mid control mod for Baxandall tone control

pedalgrinder · Post by **pedalgrinder** » 15 Dec 2011, 00:29

Hello everyone. Have you ever felt limited by the baxandall tone control and have seen circuits you like but have no mid range control. Well suffer no more here is an igenious little mod you can add and not change the way the original circuit behaves. If you try it let me know what you think enjoy!!!!!

OC26 · Post by **OC26** » 23 Dec 2011, 11:50

Simple but interesting solution. Thanks for sharing!

Hides-His-Eyes · Post by **Hides-His-Eyes** » 23 Dec 2011, 11:58

I'd be interested to see the sweep of 'bax with a mid control' compared to say, three band fender.

pedalgrinder · Post by **pedalgrinder** » 23 Dec 2011, 13:45

biggest difference you would find is one the fender tone stack is majoritly passive and also runs most if it through the treble pot. and the idea of the baxandall is that it keeps the mid point flat and then moves the treble and bass frequencys up and down with it. But especially if you have a bass guitar iam not so sure on a guitar but i know for bass your mid frequency's essentially become ultra important and the ability to adjust that scoop point becomes essential. Thats partly why i liked this circuit so much but i really think you will enjoy it on any pedal that has baxandall as if you want the baxandall back you just set the mid pot central.

OrionManMatt · Post by **OrionManMatt** » 28 Feb 2012, 04:18

pedalgrinder wrote:biggest difference you would find is one the fender tone stack is majoritly passive and also runs most if it through the treble pot. and the idea of the baxandall is that it keeps the mid point flat and then moves the treble and bass frequencys up and down with it. But especially if you have a bass guitar iam not so sure on a guitar but i know for bass your mid frequency's essentially become ultra important and the ability to adjust that scoop point becomes essential. Thats partly why i liked this circuit so much but i really think you will enjoy it on any pedal that has baxandall as if you want the baxandall back you just set the mid pot central.

What's so cool, for me anyways, is that I was just thinking today about whether there was something like this for a Sadowsky preamp that I'm trying to reproduce. I wanted to add a mid control, though. Assuming the preamp uses a Baxandall, this would be perfect.

I guess the other question I have is how one might be able to modify the mid frequency, whether sweepable, selectable or fixed.

mictester · Post by **mictester** » 28 Feb 2012, 06:36

OrionManMatt wrote:
pedalgrinder wrote:biggest difference you would find is one the fender tone stack is majoritly passive and also runs most if it through the treble pot. and the idea of the baxandall is that it keeps the mid point flat and then moves the treble and bass frequencys up and down with it. But especially if you have a bass guitar iam not so sure on a guitar but i know for bass your mid frequency's essentially become ultra important and the ability to adjust that scoop point becomes essential. Thats partly why i liked this circuit so much but i really think you will enjoy it on any pedal that has baxandall as if you want the baxandall back you just set the mid pot central.
What's so cool, for me anyways, is that I was just thinking today about whether there was something like this for a Sadowsky preamp that I'm trying to reproduce. I wanted to add a mid control, though. Assuming the preamp uses a Baxandall, this would be perfect.

I guess the other question I have is how one might be able to modify the mid frequency, whether sweepable, selectable or fixed.

Unless you want to indulge in "trial and (t)error" you'll have to do some mathematics! The 100n capacitors in the mid filter will have to be reduced to raise centre frequency and increased to lower it.

The main part of the Baxandall isn't optimised for guitar (or bass) - it's a circuit for hi-fi, and the bass control will be too low in frequency, and the treble will be too high. I'll do some calculations later to re-voice all the controls to more useful frequencies, and I'll put them up here.

There are MUCH better tone controls that you can use - the passive "James" type gives an astonishing range of control at the expense of some signal path loss (which you can easily make up with the subsequent stage).

merlinb · Post by **merlinb** » 28 Feb 2012, 12:18

OrionManMatt wrote: I guess the other question I have is how one might be able to modify the mid frequency, whether sweepable, selectable or fixed.

For the BigMUff stack you can modify it to have a mid control like so:
https://i81.photobucket.com/albums/j207 ... 1268149807

For the James tone stack:
http://www.ampbooks.com/home/amp-techno ... /james.gif
the easiest mod is to make R3 variable, which gives you a mid shift control. The bigger it is, the more the response is shifted down.

The Bax is less amenable to adding a mid control.

phatt · Post by **phatt** » 28 Feb 2012, 13:28

Interesting comment from You mictester? LOL
""Unless you want to indulge in "trial and (t)error" you'll have to do some mathematics!""

