Searching for a "mild" overdrive

[KarenColumbo]

I would love to build a little overdrive box for a good friend who owns a beautiful Ibanez hollow-body "Jazz" guitar. I already browsed literally (I hate this word) hundreds of possible builds but can't decide.

- early soft breakup, no "fizzing out" in the decay
- Drive range between "breaking up" and "smooth Jazz/Blues", not really Rock
- simple tone control, but I could always splice in the revised Muff tone stack later

We tried out the ubiquitous Tube Screamer as reference - didn't work at all, he thinks it's "too cold".

I once made a Zen-Drive-based OD for a friend's friend's friend - but I lost my notes/EagleCAD files on this and can't remember what i did to make it sound so smooth. And I can't get hold of the build to at least jot down the values and take a pic of the PCB.

What would you suggest?

[PBE6]

I built a ROG Peppermill years ago and recall that is was quite subtle, wouldn't be too hard to mod it to add a tone control too:
http://www.runoffgroove.com/peppermill.html

Some random thoughts on the rest...

I don't think the distortion that Tubescreamers make is especially pleasant on its own, and it's much better used as a mid-forward boost to introduce some breakup into a tube amp.  Part of the reason for me is that the Tubescreamer topology mixes in the  clean signal with the fuzz in a 1:1 ratio, which I don't like on guitar (but which I do like much better on bass!).  YMMV. 

John Scofield used to use (probably still uses?) a RAT distortion pedal, which is a hard-clipping pedal with a unique opamp having a low slew rate so it kills high frequency transients, and he had a great subtle dirt tone.  He also used an Ibanez Artstar.  Maybe something more RAT-like is the ticket.

If your friend thinks the Tubescreamer is "too cold", my guess is that's a statement about the lack of bass in the effected signal.  No matter which topology you choose, using a tone control that adds in some bass after the distortion stage will probably help.  I suggest starting somewhere around 400 Hz and tweaking from there.

Zany idea: what about getting a cheap EQ pedal like the Behringer EQ700 and adding a switchable hard clipping gain stage to the front end?  Not sure how noisy these pedals are, or if there's enough room in the enclosure for a daughterboard, but it would be a quick and dirty way to address the EQ issue noted above.

[antonis]

Maybe a Big Muff with only one clipping stage should do your job..
(deleting also Tonestack eliminates the need for final BJT recovery stage..)

[Mark Hammer]

The EHX Muff Fuzz is essentially a silicon Fuzz Face with modest fixed gain and a pair of clipping diodes to ground.  Remove/lift the diodes and maybe drop the gain a little more and you have a milder overdrive.

I'll put in a plug for the SDS "soft distortion" subcircuit of the old Roland Funny Cat ( http://www.generalguitargadgets.com/wp-content/uploads/geo_funnycat.pdf )  A quirky little one op-amp circuit, it basically relies on seriously bad envelope ripple to drive the gate of a FET that is setting the gain of the op-amp.  It's actually a nice unaggressive mellow overdrive that is quite suitable for someone wishing to add coloration to single-note neck-picking jazz phrasing, like if you were playing in Chuck Mangione's band.  Sadly, most Youtube demos of the Funny Cat will highlight the autowah aspects and not the SDS, which is selectable on its own.

Think of it like the inverse of the Boss OC-2.  That circuit takes the pitch of the note, divides it in half, and uses that to turn JFET gates on and off at half (and one quarter) of the input frequency.  The SDS effectively "gates" the gain of the op-amp at much higher frequencies to mimic more harmonic content than was in the original.  Not fizzy in my experience, though using a dual op-amp, with the second half used for tone-shaping might not be a bad idea.

[yanng45]

Definitely something like a HoneyBee overdrive, there's a few versions of that circuit but all in all they do precisely what you describe ! You should check out that circuit, the tone control is indeed very simple and actually pretty clever.

I did a PCB (https://github.com/effectspcbs/pedals/tree/master/BJF%20Honey%20Bee%20Overdrive) for that pedal, it's a favorite of mine and after much tweaking i always went back to the stock component's values. Awesome pedal.

[ElectricDruid]

For soft overdrive, my new favourite is something based on a differential pair. Rather than "nothing nothing nothing CLIPPPING!" as you turn up the gain control, you get a lovely soft approach to distortion, with plenty of "warmth" before you get to anything even vaguely crunchy.

I don't know a project that does this, and I haven't completed one myself yet either. But I'm sure there are some. It's a pretty obvious idea and it must have been done several times over.

