between the highs and low on the pot. Without a ground reference for the opposing frequencies that pot really won't do much but cut highs. It's basically a typical tone stack without a bass control. So the bass is always on 10. What is the goal? Do you just want a stack all your own, are you trying to preserve gain?

[Howlin' Mad Mac]

Basically I would like a quasi-Fender type TMB stack greatly simplified where there is no bass control (it's always on full), a treble control that works in reverse (brightest at "0", darkest at "10") and a switch for the mids that can jump between the "3" & "7". It would be highly desireable if the circuit doesn't rob as much gain as a typical Fender style stack as well. It's not to be different (tho I certainly am that), it's just that I really like the simplicity of one knob & a switch (as opposed to 3 knobs) yet I want more versatility than just a "tone" control. Hope that helps.

[Dave H]

One end of the 'cut' pot is still grounded. I think you want something like this.



If the schematic is too small open it in a new tab.

Dave H.

[Chuck H]

OK. Now that I know what you "expect" I can answer the original post...

The bass will always be on 10.
The pot will cut highs.
The switch will change the mid setting.

So, yes, this stack will do what you expect it to do.

For a difference between 3 and 7 on the mids use a 2.2k to 3.3kR in the scoop position and a 6.8k to 10kR in the punch position to simulate a 10k pot. Use a 4.7k to 6.8kR for the scoop and a 15k to 18kR in the punch to simulate a 25k pot.

If you want to set a fixed amount of bass attenuation (as you probably will unless you always run your bass on 10) you can use a resistor across the 22n cap that goes to the mid circuit. Anything up to 220k depending on how much bass you want to cut.

With the exception of the bass frequencies always being on 10, this circuit eats as much dB as a typical tone stack.

[Howlin' Mad Mac]

Thanks much there Chuck! Since this thing still eats about the same dB should I increase the gain going into the stack by adding a cathode follower before or even adding another cathode biased stage between the volume & the stack?

[Howlin' Mad Mac]

Yes, the one end of the pot is grounded but how does this differ from a typical Fender tone stack with the bass pot running flat out (0 ohms)?

[Chuck H]

If you typically run the bass high anyway you could just use a three position switch for the mid circuit and have one position use a 1M resistor to effectively remove the stack from the circuit, for those times when you want to wail. I'm guessing you wanted to use a push/pull pot switch for the mids to reduce front panel controls. I'd rather bypass the stack and have a front panel switch than add a triode, but it's up to you.