Bridge T- Notch Tone Control

[strungout]

Oy.

So, driven by a recent post by Mark Hammer, I re-read WGTP's post "Notch filter for guitarists of all ages" and I did a bit of experimenting to see what kind of a tone control I could get out of a Bridged T-notch filter. My goal was to be able to have a notch possibilty for my modded rat, but it went further. I doubt it's anything new to the more experienced DYIers here, though.

Of course it started simply. I had already did some experimenting with my opa2134 distortion design (only the bridge part was a resistor instead of a cap). Making either R's variable (connecting one outer lug to the wiper) was pretty obvious step, and the response was ok. Varying the one forming the lowpass with the cap to ground widened the notch, while the next R in line varied the relative amplitude of the high vs low paths. Then, stil on that same second R, instead of connecting one outer lug and wiper together, each lug went to either low or high paths and I took my output from the wiper. Drawn out on paper, I had a revelation : this looked very much like a BMP tone control, only there was no R to ground on the high path to limit how much low end it was letting through! Without that R to ground, you could blend the two paths wihtout either losing low end, or high end (except as limited from the low path). Fun!

As I was wondering what more I could do, other than having two controls to vary both R's, my eyes came upon a gloriously heaven lit dual pot! Actually, it was my desk lamp with a 100W bulb... One control to vary the two R's at the same time! And what was even better is, I could get one part of the pot to raise the resistance while getting the other to lower it. All in all, I got some very interesting tone variance with it.

Here's a diagram and some notes:



Anyway, just wanted to share. Hope a few find this interesting

Ciao.

[WGTP]

Very cool, that sure never occured to me.

Where I thought you were going at one point (and maybe I missed it), was to use a ?50K pot with the wiper going thru C1 to ground.  I usually use 22k or 10k resistors so you could vary things by twisting the 50k pot.  10k on one side 40k on the other, 25k/25k.  Or 20K and 30K or ...    

[petemoore]

PDCool too !! great idea !! Looks like you could twweek yourself all kinds of frequencies with just a dual pot and a few parts !!!

[Lonestarjohnny]

Dan Torres been sellin this mod for a long time and he still gets made fun of !
Johnny

[strungout]

WGTP: duh  :oops:  I knew I had lost track of something. Of course using a single pot with the wiper to the cap to ground would increase the resistance on one side and lower it on the other. X|
Oh well, the dual pot is still useful for the other variations.

The control is fun to play with, I still need to find the values I'll like best.

[WGTP]

Sure the dual pot will allow the resistance of both sides to go up or down at the same time.  I'm going to have to mess with this some more.  

IMHO Mr. Torres gets laughed at more for his hype than his actual products.

[lenwood]

can't you add a cap across a tone pot on a pedal and voila a t-notch filter?

[WGTP]

I don't think this would work as a tone control in a guitar because of signal lose.  If you had an active preamp, it would.  I think this one needs to be post gain.

You can use an inductor with the tone control to create a mid-notch circuit, Torres sells one.  

[Mark Hammer]

Nice work.

In response to a different thread, I posted something about creative applications of the standard one-knob tone control circuit on older Fender amps.  There may be something in there for folks following this thread.

http://diystompboxes.com/sboxforum/viewtopic.php?t=25665

One of these days, one of us will do a page on simple-but-elegant one-knob "revoicing" circuits.  Jack Orman already has a few such circuits on his site, but it would be nice for people to see a bunch of them in one place, so they could compare visually (with formulae in hand) and have a sense of what might work well in their context.

Its always pleasantly surprising how much added value you can squeeze out of a pedal with a single control.

[troubledtom]

IMHO Mr. Torres gets laughed at more for his hype than his actual products.


in response,
  you may be right  or wrong , but in california he is very well liked . that's all i can say.
 this is a cool thead and it's all good bro's.
       peace,
          - tom

[WGTP]

Sorry, no disrespect intended.  All I know of him is his site and he has some cool stuff, but the hype may be a little overdone.  Who's isn't?  

[lenwood]

Would this work??

[Mark Hammer]

Now THAT'S clever.  I like it.

[troubledtom]

Sorry, no disrespect intended.  All I know of him is his site and he has some cool stuff, but the hype may be a little overdone.  Who's isn't?  

it's cool bro
      - tt

[Fret Wire]

Nice work.
In response to a different thread, I posted something about creative applications of the standard one-knob tone control circuit on older Fender amps.  There may be something in there for folks following this thread.
http://diystompboxes.com/sboxforum/viewtopic.php?t=25665

Mark, didn't you go even further into detail on this concept on another thread? Maybe on a ROG Prof. Tweed thread? I seem to remember a thread where you were talking about this and your tweed Princeton or Deluxe?

[Mark Hammer]

Cripes, when do I *NOT* go into further detail? :lol:

[strungout]

lenwood: Yup that's a great idea. It's basically what were talking about here and in a few other threads lately, it doesn't take much to change the response of a tone circuit, and you can get alot of variety from just a few components.

The tube screamer has an active tone control that looks like it'd be interesting to add a bridging cap across the 25k pot lugs.

Mark: I certainly like that simple tone controls page idea. Thought I'd have to add some two-knobbers to satisfy the tweakier


I have a few ideas I want to explore, but it'd be great to have a circuit simulator that could give me a frequency plot. Anyone knows of one that would work under DOS or Win3.1 (so I can work on my 486, next to my mess of wires and parts).

[WGTP]

That's funny Lenwood, there is a drawing on my desk pad at work just like that, only not as pretty.

I have been simulating these with the Duncan Tonestack Modded to work for this application.  I don't know if it is perfect, but it seem to work as I would expect.  Kleber AG suggested how to do it, I will see if I can find the post.

Using the Tonestack, the diagramed circuit makes the notch deeper, wider and moves it slightly lower in frequency in the middle of the pot range and then moves it back up slightly in frequency at the extremes of pot travel.  The notch varies with the caps used and the pot resistance.

Using a dual pot with both pots working in the same direction moves the notch established by the caps higher and lower in freq.

Reversing the dual pots works like the single pot above.

Of course you could use 2 seperate pots.  Let me find that post.   :roll:

[WGTP]

http://diystompboxes.com/sboxforum/viewtopic.php?t=22908&highlight=&sid=08d2e9978150f92e12666b77ff354f17

This is great to play with.

I keep thinking this is silly, why don't I just get out the EQ, but I haven't yet.  

Mark, we appreciate the details.  

[lenwood]

Yeah, that(the thread about the James control by Kleber) is what I used to come up with a notch filter, then I thought the only difference in a regular tone control and the notch is the one capacitor. One of those AHA moments.  So I wonder then what variations would be good to use on stage etc.
Thanks for the replies guys.
Thanks WGTP for all your work and sharing on notch filters.