DIYstompboxes.com

Any ideas? I know there's a lot out there. I am looking for something that uses an easy to get IC (as in one that I may already have!!), and would kind of cover all the basses guitarwise (to put at the end of a distortion circuit). Who has an opinion on this?
-Joe Hart

Maybe the one at the tl082 datasheet?

http://www.national.com/ds/TL/TL082.pdf

(http://img.photobucket.com/albums/v165/rickydon/3band.gif)

RDV

Nice re-draw RDV.  :)

This was the circuit in question in  this (http://www.diystompboxes.com/sboxforum/viewtopic.php?t=24302) thread.

The design is intended for full audio range music applications (the control is awsome fed with a discman) so using it for guitar or bass might require some parts value tweaking to get the most out of it.

I didn't get the amount of response from the treble control that I wanted, although I used a 250k pot instead of 500k which is probably the reason right there. Also, the midrange badwidth is really wide, enough to dramatically effect the other controls in any setting. It's still on my breadboard but I haven't gotten a chance to really sit down and tweak it.

My guess is that notch type filters would be better since they're less interactive with each other in a stack. R.G.'s Simple, Easy Graphic and Parametric EQ's, plus Peaks and Notches (http://www.geofex.com/Article_Folders/EQs/paramet.htm) has all the tech stuff laid out.

As for simple and easy, I don't know if that's a reality when it comes to eq'ing. Maybe there's a chip out there specifically for an eq circuit...

The Big Muff tone control really does a nice job considering it's one control, I think basically a pot that pans between a HP filter and LP filter.

You could tweak that further by implimenting Jack Orman's AMZ tone control (http://www.muzique.com/lab/tone3.htm).

edit: I just rembered an AKAI fuzz/dist/OD pedal I used to own that had a 7 or so band EQ for the input and the output. Anyone know what I'm talking about?

Maybe cap values should be tweaked if you want different center freqs, the datasheet figure suggests this is for hi-fi

Maybe I could put online some pages of old National Semiconductor Audio Handbook, year 1980, there was some theory and some formulas with you can start to design the freqs, if anybody is interested

but that has to wait till weekend

Not to toot my own horn here but I designed one that I think sounds great and is pretty customizable and can have anywhere from 1 to as many as you want bands. Uses simulated inductors.

http://www.diystompboxes.com/cgi-bin/webbbs_scripts/webbbs_config.pl?noframes;read=206

I like it with 18Vs, gives it a little room to "breathe".

Good Luck,

Jay

Mr. Doyle, to be honest, your EQ looks too intimidating to me! I am looking for something a little simpler. Sorry! I just want some control after the distortion, but more than a simple one-knober. But I will save your schematic because it could be a really cool multi-band EQ.
-Joe Hart

RDV, as usual, you have (what seems to be) the perfect answer for me!

I was watching the thread by onboard, but he/she hasn't had a chance to tweak it and I will be taking a ride up to Toronto this weekend, so I wanted to mess with schematics on the ride (my wife likes to drive, so I'll let her!).

I think I'll use RDV's idea and then I can always tweak it after I get home and bread board the whole thing (and when onboard offers his/her thoughts).

Thanks everyone!!
-Joe Hart

Joe,

No problem, though anything active is going to be a bit complicated. Why not use a Fender tone stack? It loads down your signal but nothing a gain stage can't fix and is sure to be less complicated than an active control.

Good luck,

Jay

PS - Thanks for the "Mr." but please call me Jay.

1) Sorry to say it, but... I have yet to see a decent-and-well-behaved three band equalizer like the circuit above.  If you simulate the circuit above you will find that if you move just one band at a time it behaves nicely.  When you try to dial more complex, band interaction is awful, and overall response doesn't match with the pot's positions, as one would expect.  In particular, the circuit above has a low tone control that provides around +20 dB of boost at 20 Hz (for bass) and 20000 kHz (for treble), which is inadequate for guitars. You just can't make the bass and treble bands closer because they interact too much.

2) There is a dual version of this control which behaves exceptionally well for guitars.  It is the tone control used on the Sans Amp GT-2.  (see www.tonepad.com)  This has only Bass and Treble controls, with a mid area around 500 Hz, well suited for guitar.  You could add after it a 500 Hz mid cut/boost control and make it a decent non-interacting three band control.  In fact, the Sans Amp topology is slightly different from the typical Bass Treble equalizer, which makes the controls less dependent on each other.

3) I made a three band tone control with adjustable mid frequency with a three position switch.  With it I am able to get almost ANY tonestack response curve from the usual Marshall, Fender, Vox and BMP-style controls.  It requires a quad Op-Amp and also has a level control, smartly designed to introduce attenuation at the input and gain at the very end of the chain, so no clipping occurs on a single 9V supply. If there is interest I can post it.

Regards.

Sorry, Jay. I was raised to always use Mr., Mrs., or Ms. I teach guitar, so people are always calling me Mr. (even though I'm only 35 and still think of myself as a kid -- I guess that's what being a long hair guitarist does to your emotional developement!), and my wife and I want our son to use these titles, so it's just ingrained!!
-Joe Hart
P.S. No one here has to call me Mr., you can just call me Metal Guitar God.

stm, why must you rain on my parade?  :x I built a pedal with a standard type 3-Band tone stack and I really don't like how they interact. If your post (and all of your previous posts that I have seen on other threads) didn't make so much sense, I would just ignore you! But my logical mind prevails.

