ECE4448 L43: Diode-Based Overdrive and Distortion Effects (Guitar Amplification and Effects)

[@TheNaboen]

"When guitarplayers say gain, the really mean distortion. Although this is technically speaking a overdrive pedal and not what usually called a distortion pedal. Although the distinctions are fairly fuzzy". I laughed. Brilliant.

[@djsnowman06]

Yea I had a chuckle as well

[@totopolo2379]

I did not laugh or chuckle. You both my be amazibg at parties.... not

[@FlaxeMusic]

@@totopolo2379 Ironically you sound like the least fun person here- Nobody likes a negative Nancy.

[@fernandobotello1190]

Yeah, me too haha.

[@thewrongbike7709]

One of very few videos that actually talk physics instead of subjective impressions. Thank you.

[@zaum2002]

I’ve worked in audio electronics for 30 years and this was the best analysis of distortion pedals I’ve heard. Clear and concise. Great work man.

[@Mogwai06]

this dude has explained about everything i actually know about audio electronics or electronic circuits etc better than anyone else. for some reason hes great at explaining it all. glad i found this place because ive searched for someone who can convey it so easily and yet so accessible. i keep coming back anytime i have a question and watch some more lectures.

[@ReedRenken]

Where for school?

[@Tofu_Pilot]

@@Mogwai06 I am going to go out on a limb and say it is the fact that he is an electronics professor at a university that makes him great at explaining electronics.

[@MixMeMcGee]

“Failed gain” vs Clean gain is a GREAT distinction! That’s a really great description for quickly clarifying with guitar players! Thank you!

[@TLMuse]

Really excellent lecture. When I was an EE student at MIT (before switching to physics) back in the early 1980s, I took an analog electronics course with a section on op amps that included working out the transfer functions of op amp circuits with diodes. Fun stuff. But the lecturer (one of Senturia or Wedlock-we used their textbook, but I can't remember which one taught it!) didn't present it with the conceptual clarity you display here. And of course he didn't discuss guitar pedals. I had already built a distortion pedal as a teen guitarist, but didn't understand exactly what it was doing. Lightbulbs illuminated in my head during those lectures. Decades later, you provided even more insights. Thank you for sharing these lectures publicly. -Tom

[@Lantertronics]

Thank you for your kind words!

[@joerectifier]

Man, I had the same problem in my electronics courses at OSU….internal book that was focused on the abstraction of transistors and not nearly enough practical coursework….I’ve spent many years enjoying electronics lectures like this and learned just as you explained it

[@julianvenn4195]

Senturia and Wedlock! I still have my copy bought in 1977...it remains an excellent reference

[@joebieke8750]

Wish we had a course like this when I was getting my EE degree. Nice work!

[@philisgr8]

After building a pile of pedals, this is the best explanation of what is actually going on. Love the term "attempted gain", so accurate.

[@kwgm8578]

Hello Aaron, I have a BSE from SFSU in the late 1970's, and later earned a MSCS from Cal. Today, my engineering alma mater offers a master's program in EE/CS, but I had to do it the hard way. However, I have always been interested in both radio and electric guitar electronics, and had to figure out most of that myself. We did learn op amps and both analog and digital circuits, but the 1970s was the decade of the microprocessor, and the development of LSI to VLSI. Getting a million transistors on a wafer was all the rage, and some of my classmates went on to work for Fairchild, National, and Intel, who all recruited at my school. Now, lithography is in the nanometers. I'm so happy to be retired, but I wish I had a professor like you in my time. I enjoyed your video, as it confirmed what my ear has recently taught me. I've started playing guitar again only during the pandemic. Lately, I've been trying out pedals through my little Fender tube amp, and I've learned that all of these digital distortion pedals claim to do more than they are capable of. The Dumbler and Plexion simulators that promise "real analog sound", the Tube Screamer (without a tube!), and Distortion pedals all sound phoney to my ears. Maybe you have to grow up with the sound to like the sound of digital clipping? I grew up at the Filmore listening to the new acts of 1967 and '68 these pedals are trying to emulate. The sound is different, even if the current trace is similar. Have you done a comparison of tube vs MOS harmonic content as both go from clean into overdrive? Early in the 1980s, I knew someone at HP who demoed their new harmonic analyzer. It was an amazing box, and quite expensive -- many tens of thousands of dollars. By 2000, my home DAW had a plugin with the more resolution and better functionality done in software, than that 20 year old HP box. The beat goes on. I'll share this -- I'm grateful for the Amazon Prime free return, no questions asked policy, where I can order a few pedals for a tryout, and then send them back at the end of the month, if I don't like them. I've kept two so far -- a tuning pedal that I wish we had when I was playing professionally in the 1970's, and an analog delay pedal I gave to my grandson for Christmas last year. Sound effects are fun. Thanks again for these interesting videos, Professor.

[@joshua.merrill]

The way you described the HM-2 is exactly why I love it so much! I'm wanting to design my own version of the HM-2 that targets the frequencies I like more, so your videos are helping me understand how to go about doing that.

