Low Gain, neutral dist/OD

[PRR]

> Decoupling and setting the output impedance.

COUPLING!

De-coupling takes the sneakage out of sneak-paths, like via the power rail.

Coupling passes AC, not DC, from one part to the next. Also "blocking", depending how you think.

Yes, this mild cheat has ~~5V of DC on the Volume pot. We do not want that to upset the next pedal/amp, C6 is a coupling or blocking cap. If a heavy capacitive load (long cable) falls on an emitter follower, it can oscillate radio waves. It can also try to flow "infinite" current. R12 ensures that whatever junk you hang on the output there is enough dead resistance to limit bad effects.

[Ben N]

Whoops!  Thanks for the correction, Paul.

[Killthepopular]

I've been using some of these circuits in some songs.

This one uses the hotcake
https://youtu.be/A5-8A85gcw4

The solos on this one use the electra circuit.
https://youtu.be/lFy52vLCqvs

This one uses the ROG Eighteen on bass and guitar.
https://youtu.be/PxT1HyCNNdE

[Killthepopular]

So far I've tried 7 different circuits and the only one that actually does what I want is the red llama. I've got another 3 I wanna try. There's the son of screamer which looks pretty straightforward.

I wanna do an OCD.




I'm gonna swap the tl082 with a tl072 and the 2n7000 with the bs170. Apparently these are valid swaps. Also I'm guessing that that stuff in the top right is a bypass buffer which isn't necessary for a breadboard build of this circuit. And what kind of switch do I need for the lp/hp switch?

The other one I really want to try is the nobels ODR1 although it's a bit more complex than anything else I've tackled.




Is there some buffer stuff here that I can leave out? The j201 stuff looks like an input buffer to me and the stuff after the level pot looks like an output buffer...

[bluebunny]

I'm gonna swap the tl082 with a tl072 and the 2n7000 with the bs170. Apparently these are valid swaps.
. . .
And what kind of switch do I need for the lp/hp switch?

The 082 is a lower-noise version of the 072.  The 2N7000 and BS170 are interchangeable, but the pinout of one is spun 180^o relative to the other.

The switch is a simple SPST - closed is HP, open is LP.  Or else use two adjacent lugs on an SPDT if that's all you've got to hand.

[Ben N]

So far I've tried 7 different circuits ...I wanna do an OCD.

Seems like you're already well on your way there! 

[dennism]

"Seems like you're already well on your way there!"


I see what you did there!

[Killthepopular]

So far I've tried 7 different circuits ...I wanna do an OCD.

Seems like you're already well on your way there! 

I'm hopefully going to eventually make a generic, good sounding dirt pedal which I can just have on all the time as my default base tone. I feel like I ought to try a lot of different circuits before I settle on one, seeing as I hope to use it all the time for the indefinite future. Other guys would cycle through a dozen pedals until they found one that stayed on their board for years. I intend to breadboard numerous pedals then build my favourite instead of buying and selling loads. Actually come to think of it, guitarists' relationship with dirt pedals sounds kinda similar to marriage. They play the field for a while. They can never quite commit to any one pedal. But then they find "the one" and they never take it off their board. Maybe they still fool around a little on the side but they can never bring themselves to leave "the one".

Other circuits I've considered building but not convinced by: Rat (not fussed). Jackhammer (awesome but complicated and probably too hard clipped to be a good always on pedal). Barber LTD (sounds ok). Bluesbreaker (not a fan but I know they're popular). Sweet honey (nice but sounds a bit fuzzy). Timmy (sounds kinda mediocre to me...).

If no-one can suggest any edits to the nobels circuit I guess I'll just build the whole thing... though I'll probably need a bigger breadboard...

[Fancy Lime]

So far I've tried 7 different circuits ...I wanna do an OCD.

Seems like you're already well on your way there! 

I'm hopefully going to eventually make a generic, good sounding dirt pedal which I can just have on all the time as my default base tone. I feel like I ought to try a lot of different circuits before I settle on one, seeing as I hope to use it all the time for the indefinite future. Other guys would cycle through a dozen pedals until they found one that stayed on their board for years. I intend to breadboard numerous pedals then build my favourite instead of buying and selling loads. Actually come to think of it, guitarists' relationship with dirt pedals sounds kinda similar to marriage. They play the field for a while. They can never quite commit to any one pedal. But then they find "the one" and they never take it off their board. Maybe they still fool around a little on the side but they can never bring themselves to leave "the one".