So, I'll look at the 2-Band one on the GT-2 and add the 500Hz control you suggested.

UNLESS... you think your idea is even better. If you don't mind, would you post it? And could I use a pot intead of the switch (just for even more control because I do like messing with mids).

Thanks!!
-Joe Hart

I just took a look at the Sans Amp and I'm confused!!

Is the tone section the part surrounding IC4A with the two 100K pots? Do I just cut after the output of IC4B and before Q1? Do I include the .1 cap after IC4B and the 1K resistor before Q1 or delete these two items?

Also, what would you suggest for the 500Hz mid control?

-Joe Hart

QuoteI was watching the thread by onboard, but he/she hasn't had a chance to tweak it.... and when onboard offers his/her thoughts....

:lol:  :lol:  :lol:

Do I detect of whif of the "New chick on the block" thread now that the boat's been rocked a little around here as to the gender issue?

Seriously, the consideration is much appreciated. Just took me off gaurd to see my self refered to he/she :wink:

I'm 100% guy!

Erm, now that that's out of the way, stm is right on the money. The data sheet 3 band EQ schem we were refering to (illustrating Vref) using stock values is not really all that suitable for guitar once you start dialing all three controls.

I tried, for example, changing cap values at the treble and midrange pot wipers, but the interaction of the circuit as a whole seemed to be thrown off. Besides, I don't have a wide range of cap vaules to play with anyway. I think it was 0.047uf for the treble wiper and 0.01uf for the midrange.

At any rate, I'm sure you could come up with something marginally useable with some tinkering.

Post up, stm!

Hi,

Yesterday was at the office, and my circuits were at home.  I arrived home and first thing I did was try to post my ckt.  Phone line dead! (still dead todayin the morning!)  Now back at the office again I tried to create an account at photobucket but they say I have to wait three more hours to do it!

Anyway, I promise I'll post a non-interactive three band eq using 2 opamps (from the sans-amp 2 + a mid section) AND my special three band circuit, for the sake of the DIY community.

-----------

P.D.   I started this post writing "Hi guys", then I realized there's a gal in town, so I just left it as "Hi".  In the area I work, we used to talk about MMI (man machine interface).  Now the proper term is HMI (human machine interface).  I guess in the future we may end up with LBMI (live being machine interface), since we are being able to communicate with other animals like chimps and dolphins...

Here I go now with the circuit:

(http://tinypic.com/2rub9)

And this is the family of curves for three pots at center and max boost positions.

(http://tinypic.com/2rud0)

You need linear taper pots (not log or audio!), however, action is more constricted towards the ends of the pots, so an "S" taper pot should be used whenever possible (ha!-where do you get those without having to give an eye?).

Featrures and Disclaimers:
- There is still some interaction, but less than the combined three band controls. At least component values bewteen lows/highs and mids do not interact.
- I have not built this circuit myself, so it is untested, but in the sims looks way better than the others, and frequencies are better suited for guitar
- I am making another circuit which I will post later due to time restrictions. This has even better interaction characteristics, and center frequency can be adjusted (I am using 450, 700 and 1000 Hz), so I can get responses from many standard tone stacks.

Comments and constructive criticism appreciated.

The baxandle stack might be something to look into if you didn't like the fender. I've been digging on the Vox tone stack lately(like in the  ROG EC), but I like a lot of highs. A Marshall style tone-stack and a volume recovery stage are probably a better answer than the 3band, I haven't tried the thing meself, I just put the single supply stuff on there cause somebody wanted it in another thread a while back.
(http://img.photobucket.com/albums/v165/rickydon/SuperSimplePre-Amp.gif)
RDV

stm:
Isn't that basically a feedback-loop Baxandahl, with a separate notch filter?  The plots look pretty good, but my question is whether you couldn't get results just as good with just the 2-band Bax, since cutting B & T will give you an effective mid-boost at the center frequency?
Ben

stm:
Isn't that basically a feedback-loop Baxandahl, with a separate notch filter?  The plots look pretty good, but my question is whether you couldn't get results just as good with just the 2-band Bax, since cutting B & T will give you an effective mid-boost at the center frequency?
Ben

STM - do you think it would work to just cut out the first half of that for simple active mid boost/cut?

Thanks everyone!!!

I'm off to Toronto armed with much to ponder on the drive up and back.

Thanks again!!!!!!!!!!!!!!
-Joe Hart

Wow, this thread is getting interesting.  I see a good interchange of ideas flowing. These are the kind of threads where I learn...

-----
RDV:
-----
Your tone stack option is a valid alternative, however controls do interact and overall maximum cut/boost you can achieve is not as high/extreme as you can with active, separate band, Eqs.  A good thing though is you get the "voicing" from the particular tone stack you choose. *** Finally, the level boost section at the beginning is potentially risky, due to the fact that on single 9V power you can get clipping before reaching the tonestack.  Gain recovery stage should go AFTER to avoid this.  Then, a buffer stage would be needed BEFORE. ***  (the statements between asterisks are  now invalid since RDV changed the schematic according to these suggestions)

-----
Ben:
-----
It is true that a two-band baxandall allows you to cut/boost mids by raising or lowering both controls simultaneously. The catch is that your peak or valley is very wide in comparison to a dedicated notch/peak equalizer, so frequency control is rather diffuse, meaning that you raise the mids and some of the lows and highs as well.  Also, you don't have the chance of boosting Bass and Treble while at the same time cutting Mids, which produces a more severe effect in 3-band Eqs.  The other thing I dislike from baxandall design is that when you boost you get huge amounts of gain below 80 Hz and above 10 kHz (depending on Bass or Treble, respectively), where you don't want it or need it.  This increases potential for clipping and adding additional noise.

