Distortion EQ

[PBE6]

Following up on another thread about using Fetzers as buffers, I am looking to build a flexible distortion pedal with a simple set of controls. I think the most important aspects of a pedal like this would be the pre- and post-distortion EQ curves. To that end, I'm looking for some advice on EQ strategies.

Pre-distortion EQ:

I'm thinking a bass cut would be the most useful option here in order to decrease muddiness. The simplest solution would be to add a passive 1st order high-pass filter with a corner frequency that is variable between 40 Hz and 1 kHz.

Has anyone had good success with this type of filter for pre-distortion EQ? What frequencies did it cover? Were other solutions more effective at reducing mud? Do many players/builders find a bass boost would be desirable here too? What about a treble cut and/or boost? Or a mid-boost and/or cut?

(The distortion stage will be an opamp with clipping diodes in the feedback loop, possibly with a switch to swap them for hard clipping grounded diodes directly after the opamp. In either case, the opamp will have a high-pass filter around 40 Hz and a low-pass filter around 6 kHz.)

Post-distortion EQ:

I'm thinking a bass boost would be necessary here to make up for any bass cut on the front end, as well as a treble cut to tame extraneous harmonics. For the bass boost I was thinking about using the 400 Hz Marshall 4x12 emulation boost from www.runoffgroove.com's "Thor" pedal, which I think sounds great and adds some meaty muscle to the sound. The simplest solution for a treble cut would be a passive 1st order low-pass filter, similar to the one on the Rat, and variable from 10 kHz down to about 1.5 kHz

Do you think the Thor boost would be effective at restoring bass that was broadly cut in the pre-EQ stage? Would the notch boost still capture a Marshall-like sound regardless of previous bass cut? Have you found other solutions to be more effective at restoring bass? What frequencies did they cover? Would a treble boost ever be (generally) desirable here? Are other treble cut strategies more effective?

Let's of questions, I know - any input  would be appreciated!!

Thanks

[GibsonGM]

I think you need to hand-tailor what you're doing....meaning that for YOU, the answer might lie in one of several places.
I like to cut bass at the input, for instance...just a simple HPF, could be as simple as the right input cap working off of the input impedance.  The rest, I tend to leave alone.

Then, on the OUTPUT, you can bring the bass back, and even tweak other things for some unique sounds.  I like to you an Anderton Frequency Boost post-distortion; I will use that to boost lows and highs (again, tweaked to cover the ranges I find pleasing, by ear).   This, in effect, gives me a mid SCOOP, by slightly boosting around it! 

I think you should set up a basic distortion, like a Dist +, and play around with the front and back ends, starting with in/out caps and the tone control...see what you can come up with, what gets more to where YOU like it, and note that.  Read the stuff at AMZ!   Then, start designing from THAT point of view!   There are many 'flavors' out there....some like to boost x,y,z BEFORE clipping, others after...stuff like that.  Some things you do might add 'fizz' that you dont like, which you can remove after with just a cap.....things like that.   

It's sort of like learning to drive...people can tell you everything they know, but it doesn't mean too much until you've been there, in the seat, doing the same thing - then it clicks!

[PBE6]

Thanks GibsonGM. I agree, ultimately the decision on what sounds best will be up to me, but it's nice to hear what others have used successfully. Concrete examples can be invaluable when deciding what to breadboard first.

What bass frequencies do you find you cut most often on the front end? Up to 720 Hz like a Tubescreamer/SD-1, or a higher/lower number?  Do you ever boost the highs in conjunction with a bass cut? On a previous build I used a James EQ on the front end centered around 800-1500 Hz and found that the bass cleaned up nicely even when cut all the way, but the top end changes were subtle at best.

[alfafalfa]

Maybe my advice could help as well ?

I completely agree with your line of thinking  to avoid muddyness , predistortion -  bass cut and amplify again after the the distortion stage(s).

