Tone Stack Variations?

[Mr. Lime]

I'm curious of the different TMB tone stacks out there.
My current amp build has a more or less typical Marshall EQ and I found it to be pretty inefficient comparing to my Kitty Hawk Junior.
There's a certain difference in the arrangement of the caps and the duncan TS calculator shows that the values are not simply adoptable and now I wonder if I can replace it with success without ruin the response of the amp.

I don't know how much of the wide range of tones that are available comes from the Junior tone stack itself but can someone point out for me, what the difference is compared to the Marshall ones?

Kitty Hawk Tone Stack.png

Thanks a lot!!!

[pompeiisneaks]

The simplest way to understand it, is that the RC network for each layer controls a specific frequency, and then combining them has some alterations on how that works as well. BUT just changing the R or the C in a specific network just adjusts the overall frequencies that design impacts. The TSC does allow creating new ones I think but lists the most common ones. Each tends to impact on one another in different ways, so those are a bit above my comprehension. That being said, a pretty common tweak to tone stacks is to change the frequency by tweaking those RC networks a bit. Here's a calculator that lets you enter in the resistor and capacitor values you want and you'll get the frequency cutoff.

http://www.muzique.com/schem/filter.htm

~Phil

[xtian]

You said your tone stack was "inefficient". Do you mean, it has a high signal loss? Or do you mean the TMB controls don't make a heck of a lot of change in the tone? If the latter, here are my thoughts on the "tail" resistor.

Treble/Bass tone stacks usually have a "tail" resistor that connects the tone stack to ground, like 6K8 for Fender Princeton (in the case of the Twin Reverb, it's a 10K Mid pot), or higher value for Marshall (like 25K Mid pot). The further away from ground you lift the tone stack, the more mids, but the less effective the controls are.

So, in that schematic snip you posted, replace that 25K Mid pot with 10K, and you'll get a larger dip in the mid frequencies, but also greater response for the Treble and Bass controls.

[pdf64]

On the face of it, I think that the tone stack in post #1 should have a similar output level as a regular Marshall tone stack.
The 100nF cap is effectively the bass cap.
The 1nF and 2n2F just roll a bit of top end off.
The 250k master vol should load the stack a bit, reducing it's output compared to a 1M master.

[Mr. Lime]

On the face of it, I think that the tone stack in post #1 should have a similar output level as a regular Marshall tone stack.
The 100nF cap is effectively the bass cap.
The 1nF and 2n2F just roll a bit of top end off.
The 250k master vol should load the stack a bit, reducing it's output compared to a 1M master.

Alright, thanks a lot for the explanation, now I can see what's going on!

You said your tone stack was "inefficient". Do you mean, it has a high signal loss? Or do you mean the TMB controls don't make a heck of a lot of change in the tone? If the latter, here are my thoughts on the "tail" resistor.

Treble/Bass tone stacks usually have a "tail" resistor that connects the tone stack to ground, like 6K8 for Fender Princeton (in the case of the Twin Reverb, it's a 10K Mid pot), or higher value for Marshall (like 25K Mid pot). The further away from ground you lift the tone stack, the more mids, but the less effective the controls are.

So, in that schematic snip you posted, replace that 25K Mid pot with 10K, and you'll get a larger dip in the mid frequencies, but also greater response for the Treble and Bass controls.

Well I was referring to a Naylor SD60 TS which is way more subtle in control range than the one I posted above.
I did a tone stack ground lift by 10k which helped the mids a lot. I may try the 10k pot as well!

[Stevem]

Just first and foremost note that any tone stack that passes almost no signal when all the knobs are turned down is the type that can only cut frequency's, not boost and cut!

[xtian]

Just first and foremost note that any tone stack that passes almost no signal when all the knobs are turned down is the type that can only cut frequency's, not boost and cut!

Um... all the tone stacks we typically deal with are lossy (cut only). An active (amplified) EQ is required to boost, like in Boogie’s or Carvin’s five-band EQ.

[JMFahey]

what the difference is compared to the Marshall ones?

You ask for a comparison yet show only one tone stack, can you post both side by side?
Otherwise it´s hard to answer.

[Mr. Lime]

I know, there are many other tone stacks with more range, even semi active ones. I've been trough Merlin Blencowe's and Kevin O'Connor's books and know that there are possibilities for shifting frequencies by switching the slope resistor and capacitors.. If someone is familiar with the Voigt tone stack which is similar to the James / Baxandall, this one is pretty interesting for replacing the common TMB stacks in addition of a mid cut control.
Maybe the Carvin stacks are interesting too or take a look at the Blackstar ISF control.

The one I'm currently fighting with is the TMB from Naylor. The bass is always on max while the mids and highs are mostly very low. To me a tone stack should give lots of tonal range for flexibility and I had good results with the stack I posted above.

Here's the Naylor:

Naylor TS.PNG

My amp I'm working on at the moment has some space left over for an additional control and something to alter the mids would be nice..

Maybe someone else has great experience with other TMB stacks as well and would like to share?

[ChopSauce]

Why no "Dumble-style" tone stack - just out of curiosity?

I can hardly remember the Blencowe book section about tone stacks (TS) but I remember I haven't been really convinced by his discussion about 2 knobs TS, at first glance.

[brewdude]

I’ve used Merlin’s TB stack (I think he refers to it as a Bandmaster) a couple times and really like the result.

[pdf64]

Just first and foremost note that any tone stack that passes almost no signal when all the knobs are turned down is the type that can only cut frequency's, not boost and cut!

I don't understand the distinction, eg between a 5F6A TS (signal passes when all tones at min), DR AB763 (signal passes when all tones at min) and a TR AB763 (no signal when all tones at min)?
http://schems.com/schematicheaven.net/m ... _schem.pdf
http://schems.com/schematicheaven.net/m ... _schem.pdf
http://schems.com/schematicheaven.net/m ... _schem.pdf

Isn't it kinda like saying that any amp with a volume control can only cut volume, not boost it

As an aside, I think that the 'passive controls can only cut, not boost' hypothesis is wrongheaded.
The way I see it, active controls use negative feedback. Negative feedback reduces overall gain. Hence (all else being equal) both active and passive tone controls have insertion loss, as gain is 'thrown away' in order to adjust frequency response.
But really that too is wrongheaded, as what matters is the frequency response of the whole system and how the user perceives it.
Using the TR AB763 as an example, its TS alone can't cut treble (ie compared to a nominal mid range level), but surely any reasonable user analysis of the amp would conclude that there's a good range of cut and boost available to both treble and bass frequency ranges.

[martin manning]

Isn't it kinda like saying that any amp with a volume control can only cut volume, not boost it

You have to define the boundaries of the device you are considering. I would say a volume control (the potentiometer, a passive device) can only cut signal, just as a passive tone stack can only cut signal.

[pdf64]

Fair point, I got carried away with my analogy

[martin manning]

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.