General tech questions

Hey, Fender Amp gurus…Tone Stack Question?


On Fender Amps that only have Treble and Bass, no Mid...

My research suggests when both are on fully down to "1", that profile across the frequency range of the Amp is about as flat as it gets. Cracking the Bass pot up a notch to "1 1/2" is the other setting declared to be "most flat".

The Volume pot just raises the dBs, but the profile remains flat.

If there were a "Mid" pot control, 5 would be midpoint, then up or down changes the profile along with Treble and Bass..

Sounds right?


Not exactly.

Typically, the midrange pot is a 10K linear pot. When it is not there, like on a Princeton Reverb, the fixed resistor is 6.8K.

In effect this sets the mids at “6.8”.

The mid pot is really just a resistor between the tone stack and ground.

Up to about 10K it does indeed improve the midrange response.

In any case, a Fender amp with no mid pot is typically pre-set to about 6.8 on a mid pot (if there was one.)



But yes, setting the Treble and Bass to “1” will get you close to a flat response. But still slightly “scooped” depending on the exact amp in question.


In this case, (bass and treble set to “1”) the total gain loss though the tone stack is remarkable.


The tone stack is subtractive.

I was fooling around one day and quickly added a tone stack to a headphone amp I built, with lower value pots, but higher value caps. It really surprised me how much it sounded like a Fender.

You should try bypassing the tone stack,


So, If I want a totally flat response...set both Treble and Bass at "6.8"?


I don’t think you can neutralize the sound it makes. It’s going to have its own peaks and troughs no matter the settings.

What is balanced is something you would need to measure or decide for yourself.


I have been using the Duncan Tone Stack Calculator...

It requires a "Mid" setting.

Part of all this is to learn, part to determine the best setting when using an alternative Pre-Amp Tone Stack with the Fender Amp being essentially a Power Amplifier...

At "6.8" fixed resistor for a "Mid", cracking the Treble a bit, and the Bass a bit more is quite flat.

Now, I need to assume that Volume just raises the dBs across the board equally.


Here’s a version of the TSC you can use on the web, and you can change that R5 [RL] value. It crashes Safari on my iPad pretty often.

Changing RL doesn’t change the shape of the graph much, except to lower the dBs when the value gets very small.

You can look at the project to see how it’s using RL in the calculation.

I’m pretty convinced, having listened to a circuit with and without a tone stack, that it is never a flat response.


Back in the day, I plugged in all the values off my CVR schematic...

No doubt your ears tell you what sounds best, but the TSC gives you a visual and starting point.

No sense tone shaping something already tone shaped, best to just reproduce it and amplify.


On my CVR, using the schematic values, keeping both Treble and Bass evenly set near 1 keeps a flat profile. Compared to default, the CVR is 5dB less.

Changing Volume moves the flat profile 5dB.


The mid knob actually just widens the range of the bass control so the bass boost extends further into the lower mids. It won't do anything on it's own, and it isn't actually a mid knob. A flat setting has nothing to do with a guitar amp...electric guitars don't sound good flat.


As popular as the classic 1960s amps are, even when fully on spec/tweaked, I never thought the bass and treble controls changed the sound that much.. you turn the bass to 10 and it ain't a whole lot of bass coming in. Other amps including kool Thomas Vox just have more range in the controls... and I have all the black panels from Champ to Twin... treble bass controls on brown ones were a little better. I never got along with single tone controls anyway.


The CVR actually has pretty good Tone range. But, I also have guitars with built-in pre-amps, and then again a LR Baggs Para DI box which I use many different ways.

My other amp is a SS Chip Amp. The LR Baggs is primarily matched to that...

Just seeking the best sounds, ... like everyone else!


Always change the .047 to a .01


I haven't been inside the chassis in a while...there are a couple other reasons when I do.

I assume this will reduce the Bass-i-ness, making it more Mid-dy? That's what the calculator shows.


My mistake, thought I saw .1, this extends the Bass range.

I was going to say why not a .022?

Let me see what I have in the components box...


Calculators are bogus. Try it and listen.

Register Sign in to join the conversation