Would the notch boost still capture a Marshall-like sound regardless of previous bass cut?

What I like best for a marshalltype of grind is the brown sound in a box I and a bass boost after this. I use a Boss Ge-7 eq boosted at  100 ( a little ) , 200 ,400  more and a slight 800 Hz lift. For me this works great.

So if you want to use it in one pedal you could copy that part of the Boss eq .

Alf

[PBE6]

Thanks alfafalfa. I will take a look at the BSIAB1, I have heard good things but never gotten around to building one.

It sounds like boosting the bass around 200-400 Hz generally sounds good and powerful, especially coupled with a broad bass cut on the front end. Maybe a pre-distortion cut around the 720 Hz is about as high as most people would want to go, in order to retain some low-mid character in the final sound without adding a separate booster. I guess the Tubescreamer and SD-1 are classic sounds for a reason

Does anyone find a treble boost on the front end changes the distortion character significantly? Especially when coupled with a treble cut on the back end?

[Mark Hammer]

I've mentioned something here before that I called the "Boost-n-scoop".  Basically a Dist+ with the Anderton frequency booster just ahead of the clipping stage, and a variable Superfuzz-style midscoop after the clipping stage.  The pre-clip EQ does not have to be particularly complex, and I have nothing but positive things to say about fixed or variable bass-cut, but you'll value having something a little more complicated than merely bass-cut.

Ideally, a single semi-parametric section (boost/cut, centre freq, but no variable Q), that will let you add boost or cut, and pick the frequency you want to do it at, will yield many options for changing the tonal quality of whatever the clipping section does.  What you do after the clipping can be as compicated as you want or need it to be, but a single flexible section just ahead of the clipping is plenty powerful.

[PBE6]

Thanks Mark. A few months ago I tried building an EQ pedal based on the parametric EQ article at GeoFEX (http://www.geofex.com/article_folders/eqs/paramet.htm) and got one stage working but never went back to debug the other two. I did have a few questions about the parametric EQ circuit, but I think I'll put them in a different thread.

A semi-parametric EQ does sound like the most flexible option for adding mid-range character to the pre-distortion curve however, definitely worth trying. What range do you find works best? It sounds like a range between 800 Hz and 3 kHz covers most of the bases. I'll have to double check the GeoFEX article to see if this is a reasonable range to tackle without running into Q problems.

Also, do you ever find pre-distortion bass boost or treble boost useful in Tubescreamer/SD-1 style pedal? I can't find many recommendations for either. Maybe a static (or switchable) 1st order bass cut around 400 Hz would be a simple but useful addition to the front end.

[Mark Hammer]

Myself, I don't think one really needs to extend the pre-emphasis outside the range of maybe 200-1000hz, since it is the fundamentals and lower-order harmonics of low notes that one is most interested in when it comes to pre-emphasis.  That's what'll get you that "gronky" Billy Gibbons tone.

I think it is also worth suggesting that sometimes what people want from an overdrive with resonant pre-emphasis is the ability to mimic different cab/speaker resonances, which will often, if not always, be in the sub-800hz range.

As for a TS with resonant boost, you're talking about the often overlooked Supertube Screamer.

[PBE6]

Good advice, I will try restricting the mid-boost range to some lower octaves and see how it sounds.

Wouldn't a post-distortion EQ curve be better suited to emulating speaker resonances? By time you hit the cabinet all the signal shredding is done (speaker-slashing notwithstanding ). I really do like the www.runoffgroove.com "Thor" bass boost and it seems well-placed at the end of the signal chain, adding some beef without contributing much fizz.

Nice video btw! Never come across the ST-9 before, will have to check out the mid-boost section to see what's going on there.

[Mark Hammer]

blondegraemey has nice dry level-headed unpretentious demo videos.  They don't always cover all the things I'd like to see covered, but tend to be less sales-jobs or promos than curiosity-fueled explorations, or at least attempts to satisfy others' curiosity about a product.