----
Hal:
----
Yes, using just the second stage gives you mid cut/boost.  Scale capacitors accordingly to adjust frequency. Keep in mind that values shown are for 550Hz.  Divide caps to increse frequency, and multiply them to lower it.

OK, now I'm posting a circuit I did build, and that is very good and controllable.  No savings here on opamps, this is the no-compromise version, meaning that I am not trading functionality or performance for simplicity. Anyway, it is easier to understand and tweak in comparison to the gyrator based eqs., and eventually could be extended to more stages.

(http://tinypic.com/2s7cj)

Be advised that a buffer stage is needed BEFORE in case you are going to feed it directly with your guitar, and eventually a gain control stage AFTER to match your setup level.

EDIT: Note the 10:1 ratio in the capacitors of each stage.  I optimized the resistor values (using MicroCap 7 optimizer) and the cap ratio to maximize the Q or peakedness of the bands, so this Eq has a much more definite mid band in comparison to a 2-band baxandall tonestack.

Thanks for that great explanation, and for the cool 3-band eq (all bandpass--interesting).  Going back to your initial design, would that work something like the old Ampegs with Bax + inductor-based mid control?
Ben

Ben, I'm not familiar with the Ampeg schems, so I cannot tell.

I have yet an even better and more flexible three-band eq in which I'm working now.  It is based on the concept that with three bands you actually have two degrees of freedom only, due to the fact there are redundant combinations which differ in volume only. For instance, raising the mids is similar to cutting bass and treble simultaneously.  Also, lifting all bands by the same amount is mainly a volume change, not new equalization curves.  This is why sometimes it is stated the 2 knob baxandall is comparable to the 3-band equalizer.  The problem with the baxandall is the implicit mid band is quite wide, which is not the best for guitar.

In my design, I have a MID knob, a three position switch to set the center frequency in three steps (400, 700 and 1100 Hz), a bass/treble balance circuit or TONE control, and a LEVEL control.

With this device I can reproduce the curves from Fender, Marshall, Vox and BMP style controls, so I intend to name it Universal Tone Stack.  Besides, it works also as a three band tone control with adjustable mid frequency.  Very flexible.  I want to arrange and curves showing its performance before posting the circuit.  Perhaps I will arrange a simple web site for this purpose.

Pardon my ignorant question, but how do i calculate the frequency/cap value in stm's active three band schem?
It looks like a cool project to make a 5-band EQ based on this...
:D

Good question, Brett. I did some calculating (noticing that the only changes were the two caps and that they were in a 1:10 ratio), but the frequencies came out a little off. I would like to know they actual calculations.

Also, are the pots linear?

-Joe Hart

Hi,

I don't have a formula for calculating the frequencies, but it is just a matter of scaling the caps.

For instance, 220n/22n produces a 100 Hz peak/notch. Divide the cap values to increase frequency accordingly.

Pots should be linear, however the preferred type would be this less common "S-shape taper", which I believe it's named "G-taper".

The reason of using caps in 10:1 ratio was to obtain higher Q or narrower bandwidth.

I've been working on an improved version of the three band Eq, and now I've settled for the following bands:

Bass: fixed at 100 Hz, wide
Mid: switch selectable for 400, 630 and 1000 Hz, narrow (as shown in the above schem)
Treble: fixed at 4000 Hz, wide

The above allows greater flexibility in obtaining the response curves of most tone stacks, including Fender (400 Hz mid), Marshall (630 Hz mid) and BMP (1000 Hz mid).

Regards,

STM

Thanks for the reply!

So, to further understand how it works... for example to make the Q for the 100Hz band in your scheme wider, you would increase C9 to 220n?

Quote from: stmIn my design, I have a MID knob, a three position switch to set the center frequency in three steps (400, 700 and 1100 Hz), a bass/treble balance circuit or TONE control, and a LEVEL control.

I imagine what you have planned here is an active control, with much deeper mid boost/cut available, but it sounds, interms of functionality, anyway, something like the enhanced Big Muff Pi stack (with "Body" control) proposed by Jack Orman.

Let us know if/when you post this stuff--sounds cool, very useful.

Ben

This is my actual 3-band Eq.  I call it semi-parametric due to the switchable mid frequency selection in three steps.  If you look at the previous circuits I posted on this thread you will see I've been tumbling around eqs for a while.  This is the design I like the most so far, very flexble indeed.

Notice the Bass and Treble bands are wide.  In particular, low frequency band is suitable even for 4-string bass guitars tuned in E (41 Hz), and particularly for drop-tuned guitars.

Also, a good characteristic is that it doesn't end up at 20 Hz or 20 kHz with tons of gain as opposed to conventional Baxandall tone stacks.

In addition, boosting both Bass and Treble will produce a sort of "mid cut" effect which is DIFFERENT from just cutting the Mids (much narrower).  In this aspect, there are different possibilities to play with while adjusting the controls, and hence more curves to dial in in comparison to a two-band equalizer.