[GGBB]

A very recent thread on the same topic for reference: https://www.diystompboxes.com/smfforum/index.php?topic=122849.0.

[GGBB]

I built a ROG Peppermill years ago and recall that is was quite subtle, wouldn't be too hard to mod it to add a tone control too:
http://www.runoffgroove.com/peppermill.html

...

John Scofield used to use (probably still uses?) a RAT distortion pedal, which is a hard-clipping pedal with a unique opamp having a low slew rate so it kills high frequency transients, and he had a great subtle dirt tone.  He also used an Ibanez Artstar.  Maybe something more RAT-like is the ticket.

I'm a fan of the Peppermill too. I have a layout for one with a tone control that I have yet to try:



AFAIK Scofield at some point used a Pro Co Solo - not sure if that was after the RAT (when the Solo was released) or just for a period. No idea whether or not he still uses either one. Not sure how he got his sound out of it, but for certain he kept the gain down. RATs tend to be thin sounding at low gain, so I imagine he rolled the tone back a fair bit but not enough to make it muddy (which could easily be done).

The Solo is just a RAT with selectable clipping and a muff-style tone control with additional scoop control. The tonal variations you can get out of it are multitude. Even though the drive section is pure RAT, it can sound like a completely different pedal. I actually find it hard to dial in a very accurate RAT tone on the Solo.

[bean]

I love the Peppermill. I need to build another one!

If you don't mind etching I have layout artwork for two Barber pedals which can do laid back OD. In the overdrive section at the bottom:
http://www.madbeanpedals.com/EP/index.html

[R.G.]

There's a simple circuit that can make your distortion as soft as you like it, all the way down to none (for most signals). I had some drawings of this at one time, and it was posted in this forum, years ago, but I can't find them at the moment.
Imagine: an opamp, biased in the middle of a 9vdc supply. It's output can swing up to a little less than 9V before clipping on the positive swing, a little higher than ground on the negative swing. And it can provide some gain, from less than unity up to maybe 100,000 times for most opamps, just by adjusting the input and feedback resistors.
Put a large capacitor on the output of the opamp, and have it drive a resistor and back to back diodes to ground. If you take the output voltage at the top of the diodes, the output signal will be clipped at +/- one diode drop around ground, and can be driven to pretty hard distortion by the opamp, which is trying to drive the diodes to +/-4V or so.
You can add any amount of softness you like by putting a pot wired as a series resistor between the clipping diodes and the output takeoff point. Imagine the opamp diode, with DC offset removed by the output capacitor, driving a 1K fixed resistor, a 0-10K variable resistor, and then two diodes back to back to ground. The output voltage comes off the junction of the 1K resistor and the 0-10K variable resistor.
Obviously, if the variable resistor is 0 ohms, it's just as fuzzy as the two diodes by themselves. But as you dial up the variable from 0 ohms towards 10K, the output is more and more composed of the clean signal from the opamp, very little from the clipping diodes.
It's really quite a fun circuit. It's one wart is that the output volume also rises as more and more clean signal is added by increasing the 0-10K.
You can tame this by setting up the circuit with two fixed resistors, and adjusting one. When you get it where you like the sound, measure the pot value and insert the closest standard value of fixed resistor.

[KarenColumbo]

Wow, thanks all! What a menu! Could someone reup the AFEA drive schematic again? It's been photobucketed

[bluebunny]

Wow, thanks all! What a menu! Could someone reup the AFEA drive schematic again? It's been photobucketed

The eejits at botophucket have really excelled themselves this time: now everything is blurred beyond recognition!      If Mark doesn't get there first, I'll try to remember to post a copy from my stash when I get home later.

[Fancy Lime]

Hi Andreas!

I've been experimenting with a bit of circuitry that is supposed to become a stack-in-the-box / recording preamp. The core unit is quite simple. Just a buffer, booster, inverting opamp with clippers, and a TS style tone stack. I wanted MOSFETs in a hard clipping configuration and I wanted to avoid opamp clipping, and this was the easiest way to do that, which I could think of:



The important point about the clippers is that the configuration is "hard" meaning that the highest possible saturation causes infinite gain reduction, but at the same time the knee of the clipping is soft. That produces very musical crunch, at least to my ears. Very nice initial break-up, not unlike a Blues Driver. And it can get very distorted if you want it to. TBH, I like this kind of setup a lot better than the classic "resistor in series with clipping diodes" way of making the clipping soft, especially around the point of incipient break-up.