My thought,, Yes But even if one spends time to learn the maths one still won't know how the maths will sound when finished?
So for those with limited experience you are left between a rock and a hard place,, ouch!

A few words from my experience with audio stuff may help some,,Or put in real terms,,How a poor man can learn to come to grips with circuits.
And BTW I've done all this on a shoe string budget.
Go buy a bread board kit and throw in some parts and add a plug pak and like stuff. Now D/load some sims and work between the two.

Next;
Wire up the circuit you wish to play with then STOP. Now go simulate the same thing. Use the *Bode plotting or AC analysis* screen so you can observe how the circuit reacts to different settings of the Tone controls.

Now you have a system which allows you to not only SEE the difference but you can also HEAR the result.

Now it's just a matter of swapping a few R's And C's to find the magic.
I've not yet been able to find a faster more accurate way to study a circuit in a relatively short time frame for the cost outlay. Winky.

Bear in mind I Failed at maths and never finished skool.

So if I can do it So can you

For me I'm far to old to go back and learn all that is needed to be a competent technical person but I wanted to learn to understand why certain things worked and other systems don't fair so well.

The above setup has allowed me to learn what would have taken me years of struggle. Here is a screen shot of my not so famous tone circuit which I believe is far superior over most of the more popular Tone systems for guitar Amps.

FWIW,,My observations of tone systems for guitar, in general;
If you want to boost X freq then boost big round curves, not peaks. (inverted scoops, see my PhAbbTone Plot as example)
Now if you want to cut, then use deep narrow notching circuits. Some parametrics work well but most folks don't understand how to use them correctly. (Parametric systems tend to work far better in Cut mode NOT boost mode. Hint)

Sadly the mindset of the average player is Primed by human nature and add some BS advertizing that MORE is always better than less when in fact the opposite will likely attain far better results.

For Tone systems to be Convincing you need to pull the frequency *You don't want* OUT.
Shallow scoops rob the energy from your signal and often become dead pan and are nowhere near as convincing as deep narrow cuts.

Baxandall tone circuits tend to work on boost which is fine but I've had far better success with the Dave Reeves (HiWatt) inspired mid cut ability of my PhAbbTone circuit. Stuck in front of a stock Fender Dudville 212 will open your eyes and drop a jaw or two

It will then actually sound like a ,,,, well a fender amp.

I'm adding my contour filter circuit to show how to add even more tonal extremes. This filter takes over where your other tone circuit ( whatever you use) leaves off.

This is capable of deep narrow -20Db notching which is sweepable from about 600Hz < 2,500Hz.
Metal freaks take note; The term often used to describe metal tone is *Mid scooped tone*. Trust me you will have far better success with a *deep narrow notch*. If you are chasing those tones then add My contour/notch filter *After* your dirt boxes.

For me I'm loving the extreme tonal abilities of these two systems when used together,
The PhAbbTone and the Contour filter. winky.

@ pedalgrinder;
Far too busy at the moment to sim or test the idea shown but it should now be obvious that *IF* it can produce a deep notch then I'd say you are onto something good.

Final words;
The greatest guitar sounds are so because of what you *Can't Hear*
For tone controls to work you have to take something away,, not add.

Hope it helps someone sort through the maze of confusion. Have fun, Phil.

: PhAbbTone Response curves

: Sweepable notch cut filter

OrionManMatt · Post by **OrionManMatt** » 28 Feb 2012, 16:24

Thanks for the direction, guys.

The Sadowsky preamp is for bass and has boost-only levels for the low (40 Hz) and high (4kHz). The schematic is around here somewhere. Ah, here it is (download/file.php?id=10842&mode=view). It seems to be derived from an old Fender tone stack. So, actually, I don't even think this even qualifies in this discussion... Whoops.

phatt · Post by **phatt** » 02 Mar 2012, 13:51

Some interest from a member for single supply for the notch filter so go have some fun. (circuit down the bottom)
(my email is on the circuit if you need help.)

My Email tells me I have a PM here but it's not showing up? Oh well never mind I'll post it here for You and all other who might like to build it.

IF you remove the input buffer it will suffer signal loss due to the low Z of U2 input. Now Rather than spend forever trying to redesign it, I find it far simpler to add the buffers as it guarantees it to work with almost any equipment and saves me from having to go back to college for 4 years to learn the maths,,

I'm actually using this on a single 18VDC supply and it works very well. I did try a 9Volt setup and it shows the same promise but I'd guess if placed late in the signal path it might hit the rails and add unwanted distortion though that may not bother heavy metal players.

