Getting more Mid control

[Nolatone Ampworks]

Hey folks,

Has anyone figured out how to get more control over the mids on a typical cathode follower driven tone stack seen on Fenders/Marshals/etc.?

It bugs me how they are all tied together and I've done a lot of experimenting with alternative configurations, but they all have some other sort of downside, which I guess is why so many use this classic (I look at it as the lesser of the evils).

Anyhow, curious if anyone has anything to share on this.

[phsyconoodler]

On say a Fender blackface tone stack,just increase the mid pot from 10k to 25 or even 50k.
Take s good look at what the mid pot is doing in the stack.That will tell you a lot.
On Fender amps with no mid pot,the mids are 'set' with a 6.8k resistor to ground on the bass pot.Experiment with different values and see what you end up with.

[Nolatone Ampworks]

On say a Fender blackface tone stack,just increase the mid pot from 10k to 25 or even 50k.
Take s good look at what the mid pot is doing in the stack.That will tell you a lot.
On Fender amps with no mid pot,the mids are 'set' with a 6.8k resistor to ground on the bass pot.Experiment with different values and see what you end up with.

I would love to hear a detailed description of how this works because the way my brain is working on it it'd be possible to shunt everything to ground if you set the middle control wiper all the way to ground stop, and that's clearly not the cause in reality.

There's obviously something I'm missing!

[scottl]

Try doing a Dumble stack. Seperate gorund paths for bass and mid. You can experiment with slopes (100K or 150K) and midcaps. This design gives a much different control of mids.

Hey folks,

Has anyone figured out how to get more control over the mids on a typical cathode follower driven tone stack seen on Fenders/Marshals/etc.?

It bugs me how they are all tied together and I've done a lot of experimenting with alternative configurations, but they all have some other sort of downside, which I guess is why so many use this classic (I look at it as the lesser of the evils).

Anyhow, curious if anyone has anything to share on this.

[Blue Strat]

Compare Fender and Marshall tone stacks.

[Nolatone Ampworks]

Try doing a Dumble stack. Seperate gorund paths for bass and mid. You can experiment with slopes (100K or 150K) and midcaps. This design gives a much different control of mids.

The one I've liked best so far sounds like this (I need to look up a Dumble schematic). The bass and mid were after one stage, and the treble was after another. The mid control on that one works exceptionally well but I'm wanting more control over the treble. I'll probably revisit that circuit and see what I can do about treble. The first way I tried to mod it for more treble control also dropped the gain and thinned out the tone. No dice on that one!

I DID do some mods to the Fender style stack today that really opened up the possibilities, but still not happy with it overall.

[Nolatone Ampworks]

Compare Fender and Marshall tone stacks.

Depending on which Fender and which Marshall, they look very similar, in many cases almost if not identical.

[Nolatone Ampworks]

Try doing a Dumble stack. Seperate gorund paths for bass and mid. You can experiment with slopes (100K or 150K) and midcaps. This design gives a much different control of mids.

Hey Scott,

Which model are you refering to? I see all different sorts of tone stacks on the Schematic Heaven Dumble page.

Thanks,

Paul

[mark norwine]

want controllable mids? go with a baxandall box

[TimmyP]

Here's how they work: http://www.duncanamps.com/tsc/index.html

[Nolatone Ampworks]

Here's how they work: http://www.duncanamps.com/tsc/index.html

Yeah, I have that, and it tells you what changing values does to the curves, and is adequate if you don't mind a sheer cause and effect explanation, which really should be enough...but I'm just too curious.

[Nolatone Ampworks]

want controllable mids? go with a baxandall box

Doesn't a Baxandall do low and high shelf? I wired one up once and didn't like the way it sounded in that circuit. I'll have to revisit it though.

[Mdd59]

I believe that in most guitar amp circuits the TS is a loss-type circuit. It only cuts. In the typical fender stack, when you increase the bass or the highs you're actually reducing the cut going to ground.

Typically the guitar PU puts out a bunch of mids and most TS drastically cut the mids. It appears to me that on a Fender TS, increasing the mids actually raises the level of the entire TS. That's why some gain mods just switch the entire TS out of the circuit.

I usually add an adjustable mid pot on the two knob Fender circuit because it allows a little more drive to occur through the circuit but doesn't really add much mids to my ear. The way I think about the TS is that if you reduce the high and low then the mids appear more prominent. Increasing the highs is actually reducing the high cut and could also be done by increasing the bass cut. Lows are the same idea, reduce low cut and increase high cut.

[Nolatone Ampworks]

I believe that in most guitar amp circuits the TS is a loss-type circuit. It only cuts. In the typical fender stack, when you increase the bass or the highs you're actually reducing the cut going to ground.

Typically the guitar PU puts out a bunch of mids and most TS drastically cut the mids. It appears to me that on a Fender TS, increasing the mids actually raises the level of the entire TS. That's why some gain mods just switch the entire TS out of the circuit.