[@rogerw4024]

Thank you for sharing your time and knowledge with everyone, you videos have given me inspiration to go back down this road. Hind sight, I wish I would have went back to get my EE degree at devry in Phoenix after my car accident.

[@StevenRoby]

One of the best videos I've seen lately, and your explanations are very clear. Put my EE degree to some use. Thank you.

[@gedofgont]

that circuit simulator just made me gasp. thanks so much!!!! i'm just starting to learn this stuff and tinker :)

[@remi603]

Best video i have seen about od and ds effects so far. I am a student in engineering and I'd like to create my own guitar pedal so that'll definitely help me. Thank you very much !

[@Lantertronics]

You are welcome! :)

[@ayoitscat]

This is the exact video I spent months looking for when I first tried learning circuit design for pedals. I wish I'd found this sooner.

[@giordash]

I am an electronics hobbyist (at best) and this was extremely helpful. While I’ve learned a lot, much of what I’ve gathered has come in seemingly unrelated bits and pieces. This video just connected them all. Thank you!

[@Mogwai06]

im with you there. thats me too

[@sdkee]

One little nitpick: the primary purpose of an overdrive pedal is to gain the signal up (often with frequency emphasis) in a mostly linear way so that the preamp section of a tube amp goes nonlinear in a desirable way. Usually these circuits also have clipping diodes like a distortion pedal, but are doing so little clipping that it would be hard to notice if you listened to the output of the overdrive pedal directly. Of course if you turn the gain up then the diodes start clipping noticeable and then you're using it as a distortion pedal at that point. As the difference is how much you turn the gain knob, a large number of pedals are suitable for both uses.

[@Lantertronics]

The Klon in particular seems to have a particularly wide clean range. (Of course the Klon circuit itself is extremely interesting).

[@TLMuse]

It seems to me that this definition of "overdrive" is confusing overdrive pedals with boost pedals. Of course, there is no "official" definition of any of these. But my understanding is that overdrive pedals are designed to introduce at least *some* audible distortion of their own into the signal, albeit not as much as "distortion" or "fuzz" pedals. Maybe the main difference wrt to boost is that boost pedals mainly stay clean over their full range of settings, and perhaps overdrive pedals "clean up" at lower boost settings, only adding audible distortion of their own once you get up above low levels of boost. -Tom

[@TheMantis1point0.2]

I know I just learned more in this 20 min video than I have in the past month watching an assortment of other videos on KZbin. The information was easy to digest and I'm finding that the videos and information are very linear and that the knowledge carries through. I'm 40 years old building a new life, music has been but electronics will be my new focus and attention at this mid stage of my life. Thank you for being on here and presenting us with this knowledge. I greatly appreciate it. Randy.

[@Lantertronics]

Thank you so much for your kind words!

[@rubhern8187]

enjoyed this very much. 🎉🎉🎉 This will be very helpful in building my first pedal. i must say great resource and help from Texas Instruments and Analog Devices. i was surprised by the amount of Phd students and research engineers interest in pedals from TI and AD. This channel will now be my go to Subs and liked.🎉🎉🎉

[@BrianClem]

You can have this as a college class?!! Wow. That's really awesome. Those in the class should be honored to be learning this!

[@zachp7684]

Horrific is in the ear of the beholder. Excellent breakdown. Thanks.

[@Lantertronics]

You are welcome! :)

[@TheDogPa]

Indeed. Always liked my HM2, but I really hate modern metal.

[@Windkind0]

The two serial crossover-distortion diodes in the heavy metal distortion pedal serve a particular reason: It might act as a poor mans noise gate, so your guitar actually "shuts up" when you are not playing something. This kind of gating can be artistically useful and some pedals (mostly fuzz pedals) even have a dedicated control for this kind of gating (although I am not sure how it is typically implemented).

[@Lantertronics]

Huh... that does make sense. A kind of terrifying sense. ;)

[@DollysplitBand]

WOW

[@PointlessExistence]

Exactly. Its a noise gate.

[@Lantertronics]

@@PointlessExistence Talk about cutting corners. ;)

[@benakanecrophile2878]

@@Lantertronics the tones from a boss HM-2 are for sure terrifying in Swedish death metal. It's not a great tone but it's nasty sounding in a way that not many other pedals are.

[@mickeythompson9537]

The two diodes in series with the signal on the HM-2 are reckoned to be a noise gate - no conduction under a certain threshold.

[@Blinkerd00d]

I'm a pedal builder and EE, and I must say.... this was very well done. I wish I had something as helpful when I first started designing my pedal circuits. Most pedal builders are not EE, in fact Im the only one I know, but the community is definitely full of brilliant and creative minds. For some very interesting (and to me, impressive) circuit designs- look into the pedals of Jason Lamb. He worked for DOD in the late 80s early 90s and he went his own way.

[@beasterfield321]

On the Boss Heavey Metal schematic, the diodes that you thought were discussing are actually acting as a gate to noise that's produced with heavy distortion/amplification. the signal has to get to a specific voltage dictated by the forward voltage of the diode to continue through the circuit. this allows hissing and buzzing to be quieter while allowing the gtr signal to go through. hope that makes more sense.