For a pure low-gain drive, you might want to reduce the gain pot to 100k. C4 and R8 make a treble boost with a corner frequency of 709Hz. You might want to play with those to change the pre-gain and the color to suit your friends tastes. The tone stack is not fine tuned yet. Playing around with the value of C6 is definitely a good idea. This is all very much work in progress, so YMMV, but it may be worth giving a try. I really like the sound so far.

Hope that helps,
Andy

[Ben N]

I think the Zendrive was a good option for a "warmer" drive; you should be able to find schematics &/or layouts on the interwebz. Alternatively, I've got two drives on my board right now that might fill the bill, a Nobels ODR-1 clone (flatish mids, rather bassy, lots of chewy harmonics but very nice top end with no sizzle; PCB by Aion with added bass rolloff control) and a Timmy clone. Between them, the Timmy is definitely a "bitier" sounding OD/boost, although the clipping switch lets you gin up the harmonics, too, and it also lets you contour your eq pretty effectively.

[KarenColumbo]

I think the Zendrive was a good option for a "warmer" drive; you should be able to find schematics &/or layouts on the interwebz. Alternatively, I've got two drives on my board right now that might fill the bill, a Nobels ODR-1 clone (flatish mids, rather bassy, lots of chewy harmonics but very nice top end with no sizzle; PCB by Aion with added bass rolloff control) and a Timmy clone. Between them, the Timmy is definitely a "bitier" sounding OD/boost, although the clipping switch lets you gin up the harmonics, too, and it also lets you contour your eq pretty effectively.

Yeah, I built a Timmy just for heck of it recently. I found the tone pots waaay too redical - quite hard to dial in useful (= warm and pleasant) values there. And it gets nasty quite quickly so I gave it away to a friend who plays nasty music and is delighted about my box

[KarenColumbo]

Hi Andreas!

I've been experimenting with a bit of circuitry that is supposed to become a stack-in-the-box / recording preamp. The core unit is quite simple. Just a buffer, booster, inverting opamp with clippers, and a TS style tone stack. I wanted MOSFETs in a hard clipping configuration and I wanted to avoid opamp clipping, and this was the easiest way to do that, which I could think of:



The important point about the clippers is that the configuration is "hard" meaning that the highest possible saturation causes infinite gain reduction, but at the same time the knee of the clipping is soft. That produces very musical crunch, at least to my ears. Very nice initial break-up, not unlike a Blues Driver. And it can get very distorted if you want it to. TBH, I like this kind of setup a lot better than the classic "resistor in series with clipping diodes" way of making the clipping soft, especially around the point of incipient break-up.

For a pure low-gain drive, you might want to reduce the gain pot to 100k. C4 and R8 make a treble boost with a corner frequency of 709Hz. You might want to play with those to change the pre-gain and the color to suit your friends tastes. The tone stack is not fine tuned yet. Playing around with the value of C6 is definitely a good idea. This is all very much work in progress, so YMMV, but it may be worth giving a try. I really like the sound so far.

Hope that helps,
Andy

Oh yes it does! Thanks fot this, that's an excellent base camp for further exploration!

[KarenColumbo]

I feel compelled to thank you all yet again - there's a wealth of stuff in this thread that keeps me occupied (and keeps me from doing stupid things with my tube amp project)

[digi2t]

Durham Sexdrive. Not fizzy at all. Quite warm. At least with my gear.

[Ben N]

Yeah, I built a Timmy just for heck of it recently. I found the tone pots waaay too redical - quite hard to dial in useful (= warm and pleasant) values there. And it gets nasty quite quickly so I gave it away to a friend who plays nasty music and is delighted about my box

I get that, Andreas. It took me a while to get comfortable with the controls, and I use it with the gain pretty low--about 9:00-10:00 o'clock--so it's more of a boost with a little bit of edge, either for a lead boost on other OD/distortions, or for a kind of "clean plus" tone riding the guitar volume control to fade the grit in and out. For a more rounded, all-around pleasant OD tone, I think the ODR-1 is more the ticket. It's a "no bad sound there" kind of box. For me it took the place of an OCD clone and an MXR Distortion III.

[yanng45]

The Timmy can be weird yeah, it's not my type of OD anyway since i usually like pedals with more character. I still think it has a great advantage as it can sound "ok" in front of literally any amp if you dial it that way :
- Start with Gain, Bass, Treble all the way counter-clockwise (ie no cut on the tone pots if you went with the original wiring) and Volume on half. Set that way there should be minimal differences between the bypass and affected sounds.
- As you increase the gain, correct the EQ with the two cut controls.
- When you're done, adjust the Volume to taste.