This is the schematic.  Notice an input buffer and gain leveling stage are needed.

(http://tinypic.com/1649ba)

These are the performance curves for each of the bands set at maximum boost.  Mid band shown at 630 Hz only.

(http://tinypic.com/1649hk)

Ben: I abandoned the TONE+MID circuit because it was less flexible than the three-band eq.  Anyway its simplicity is interesting and it has much less interaction between the tone and mid frequency controls than the AMZ Body control because of the use of an active design with separate op-amps.  Unfortunately I don't have it here at the office to post it.

Best regards,

STM.

Hi STM,

I am about to build a preamp with EQ active control and I studied your 3 band schematic and  found it very very interesting.

However, I am just wondering something about +/-15dB. In my understanding, with your schematic you can only boost the bass+ 15dB by raising the 100k pot ? Is it true ?
IN fact your can not decrease -15...a  band ? Am I right or not ?

Thanks for your feedback.
Space Jm

Hi Space Jm,

The circuit has BOTH boost AND cut capability.  The curves in the above picture show only the boost capability so as to simplify the graph.  Cut curves are mirror images with respect to the 0dB line.  Don't forget adding a switch for the midrange frequency greatly expands the flexibility.

If you want a simpler design you may try the Tonemender also, which is allows getting most of the Fender, Marshall and Vox tonestack curves: http://www.runoffgroove.com/tonemender.html (http://www.runoffgroove.com/tonemender.html)

Best regards.

Hi STM,

Thanks very much for this very clear explanation. ;D I will try this week end.
See you later.

Quote from: stm on August 20, 2004, 10:23:30 AM
(http://tinypic.com/2rud0)

what program did you use for those simulations?

STM,

I just check the Tonemender, is it an active EQ of not ? Because I can not see 1Aop for each band like your design...
Thanks

G'day gents, I'm a little late to this one.  Apologies.

The original request was for a dedicated 3-band thing to tack at the end of a distortion circuit.  I'm going to be a bit of a heathen and suggest that much of what has been proposed so far is more or less inappropriate to this particular task.

Why, you ask?  Well, let's start by asking the question "What are equalizers normally used for?".  The average EQ unit, regardless of how many bands, is intended to address a signal whose properties you have absolutely no idea about.  Could be a symphony coming through large home speakers.  Could be a kick drum you're trying to keep from generating wolf-tones in a small performance space.  Could be a singer with a reedy voice you're trying to make sound a little huskier.  The point is that the bands, bandwidth, and number of controls, are really a function of not knowing what the unit will have to do in future.  The epitome of this is the multi-band parametric EQ where you have adjustable selectivity and resonant frequency "just in case".

But what about distortion pedals?  Well, by definition, they add harmonic content, and by popular demand they should generate less fizz and better fizz-to-fuzz ratios, in which case any sort of Baxandall type treble boost function is a sort of irritant at worst, and moot at best, since half of what it does is to introduce more of what we apparently don't want.  Additionally, where non-fuzz EQ systems are intended to eliminate undesirable characteristics (and unintelligibility in a mix can be thought of as one of those), EQ on a pedal is really intended to change character, both in terms of emotional properties and in terms of personage. 

So what is it about the "character" of a fuzz that strikes us as important to pay attention to?  Well, I don't think this is anywhere near an exhaustive list, but certainly one of the things that is important to us is how "angry" the pedal sounds.  Some overdrives sound in earnest, while some fuzzes sound irritable and still others sound positively angry and overwrought.  The emotional tone of the output is partly a function of the distortion control, but also a function of the extent of upper harmonic content that comes out.  Showing "restraint" involves cutting back or filtering out the raspiness.  And that is likely best done with some sort of lowpass filtering whose properties would depend on how much nonadjustable filtering occurs elsewhere in the pedal, plus how much additional harmonic content is introduced by the clipping circuit in the first place.  It is easy for me to imagine contexts where there is a need for more aggressive lowpass filtering, and other contexts where something as flaccid as what you get on a TS-9 is perfectly adequate.  Does anyone need treble boost?  Depends where it goes.  Upper-mid/lower-treble boosting capabilities are great for pre-clip applications since they change the quality of the distortion produced, and indeed you'll find a number of pedals that use fixed resonant pre-boosts to do just that (A lot of DOD's pedals really differ in terms of the pre-boosts used).  On the output, though, I generally find that a Rat-type lowpass filter has tremendous power in changing the critical high end that determines perceived character.

Another aspect of distortion character might be called personage.  Some units have a distinctive personage much like Dustin Hoffman's Ratzo Rizzo character in "Midnight Cowboy", or some roles that Ben Stiller has had; small, puny, bereft of physical power, but so irritable that you just get out of the way.  Here, we are often discussing units that produce a more nasal, strident, and bass-weak (or at best bass-neutral) sound.  Jordan Bosstone could be the poster child for this.  At the other end of the spectrum are those units whose personage is the sort of character that picks up your 4 x 12 stack, mutters "Where do you want it?" in a surly tone, and tosses it in the van without blinking or sweating. here, we are often talking about a sturdy big bottom, some mid scoop to accentuate the bottom, and just enough upper mids and treble to indicate determination and force of will.

What I get out of this ridiculous digression is the sense that the "ideal" 3-control for a post-clip EQ would be a variable lowpass filter (with maybe a bit of resonance), a nice shelving bass control, and a midrange resonant cut with a very shallow and broad scoop.