[@robertmarbun]

Thank you Dr Aaron for your very clear explanation

[@Lantertronics]

You are welcome! :)

[@chadissimusrex8038]

Finally an explanation like this, on various types of overdrive/ dist! Thanks!

[@Lantertronics]

You are welcome! And welcome to the channel! You will find lots of fun stuff here. :)

[@atrumluminarium]

18:26 yes it is horrific and ridiculous, but also sounds insane. The HM-2 was used a lot by the early Swedish Death Metal scene. I think Entombed's Clandestine record is the best recording of that pedal in action and very worth listening to in my opinion

[@binface9]

What do you think of the user of HM2 on records produced by Kurt Ballou? It seems like he's made a career of the back of the circuit (and being a bloody nice bloke).

[@maks_0427]

Don't those diodes work as a noise gate?

[@atrumluminarium]

@@maks_0427 Well "kind of". They only do that for lower tuning because higher notes oscillate faster than the diode switching rate. Even then the noise has to be of smaller amplitude than a certain threshold so it's more like a "poor man's noise gate" so to speak. On the other hand, the pedal also has a weird quirk where sometimes the circuit starts to oscillate when it's maxed out and it lets out a horrible squeal so in some cases it can add more unwanted sounds

[@maks_0427]

@@atrumluminarium ohh okay, interresting

[@Mogwai06]

@@atrumluminarium wow i dont think id seen any of that info before. thanks!

[@Zhou_Kylr]

Impressively simple but clear explainations about overdrive and distiortion pedals, great video, thanks a lot

[@mbuiltpa]

I’m so thankful for this video! Educated me by leaps and bounds!

[@Lantertronics]

Thank you for your kind word! I suggest checking out my whole Guitar Amplification and Effects playlist. You might also enjoy my ECE3400: Analog Electronics playlist.

[@getenlightened]

Thanks for this video. The animated circuit finally helped it all make sense for me. ( after deep diving into what OpAmps are actually doing ). I hope you'll consider more pedal fx circuit analysis videos. Good stuff. Thanks again.

[@Magnetron33]

I have hated distortion pedals for decades, but I heard a couple excellent players that I respect use an OCD. I bought one and love it. very versatile. Everything I have ever wanted in a gain pedal. has a bit of compression too. Interesting vid! Thak you!

[@jameslin7718]

Two back-to-back diodes connected in series in the signal path are used to block small signals, similar to a noise gate.

[@rohankeenoy2199]

Great lecture, wish I had a course like this at my school. Thank you for sharing.

[@Lantertronics]

Thank you for your kind words!

[@ringsystemmusic]

This is a treasure trove of information for someone like me that’s just getting started in pedal design! Thanks!

[@ex-genaumproject8533]

Really simple and well done explanation about how a pedal distortion works. I will check out more of your videos for sure

[@shean4]

Another great breakdown of circuit elements. Thanks.

[@Lantertronics]

You are welcome!

[@vlastimilelias]

Thanks for another great lesson. Worth to say that important part of the overdrive/distortion character is toneshaping before clipping. In opamp based it is often frequency dependant gain. Sometimes diode clipping is frequency dependant (eg. BigMuff).

[@vlastimilelias]

And have you noticed really clever design of the Blues Breaker? With one pot you are changing gain of both opamp stages, brilliant.

[@Lantertronics]

@@vlastimilelias I never quite wrapped my head around why they were doing it, but now that you mention it, that makes sense.

[@baranelitez8016]

@18:40 I've heard somewhere that tthe crossover distortion diode pair functions more like a "poor man's noisegate" and that might be the reasoning behind it.

[@Lantertronics]

Yeah, since I posted that several people have wrote me to say in practice that particular configuration doesn't contribute to much to the overall distortion characteristics per se.

[@mbermar]

Greetings Professor from Brazil! Great content, with great selection of pedals for examples. Thank you a lot.

[@Mark_of_the_Bear_Studios]

Check out the curcuit for Plumes od by Earthquaker Devices - it has three different clipping settings: 1)Symmetrical diode clipping, 2)Assymetrical diode clipping, and a no-diode, op-amp only clean boost, switching the diode sets completely out. One of the best TS style pedals on the market, and quite versatile

[@dangoldbach6570]

This professor rocks. Literally. I WISH my professors actually knew who Rett Shill was... You don't get how cool guitar pedals are unless you actually play. Coolest professor EVER right here kids.

[@Lantertronics]

Thank you for your kind words!

[@dangoldbach6570]

@@Lantertronics the best learning ever is from someone who can take theory and make it translate to something really cool. Stewmac should partner up with you on explaining their pedal kits! I built one of their ghost drives and It sounds awesome. I know how to drive a soldering iron, what a resistor does, what an op amp is and what a diode does. But, I still am mystified WHY it does what it does. Your videos are really good at unpacking that.

[@snuffbox2006]

Wow! Amazing video. Finally a professor who can explain things in a way that is easy to understand.

[@JamesPearson]

Thank you so much for sharing this, I'm looking into building a distortion module for my DIY modular synthesizer and this has provided me with a solid foundation. Brilliant presentation, thank you again.

