Pedal Treble Cut Ideas

[mickeybellinello]

Hi to all!

Here I am again!

This time, I think, the question is pretty easy. Which are the possibilities to add a low pass filter on a stomp box?

I mean, I built a modified fuzz face for my bass...it sounds amazing for me but in some situation (mainly when I not use my rig) it has too much high frequency.

What do you suggest to add a simple circuit that cut off some treble (with the possibility to select how much treble cut, like a guitar tone centrol)?

Thanks So

[Mark Hammer]

One of the simplest and least problematic ways is the SWTC, whether the original or the numerous variations that Jack Orman came up with:  http://www.muzique.com/lab/swtc.htm

[antonis]

A more brute solution is to place in parallel to Q2 Collector resistor a series combination of cap + pot (wired as variable resistor)

But, any of SWTC mods is strongly recomended..!!! 

[Rob Strand]

One of the simplest and least problematic ways is the SWTC, whether the original or the numerous variations that Jack Orman came up with:  http://www.muzique.com/lab/swtc.htm

Hey Mark, is that your tone control?

I can't believe it. I drew that exact circuit today for the DOD 250. I credited 'kleuck' for it.

It gets around the level problem really well.

EDIT:

Don't worry I found it.   I'll update the schematic and put you in the  credits.
http://hammer.ampage.org/files/SWTC.gif

Done.

[Mark Hammer]

I highly doubt it is "my" tone control.  But I guess I helped to popularize it a bit by giving it a gimmicky name that got people's fancy.  And, as a former public servant, the idea of an acronym that rolls off the tongue easily, is hard to resist.  Jack took it farther than I ever could.

Many op-amp-based designs provide opportunities to usefully limit bandwidth via the value of caps in the feedback loop.  And, since the manufacturer often has no idea of the context in which the pedal will be used, they often allow for as much bandwidth as is possible, assuming that if there is too much at the top or bottom the user will use amplifier controls to address it.  One can increase the value of those feedback caps to rein things in, although that tends to be a step-wise, rather than continuously variable, adjustment.

When I make an overdrive for myself, I often operate under the assumption that I will be switching from a bright clean tone from single-coils to a darker thicker tone from the pedal.  Since the overdrive is going to accentuate harmonic content, and the amp is already set to do just that for the clean tone, there is a need to "tame" the top end of the overdrive sound such that the pedal and amp settings do not synergize to produce speaker, ear, brain, or reputational damage.

[Rob Strand]

I highly doubt it is "my" tone control.  But I guess I helped to popularize it a bit by giving it a gimmicky name that got people's fancy.  And, as a former public servant, the idea of an acronym that rolls off the tongue easily, is hard to resist.  Jack took it farther than I ever could.

You might have been the first one to come up with it.  It solves the problem of the tone control affecting the level in an elegant way.   The cop-out solution is to add a buffer, which is what most people do.

When I make an overdrive for myself, I often operate under the assumption that I will be switching from a bright clean tone from single-coils to a darker thicker tone from the pedal.  Since the overdrive is going to accentuate harmonic content, and the amp is already set to do just that for the clean tone, there is a need to "tame" the top end of the overdrive sound such that the pedal and amp settings do not synergize to produce speaker, ear, brain, or reputational damage.

That's the main problem with overdrives without a tone control.   The MXR Distortion+ and the DOD 250 are a bit overbearing going from clean to even mild amounts of overdrive.

[mickeybellinello]

One of the simplest and least problematic ways is the SWTC, whether the original or the numerous variations that Jack Orman came up with:  http://www.muzique.com/lab/swtc.htm

Thanks so much! Great solution!

Due tuo the fact that the topic is very similar, i'll ask directly here.
I'd like to make a pedalt to put it al the end of my pedalboard.
I'd like that this pedal has the function of active highpass (and have a pot that let me choose the cutoff point) and active lowpass (another pot for cutoff) and a very important thing is that it is more transparent as possibile.

Do you have some tips about schematics or resources about this kind of thing?

Thanks

[Mark Hammer]

Sure.  Consider any non-inverting op-amp gain stage.  I'll use the Rat to illustrate, although we're not heading for the same sort of gain.

You'll see that there are two ground legs setting relative gain: C5/R4 and C6/R5.  C6/R5 sets the basic gain for the overall bandwidth, rolling off low end around 60hz.  C5/R4, on the other hand, increases the gain substantially, for content over roughly 1500hz.  Both work concurrently.

What some folks will do is install a pot to vary the resistance along each leg.  If the value of R5 is decreased then gain for everything - low and high - is increased.  If R4's value is increased, then the top-end boost is reduced.