Is this "enough"? Well, to be fair and honest, and to echo the cornucopia of distortion tones that people have exhibited in this forum, a great many distortion circuits come with their own intrinsic character, and it is folly to think that we can turn any single one into any single other simply by dint of the EQ controls on board.  The difference between a Big Muff, a Fuzz Face, and a Scrambler is a whole lot more than the EQ settings.  So maybe the thing to consider is what the range of personalities a given circuit can have, and design an EQ circuit to make them more visible/audible/accessible.  This is clearly an argument for the idea that there can be no single "generic" 3-band system, regardless of how well it is designed (and Sebastian's stuff is always top-notch). 

Instead, the ideal 3-control system should be planned out based on:

• the inherent character of the clipping circuit itself, including any fixed filtering it might use (e.g., small input capacitors)
• whether the EQ is going before or after the clipping circuitry, or even divided up between those locations
• what sorts of personality changes can be extracted from the unit
• how huge a contrast from the bypass tone the units "default" personality is

To add my 2 cents, reviewing frequency response curves of various 12" speakers such as Celestion and Emenance, it appears that most have various amounts of dip (from 0 - 10db) at around 1.5Khz and boost at around an octive higher at 3 to 4Khz.  Most are fairly smooth from the 1.5Khz dip down to their bass limit with slight differences in the mid-range. 

To simulate different speakers (which I think is an often overlooked contribution to the tone) a pretty narrow dip at 1.5Khz and boost at 3Khz is needed, along with a boost and cut at 750Hz and 200Hz.  The low 200Hz should cover the difference between a 4-12" stack and an open back single 12" cabinet.   :icon_cool:

Hey Joe H!

Here's a suggestion no one's tabled yet (I think): If you want the ultimate in CONTROL, you could try a state-variable filter (a la Anderton's Super Tone Control).  It only requires a quad op amp, very few parts, and it'll give you just about every response-curve in the book.  May take up a bit more knob real estate than you want though.  FWIW.

Joe K

The Tonemender is a passive tonestack wrapped around buffers to allow having unity gain or even boost capabilities without loading your guitar.  The tonestack topology comes from a Fender tonestack and its values have been optimized for:  1) clean guitar equalization,  2) smooth and progressive control throughout the rotation of each pot,  3) reproducing as much as possible of the traditional fender, marshall and vox responses in a single unit (thus the switchable mid frequency).

On the other hand, I also use the proposed 3-band active equalizer to buffer and adjust my guitar eq prior to other effects.

You can still use the 3-band or tonestack tonecontrol approach to adjust the bass and mids at the output of a distortion pedal, however the high control might not be adequate if you don't provide extra high frequency removal.

Hello STM,

I just finish to build your Active EQ and it works fine ! Very nice...On the out, I add a « level setting » with 4558 AOP , copying the Boss GE7 « level » setting. It allow me the adjust +/- 15dB correction !

I did not put the 3 kind of Middle...just the 630hz first, I can not get the other values for capacitors in my dusty stock...

I just want to know something else : Could you give me the formulas to calculate the center freq and the Q factor...I can not get them when simply reading your schematic.

Thank  a lot ! Now I am building the housing of the stompbox...

Hi, sorry for bringing this old thread up, but I want to build the last EQ circuit displayed here, and I have some doubts about the schem. I drew the things I have doubts about in red. Could anyone confirm if my drawing is righ or wrong? Thanks.
(http://i68.photobucket.com/albums/i5/Morocotuco/stm3BANDeq.png)
Morocotopo

Hi, There are two important problems in the above schem:

1) All the +INPUT of the opamps should go to Vcc/2 or Vref instead of ground, otherwise you won't get any sound. This is required for single 9V operation.

2) The input impedance of the first stage is low and varieswith the pot setting, thus an input buffer is needed. This circuit was drawn as a building block, rather than a full pedal, thus your questions are valid.

I'd suggest you try this simplified version which I like better:

http://aronnelson.com/gallery/STMs-Circuit-Ideas/Three_band_Eq_non_interacting_bands (http://aronnelson.com/gallery/STMs-Circuit-Ideas/Three_band_Eq_non_interacting_bands)

Input buffer is still necessary though.  Vref = Vcc/2 or 4.5V.

I like the active Baxandall tone control and would add a addtional mid-pot.
The Xotic- and TC-ODs use it too, the schems are on the net, so I would use it as a base and maybe alter some values to taste.

JHS

Thanks for the answer STM, I kind of suspected that the + ins should go to Vref, but wanted confirmation by a more knowledgeable source (that´s you!  :icon_mrgreen:). So, the usual two resistor voltage divider and cap there. About the in buffer, I didn´t put it in the drawing because I´m thinking of using this as a post distortion tone control(s) for a BSIAB2, eventually doing away with the original circuit tone pot and associated parts, the idea being getting maximum tonal flexibility. Or should it be there even for this use? My guess is that it wouldn´t hurt...

Thanks everybody

Morocotopo

Hi

QuoteAll the +INPUT of the opamps should go to Vcc/2 or Vref instead of ground, otherwise you won't get any sound. This is required for single 9V operation.