[@BryanDenham]

this was extremely helpful , thank you so much for these videos i enjoy them a lot .

[@bryandraughn9830]

I thought you were me for a second. Peace

[@Roderick_Legato]

11:38 -10 points to tonegeek for missing junction dots. The node at op-amp pin 2 - yeah, you can figure it out, but it is ambiguous.

[@RichardJohnson_dydx]

This is really cool. I'm not a EE major (mechatronics engineering) but I built a preamp for one of my projects. It was basic, with a noninverting gain stage, low and high pass filters that I controlled with a pot. And a final output gain control. It sounded great with music but not so good with a guitar. I wish I found this video last semester.

[@valueofnothing2487]

Best source of information on the entire internet. This is amazing Is the digital distortion less fizzy? It's probably not in the scope of this class at all but it has become more popular as people search for the longer sustaining notes without a lot of fizz or losing the low end.

[@Lantertronics]

The nice thing about digital signal processing algorithms is the level of flexibility you get -- just look at all the high quality pedal and amp simulations that are out there. So a DSP isn't any more or less fizzy than an analog circuit -- it depends on the particular algorithm and the particular circuit.

[@TLMuse]

​@@Lantertronics "DSP isn't any more or less fizzy than an analog circuit -- it depends on the particular algorithm and the particular circuit." Well, there are issues that arise in the digital realm than lend themselves to producing unpleasantly "fizzy" algorithms with a naive implementation of the processing that happens in an analog circuit. Aliasing in particular is an issue both for linear processing like EQ, and nonlinear processing like distortion. In a straightforward DSP implementation of an analog circuit, high frequency content (from the input, or generated by nonlinearities) that would be inaudible or filtered to inaudibility by subsequent analog circuitry can be aliased to easily audible frequencies that are not euphonious. Algorithms that fail to properly account for this can sound "fizzy" or unpleasant. So you have to think about more than the equivalent analog circuit when doing audio DSP. -Tom

[@crimadellaphone9374]

Great information, it's nice to finally find a source of more reliable information that also shows examples. And from my own state nonetheless. I'll be subscribing, I'm just learning this stuff, electrical circuitry, as a hobby.

[@urssounds]

These videos of yours are such an amazing resource! Thx!

[@xavierdumont]

So glad you are doing this series. I've been trying to make my own pedal board and it's been a complete failure. Hopefully this series will provide some insight!

[@Lantertronics]

Good luck with your board! (I'd recommend checking out Rhett Shull's videos on the topic; I think some of them are on his channel but some are on Rick Beato's channel).

[@xavierdumont]

​@@Lantertronics Thanks! I definitely will. I've also been reading Self's book on audio and watching relevant info on YT. But without proper EE training, it's hard to know what's wrong (like, why are all my boards so goddamn noisy?!?!).

[@Lantertronics]

@@xavierdumont Re: noise, are you having problems with hiss or hum (or both)? P.S. I love Self's book. It's really the only book out there like it.

[@bak4320]

Brian Wampler (Wampler Pedals) also dives into guitar-related distortion info on his YT channel

[@xavierdumont]

@@Lantertronics I think it's mostly Johnson noise. I know using too high resistor values can negatively affect the overall amount of noise, but I feel like cap types play a big role here too. It would make a great subject for a future video!

[@Aleph_Null_Audio]

With regards to the diodes in series in the HM-2, crossover distortion is usually pretty unpleasant, but it's mostly being masked by the other kinds of clipping going on in the circuit. Also, by blocking signals below a certain threshold the series diodes create a primitive gate of sorts. This may help reduce the noise associated with high gain.

[@prattacaster]

Yep, it's a noise gate. PV uses it in some tube amps, I think also bypassing the parallel diodes with a 1 meg resistor, this may reduce the crossover.

[@KyleKalevra]

The distinctions between distortion and overdrive are fuzzy? Lol Awesome analogy.

[@EDWINPIERCE168]

For a fact, I never thought of gain as anything. It was like a black box. I started playing about 25 years ago. A masters in music is one of my three advanced degrees. I had a daw early on so maybe I’m not a “guitar player”. I knew that clipping was bad and good. I knew the gain knob made it louder and more distorted. A gain boost boosts gain, “boost pedal”. Other boost pedals include OD, distortion, and an EQ pedal (see Kerry King). An EQ can be a boost, but a boost generally is not an EQ, unlike an OD or distortion which both either necessarily or optionally offer some tone sculpting.

[@markhammer643]

I am the proud owner of a 62 year-old "tweed" Fender Bassman. I bought it 30 years ago and have no knowledge of the previous ownership, so I have no knowledge of any changes made to the circuitry. However, when purchased, the Presence control operated in what would nowadays be considered reverse fashion. That is, as the control was turned clockwise (up to "12"), the resulting tone got *duller*, rather than brighter. It appears as thought the intent of the control was to counteract the harmonic content coming from the output transformer, using negative feedback, and "tame" the amp into something closer to linearity.

[@Lantertronics]

Yeah, it sounds like something is odd with that presence control. I'll talk about presence controls later in the course; basically you are right, the negative feedback from the transformer is intended to help the power stage act more linearly. Negative feedback lowers gain; by changing how much of a given frequency feeds back you can change the frequency response, but in a kind of weird way that interacts with other things in the amp so it's not a simple tone control.