Some pedal designs will use adjustment of that ground leg to alter low-end response.  Most folks familiar with Tube Screamers will know that the low end is rolled off to yield a more consistent clip across the fingerboard.  Since that occurs at the forfeiture of "balls", many designs mod the circuit by upping the value of the .047uf cap on the ground leg to increase bass.

Let's put this to work.  Change the feedback path in the Rat to 10k (use any standard op-amp), and make C6/R5 .047uf and 6k8.  In tandem with the 10k feedback resistance, that gives us a basic gain of about 2.5x.  So, enough nudge for a discernible boost, but nothing overwhelming.  More importantly, the bass rolloff (at 6db/oct) is around 500hz.  Let's stick in that second leg, making C5 .47uf and R4 4k7.  That provides a gain of around 3.1x with a rolloff at 72hz.  So, a bass boost, compared to what C6/R5 does.  IF, however, we stick a 50k variable resistance (pot) between C5 and R4, that can reduce the boost created by that leg from 3.1x down to about 1.2x, with a rolloff beginning around 6hz.  As we decrease the setting of that pot, we begin to raise the gain set by that leg, and apply it to more of the low end.  Note that this cannot boost low-end specifically.  It can only adjust how much the bottom is cut.

The simpler approach is just to switch the value of the low-end-limiting cap with something like a 3-position toggle, but what I described provides variable bass cut.  Used in tandem with the SWTC, you'll have adjustable bass and treble cut.  The suggested circuit provides some gain overall, but that's what the volume pot is for, right?

I have to scoot off for the day, so maybe one of Jack's circuits does what I describe in a simpler and more elegant manner.  A bit too rushed at the moment to determine that.  I'll check in later today.

[mickeybellinello]

Sure.  Consider any non-inverting op-amp gain stage.  I'll use the Rat to illustrate, although we're not heading for the same sort of

...

I have to scoot off for the day, so maybe one of Jack's circuits does what I describe in a simpler and more elegant manner.  A bit too rushed at the moment to determine that.  I'll check in later today.

Thanks so much for the explanation! Very precious info!
I've also found this schematic
http://www.madbeanpedals.com/projects/_folders/VFE/pdf/VFE_Pinball.pdf
I don't need the "tilt" funcion of course.
Another question. How could i set the cutoff "size "?
I mean i see some frequency are xxx dB cutted, some less or more..
Hope ti explain myself in a Clear way

[Mark Hammer]

The Pinball is basically a more complex, and more powerful, active version of the Big Muff Pi tone control.  The BMP provides a 6db/oct "single-pole" highpass and lowpass filter, after the clipping sections, and the Tone pot pans between them.

The Pinball provides 2-pole (12db/oct) tunable highpass and lowpass filters, whose outputs are panned between, with the Tone pot.

How much and how steep a treble cut a person needs is a matter of taste and circumstance, I suppose.  Just note that the shallower the filtering (i.e., 6db/oct, versus 12, 18, or 24db/oct), the lower the corner frequency has to be to achieve audible treble cut, since shallow rolloffs still allow much treble to pass through largely unaffected.  So, to illustrate, at 6db/oct , with a 1khz corner frequency, content at 2khz is only 6db lower, and content at 4khz only 12db lower.  With a 2-pole filter, content at 2khz is 12db down, and content at 4khz 24db down.  In short, if the filtering is steep, you can afford to be ore "generous" in where you locate the corner frequency.  The SWTC-type control is a simple single-pole filter.

[mickeybellinello]

The Pinball is basically a more complex, and more powerful, active version of the Big Muff Pi tone control.  The BMP provides a 6db/oct "single-pole" highpass and lowpass filter, after the clipping sections, and the Tone pot pans between them.

The Pinball provides 2-pole (12db/oct) tunable highpass and lowpass filters, whose outputs are panned between, with the Tone pot.

How much and how steep a treble cut a person needs is a matter of taste and circumstance, I suppose.  Just note that the shallower the filtering (i.e., 6db/oct, versus 12, 18, or 24db/oct), the lower the corner frequency has to be to achieve audible treble cut, since shallow rolloffs still allow much treble to pass through largely unaffected.  So, to illustrate, at 6db/oct , with a 1khz corner frequency, content at 2khz is only 6db lower, and content at 4khz only 12db lower.  With a 2-pole filter, content at 2khz is 12db down, and content at 4khz 24db down.  In short, if the filtering is steep, you can afford to be ore "generous" in where you locate the corner frequency.  The SWTC-type control is a simple single-pole filter.

Thanks So Much for the explanation! 

[Mark Hammer]

You're welcome.  It's what I do.  Others come up with brilliant designs.  Me, I just explain things.  Hopefully, in a way that brings newbies up to speed.