Or maybe use single supply opamps.  Equalisers are one of those things where single supplies are good value because it saves lots of unnecessary track length.
The LM324 is a quad device that should suit these designs.
cheers

Meh, i just made a 3 band EQ similar to these ones. For a days effort and AU$20 i'd have to say i should've just bought a brand name EQ pedal.

My 2 cents: If you have any doubts about the plans you see here (or even if they'll give you the desired result) consider paying the extra money for something with a ___ day money back guarantee   ;)

What a great thread !
I missed it before i built the tonemender for my "multibox" which include 3 effects before Supreaux/Matchbox/thunderchief and then going into tonemender/SSS/Condor (thanks STM the SSS/Condor combo is truly great!)
I like the tonemender but sometimes it's a bit confusing and I need more transparent control over bands...
Your non-interactive 3 bands is certainly what I need ! But i don't see the 3 mid pos switch in the schem..
Anybody have a vero layout for this ?
What I would love from you STM is a graph that shows the curve effect of the tonestack at the end of the greats ROG amps sims.. (15k/22n to ground, etc).
Thanks if you can do it ! But just an explanation would be cool too and i guess i should launch a new thread for this because i have a few questions about the condor too...

I plan to make a perfboard /PCB layout for this, just give me some time, when I do, I will post it. Since this schem and the one suggested by stm  (http://aronnelson.com/gallery/STMs-Circuit-Ideas/Three_band_Eq_non_interacting_bands ) are similar, the only difference being the parts values, it should be useful for building both and deciding wich one I (or you) like best  ;D.

Thanks stm for your schematic and generous help

Morocotopo

Sorry to Bumb an old thread like

Just been using the search function and came up with this thread.  I'm looking to put a 3 band Eq into a Big Muff clone I am making right now.  I was just wondering if anyone has built these circuits?

The schem on the first page looks like it could be suitable for my needs and also  http://aronnelson.com/gallery/STMs-Circuit-Ideas/Three_band_Eq_non_interacting_bands (http://aronnelson.com/gallery/STMs-Circuit-Ideas/Three_band_Eq_non_interacting_bands) this one.

I was thinking of splicing this into the Big muff circuit between Q3 an Q4 in place of the tone stack.

Only other spanner to throw in the works I have built the muff with PNP trannies would it be a problem mixing positive ground with this circuit or wouldnt it matter a hoot?  Any ideas or wisdom greatly appreciated

Can anyone explain how that Mid Boost circuit works? And how did you calculated the center frequency as 500Hz?
I would so Love to know that.

Quote from: stm on August 20, 2004, 10:23:30 AM



(http://tinypic.com/2rub9)

Quote from: stm on August 20, 2004, 04:24:34 PM

(http://tinypic.com/2s7cj)

I've just built STM's tone circuit and it's a beast! Very clean, fairly simple to breadboard. Double check your lines as you breadboard it as I didn't and had to start over at one point. It also needs a .1 uf Cap at the beginning and end. Also, Vref is 1/2 of your input voltage. So if you are powering this via 9v you will need to make a voltage cutting section on your circuit to create Vref or this circuit won't work.

Good luck!

Quote from: axe_mechanic on April 01, 2014, 01:31:41 PM
I've just built STM's tone circuit and it's a beast! Very clean, fairly simple to breadboard. Double check your lines as you breadboard it as I didn't and had to start over at one point. It also needs a .1 uf Cap at the beginning and end. Also, Vref is 1/2 of your input voltage. So if you are powering this via 9v you will need to make a voltage cutting section on your circuit to create Vref or this circuit won't work.

Good luck!

Interested... I have been eyeballing this circuit for a while now. How are you using it? What are you using it with?

^ cool, so does this have nice control seperation too?.. (non interactive)

Cool circuit.

Quote from: deadastronaut on April 02, 2014, 04:04:25 AM
^ cool, so does this have nice control seperation too?.. (non interactive)

It should do. Would benefit from a high-impedance input - a 4th op-amp could do this nicely...
Edit - I notice that STM mentioned this earlier in the thread.

cheers sam,

would this tack on nicely onto the spitfire ? straight off the Q5 source?...ive been messing around with tone stacks, but this looks pretty nice.

http://www.aronnelson.com/gallery/main.php/v/chickpea/SPITFIREV3.jpg.html?g2_imageViewsIndex=1

It should do - the output impedance of Q5 is set by R11 and is reasonably low.
If it loads down the first band of the EQ, then you can try to drop the value of R11.

If you only want 2 bands of EQ, you could get away with a single dual op-amp. If you want 3, then you could use the 4th op-amp as an output buffer...

Have you tried a FMV tone stack after Q5?

cool,

yeah tried all of them in the tsc, with variations ...but i just don't like the interaction, seperation is what i'm after really...being able to add/subtract without the others adjusting would be great.

3 band sounds ideal...so it's opamp time..i'll whip it up on breadboard...i already have the spitty on bread, so i'l just knock this up ..

ok i have it on breadboard, all 3 pots working fine..

output buffer:  straight out of above circuit into spare opamp : pin 5 ...6 + 7 joined...then out 7 to output...but very quiet. ???

edit:  ok now, i forgot the 100n caps... ::)

(http://i.imgur.com/cFJAOJC.gif)
Necro-posting, deal with it sucka!


Built this one today, not bad. I edited the schematic so the circuit has an input / output buffer with the capability to boost the volume a little bit if needed. Way easier to follow if you are new to building stuff.

