Tone Stack Variations?

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roberto
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Re: Tone Stack Variations?

Post by roberto »

Thanks martin!
Mr. Lime
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Re: Tone Stack Variations?

Post by Mr. Lime »

roberto wrote: Mon Nov 20, 2017 10:51 pm I think you missed one cap from slope to bass pot.
The 2n2 cap is typical of some 50W Marshall combos and hig gain amps as well.
That configuration of the treble pot makes it a quasi-logaritmic.
Try a Logaritmic like Bogner does.

You cannot say if certain mids are important "a priori".

It depends on the overall configuration of the amp.
In some of my amps I have the classic Soldano EQ, in some a inbetween Marshall and Soldano with 39k as slope and 33n as bass cap, in some others an eq with independent bands and reduced interaction between the controls. And Fenderish EQs as well.
The 68n input cap is basically the bass cap and together with the 500k bass pot it should act similar as the 22n/1M combo but with slightly more bass but the logarithmic treble pot is a good point.
I tried different "bright" controls as well, like on Engl or Hiwatt, even semi active between cathode and grid. In some amps the Vox Hi-Cut circuit works pretty well, in others it really makes not much different to the simple treble control of the tone stack. The Peavey XXX circuit is cool for solo boosting certain frequencies but as a stand alone tone stack in my opinion rather boring. I guess the Baxandall / James stack would be a sufficient replacement..

The Naylor circuit is pretty bright and cuts a lot of bass and I'm excited about shifting mids without raising the highs.
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roberto
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Re: Tone Stack Variations?

Post by roberto »

It could be interesting to see how a four-knob independent-band eq should work on a guitar/bass amp.

Imagine to split the three parts of the eq to avoid interdependencies, starting from here:
https://robrobinette.com/images/Guitar/ ... ilters.png

First control is easy: treble cap and a 250k lin pot to ground. It will be needed a bit of resistance on the wiper for the mix with other controls (à la plexi gain pots), but let's see it later.

By connecting the mid and bass pot the same way it's connected the treble pot, you can choose the amount of mid and bass without affecting the frequency of the two. Or better, with a variable slope you can choose the frequency of the two, independently from their position. So you can choose "that" amount of bass and mids, at "that" frequency. Again two different resistors on wipers, to properly mix with other controls.

I will do some simulations to see how it works.
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M Fowler
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Re: Tone Stack Variations?

Post by M Fowler »

There is also variable slope resistor using a pot many have used in Marshall type builds.
Mr. Lime
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Re: Tone Stack Variations?

Post by Mr. Lime »

roberto wrote: Tue Nov 21, 2017 4:58 am It could be interesting to see how a four-knob independent-band eq should work on a guitar/bass amp.

Imagine to split the three parts of the eq to avoid interdependencies, starting from here:
https://robrobinette.com/images/Guitar/ ... ilters.png

First control is easy: treble cap and a 250k lin pot to ground. It will be needed a bit of resistance on the wiper for the mix with other controls (à la plexi gain pots), but let's see it later.

By connecting the mid and bass pot the same way it's connected the treble pot, you can choose the amount of mid and bass without affecting the frequency of the two. Or better, with a variable slope you can choose the frequency of the two, independently from their position. So you can choose "that" amount of bass and mids, at "that" frequency. Again two different resistors on wipers, to properly mix with other controls.

I will do some simulations to see how it works.
Have you been succsessful?
M Fowler wrote: Tue Nov 21, 2017 4:29 pm There is also variable slope resistor using a pot many have used in Marshall type builds.
Yeah, this one offers a wide range but I don't think it's very practical playing on stage so I would keep it rather simple by a flick of a switch. I like the idea of having only as many knobs and switches as necessary to archive a good and flexible sound. That's somewhat the art of the design in amp building to me.
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roberto
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Re: Tone Stack Variations?

Post by roberto »

Nope Lime, I've done a general design on the plane, but I'm just back in hotel now and frankly speaking after a long day I prefer to visit Doha than work on this eq.
pdf64
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Re: Tone Stack Variations?

Post by pdf64 »

roberto wrote: Tue Nov 21, 2017 4:58 am It could be interesting to see how a four-knob independent-band eq should work on a guitar/bass amp.

Imagine to split the three parts of the eq to avoid interdependencies, starting from here:
https://robrobinette.com/images/Guitar/ ... ilters.png
I don't think it would be feasible.
The mid control is variable level of shelf between the treble and bass; I don't think it's viable to split that shelf into 2 bands.
Also as we're limited to 6dB/octave slopes, and the bandwidth of interest is quite small, there just isn't enough available to divide it into 4 and effect much change within each independently.
Need to move to 12dB/octave slopes to do that, eg with inductors.
Mr. Lime
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Re: Tone Stack Variations?