[@markhammer643]

@@Lantertronics We tend to forget that, for the first dozen or so years of Rock & Roll's existence, carrying on from jazz and R&B, distortion was something to be avoided, and products were designed and intended, to provide volume WITH clarity and linearity. Similarly, we tend to forget that, well into the late 1960s, many if not most guitar players relied on medium-to-heavy gauge strings, and in some instances flatwound (we tried to avoid audible finger-gliss). Processing of guitar signal was partly predicated on the signal properties and "string behaviour" that would provide. I own a device, made by Guild at the cusp of the '70s, called the Tri-Oct. I refer to it as the missing link between fuzzboxes and guitar synthesis. It comprises six discrete octave-dividers (one per string) to achieve polyphonic octave division (mixed down to mono output), and comes with a proprietary divided pickup for the task. The pickup's size forces it to be placed in a location where there is too much mistracking because of how widely the string vibrates there (we eventually learned that divided pickups needed to be placed by the bridge, or under it, for good string separation). So how could such a poorly-designed product be expected to sell? My guess is that it was predicated on use of much stiffer heavy-gauge flatwound strings, that would not wiggle enough to bleed through to adjacent pickup points; a not unreasonable assumption for the time.

[@possible-realities]

@@markhammer643 How does heavier string gauge influence the signal properties, other than reducing the bleed between adjacent pickups?

[@markhammer643]

@@possible-realities The more ferromagnetic material one "wiggles" near a pickup coil, the more voltage is induced in the coil (string-to-pickup distance being equal)***. Some noteworthy players over the years opted for use of heavier-gauge strings, tuned down a step or so, to achieve the flexibility/bendability of lighter strings. I had the pleasure of meeting guitar whiz Joey Landreth a few years ago. When I made a passing comment about the multi-lever palm pedal he had on one of his guitars, he handed it to me to try out, and I found it impossible to play. He uses an .019-thru-0.63 string set. How he is still able to bend those is beyond me, but I like to joke that if I ever have a pickle jar that I can't open, I think I know who to call. ***Which is why wound strings generate more voltage than unwound. I have a pet theory that the serious bass cut used in the venerable Ibanez Tube Screamer was intended to yield roughly equivalent clipping across the entire fretboard. Keep in mind that the clipping diodes conduct in response to *absolute* forward voltage. So, if one wants the same degree of clipping for the lower and higher notes, one needs to reduce the amplitude of those lower notes. Consequently, the TS is designed to apply decreasing gain for content below about 720hz. Of course, that is just how THAT particular goal was met through design, and is not any sort of "must have". Indeed, the greater amplitude produced by heavier gauge wound strings can be thought of as an available choice for the musician to generate *more* clipping/harmonic-intensity simply by making use of lower notes on the lower strings. It's a bit like a turn-up-the-distortion control, in the form of string/note choice. Make sense?

[@jawsxx8683]

A distortion pedal is to push the amp into distortion whereas the fuzz is to emulate a broken speaker. The diodes are placed in the circuit in a different location.

[@Lantertronics]

You might enjoy my lecture on fuzz pedals (it's a companion to this one): kzbin.info/www/bejne/rqbdhWp5iL6nr6s

[@jackhack1972]

Awesome somebody else to find that uses that same circuit Sim app as I really like that app

[@feudiable]

18:36 I have found the series diodes D6/D7 don't actually provide a huge crossover distortion. Couldn't we consider them as a "diode divider" with the D9/D8 diodes? I get the impression that combined, they actually cancel out some of the effects.

[@Lantertronics]

I've had some folks tell me that they're really acting more as a super primitive noise gate than a deliberate distortion mechanism.

[@drumbyte]

Fantastic job teaching! Makes me want to go back to school:)

[@Lantertronics]

Thank you for your kind words!

[@Terribleguitarist89]

Annnd I've found a new channel to nerd out on...

[@Lantertronics]

Welcome! :)

[@joerectifier]

Outstanding lecture….and FUN!

[@ICPolyman]

The two back to back diodes in series act like a capacitor when the diodes are in their non conducting stage, so the signal isn't totally blocked

[@marcel_max]

Great video! Don't forget to ask Marty McFly, he knows a lot about this.

[@justovision]

When I've scoped a hard clipping circuit it has some pretty square edges on the cutoff with silicon diodes. In my understanding that's how you get the harmonics that are desirable for a hard clipping circuit. I have a rat I modded with switchable silicon, germanium and LED clipping stages. Pretty common mod but great for "hearing" how the diode's clip. For a one off germanium is nice because they're so inconsistent you can dial in a bit of asymmetry (as a treat) just by testing the forward voltage of each diode and picking ones that vary to your taste.

[@justovision]

The Falstad circuit simulator is great but I wonder if they're doing some kind of interpolation to deal with what ever time base the javascript simulation can handle?

[@Lantertronics]

I think various companies have put so much effort into optimizing Javascript that they're probably not needing to cut too many corners. (Just a guess, though).