(http://i.imgur.com/OMKz527.png)

You don't need these caps:

(http://i67.tinypic.com/28hq742.gif)

10uFd into 1Meg at input will carry sub-sub-sub-sonics. 0.01uFd is a reasonable value. And less leakage than an electrolytic.

Strongly suspect the three bands could be done in one opamp. Opamp magic.

I wanted to make the eq bass compatible but I guess the 10uF is a little overkill. Thanks for pointing that out PRR.

Hi everybody,

I like to bring this thread back again :D I've used the EQ from STM (well, the mid-control part) quite a bit in the last time... superb control and extremely good noise ratio... Really enjoying this circuit!

What I´d like to ask (or request help) is how to exactly scale the caps for frequency selection... I´ve learned from my MXR 6-Band that I want to boost at 800hz and 1.6Hz for about 6db using a specific amp/guitar combination into the gain channel.. thats why I want to build these two bands using the EQ design from here (best noise performance I´ve seen so far). But the caps don't seem to scale linear: 440/56 != 630/33 != 1000/18.

So my question is, which cap values do I need for almost exactly 800hz and 1600hz ?

Regards, Anthony

Edit: Corrected frequencies :D

From what I can see the actual frequencies of the MXR 6-band are 784Hz and 1.8kHz.
Using STM's circuit, to match these frequencies, I get  27n/2n7 and 12n/1n2.

However, the final response of the MXR circuit with two bands boosted is *quite different* to STM's circuit with two bands boosted.  This is normal as the two circuit add bands in a different manner.

The bandwidths of the MXR are more narrow and when two bands are added the shape of the bands skew such the frequencies skew upward.

STM's circuit is a cascade structure (series).  You can also use these "Bohn Equalizers" in a parallel structure like this:
[link remove until I find the ckt]

I did not see if the response of this structure matched the MXR closer.

The bottom line is different equalizers structures produce different results.
The MXR circuits are probably one of the worst for trying to understand how the bands interract.

> the caps don't seem to scale linear: 440/56 != 630/33 != 1000/18.

They should. But those are not the values on the "STM" on this page. In a 4-page thread, maybe you are pointing at another plan?

(https://s30.postimg.org/70bec1xvl/STM_800_1600.gif)

Thanks for the answers!

I've taken the values from here:

Quote from: Morocotopo on September 16, 2006, 01:33:26 PM
Hi, sorry for bringing this old thread up, but I want to build the last EQ circuit displayed here, and I have some doubts about the schem. I drew the things I have doubts about in red. Could anyone confirm if my drawing is righ or wrong? Thanks.
(http://i68.photobucket.com/albums/i5/Morocotuco/stm3BANDeq.png)
Morocotopo

Well, I'll try the values you have provided... Currently I've breadboard the middle part with a TL072 and used the first half as a simply buffer (voltage follower). I only had a pair of 22n/2.2n caps at hand... but this covers the frequencies already pretty good... and it fits so well that it also nice always on into the clean channel... noise is really good, even on breadboard. I get some really low noise hum (which will disappears once it is shielded) und almost no hiss - perfect! - and way better noise performance than the MXR.

I guess Ill build two of these one-knob-units into one or two enclosures and be perfectly happy :D

Just some math for background:

100 / 220 ~ 0.45
700 / 33 ~ 21.21
1600 / 14.4 ~ 111.11
5000 / 4.7 ~ 1063.82

I was expecting the relation of freq / cap to be consistent... obviously it is not the case :D Is there an easy formula to calculate the cap(s) for  a given freq?

Quote
I was expecting the relation of freq / cap to be consistent... obviously it is not the case :D Is there an easy formula to calculate the cap(s) for  a given freq?

The formula for that circuit is quite big.

See Equation 9 and figure 9:
http://leachlegacy.ece.gatech.edu/ece4435/f02/equalizer.pdf

The reason the caps don't scale like you expect is because the pots stay fixed at 100k but other resistors are in different proportions.  The Bass and Treble are have the same resistors but the Mid is different.  The values under the mid circuit should all scale up as you would expect:

(33n*630) = 20790
(56n*400) = 22400
(18n*1000) = 18000
Average 20400 with +/- 10% due to the fact the frequencies are nominal.

It's like Large Cap * Freq = 20400

The other circuit in this thread has different resistor proportions but they are consistent.

Not also the circuit you posted is +/-16dB whereas the other one in the thread is +/-14.5dB or so.   If you look closely and compare the resistors for the Mids in your circuit and circuit you can see they are close.  The difference is what gives one circuit a different boost/cut over the other.

[Edit: Added link to formula]

The Morocotopo drawing's freqs are close but not quite. According to SPICE the numerical idiot we get 16.5dB peak at:

56n, 5.6n = 393Hz  {"400"}
33n, 3.3n = 667Hz  {"630"}
18n, 1.8n = 1,220Hz  {"1K"}

> some math for background:
> 100 / 220 ~ 0.45

Without deriving I multiplied C times F.

56n * 393Hz = 22,008
33n * 667Hz = 22,011
18n * 1,220Hz = 21,978

For given filter ratios (width), C*F is a constant? (0.1% rounding error.)

So for the *narrow* band, use 22,000, divided by F, read that as nFd. Then also get a second cap 1/10th the size.

Sorry for reviving an old topic ...

