one-knob tone stack

[burt_toast]

So, after starting with a sort of EL34 Hoffman Stout-ish build, I've slowly tweaked it until it's almost straight-up Plexi. I don't have room for all three TMB pots, so I've done the fixed-Bass-and-Mid thing, with a variable Treble. Do my tone stack fixed resistor values look alright? The amp's a monster, and sounds great. Just curious. Thanks fellas
cheers, Scott


ps, thanks Tubenit for suggesting to add the CF

[tubeswell]

‘s one way of skinning the cat

[tubenit]

The values look fine to me. 

Another thing to ponder IF you wanted to adjust the bass or mid is the use of a dual gang pot. 

For example, one can use a dual gang 500k pot and then put a 470k resistor on the outside lugs of one pot effectively making is sort of a 250k pot.  You can use sort of a Fender/Marshall tone stack topology for this.

The idea would be to adjust one of the pots with a paralleled resistor to reflect a range that you wanted. You might want a 1M dual gang pot and then parallel a resistor across the outer lugs on one of the pots to get a 220k to 250k treble pot. 

A 2nd option would be the use of a dual gang pot with a James/Baxandall type tone stack.  I've done this before and liked how it worked out.  The James tone stack can simulate a mid-boost or a mid scooped tone.  So, with one knob, you can adjust between those two.  You'll have to experiment with the values you like, of course.  I've got some values that I personally prefer using for this.   The free program  Duncan Tone Stack calculator is quite useful in this regard. 

Just tossing out some thoughts to ponder, NOT saying you should do either of these & I probably wouldn't IF you're truly happy with you already have. 

A 3rd option would be to use a spdt with paralleled or a series resistor to change the value on the fixed bass resistor OR you could use a dpdt mini-toggle with paralleled resistors to change values on both the bass and mid range.

A 4th option would be a spdt to parallel a cap to change a .02 to a .04 in the tone stack.

Lots of options there.  You could use a pot with a built in dpdt pull out knob.

with respect, Tubenit

[tubeswell]

There are a number of 1-knob tone control options. The tweed Princeton tone control is highly effective for minimal signal insertion loss. The tilt control (a.k.a. ‘Big Muff’ tone control) can also be effective depending upon the values chosen - for a little more loss, but a very flat response at the mid pot rotation point.

[jordan86]

I you stick with a Marshall tonestack, I’d probably want more like 150-250K on the bass resistor. I’d also be sad to not have a full 25K option on the mids. Maybe do a full 25k on mids, with another 33k on a mini switch in parallel so you have 15k and 25K options. Switch would be easy to add.

[jordan86]

I presume you have seen this page.
https://chasingtone.com/guide-to-single-knob-tone-controls/

[burt_toast]

...exactly, Jordan86
it's got hoofy 4x12 low end for DAYS, but I may tweak the mids back up to 25k. I dislike too many options in general, and actually love having fewer knobs on an amp - may incorporate this semi-fixed stack into future amps, even if I have room!


thanks fellas

[roseblood11]

A 2nd option would be the use of a dual gang pot with a James/Baxandall type tone stack.  I've done this before and liked how it worked out.  The James tone stack can simulate a mid-boost or a mid scooped tone.  So, with one knob, you can adjust between those two.  You'll have to experiment with the values you like, of course.  I've got some values that I personally prefer using for this.   

Can you show your preferred values, schematics... please?
 
I'm planning a similar one-knob tonestack for a clean boost inside the guitar. And maybe for a small practice amp later.

[tubenit]

Try these values using the Duncan Tone Stack Calculator.  Move the treble and the bass equal amounts of increments as you look at what this does.


Now try it again, using a 500ka bass pot and a 500ka treble pot as a dual gang potentiometer.   I've used both 1MA and 500ka volume pots. 


It's a personal choice and preference thing, of course.  These values seem to work well for me.


With respect, Tubenit

[kagliostro]

Using a TMB like you did, a more versatile option will be to use the 3 standard pots but place only one on the faceplate, this way you can fine adjust for middle and bass than using fixed resistors

An alternative

A dual concentric pot (2 concentric shaft)

https://guitarelectronics.com/alps-stacked-250k-dual-concentric-pot/

and only one resistor (or hidden pot)

Franco

[tubeswell]

Dr Z Carmen Ghia is another interesting one-knob tone control.

[jordan86]

Dr Z Carmen Ghia is another interesting one-knob tone control.

It is! I am building it into an amp now. I actually reached out to this guy and he was kind enough to build it into his interface. So you can tweak and see what it does. Note: these are the values used in the Dr Z Stangray. But if you plug in the Carmen Ghia / Phoenix values (which you can do in this interface) it looks and reacts almost the same.

https://www.guitarscience.net/tsc/drz.htm#RIN=38k&R1=330k&R2=330k&RT=1M&RL=1M&C1=10n&C2=120p&C3=4700p&RT_pot=LogA

[thetragichero]

i recently built a sort of stangray clone (fixed bias pair of 6v6 instead of the quad of el84) out of an ao-43 chassis and it is a pretty interesting tone control. added tone bypass switch is nice if you're wanting to get more overdrive (at least in the single ef86 amp)

supro thunderbolt/tilt/big muff tone control can be nice and you can tweak values to get flat mids