[@esgunduz]

super duper explanation. thank you, by heart 👏👏👏

[@gatorguy58]

I love videos and content like this

[@synthnerd4539]

I was reading recently that although germanium diodes have a lower forward voltage than silicon, they also have a softer curve into clipping. It's not something I've measured but it's an interesting point. I wonder what transistors wired as diodes look like on a scope?

[@georgegkountouras4311]

I'm doing pedal simulations and it's interesting to observe the efects of Silicon versus Germanium, parametric feedback, soft versus hard clipping, cascaded diodes, symmetric versus asymmetric clipping and so on.

[@possible-realities]

If that is true, that should be the main difference I think? You can always change the gain before and after the diodes to account for the difference in forward voltage.

[@savingcaustic]

Thank you so much for this!!

[@Lantertronics]

You are very welcome! You should check out the entire ECE4448 series. :)

[@clearz3600]

As a nerd and a guitar player I approve of this video :D

[@Lantertronics]

As a nerd and guitar player I approve of this comment. :D

[@llwonder]

I never realized that all pedal circuits are based around diodes. I always thought that BJTs were driven into saturation or cut off which caused the distortion.

[@luisseda8657]

Good content,pal,but at 13:27 the firsts bluesbraaker stage IS inverting.Already foolowing you,great!

[@Lantertronics]

Hi! Thanks for the follow! I'm not quite following you about 13:27 though -- are you talking about the op amp with the diodes in the feedback loop? I think I say that is inverting.

[@teslate]

Electronics pendant here :) Isn't the Boss DS-1 distortion stage inverting - input in to pin 2 of a single DIL op amp? Also, I found germanium diodes have a less abrupt turn on voltage or a softer "knee" than silicon diodes which give a less aggressive distortion. As an old audio electronics engineer, I still learn from each video you make! What a great resource they are.. I'm even starting to get more of the in depth math(s). Thanks!

[@Lantertronics]

Oh my goodness, that pin demarkation of the on the DS-1 is weird! It must be some sort of typo... if what's marked as pin "2" really is the negative terminal, and what's marked as pin "3" is the positive terminal, then that op amp would be wired with POSITIVE feedback, and would fly towards one of the rails and stick there (I think). The redraw of the schematic on the Electrosmash website shows it as I interpreted it (which is the only way that makes sense). If anyone reading this can shed more light on this, please do. If it was an actual inverting configuration, then the + terminal would be hooked to some sort of reference (like 4.5 V here).

[@Lantertronics]

Thank you for your kind words!

[@Lantertronics]

Yeah, the Germanium is apparently important to the Klon design.

[@unrelatedactivities]

@@Lantertronics I also thought it was a typo, but seems the TA7136 used in that version has a weird pinout (pin 2 is the non-inverting input).

[@shakeorefined2514]

Great info, thanks!

[@Lantertronics]

You are welcome! :)

[@zingzing6550]

The Boss HM with the germanium diods...listen to Entombeds albums Clandestine or Left hand path, and you can hear what the Boss HM pedal can do. Its called the chainsaw distortion.

[@Meska_Statik]

amazing as always !!!

[@Lantertronics]

Thanks!

[@Meska_Statik]

@@Lantertronics i didn't go to school very long, but you'r work let me learn so much ;)

[@Lantertronics]

@@Meska_Statik Glad to help!

[@possible-realities]

17:34 Is this really soft clipping? It's an inverting op amp configuration and there is no resistor in series with the diodes, so the result should be hard clipping in the sense that once the diodes start to conduct, the output voltage can not go any further? Or did you just mean that the circuit topology is the same that is used for soft clipping?

[@francescodamico7903]

Nice and clear ! I am ignorant in electronics, i am a guitarist. ... but reading within pages in electrosmash i learned (or i thought i learned) that the real main diff between distorsion and overdrive is often just the resulting global eq. Where distorsion pedals have mid frequency scooped and overdrive padals have mid pass (as combination of hi and low cut). In the OS-2 Boss this is more evident. Of course the type of clipping is also improtant but maybe not the only parameter to be considered. Is it right or have i been misunderstanding it at all ?

[@akkudakkupl]

That Boss heavy metal pedal has crossover generating diodes probably because a tube power amplifier driven to overdrive will get less and less bias eventualy going into crossover.

[@JonDeth]

Well covered and brilliantly clarifying. Sometimes when I look at what a fuzz circuit actually is in contrast to an overdrive design, I still get a little annoyed lol.

[@Roderick_Legato]

7:54 So, a trimmable gain stage in front of this could give you a decent triangle-to-sine converter.

[@Roderick_Legato]

@@Nordl3 The waveform from a triangle oscillator will not change with frequency.

[@Lantertronics]

Actually, there are some tri-to-sine converters, like in one of the PAiA designs, that look an awful lot like one of these guitar overdrive circuits!

[@Lantertronics]

See 11:13 here: kzbin.info/www/bejne/jJCkq3V3pNWFiZo

[@Lantertronics]

@@Nordl3 I think all the various tri-to-sin converters have different tradeoffs. In any case, in most musical applications the purity of the sine wave isn't tooooo critical (compared with say in communications applications).