... this is my first post

I mainly have experience with guitar electronics and I've been dabbling with passive filters... so active filters is new for me. I'd like to make STM's 3 band eq into a pedal. I only have experience building booster pedals at this point...

I have trouble understanding how to read the schematic. Please see image below.

(https://s1.postimg.org/1mlxnxjed7/STM-800-1600-_Questions.jpg) (https://postimg.org/image/1mlxnxjed7/)


I have several questions: (I've been googling and reading Electronics for Dummies ... and I haven't had any luck understanding more unfortunately).
1. I have trouble understanding how to wire the ICs. There are 8 pins but not all the ICs involved in the circuit seem to use all 8 pins?
2. V1 (orange arrow) is the input?
3. Where does the power supply come in (orange circle)?
4. The right part of the circuit is the volume knob?

I realize that the questions sound like basic circuit reading questions, so if you have any links that would help me understand that would be great also!

Thanks for the help in advance,
LTNPD

I'd prefer to control the bass before the distortion and the rest after it...

Hi Ltnpd,  welcome to the forum!

Yes, some basic questions, but that is ok.  If you have more questions, feel free to make a new topic "Beginner's questions" or something like that, and we'll all jump in for you! 

1. I have trouble understanding how to wire the ICs. There are 8 pins but not all the ICs involved in the circuit seem to use all 8 pins?
If you look closely, you see "IC1A" and "IC1B", etc.  This is showing us that the circuit uses dual opamps...2 opamps in one IC package.  So the package only needs one power connect, and one ground, leaving 4 inputs and 2 output pins per dual opamp chip.   In other cases, maybe only one half of the dual opamp is used, and the other half isn't part of the circuit....or, in that case, you may sub a single opamp.

2. V1 (orange arrow) is the input?
Yes

3. Where does the power supply come in (orange circle)?
That is the bias supply...power would come from the "top", and points marked "Vcc" (in other cases, "Vref", "Vbias" etc) are connected between the 2 resistors.   This network is assembled somewhere convenient on the PCB when you wire it up.  You don't want power to pass over signal lines, if you can avoid it, but otherwise you place this where it makes sense.   Near where the power enters the PCB is of course best practice...and you take your power to the ICs from there.

4. The right part of the circuit is the volume knob?
Yes. The 1M pot in the feedback loop of the final opamp is setting the gain of the opamp...which is boosting the output signal. 

Ah... thanks GibsonGM! That clears a lot!

I was thinking of posting a new thread as a beginner question but since my questions are also specific to this circuit, I thought it would be best to post a reply to this thread. I'm sorry if I violated any rules. :(

Having this new knowledge and information... I have more questions also... (sorry!):
1. ... So what you are saying is that basically OPA2134 ICs have two opamps. Just to be clear... So IC1a and IC1b is the same single IC but one opamp (IC1a) is for the buffer section of the diagram and the other opamp (IC1b) is for the bass section of the diagram?
2. Also... (See photo attached below) Do all the "+9-18V" points (green arrows) connect in parallel to the battery (bias/power supply)? ... if so, wouldn't that mean that IC2a and "IC3 A and B" are technically connected twice to power (once via "+9-18V" and another through Vcc/2)?
(https://s1.postimg.org/74w15kalor/STM-800-1600_-_Green_Arrows.gif) (https://postimg.org/image/74w15kalor/)

Thanks again!
LTNPD

> another through Vcc/2)?

That's not really "power".

The audio can swing (almost) from zero to +18V. But audio swings both ways. To allow this, we "bias" it to half-way between zero and +18V. The two 10K lower left make a half-voltage reference from the zero and +18V.

Can you clarify the output stage opamp connections?

Hi Paul and folks, sorry for reviving an old thread,

I am testing this circuit (just the mids section) and I would like to swap the 100K pot for 50K. I am doing so and I notice the response and probably the curve is not the same.

Any hint on what I should be targeting to get the same curves and response of the original circuit, but with a 50K potentiometer?

Thanks very much in advance!

David

Quote from: PRR on January 08, 2017, 12:36:02 AM
The Morocotopo drawing's freqs are close but not quite. According to SPICE the numerical idiot we get 16.5dB peak at:

56n, 5.6n = 393Hz  {"400"}
33n, 3.3n = 667Hz  {"630"}
18n, 1.8n = 1,220Hz  {"1K"}

> some math for background:
> 100 / 220 ~ 0.45

Without deriving I multiplied C times F.

56n * 393Hz = 22,008
33n * 667Hz = 22,011
18n * 1,220Hz = 21,978

For given filter ratios (width), C*F is a constant? (0.1% rounding error.)

So for the *narrow* band, use 22,000, divided by F, read that as nFd. Then also get a second cap 1/10th the size.

QuoteAny hint on what I should be targeting to get the same curves and response of the original circuit, but with a 50K potentiometer?

If you want to change the pots from 100k to 50k and preserve the response:
- half the resistor values
- double the cap values

Hi Rob, thanks for your reply!

I know the workaround you proposed works perfect on passive tonestacks (like Fender) and other "simple" circuits, had no idea it would work as well in this application.

Will check and let you know in any case.

Best,

David

Quote from: Rob Strand on August 29, 2023, 08:13:49 PM

QuoteAny hint on what I should be targeting to get the same curves and response of the original circuit, but with a 50K potentiometer?

If you want to change the pots from 100k to 50k and preserve the response:
- half the resistor values
- double the cap values