Stupidly wonderful tone control

[Transmogrifox]

You know you've done it when you leave everybody scratching their heads saying, "It's so simple, why didn't I think of this years ago?"

Thanks for enlightening us all.  That's a beautiful work of genius and it may end up as a high end roll-off for a high gain LM386-based distortion I brewed up recently

[Doug_H]

You know you've done it when you leave everybody scratching their heads saying, "It's so simple, why didn't I think of this years ago?"

Yeah, I know...  I keep thinking I must have seen this somewhere before... Maybe it's in an amp or hifi circuit somewhere. :?:  But it doesn't matter- even if it does exist in some form or fashion, it was a nice "voila" moment that Mark had on his own. And I'm glad he shared it with us.

Doug

[Jason Stout]

Mark, that tone control is elegant! Here it is for anyone who cares to see it in schematic form.

Code Select Expand


            100k       10k(tone)
             ___       ___
       -----|___|-----|___|-----.
                        A       |
                        |       |
                        |      .-.
                       ---     | |<-----
               0.018uF ---     | | 50k(vol)
                        |      '-'
                        |       |
                        |       |
                       ===     ===
                       GND     GND

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)



EDIT: I see mark has a write up on it at his page. http://hammer.ampage.org/

[Paul Marossy]

Mark, that tone control is elegant! Here it is for anyone who cares to see it in schematic form.

Code Select Expand


            100k       10k(tone)
             ___       ___
       -----|___|-----|___|-----.
                        A       |
                        |       |
                        |      .-.
                       ---     | |<-----
               0.018uF ---     | | 50k(vol)
                        |      '-'
                        |       |
                        |       |
                       ===     ===
                       GND     GND

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)



This was my interpretation of Mark's original post, but the drawing Mark linked later on in the day looks different than this...

[vanhansen]

That's cool as heck, Mark.  I may have to try this in my Sixteen Overdrive circuit.  It doesn't have a tone control now and I didn't want a full 3 knob tone stack.  This looks perfect.

[puretube]

now how about a switchable nF or half across the outer tonepot lugs?
(variable notch bridged-T).

[Mark Hammer]

now how about a switchable nF or half across the outer tonepot lugs?
(variable notch bridged-T).

Well there you go!  Proof positive that:

a) international cooperation is a good thing, and
b) two heads ARE better than one!  

Okay, let's take it a step further.  Let's leave one end of the bridging cap tied to the junction of the two pots, and send the other "free" end to the common of a 3-way SPDT toggle.  The toggle now reroutes the free end to ground, to nowhere, OR to the other end of the tone pot.

This yields the original configuration of a variable lowpass, the tweakable bridged-T you wisely noted, plus a bizarre sort of 2-pole lowpass with a quirky sort of response.  Note that when the tone pot is set at max resistance in this latter setting, the two caps now become parallel caps, increasing the combined capacitance and lowering the rolloff frequency.

Man, that's a whole lotta tonal possibility for a pot, two caps, and a toggle!

If a person wanted to get truly freaky, use the 3-way toggle as described, but have one of the side positions bridge the input and wiper of the volume pot for a treble bypass, and the other side position birdge the T as described.  This could provide crude types of bandpass, notch and lowpass response.  I like it!

[puretube]

where are the "simulator-guys" ?

[StephenGiles]

Terrific stuff Mark, now I'm thinking of 2 optos to replace the tone pot, each driven by a LFO  in opposite directions................
Stephen

[puretube]

http://diystompboxes.com/sboxforum/viewtopic.php?t=35068...
:wink:

[analogmike]

Nice simple circuit! Will have to try it someday.

[will]

Hi Mark,

I tinkered with it and settled on something very close to this: http://www.geofex.com/FX_images/mhtsf.gif  I like it a whole lot more than the original, though I wasn't aiming for any sort of serious fuzz.

Remove the 2-pole active lowpass on the right (from the 100k pot half all the way up to, but not including, the 10uf cap), and insert the SWTC between the 10uf cap and the output pot and you'll be home free.  Personally I like to keep the potential volume so that I can set the drive low for just a little grit and still have enough output to overdrive an amp.