[@ConsanguinitySlam]

When building an HM-2 clone, I had to bypass that weird pair of diodes to get my pedal to output anything, gave me a lot of issues.

[@Lantertronics]

Interesting! (Just making sure --- were you using germaniums in that spot? Silicon diodes would definitely gate more aggressively).

[@ConsanguinitySlam]

@@Lantertronics yep, they were germanium with a forward voltage of around 400 mV according to the data sheet. they were sourced from very old Russian military surplus so i’m unsure of the quality. they may have had a relatively high internal resistance causing voltage drop across them, i believe my multimeter showed 2 kOhms in a continuity test when the diode was forward biased.

[@Lantertronics]

@@ConsanguinitySlam Interesting! Yeah... I can't quite wrap my head around what's going on there.

[@JamesReedy]

I’m 🌽 fusion, the input and output emitter followers on the Ibanez don’t appear to be biased at all?! That’s not an amp that’s a rectifier with gain. The boss clearly had a biasing network at the base to set the emitter at some median voltage so you can get some reasonable swing in both directions.

[@JamesReedy]

Nevermind, I really hate when peeps use triangles pointing downward for power supplies 😐 I see it now…it’s also a shitty design with high beta dependency. The boss design is a bit better thought out tho could be improved on for pennies.

[@heggy_69]

I wonder if anyone gave in a Nobels odr 1 or something as an example of both hard and soft since it has both lol. Also really like crossover distortion, should check out the zvex machine I think that pedal has it deliberately, I think the lovepedal Karl is the same circuit

[@Lantertronics]

I just looked up the Nobels schematic, that is interesting!

[@bevo65]

A hell of an engineer! 🤘

[@AnalogDude_]

i used the MXR distortion in a eurorack module plus some little improvements i added, i used LEDS. there is video on it in me account. Told ya, the Falstad simulator is very good or good. Most components are clear, accept the inductor. do you have some E.Q. schematics using them and being able to do a "tutorial" about that, how inductor work on audio? with cut / boost audio. i have also build the "Paya" 4 band EQ, but this uses capacitors, but is able to cut and boost. do some special opamp config, Have you seen the compressor schematic of "the Engineer'S Thumb Compressor Circuit Design Electronic Valvewizard"? ... and Danish clone of S.L.L. compressor using DBX vca's. Thanks for another very good video.

[@Lantertronics]

If you are interested in inductor EQs, check out the Pultec schematics.

[@AnalogDude_]

@@Lantertronics i "sourced" the transformers, "LL5402" at like 55€ each. but what about the the mains transformers, stepping down from 220 Volt to 12 Volt and using another transformer to step up the 12 Volt tot 220 Volt? ... for the for the Tube.

[@Lantertronics]

@@AnalogDude_ Uhm... I'm not sure why you'd want to use two transformers to not actually change the voltage?

[@AnalogDude_]

@@Lantertronics I'm talking about the "Gyraf pultec PEQ1A schema" found on a french audio website. I think that's the one you refer too and it's contains these transformers so you can use XLR balanced jacks for in/out. as well the step down and step up transformers from 220 Volt to 12 volt and from 12V back up again to 220V. witch is kinda weird in this schematic. Correct?

[@Lantertronics]

@@AnalogDude_ Are you talking about this link? www.gyraf.dk/gy_pd/pultec/pultech.gif

[@ckngmad1357]

I'm learning a lot man, it's easy to understand and informative thank you 🙏🙏 Can u please do analytical schematic of Mountainking Megalith please? Cause that pedal is the heaviest fuzz ever in universe Crazy unstable low end texture

[@Lantertronics]

Found schematic here: music.codydeschenes.com/wp-content/uploads/2013/12/Mountainking-Electronics-Megalith-Schematics.png

[@Lantertronics]

Let's see -- the first two transistors form an NPN shunt-shunt stage as is typical with silicon-based Fuzz Face circuits. There's a switchable notched filter connecting the output of that to the input of a common emitter amplifier. The "more knob" changes both the biasing and the amount of emitter degeneration. I'm guessing that the CE amp provides some additional distortion beyond the usual fuzz face.

[@Lantertronics]

I confess I have no idea what the LED in the middle of the schematic is doing; the way it's drawn it should always be reverse biased and hence off.

[@Lantertronics]

Oh, and I see there's a switch to let you select whether to use the final CE amp or not, so if you have it switched out it's more like a regular Fuzz Face.

[@MoraFermi]

> "The difference between overdrive and distortion is pretty fuzzy." I see what you did here. :D

[@ttoommmmiiee]

Hi Aaron, I really enjoy your videos. Watching this made me wonder about Jurgen Haible's Wasp Filter. It has a distortion circuit that I can't quite correlate with these designs. I would love to hear your analysis of the Wasp circuit as a whole - it's quite idiosyncratic.

[@Lantertronics]

Oh, I was just thinking about that the other day... because there IS an pedal that uses CMOS inverters biased to operate in as analog op amp like things. It's the Blackstone Appliances MOSFET overdrive. (Reverse engineered schematics are online).