Post by Mr. Lime »

On my current preamp build I tried Merlin's Boneray tone stack with good results. I would like to take this one even further with independent bass and treble control instead of the BMP tilt control with bridged T mid filter.
I took the idea from AMZ's dual tone control and scaled the values. Haven't tried it yet and I'm not sure if the isolation resistors in brackets are high enough to prevent interaction.
My next consideration is a parametric mid control to replace the bridged T filter.
TMB Alternativ Tone Stack.PNG
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roberto
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Re: Tone Stack Variations?

Post by roberto »

pdf64 wrote: Fri Nov 24, 2017 11:36 am I don't think it would be feasible... -omissis- ...as we're limited to 6dB/octave slopes, and the bandwidth of interest is quite small
well I have to say that I don't like scooped sounds (mid pot has done ectars of dead sounds on young and/or unexperienced players). My personal tastes are to keep mids 99% of the time above five, and I liked a variation I did on the old single-pot Selmer Eq (later used also on some Dr. Z), in order to reduce the scoop (or increase the mids, as you prefer to look at it). So that one could not be an issue, personally.
Mr. Lime
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Re: Tone Stack Variations?

Post by Mr. Lime »

Here's my try on a simulation of the ranges, I hope I did my homework well for the circuit above:
Sim Tone Stack BMP.PNG
I also took a look at the Blackstar ISF and scaled it for tube amps. The values seem to be very similar to a standard Marshall stack. The stereo pot acts a lillte weired as it only makes a difference when the mids are very low. On one extreme the circuit is very bright while on the other one it acts like a treble cut. I found it not to be very useful. There might be better 4 knob tone stacks out there..
ISF.PNG
ISF Sim.PNG
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Colossal
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Re: Tone Stack Variations?

Post by Colossal »

Good work. Thanks for posting your results. It is interesting reading.
ChopSauce
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Re: Tone Stack Variations?

Post by ChopSauce »

Great, I wish I knew wich software you're using to calculate (& plot) these figures.

I read very mixed reviews of the ISF, anyway.
brewdude wrote: Sat Nov 18, 2017 1:13 am I’ve used Merlin’s TB stack (I think he refers to it as a Bandmaster) a couple times and really like the result.
I am currently reading him again. He recommends - on the pre-amp examples of the last pages of the book - also inserting an additional & separated mid control, one stage before.

NB: Merlin recommends putting the tone stack at the last stages, though.
caps8419
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Re: Tone Stack Variations?

Post by caps8419 »

Chop, use LTSpice to plot and design these AC lines.

http://www.linear.com/designtools/software/
Mr. Lime
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Re: Tone Stack Variations?

Post by Mr. Lime »

Colossal wrote: Wed Jan 24, 2018 7:00 pm Good work. Thanks for posting your results. It is interesting reading.
You are welcome.
ChopSauce wrote: Thu Jan 25, 2018 11:07 am Great, I wish I knew wich software you're using to calculate (& plot) these figures.

I read very mixed reviews of the ISF, anyway.
brewdude wrote: Sat Nov 18, 2017 1:13 am I’ve used Merlin’s TB stack (I think he refers to it as a Bandmaster) a couple times and really like the result.
I am currently reading him again. He recommends - on the pre-amp examples of the last pages of the book - also inserting an additional & separated mid control, one stage before.

NB: Merlin recommends putting the tone stack at the last stages, though.
Yep, LT Spice is the way to go but I'm sure there are even better tools to show tone stack ranges in detail.

Well the ISF is more or less a marketing trap, you get better results by putting treble cap and slope resistor combo on a switch and shift the mids. I did that in a Naylor SD60 circuit and it works fine and you can choose the mid scoop ranges better.
The pot in the ISF doesn't do much in between the extremes, it's all passive with a very limited range. I expect Merlin's preamp design with bandmaster and bridget T filter with variable Q to behave rather similar as it also seems to cut the highs.

It depends on the gain structure where the TS fits best. In almost all high gain preamps where the distortion comes from the stages in front of the TS in makes more sense to have a EQ at the end of the chain. When PI and power amp distortion is wanted, you can put the TS early in the preamp to not overdrive the preamp gain stages too much while they hitting the PI harder into clipping. An example for that are the Trainwreck Express or Komet Concorde circuits. Where it doesn't work as well are the Mesa circuits that I always found to be very muddy and inefficient.

The Peavey XXX circuit and some other models have an interesting local Feedback tone stack which looks like a active Baxandall. Some years ago I had a XXX and the EQ wasn't bad but it lacked some versatility.
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M Fowler
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Re: Tone Stack Variations?

Post by M Fowler »

My favorite Tone section is an amp with Volume control. My second choice is an amp with Volume and Tone controls.
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