Other circuits I've considered building but not convinced by: Rat (not fussed). Jackhammer (awesome but complicated and probably too hard clipped to be a good always on pedal). Barber LTD (sounds ok). Bluesbreaker (not a fan but I know they're popular). Sweet honey (nice but sounds a bit fuzzy). Timmy (sounds kinda mediocre to me...).

If no-one can suggest any edits to the nobels circuit I guess I'll just build the whole thing... though I'll probably need a bigger breadboard...

A Wise Man once said: "Give a man a fuzz and he'll jam for a day. Teach a man how to build a fuzz and he'll never jam again." Someone on this forum has or had this as their tag line, I don't remember who, though. All I can say from my experience is that committing to one sound and never wanting to change or improve it is something that only happens to people who don't know which way round to hold a soldering iron. I started with similar ambitions: Just build the "one" bass fuzz that I want and that does not exist and then use that 'till kingdom come. I haven't had a band since and still develop a bunch of ever so slightly different fuzz pedals each year. Taste keeps changing and with each new pedal, new ideas pop up. Doesn't mean you will fall down the same rabbit whole but let me warn you from all of us down here, it is a damn slippery slope.

On a more cheerful note: No point bothering with the BS170's in the OCD. The way the MOSFETs are used here, only the body diodes are active. That means you can replace them with pretty much any silicon diode without an awfully big change in sound, if you adjust C10 accordingly (by ear). Forward biased Zeners will probably be the closest match. If you want to take advantage of the high capacitance of MOSFETs (which to me seems to be the only good reason to use MOSFETs in that configuration), you'll want to use essentially any type of MOSFET *except* 2N7000 or BS170, since those have very low input capacitance values (both 60pF) for a MOSFET. The IRF540 power MOSFET for example has a whopping 1700pF and will give you a much mellower clipping from the body diode. But for the sound you are after, I would suggest BS170 or 2N7000 "used right" (second example on Jack Orman's ever helpful page http://www.muzique.com/lab/zenmos.htm)*[see EDIT below]. This way there really is a big difference in using MOSFETs and the result is very nice and dynamic. Some would call it "tube like", which I don't find helpful but I see where that description is coming from. For this clipping arrangement, I would go to a 18V power supply, else you will only get relatively mild crunch tones before the first opamp stage starts to clip. I would also definitely use an opamp that sounds good when it clips. JFET input opamps such as the TL072, TL082... clip very nastily. The good old NE5532 (BJT input) clips much more musically, my personal favorite for clipping is the NJM2068 (may be hard to come by, though). Rail-to-rail MOSFET opamps such as the TLC2262 are probably the best choice for the sound you seem to be after. Sans amp use them a lot in their amp simulations and simply overdrive the opamps, so that may give you an indication that clipping the right opamp is not a bad thing (whereas clipping the wrong one very much is). With a TLC2262 you'll be limited to <16V supply but since it is rail to rail, and clips nicely it will probably sound good with 9V, too, in an OCD with the "example 2" MOSFET clippers. MOSFET opamps are a bit noisier than good BJT opamps but the TLC2262 is still less noisy than a TL082, so that should not be a massive problem.

Hope that helps,
Andy

EDIT: I forgot to mention that you can also use Schottky diodes with a low forward voltage, such as the 1N5817, to keep the body diodes from engaging. You can do this by adding two 1N5817's to either example 1 or example 2 on Jack's page. Trying to figure out how will be a good mental exercise (plus, I have nothing to draw with me right now). This will lower the clipping threshold by about 0.6V and thus give you a bit more distortion.

[GGBB]

The 082 is a lower-noise version of the 072.

Other way around actually. 072 is lower noise version of 082.