[@freddykruger3320]

That boss heavy metal distortion has such a unique sound. Behringer make a clone but for some reason it isn't the same despite all their other analogue clones being identical. I wonder if they neglected to use germanium diodes to cut cost and it changed things? Or if perhaps that oddball cross diode set up you mentioned at the end wasn't implemented correctly and changed it up.

[@MixMeMcGee]

I’m very curious why a diode bridge can be used to create a softer soft clipper. I’ve been working on better understanding Mr. Neve’s use of a diode bridge as a control voltage/soft clipper in his classic diode bridge comp/limiters - finding this technique very interesting!

[@Lantertronics]

Ah! This is an important distinction to make: the kind of clipping we talk about in distortion and overdrive and fuzz effects is VERY different that what compressors and limiters do. The diode bridge in a Neve compressor is not being used as a clipper as described in this video. The nonlinearities I describe here act instantaneously on the signal. A compressor like one of Neve's or an 1176 or an LA-2A is looking at the *average* energy in a signal, usually rectifying the signal and then heavily filtering it that rectified version, and then reducing the gain (or not) based on that. That's the "side chain." The diode bridge really has two inputs -- one is the main audio signal, the other is the control signal used to control the amount of gain. By changing the amount of bias current running through diodes you effectively change their dynamic resistance. An 1176 uses the voltage on the base of a JFET as its dynamic resistance element. The clippers I describe in the video just have a single input, the signal. A compressor/limiter gain control element has two inputs.

[@Lantertronics]

That said, I have seen people use diode bridge structures as clippers (again, that's not how Neve is using it). Check out this paper by my colleague Marshall Leach, where he uses rings of Zeners: leachlegacy.ece.gatech.edu/papers/fmlimiter.pdf

[@MixMeMcGee]

Thank you so much! This paper is rad

[@Lantertronics]

@@MixMeMcGee Happy to help!

[@Lantertronics]

@@MixMeMcGee Marshall was amazing. You should check out his website (If you just google Marshall Leach) it's the first hit.

[@johnsuede]

The germanium diodes 18:28 D6andD7 are a noise gate in the Heavy Metal😊.

[@JacksonHicks-e1m]

every time they said gains my brain went straight to flexing

[@robertmann9822]

The catalogue for National Semiconductors, 1983, featured in an appendix a simple circuit for a fuzz box, using diodes in the feedback of an op amp. One of my students, and independently a phone technician, constructed this 'fuzz' circuit. i phoned in to National Semiconductors the fact that both these specimens turned out to be low-noisse preamps, yielding NO distortion. Whoever I struck on the phone predicably intoned 'diodes in feedback of op amp - will give distortion. They wouldn't believe me that their circuit did NOT work as claimed.

[@danmargetic]

Isn't the inverting clipper you demonstrated also in fact a hard clipper? Because when those diodes conduct, the feedback of conducted diodes prevents ANY additional output voltage. It would be the soft clipper when some additional resistor is IN THE SERIES with the diodes. That would make it a soft clipper, I think. Am I right?

[@andywander]

Thanks for the video. I'm curious, though, why did you use triangle wave input instead of sine wave?

[@Lantertronics]

It makes the exact nature of the nonlinearity more clear. With a sine wave, it's already a bit rounded off, so it can be hard to tell what additional rounding the nonlinearity provides.

[@bozakarlin9034]

Great video, thanks.

[@derekgve]

When you do the analysis of the Bluesbreaker and you point out the voltage divider on the single sided PS you call it a local ground. Is that the same as bias voltage? I assumed that the 4.5V was meant to bias the signal up so that it doesn't dip into the negative. I am a bit of a noob with this stuff so please let me know if I am wrong.

[@Lantertronics]

Ah, yes. When I say "local ground" I mean the bias voltage, I think of the 4.5V as being a new created "ground reference" for the signals. That's just the way I like to think about it -- that's not standard terminology.

[@derekgve]

@@Lantertronics thanks a bunch for the reply. I'm not sure if you have a video or if there is a good one out there that explains what is happening in the diodes to clip the signal. IE: is the clipping occuring in the diode or is the diode causing the op-amp to clip? If it is in the diode, what is happening to the voltage and why? Etc... Your videos are fantastic by the way!

[@Lantertronics]

@@derekgve The op amp itself isn't clipping -- if the output of the op amp hits the limit defined by the power rails, that's typically a hard clip sound (there are some pedals that use that effect). The way to think about it is to think about the current-voltage relationship of a resistor and the current-voltage relationship of a diode and think about what currents are flowing.

[@degoyen]

1+(10K/1K) I see what you did there!

[@Lantertronics]

"But this one goes to..."

[@abelcorvalan3664]

What's that simulator? That's so great. Awesome signal analysis!!!

[@Lantertronics]

Look up falstad.

[@Lantertronics]

www.falstad.com/circuit/

[@AlanW]

This was fascinating, thanks! Any chance you have a video explaining why the tube-screamer type overdrives sound like they have unclipped signal mixed in?

[@noodlezeep5159]

A gain of 11 ... I see what you did there :D

[@Lantertronics]

:) :) :) :) :) :) :) :) :)