Simplifying a tone stack?

[hanumanlangur]

Hello, I am interested in building a Fender/Marshall-style tone stack, but with fixed value resistors rather than potentiometers. I know that I can simply replace the pots with the equivalent two resistors to get the tone controls I want. But I am wondering if this design could be simplified since the pots have been eliminated (without changing the tone from the original)?

I suppose I could use the original circuit with trimmers, but I really like to simplify things whenever possible.

[nico.verduin]

De impedance of the circuit varies with the frequency admitted to the tone stack. I doubt there is much to replace.

[Don Moose]

Have you tried something like the 6G2 Princeton's tone control? 2 caps, 1 pot (or 2 resistors).

Find it at the FFG

[hanumanlangur]

Have you tried something like the 6G2 Princeton's tone control? 2 caps, 1 pot (or 2 resistors).

That is a nice tone control (very simple and elegant), and closer to what I would like to come up with in the end. But I'm mostly interested in taking the existing Marshall tone stack and simplifying that if possible.

I think maybe one of the limiting factors is my knowledge of electronics. Maybe if I knew more, I would be able to design a fixed-value tone stack that gives a similar frequency response to the original.

[Don Moose]

If you have a Windows machine, wander over to Duncan's Amp Pages and snag a copy of the Tone Stack calculator. It's a nifty tool for graphing the frequency response of some well-known tone stacks - and it lets you fiddle with the values (IIRC). No provision for designing your own, that I recall, but worth a look.

Hope this helps!

[Earl]

I'm not sure I understand this completely. You really can't duplicate the tone stack circuit without using the tone stack parts. As mentioned, you can opt out for the 6G2 "tone" control...my personal favorite....or construct some set of filters that form the response you desire.

MPO is that if you use a tone stack with some fixed response, there will be a day when you wish you had some knobs.

[Don Moose]

True dat, but the man asked.

I just remembered an example of what hanumanlangur was looking for - the OD section of a Mesa Mk series has what amounts to a fixed 'stack. Is schematicheaven back up?

Hope this helps!

[jrfrond]

You will find this fixed tone stack setup exactly in the Fender Champion 600, and also 6G6 Bassman designs, whereas the tone stack is used for shaping, and bass/treble controls are elsewhere in the circuit (on the Bassman only). In the case of the 6G6, the treble control is a simple pot/cap shunt to ground, while the bass control involved a bypass pot across a small-value cap. There's a lot going on, but the 6G6, particularly the "-B" version, is one of the finest-sounding amps Fender has ever built.

[Hardtailed]

I think it would be interesting to know what you are trying to achieve exactly.

If you merely want to simplify a circuit to make your first build easier, I might suggest that the tone stack is not the best part to start. It's actually pretty simple in execution: 3 caps next to each other, a resistor, and the pots.
Hardwiring it would require creating voltage divider which would add more parts on the main board.

The classic B/M/T tone stack is so elegant in its simplicity.

If you want to simplify your build, I suggest starting with a simple circuit, not attempt to modify (which might becomes way more complex than you thought, even though you were only trying to simplify).

To be honest, modifying existing circuits is where building gets fun for me, but I can spend months planning a design before heating the soldering iron. I need to make sure I completely understand what's happening, why and how it works, etc.

[J M Fahey]

Hi hanumanlangur
What are you exactly trying to do?
That's not clear, that's why you get so many different answers.
Do you want to have *one* favorite equalization and be happy with that?
Do you want to use less potentiometers but still be able to change your sound?
Both statements above contradict each other.

[loudthud]

The basic Fender tone stack can't get much simpler. The Bass and Mid controls are rheostats so one fixed resistor will do the job. The treble pot is a voltage divider so you could just use two fixed resistors. Marshall connects the mid pot a little differently but you can combine two parts of the Bass and Mid pots as one fixed resistor.

For the treble pot you could just use one resistor of say 220K and tweek on the treble cap to adjust the amount of highs getting through. There, you saved one resistor and one eyelet.

[wizard333]

My question would be the same: What are you trying to do? Whats your end-goal? The tone stack really doesn't get much simpler than Fender/Marshall, removing the pots would only remove versatility.

Are you going for the Randall Smith thing where there is a dummy stack in the middle of the gain staging?

[ThermionicScott]

The OP hasn't visited in more than a year, so maybe he got the answer he wanted?

- Scott