[Killthepopular]

A Wise Man once said: "Give a man a fuzz and he'll jam for a day. Teach a man how to build a fuzz and he'll never jam again." All I can say from my experience is that committing to one sound and never wanting to change or improve it is something that only happens to people who don't know which way round to hold a soldering iron. Taste keeps changing and with each new pedal, new ideas pop up.

My dad keeps reminding me "it's human nature to never be satisfied with what You've got." Maybe he's right. But on the other hand this is the first time I've gone through a bunch of different circuits to find "my sound". Maybe I will settle on something I'm happy with. I just thought I'd spend some time following it up and see if it looks like a project that has a conclusion or like an abyssal rabbit hole. So far the number of circuits I've tried seems like a reasonable number...

No point bothering with the BS170's in the OCD. The way the MOSFETs are used here, only the body diodes are active. That means you can replace them with pretty much any silicon diode without an awfully big change in sound, if you adjust C10 accordingly (by ear).

Ok. I'll try the bs170s but I'll also try some other diodes (I really like 1n4001). I might try using them "the proper way" too although I already tried that with the electra circuit and I wasn't so keen on the sound.

Rail-to-rail MOSFET opamps such as the TLC2262 are probably the best choice for the sound you seem to be after.

Ok. I'll order some. Presumably they have the same pinout as the tl082? I was also going to mod the son of screamer to sound like a ts9dx. I really like the sound of those other modes (less rolling off of low end, more headroom). I'm assuming that the sound of the ts9 dx comes from the opamp clipping to a large extent. Would the tlc2262 be a good choice there too or should I go for a 4558 if I want the same sound?

[Rob Strand]

So far I've tried 7 different circuits and the only one that actually does what I want is the red llama. I've got another 3 I wanna try. There's the son of screamer which looks pretty straightforward.

I admire your persistence.

Is there some buffer stuff here that I can leave out?

Only the output buffer.  Don't remove the input buffer, you could replace it with a BJT or opamp buffer if you don't want to use a JFET.    Unfortunately it's not possible to strip that circuit back with having built the whole thing then *you* deciding what you don't need.

[GGBB]

Ok. I'll order some. Presumably they have the same pinout as the tl082? I was also going to mod the son of screamer to sound like a ts9dx. I really like the sound of those other modes (less rolling off of low end, more headroom). I'm assuming that the sound of the ts9 dx comes from the opamp clipping to a large extent. Would the tlc2262 be a good choice there too or should I go for a 4558 if I want the same sound?

Keep in mind that input impedance can have a significant impact on overdrives. The TL072/82 and others use JFET input sections to deliver a high input impedance. 4558 and others are BJT based and have lower input impedances. Much like actual JFETs vs BJTs. Fulltone recently updated the OCD and gave it a JFET input buffer to bring Zin up from 330k to 1M. It sounds quite different. That Pedal Show did a comparison very recently - rather long as their videos usually are but very interesting to hear.

So when you are comparing opamps, sometimes the differences you'll be hearing are due to the input impedance of the opamps. It would make sense to be aware of that so that your comparisons are apples-to-apples as much as possible. Note also that you could change the character of any opamp by adjusting input impedance in the circuit. You might find that an opamp you weren't crazy about sounds really good with a bigger or smaller bias resistor or with a JFET buffer in front (or maybe by removing a buffer).

[Killthepopular]

So far I've tried 7 different circuits and the only one that actually does what I want is the red llama. I've got another 3 I wanna try.

I admire your persistence.

Actually tbh the transistor based drives (eighteen, barbershop, peppermill) also pretty much did what I wanted but I didn't care for the sound. Too crispy. I think i prefer the sound of opamps being overdriven.

Don't remove the input buffer, you could replace it with a BJT or opamp buffer if you don't want to use a JFET.

Hm, I really like the sound of the nobels but it's about twice the size of any circuit I've tackled so far... Think I'll shelve it for now.

[Killthepopular]

Keep in mind that input impedance can have a significant impact on overdrives. The TL072/82 and others use JFET input sections to deliver a high input impedance. 4558 and others are BJT based and have lower input impedances. Much like actual JFETs vs BJTs. Fulltone recently updated the OCD and gave it a JFET input buffer to bring Zin up from 330k to 1M. It sounds quite different. That Pedal Show did a comparison very recently - rather long as their videos usually are but very interesting to hear.