Play around with C5 and C6 values if you wish to change the freq sweep points. The original had 2n2 but I had none

Don't make R6 lower as it could get funny.
R8 was 50k in the circuit I found but sims and *REAL* testing showed that t10k works fine and helps to keep the noise down,, although it is not very noisy I like to cover any potential issues.

Most will want to raise R2 to some insane value but expect the noise to go up along with it.

----@ Pedealgrinder,
I did find time today to run some quick and dirty simulations of your mid freq control circuit and it's not doing much to impress me but I'll work on it again and see,, I may have missed something.

@ OrionManMatt,
NOTE; The PhAbbTone peak of the bass is smack on 40Hz. Hum now what was the frequency of the Fat string on a four string bass? Wink.
I doubt a couple of fets will fair any better? but hey I could be wrong.

cheers,, Phil.

teemuk · Post by **teemuk** » 03 Mar 2012, 10:25

Ironically, the most overlooked option of adding a mid-range control to Baxandall circuit is also the simplest: Just add a simple mid-range band control circuit in parallel with the usual Bax stack.

phatt · Post by **phatt** » 03 Mar 2012, 12:59

Thanks Teemu,
OK it answers the Question Asked but IME, There are better tone systems.
To my Ears at least,, that circuit pulls far to much Bandwidth when you full cut the mid knob.

The PhAbbTone just jumps out at you as the bass is big and round and the treble is not muddied by to much midrange.

That said some folks love baxandall tone circuits for guitar. I guess it comes down to what they have heard or have not been able to compare.

Phil.

pedalgrinder · Post by **pedalgrinder** » 07 Mar 2012, 09:37

yeah but what your missing teemux i agree with you is the baxandall ability to scoop or raise your mids. A lot of people love that tone section for how it responds the option i put there doesn't affect how the original baxandall responds if you don't want it to. Where the option you have put forward and may i say nothing wrong with it. will affect it.

Throbb7 · Post by **Throbb7** » 07 Mar 2012, 17:52

I was just looking at the Boss Rod 10 and it is similar.

http://www.aronnelson.com/gallery/main. ... c.jpg.html

stringtheory · Post by **stringtheory** » 29 Oct 2021, 23:26

Quick reply for the moment. I thought I'd add some perspective regarding mid controls.

The vanilla Baxandall circuit is not conducive to direct addition of a mid control. If you're working with opamps, you can easily add a separate isolated stage with the Bax control, but that's not really adding anything to the Bax circuit itself.

Same deal for Fender stack. The mid control does not literally add mids. It prevents the bass-treble circuit from subtracting as much midrange, which is not the same thing. (See "Insertion loss"). If you turn the Fender mid control to 10, and turn the bass and treble to 0, you get flat frequency response, not a mid peak. So the same would relate there.

In both cases, if you're designing with tubes, it's not nearly as easy, given that you'd need to find another tube stage to serve as similar isolation to the opamp equivalent above. But if you're designing the amp from scratch, it's easier. I always added mid circuits to my own tube amp designs. So I know the sounds pretty well. Some advice:

Mid controls for guitar benefit from limited Q on boost, but you can do high Q on cut without sounding shrill.

The optimal mid boost frequency for guitar (jazz, blues) will be around 800 Hz. Again, limited Q to avoid sounding like a wah pedal.

Boosting at Fender's mid-cut frequency (300 Hz) will sound muddy. 800 Hz will sound forward and punchy.

The optimal mid cut frequency for guitar will be around 300 Hz to 350 Hz. That's what Fender and most other cut-only circuits use.
And again, Q can be much higher for mid cut. The Fender stack can do a very sharp mid cut at 300 Hz. Due to opposite phase shifts around the treble vs bass sections, mids get phase-cancelled around 300 Hz when the two 'sides' are added together again.

The general theme: You'll benefit from asymmetric response in the boost circuit and boost frequencies. Guitar is unlike hifi in that you can get away with whatever sounds good, so the options are wide open for experimentation (which is how I learned about tone circuits over the years: Figuring out "WHY does that change sound better?").

Yes, it sounds like a real pain to retrofit mid boost for tube circuits, but if you like forward-sounding jazz tones, or punchy 'Supro' blues sounds, it's well worth it. For surf or scooped metal, I wouldn't bother. You'll already be getting mid cut by turning bass and treble controls up.