I built a few CMOS circuits: Insanity, 3 legged dog, Frank Clark's Hot Harmonics and Double D. I really liked the Jiggle section of the Double D. It sounded quite Fender-ish.

Just wondering if you or others have tried integrating the CMOS section of your Tube Sound Fuzz into an amplifier emulation like Runoffgroove’s Professor Tweed?  http://runoffgroove.com/professor.html

Basically replacing the op-amp in your TSF circuit with the 1st stage, volume control and tone circuit of the Professor Tweed circuit. Then use the CMOS section of your TSF circuit starting from 100K to the output of the 2nd CMOS section. Build an buffer like an emitter follower. Then take the output coupling cap 22n and the dual low pass filters of the Professor Tweed circuit. You could even replace the 1st low pass filter with your simply wonderful tone control.

I’m imagining it might sound pretty good. I would love to get the tone of a Fender Deluxe Reverb clean through cranked. I’m itching to try this but we are currently selling our house so I can’t mess it up with the circuits right now. My wife would kill me.

Regards,

[Doug_H]

Thanks for the diligent corroboration Doug.  

Not a problem, Mark. I've got something on the breadboard with a variable LPF. I'm going to try this approach and see how it compares.

Doug

[amz-fx]

I keep thinking I must have seen this somewhere before... Maybe it's in an amp or hifi circuit somewhere.

There is a Pultec passive EQ that uses this T-type configuration  

regards, Jack

[Mark Hammer]

A-HA!  I figured it was too damn simple to have never been thought of.  Should I assume that said EQ has an LC combo going to ground instead of just a cap?

[puretube]

http://v3.espacenet.com/origdoc?CY=gb&LG=en&F=4&IDX=US3514723&DB=EPODOC&QPN=US3514723
?

[Mark Hammer]

I was just exchanging notes with Doug Hammond about this, and the idea occurred to me.

Imagine the following.  Two inverting op-amps, both with diode pairs in the feedback loop, à la TS-9.  Lets give the first one a gain of 40 or so, and the second a gain of maybe 20.  That's 800 when multiplied, but the diode pair in the first stage will keep the signal amplitude form the first stage "under control".  It will also fuzz up the signal and add treble content, which the 2nd clipping stage will now exaggerate even more.  A gain of 20 in stage 2 isn't all that much but when you start out with a hefty signal, you reach clipping threshold more often.

Okay, bear in mind that the gain of an inverting op-amp is derived from the ratio of the feedback to input resistor.  Now, let's make that input resistor the pot of our SWTC.  So, a 10k pot in series with a 1k-1k8 fixed resistor goes to the "-" pin of the op-amp and we use a 220k feedback resistor.  The wiper of the pot connects to ground through a cap.  What we have is a between-stages tone control that varies the treble content of what gets transferred between clipping stages.

So far so good?  Great, because here comes the spiffy part.  We make that 10k pot one half of a dual-ganged pot, and stick the other half of the pot AFTER the second clipping stage.  What we have here is a very simple pre-clip-post-clip EQ control in one knob that not only feeds the 2nd clipping stage more treble but also "shaves off" less of the treble post-clip, all the while having little impact on signal level because all that changes is essentially the "location" of the treble bleed cap along the pot's resistive strip, NOT the pot's resistance.  Hot damn, I'm tickled with myself this morning! :lol:

Note that there is no reason why the treble-bleed caps have to be identical value, or why the adjustment range for each pot half HAS to be identical.  On paper, anyways, this should provide a single tone control that can change the character of the distortion generated, not just the degree to which the treble is "tamed" post-clip.

[WGTP]

Cool idea.  I had thought about doing that with 2 BMP tone controls and a dual gang pot.  Haven't gotten around to it so far.  

[aron]

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[lovric]

David Lindley told GP long ago that he thought Simply Wonderful was a great stage name. His music is beautiful.