Tone Stack Variations?

[M Fowler]

Just use a Fender Twin Reverb tone stack it works very well.

Mark

[nworbetan]

Here's a comparison of four TMB tone stacks. Except in the Marshall, an extreme treble or bass cut is seen in the plot where all combinations of the controls at three settings are shown. In the other plots, where one control is swept while the other two held at 50%, this interaction with the mid control doesn't occur. Marshall did not connect the mid pot as a variable resistor, so the bass pot is always well above ground.

I've been curious about Hiwatt tone stacks for a little while, especially since they're not in Duncan's Tone Stack Calculator. Can you specify which version of the Hiwatt tone stack you modeled? Does it exactly match any of the schematics on http://hiwatt.org/tech2.html ?

[martin manning]

They all seem to be similar, but see "Late '70's Two-Input Preamp."

[nworbetan]

Thanks! They do look really consistent throughout the decades, but there's also enough oddballs listed that I wanted to make sure.

[pdf64]

Here's a comparison of four TMB tone stacks. Except in the Marshall, an extreme treble or bass cut is seen in the plot where all combinations of the controls at three settings are shown. In the other plots, where one control is swept while the other two held at 50%, this interaction with the mid control doesn't occur...

Sorry, I don't quite get what is meant be this, would you mind explaining?

[roberto]

While waiting Martin, I try to describe his statement.

Imagine a Fender and a MArshall tonestack (just those for simplicity, but you can apply to others).
Fender first: set mids at zero and bass at zero. The bass is directly grounded, so they are greatly reduced, while treble is quite uneffected.
Marshall second: set mids at zero and bass at zero. The bass is in any case 25k above ground, so bass isn't reduced so much.

So Marshall is not affected in the treble/bass extreme cut (when treble and/or bass is set at zero), while all others are because of the way the mid pot is connected, so is affecting other controls.

[martin manning]

Yes, basically there is much more range (T, M, and B) when all three controls are in play than there is when each is varied individually. For example the treble range available on the Marshall expands quite a bit, but still not nearly as much as the Fender. That’s not to say that all those combinations are usable, though.

[roberto]

Martin, have you done the sims with the different source impedances?
Looking at the shape of the curves I guess so, just to be sure.

[Groove1]

Does it make sense to build a fender tone stack behind a cathode follower? For example, as a replacement in an 18 watt TMB amplifier? For a better response?

Groove

[roberto]

Not as is. The frequency response will vary alot from the Fenderish you would like to have.

[Groove1]

Thanks Roberto, so I will keep it like it is now. This is the better way.

Groove

[roberto]

It is not my purpose to stop you from experimenting.
If you want to use a Fenderish eq, you can "tranwreckize" your 18W: gain stage, fenderish eq, gain stage, cold stage, phase inverter. Of course the eq will react differently.
Otherwise you can try a baxandall eq. I suggested a modified version of it, years ago, on this forum, you can search it.

[Mr. Lime]

Well, ever heard about the Blackstar ISF Control?
It alters the mid frequency dip and simulates typical "american" and "british" voicings. Lot's of marketing for sure but what are those typical mid frequencies?
According to the common Graphic EQs and Marshall tone stack graphs the classic guitar mid dip lays somewhere around 800 Hz.
Many other stacks seem to have the dip below 800 Hz and sometimes even on 1 kHz.

We can simply add a switch changing the slope resistor and treble cap to shift the mid frequency response while the highs and lows nearly remain the same.
I simulated the switch with 100p/33k, 220p/56k and 330p/78k absolut values:

Frequency Response.PNG

Haven't tried it yet in my amp but are those mid frequencies are basically musical and practical?

Here's what I would try next in my amp:

Tone Stack Mod Idea.PNG

The mid pot is moved to act additional as a tone stack lift which makes it way more effective in range. I like this constellation a lot.
The 2n2 high cut may be omitted, I would have to try what sounds best..

[martin manning]

Martin, have you done the sims with the different source impedances?
Looking at the shape of the curves I guess so, just to be sure.

Of course!

[roberto]

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.