Noob question - Bass, mid, treble control for overdrive/distortion

[jfrabat]

Hey, guys.  I am looking to add Bass, Mids and Trebble control to a distortion/overdrive pedal I have (schematic below):



How do you recommend I go about doing it?  3 filters with one pot each was my idea, but what do you think?

[Mark Hammer]

Do you want the tonal adjustments to change how the distortion occurs, or simply filter out what the clipping circuit provides?

[Fancy Lime]

Hi Felipe,

the obvious question here is: are you sure you need a 3-band EQ? A reasonably good 2-band EQ is going to be more complicated than the whole rest of your circuit. 3-band is quite a bit more complex still. Tom has a good article on the Boss Metal Zone on his home page, which has a very flexible 3-band tone control with semiparametric mids (can be easily converted to non-parametric by changing 1 stereo pot to two resistors). See here:
https://electricdruid.net/boss-mt-2-metal-zone-pedal-analysis/

You could at that to the end of the electra distortion. If that really is what you want. I would instead suggest to go with a Big Muff style tone control with switchable mids and a buffer at the end. If the frequencies are chosen wisely, that is usually more useful than a full 3-band and A LOT simpler.

Cheers,
Andy

[jfrabat]

Hi Felipe,

the obvious question here is: are you sure you need a 3-band EQ? A reasonably good 2-band EQ is going to be more complicated than the whole rest of your circuit. 3-band is quite a bit more complex still. Tom has a good article on the Boss Metal Zone on his home page, which has a very flexible 3-band tone control with semiparametric mids (can be easily converted to non-parametric by changing 1 stereo pot to two resistors). See here:
https://electricdruid.net/boss-mt-2-metal-zone-pedal-analysis/

You could at that to the end of the electra distortion. If that really is what you want. I would instead suggest to go with a Big Muff style tone control with switchable mids and a buffer at the end. If the frequencies are chosen wisely, that is usually more useful than a full 3-band and A LOT simpler.

Cheers,
Andy

Thanks, Andy.  Let me read it, and, if I understand it, breadboard it.  I was reading this article, but I took about as much from it as if it would have been written in Chinese!  I did not understand ANYTHING!

[Fancy Lime]

Hi Filipe,

hmmm... R.G.'s article on EQs and gyrators is generally considered essential reading (and understanding) around these parts if you want to design an EQ that is more complex than the standard passive tone stacks. Here is a good online calculator with visualization for many different simple EQ types:
https://www.guitarscience.net/tsc/info.htm

My recommendation: Build a Big Muff tone stack and play with the values. See what you like and dislike about it. Then move on to a 2-band (like the James), do the same. If you still feel you need that third band,try a Fender or Marshall tone stack. If that still won't cut it, start thinking about gyrators and semi-parametric stuff.

After a passive tone stack and before the volume control, you will want a buffer. Without a buffer, the ton stack will interact with the volume control and not do what it is supposed to, depending on the volume setting. Here's a good resource:
http://www.muzique.com/lab/buffers.htm

Hope that helps,
Andy

[Mark Hammer]

Note that if the tone controls are active, that will require additional semiconductors, whether chips or transistors.  And if the controls are passive, there will be some signal loss, which will also require a gain-recovery stage.

That's one of the reasons why I ask whether you anticipate changing the tone before or after clipping (or maybe even both), since that will determine not only where any active stages are situated but also what form they take, and how complicated the final circuit would be.

The simplest possible configuration would be one in which you use a 3-position toggle to change the value of C1 and achieve different bass rolloffs before the clipping, and a second 3-position toggle to select caps placed in parallel with the clipping diodes and tame the treble.

[PRR]

> add Bass, Mids and Trebble control

Always steal from the classics.

[Mark Hammer]

That will certainly "work", Paul.  But will it have any oomph to it unless gain and volume are dimed?  Most likely not.  I'm not saying it is inappropriate for this circuit, just insufficient.

[jfrabat]

I am actually thinking of skipping the VOLUME pot, and go directly to a HIGH/LOW tone ontrlo from Boss:



And then into a sweepable mid control:



Then the Volume pot  (would I need an output buffer?).  Let me see if I can draw it in eagle

[pinkjimiphoton]

check out barry's tonetwEQ circuit on guitarpcb.com nice useful versatile circuit, small foot print too if ya use his boards.
i use it a lot in dirt boxes these days if i need three band tone controls.

[Elijah-Baley]

I found in the tone twEQ an atttractive active 3-band equalizer project, but I didn't try it, yet.
I have a 2-band Baxandall tone stack board, (that I guess it's a good possibile 2-band eq for jfrabat in case he wants to do something easier), and bass and high work really fine.
About the tone twEQ, I'm still wondering how much is effective the mid control. I hope it works fine as well the other controls.

[pinkjimiphoton]

i've built a bunch of them, standalone or in other projects, they work great. the mid control works fine, ya get +/- 15db i think.
if ya need more control, you could probably add a bigger mid pot, but it may change the slope of the eq some. i've used "Wrong" pots in a few of them, still seem to work well... 50k, 250k even 1m, tho at 1m it can oscillate some.

i use one of these sitting standalone on top of my amp, last thing in line as a buffer so i can tweak stuff without having to try n see the amp settings live. pretty groovy circuit.

[jfrabat]

check out barry's tonetwEQ circuit on guitarpcb.com nice useful versatile circuit, small foot print too if ya use his boards.
i use it a lot in dirt boxes these days if i need three band tone controls.

Oh, I LIKE IT!!!  This is what I was looking for!  Do you typically use it before or after the gain stage?

[Ben N]

That's very similar to the tone stack in the JHS Angry Charlie v3, which comes after the distortion.

[jfrabat]

So something like this should work, right?

[pinkjimiphoton]

i would use it after the distortion. depends on the circuit, like most things it will do different things depending on whether pre or post. it will drive the distortion harder before, but probably be more useful after.

in my applications, if i use it, i usually use it to replace tone stack stages, like in a big muff pi. works great.

[jfrabat]

Thats how its setup in the schematic above.  I am still new at this, so I took out what I think was the filter from from the Tone TwEQ diagram (the overdrive alreaady has one, right?) but I need someone with more knowledge than me to check it.

By the way, the cap after the in (shown as 100uF) and before the out (shown as 220uF) will both be 68uF.

Anyway, let me know if this will work...  I intend tonstart breadboarding once I get back home Thursday!

Felipe

[antonis]

By the way, the cap after the in (shown as 100uF) and before the out (shown as 220uF) will both be 68uF.

Input cap forms a high-pass filter together with Emitter resistor + emitter intrinsic resistor in parallel with 2M2 NFB resistor,  the later seen A+1 times lower, where A is individual stage gain.
Output cap makes exactly the same with OUT pot, in parallel with next effect input impedance..

If you make the respective calculations for both extreme low & high pots settings, you can verify (or not) if 68μF is adequate for the frequency band of your interest..

[ElectricDruid]

I love your drawing style, Felipe. That schematic is beautiful.

T.

[jfrabat]

I love your drawing style, Felipe. That schematic is beautiful.

T.

I will consider it beautiful if it actually works!   

Input cap forms a high-pass filter together with Emitter resistor + emitter intrinsic resistor in parallel with 2M2 NFB resistor,  the later seen A+1 times lower, where A is individual stage gain.
Output cap makes exactly the same with OUT pot, in parallel with next effect input impedance..

You lost me here...  Noob issues...

If you make the respective calculations for both extreme low & high pots settings, you can verify (or not) if 68μF is adequate for the frequency band of your interest..

How do I do this?