So when you are comparing opamps, sometimes the differences you'll be hearing are due to the input impedance of the opamps. It would make sense to be aware of that so that your comparisons are apples-to-apples as much as possible. Note also that you could change the character of any opamp by adjusting input impedance in the circuit. You might find that an opamp you weren't crazy about sounds really good with a bigger or smaller bias resistor or with a JFET buffer in front (or maybe by removing a buffer).

Yeah I saw that episode the other day. There was a big difference in the amount of high frequences in the two OCDs.

I guess I'll just stick with my tl072s for now and maybe try tinkering with input impedance once I get the circuit running.

[Ben N]

I'm hopefully going to eventually make a generic, good sounding dirt pedal which I can just have on all the time as my default base tone. I feel like I ought to try a lot of different circuits before I settle on one, seeing as I hope to use it all the time for the indefinite future.

You're not wrong, even if this quest can be a little maddening, and even a little self-defeating. I'm on a similar quest--even if without quite the same programmatic focus and persistence. Given the range of drives you've tried, in terms of gain and eq, it's hard to know what you're really after, but in my experience only three have ever scratched that particular itch, a DOD FX-50 (the one without the tone control), an MXR Distortion III, and, the current choice, a near-clone of the Nobels ODR-1 that I built on the Aion Andromeda PCB. I really like the ODR-1. While I'm sure it's not for everyone, it's worth checking out. Past failed candidates have included an OCD clone, Boss BD-2 and OD-3, and a Barber Direct Drive. Like you said, I didn't connect with the Timmy in this application, but I find it useful for stacking and boosting, or alternating more of a mid-focussed sound with the ODR-1.

[Killthepopular]

I'm becoming interested in the idea of adding a TMB tonestack. It's effectively an "amp emulator" that i want to build, partly to be used in conjunction with my cab sim pedal. Seems like adding a proper amp tone stack would make sense... Would this be fairly easy to do? What would the downsides be? I understand that there will be an output level drop but with a circuit like the red llama which seems to have a crazy amount of output I assume this wouldn't be a big issue.

Apparently tone stacks tend to always cut a bit of mids so presumably this might mean that using a pedal with a tone stack into a standard amp with a tone stack could result in an overly scooped sound? OTOH a lot of people seem to think the guvnor sounds great going into the front of an amp so maybe it's not such a big deal. Perhaps a wise move would be to include a switch to bypass the tonestack...




Would it be as simple as replacing the 10uf cap with the marshall tone stack from the duncan amps tone stack calculator?

[GGBB]

Not really all that "low gain" - and now no longer neutral.

A good tone stack might be trickier than just a tack on. These too are affected by surrounding impedances, so the traditional stacks are designed around specific Zin and Zout characteristics found in their respective amp stages. So some adjustment and tweaking will probably be in order. Amp-in-a-box has been done many times in many ways so there are plenty of examples out there to learn from.

[Killthepopular]

Not really all that "low gain" - and now no longer neutral.

A good tone stack might be trickier than just a tack on. These too are affected by surrounding impedances, so the traditional stacks are designed around specific Zin and Zout characteristics found in their respective amp stages. So some adjustment and tweaking will probably be in order. Amp-in-a-box has been done many times in many ways so there are plenty of examples out there to learn from.

Is the impedance the resistance between the first and last component of a circuit when Measured with a multimeter? Or rather, the resistance between the input and output?

[GGBB]

Is the impedance the resistance between the first and last component of a circuit when Measured with a multimeter? Or rather, the resistance between the input and output?

Not exactly, but resistance is part of it I think. Impedance (Z) is a little above my pay grade, so I'll tell you how I understand it. Z is related to both resistance and reactance (which relates to phase). In our case we're concerned with audio frequency AC - so a simple DC measurement of resistance is not the same thing at all. Anywhere you have resistance, capacitance and inductance you have an AC filter of some sort, which creates reactance thereby affecting Z. Tacking a filter - which has a certain Z - after or before some other Z, changes the result of the individual pieces. We often refer to that kind of thing as loading. In audio we use high Zin and low Zout buffers when we want to minimize loading effects.