I usually add an adjustable mid pot on the two knob Fender circuit because it allows a little more drive to occur through the circuit but doesn't really add much mids to my ear. The way I think about the TS is that if you reduce the high and low then the mids appear more prominent. Increasing the highs is actually reducing the high cut and could also be done by increasing the bass cut. Lows are the same idea, reduce low cut and increase high cut.

Absolutely, it's always been clear to me that the tone stack is about deciding what goes to the next stage, and what goes to ground.

Still would love to hear a description of the theory (within reason, some guys just TOO hocus pocus!) behind that particular circuit. Most others seem pretty easy to me.

[Nolatone Ampworks]

BTW, the Duncan tool IS very usefull as Timmyp pointed out. I should be using it more. It would be fun to get into doing new models. Maybe later.

[Blue Strat]

Depending on which Fender and which Marshall, they look very similar, in many cases almost if not identical.


Are you looking at component values?

[Blue Strat]

Yeah, I have that, and it tells you what changing values does to the curves, and is adequate if you don't mind a sheer cause and effect explanation, which really should be enough...but I'm just too curious.


AC circuit theory maybe? It's what most amp designers learn very early on.

[Nolatone Ampworks]

Are you looking at component values?

Yes.

[Nolatone Ampworks]

AC circuit theory maybe? It's what most amp designers learn very early on.

Most amp designers just use the same old values from the same old schematics.

[Blue Strat]

Most amp designers just use the same old values from the same old schematics.

A lot of them aren't designers per se.

You were curious about the fundamentals so I pointed you toward the area of electronic study which will answer your questions.

[Nolatone Ampworks]

A lot of them aren't designers per se.

You were curious about the fundamentals so I pointed you toward the area of electronic study which will answer your questions.

Thanks. We DO tend to put a lot of emphasis on DC theory don't we.

[Nolatone Ampworks]

BTW. I found almost precisely what I was looking for. Actually found it a long time ago, but forgot!

Now I have to learn Laplace notation. Argh! Where's Todd Shock when you need him! :-)

[Blue Strat]

BTW. I found almost precisely what I was looking for. Actually found it a long time ago, but forgot!

Now I have to learn Laplace notation. Argh! Where's Todd Shock when you need him! :-)

LaPlace would probably help. If I recall, that's 2nd year BSEE stuff.

You could probably even get away with just algebra and RC circuit configurations.

[BJF]

Hi,

Perhaps you can look at the tonestack you are refering to as a modified T-filter. To analyze such a circuit would require about 24 pages of computation to see the effects of loading and source, just given one set of values and just varying the treblepot.

The first question to ask is what is it that needs to be removed for this thing to sound good?
With passive filtering you'd always remove something to gain somethingelse........

If you are familiar with T-filters and Baxendal you can take a shortcut.
Like this a T-filter is a midcut filter that gives one trebleflank and one bassflank and you can adjust the heights of these flanks. Oh and the point being to use a midcutfilter primarily to extend the available outputpower by lowering intermodulation. Of course if you'd cut mids at say 400Hz, you'd get more treble aswell since much of the energy in a guitarpickup is in the midrange and as you dampen a part of that the amplification in the treble and bass will increase. You could see how the typical tonestack as used in Fenders would be derived from a Baxendal only that you'd have treble on full and the 'reference resistor' ( the one that sets the reference damping) is now variable and then you custom tune the filter to the response you'd like.

What I am saying here is that if you know the effects of these circuits you may not have to compute each step- for this a computorprogram would be prefered as it would involve a long series of iterations. Yet if you follow the explinations on how the passive Baxedal net works you have also the tools for the T-filter and the function of the T-filter is also available at least at any decent library.

You can hear if you replace the resistor often refered to as slope resistor how the midnotch changes.

OK so try this start with a Baxendal and then allow tuning of the reference resistor.......and voila you have added a midrange control.

If you'd like to go fancy you can construct active filters employing feedback and you could for instance place Twin T Notch filter in the feedbackloop and get a midboost. By offsetting the flanks from a true TTN-filter you can alter the shape of the midboost..........and then just listen to what you want to add.

Active filters always give distortion and usually low headroom and will need to be carefully constructed to avoid side effects.

Feedback systems with vacuumtubes is no more difficult than that of single transistors allthough the impedancelevels are different and the open loop gain is lower in tubes.

Checkout feedback systems for tubes for extended fun.

I'd say though that effective filtering employs the least amount of filters that removes, or sometimes adds the desired range and in this there's no hocus pocus but just the same kind of thinking you'd employ when eq-ing a recording: What is it that sucks and how can that be most easily removed?

Effectiveness is maybe then the easiest controls to desired settings and again what is it that needs to be controlled.

Further more bass-and trebleflanks are limited in various positions in the amplifier and this may also be an effective way of controlling what distorts and when and how.

Oh well just a few thoughts

Have fun and enjoy
BJ
Affiliations
BJF Electronics
Sweden
www.bjfel.org
www.mpamp.com

[Nolatone Ampworks]

BJ: Good stuff. Thanks!

Paul