Adding tone stack to a distortion circuit?

[Chris Goodson]

I'm messing around with the new clipper circuit.
http://www.runoffgroove.com/newclipper.html
So far I've put in a 4558 and for clipping I added in this- LED\SI\GE -in that order on each side.  I've read on here about stacking op-amps so I just tied both inputs and outputs together, although I don't think it made a lot of difference.  I like the sound it's getting when I crank the guitars volume wide open but it sounds sort of fizzley at lower volumes.

Anyhow to get to my question. I want to add a tone stack to it.  Where does this fit in to the circuit? Should I use the other side of the op-amp for recovery instead of what I've done with it?  I downloaded Duncan's tone stack calculator last night and I think something like the Bench stack might be cool.  Would this be a good one for a distortion pedal?

[petemoore]

Ill take a stab, others have more EXp with this though.
 New Clipper won't have enough output to push tone stack I don't think.
 Since you used a 4558 [my personal favorite] you should have another unused side, with that side I would put a booster [Micro Amp? Same Mfr. ..] then a tone stack [reversing the order would make the Micro Amp a post Tone Control gain recovery stage.
  AMZ Tone Controls...real good place to start there, use the pages frequency charts, text, and schematics to make your choice, However you might like to have a heavy mid scoop...whatever...you can maybe use some sockets or breadboard to find your personal favorite TS cap/res values.

[Mark Hammer]

Tone stacks can fit in different places.  Situated before the clipping section, they will alter which frequency bands clip more easily.  Situated after the clipping section, they alter what harmonic content makes it to the output.  Generally speaking, the most flexibility will occur if there is some rudimentary means for doing both.  Dig around, and I think you'll find that many of the various distortion pedals that DOD makes essentially vary in terms of the kinds of tonal pre-emphasis before the clipping circuit.  That's not to diss the pedals themselves, but rather to emphasize that pre-emphasis/de-emphasis can radically alter the character of a distortion.

Of course, where they fit in is separate from where they CAN fit in.  If it's an active tone stage, you can stick it in just about anywhere.  If it's a passive stage/stack, then you need to either feed it a very hefty signal to compensate for the passive signal loss, or else follow it with some sort of gain-recovery stage to compensate.

I'll draw your attention to some of the earliest Maxon/Ibanez variations on the Tube Screamer, which had the standard tone-control stage situated BEFORE the clipping stage.  Of course, since the clipping adds harmonic content, and since the tone control could not filter it out in those instances, I suspect the tone control was moved in later versions to smooth out the sound.  One of the general principles this raises is that, whatever, and wherever you stick tone controls, it is helpful to have a treble-cut control somewhere near the exit point of the effect, just to keep fizz and hiss under control.

For a simple active pre-emphasis stage, I recommend taking a peek at the Anderton mid-range booster circuit.  Jack Orman has the schematic posted, I believe.  A very simple one op-amp stage that can have variable boost at any of several different frequency bands, and which is easily defeatable with a SPST switch on the back of the boost-level pot.  That, plus a simple treble cut or switchable notch filter, can produce a striking variety of sounds.  The modified BMP tone circuit that Jack elaborates on at AMZ (check the "presence" article in the lab notebook) also provides much flexibility, but should either be preceded by lots of gain or followed up by a gain-recovery circuit.

[Chris Goodson]

Is there simpler gain-recovery circuit I could add than the micro-amp?

[Mark Hammer]

A single-transistor circuit like the one in the BMP.