Master Op-Amp Imperfections With This DIY Sawtooth Oscillator Design

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Operational amplifiers (op-amps) have imperfections! Things like input offset voltage, input offset currents, input bias currents etc. We are making a sawtooth core voltage controlled ocillator (VCO) in this video, which requires us to use an op-amp integrator, and deal with all the imperfections that comes with it! We'll use a trusty JFET to reset the integrator, all controlled by a simple op-amp comparator circuit. Enjoy! :)
Patron Video: www.patreon.com/posts/6923742...
Schematic: drive.google.com/file/d/1Qwm4...
00:00 Intro
00:16 Oscillator Core
00:55 Op-Amp Integrator
1:50 Drift
2:12 Input Offset Voltage
3:49 Resetting The Integrator
5:05 Op-Amp Comparator
6:20 Comparator Hysteresis
7:50 Charge Injection
8:24 Signal Conditioning
9:20 Oscillation Frequency
10:10 Linear vs Exponential Control Voltage

[@robjordan63]

Yours is about the only channel I don't play at 1.75x speed. Amazing pace!

[@TheAudioPhool]

Glad to hear it! I'm learning loads about editing as I make every video so this means a lot!

[@davidjohnston5329]

I had to watch it several times at 0.5 speed. Jezus, the pace! Good video non the less!

[@MadScientist267]

Having the attention span of a gnat isn't useful.

[@questionman5]

Solid editing :) That was such great delivery, no fluff just great process explanation!

[@TheAudioPhool]

Thanks! I edited this one a little different from usual so your feedback is very useful!

[@questionman5]

@@TheAudioPhool I guess my only addition is that I went to school for EE, and this video buzzed along. I don’t think it’s entirely beginner-friendly and that might be why I liked it; I liked the pacing and if your goal is to teach people with some technical training how to apply that to music, then it works well. Idk how this maps to beginners though.

[@jeffsternon5062]

FINALLY somebody that is able to explain well and in a straightforward way... You sir have earned yourself a new sub ! I'm going to look deep in your content soon

[@MatiasDLevy]

Your videos have really gotten so much better in terms of production and editing, good work!

[@TheAudioPhool]

I really appreciate that. Spent this summer really trying to learn about editing and animation etc. It's all new to me!

[@davidrysdam902]

I've been seeing a steady increase in video quality, but this one is off the charts. Cutting dead air, enhancing points with words and zooms and manim are all really great!

[@gillywild]

Absolutely the best explanation of this subject, ever. :)

[@TheAudioPhool]

High praise!!

[@Babysqid]

Just finished off a restoration of a moog prodigy and this is pretty much the type of oscillator it uses. Figured it out in broad strokes (they weren't malfunctioning I just like studying schematics) but it's nice to have details fleshed out like this.

[@TheAudioPhool]

Sounds awesome!! Glad I could help you out a bit

[@matthewbutler71]

I am incredibly impressed by the quality of this channel and the information you are providing. As an EE undergrad, I wish I got this level of insight from my professors!

[@hanangonen8732]

I love your channel . Practical info for the practical eng .

[@TheAudioPhool]

Thanks Hanan! :)

[@PATRIK67KALLBACK]

Thank you for a great explanation of these different circuits!

[@TheAudioPhool]

You're very welcome! Thanks for watching!!

[@reneschmitz4845]

Ah the good old ENS-76 VCO.

[@TheAudioPhool]

Are you THE René Schmitz?!

[@reneschmitz4845]

@@TheAudioPhool Yes.

[@TheAudioPhool]

Wow! I'm a huge fan of your work. :) Hope you enjoyed the video!

[@reneschmitz4845]

@@TheAudioPhool Sure I did.

[@biswajit681]

Outstanding video

[@TheAudioPhool]

Thanks!!

[@planker]

Thanks. Gotta do this one, I'm excited.

[@TheAudioPhool]

You can do it!

[@dannyroessler]

Great! And a big thank for this kind lesson again

[@davesdigitaldomain]

I've just come across your channel and it's very good, please keep the videos coming you have what it takes to do well. I just subscribed

[@flywittzbeats4008]

Just discovered your channel. I’m home. Lol

[@tomhague1162]

Excellent series. You are refreshing principles I learned 50 years ago, some of which I didn't fully understand at the time. I can't say I fully understand now but the theory is there. Placing voltages used on your schematics would be helpful as many voltages were used throughout the series and they get a bit confusing. Keep up the good work. I look forward to more in this series.

[@TheAudioPhool]

Appreciate the kind words and feedback! Always helpful knowing how I can make the videos clearer :) thanks for watching!

[@t1d100]

I learned stuff; kewl! Thank you.

[@TheAudioPhool]

Thanks for watching!

[@jeffripley9062]

Awesome vid! Thanks so much

[@TheAudioPhool]

You're very welcome!

[@bheloniousmunch2953]

Thanks for all your videos - they are so easy to understand (sometimes with a second viewing..) I’ve got an older analog scope and was thinking of getting a newer Digital one - can’t read the model number on yours but it’s a Rigol correct? Any suggestions?

[@arnaudlapierre202]

Thanks! I just started designing modules and I was literaly looking for this kind of video for months. Do you think it's possible to use this kind of oscillator with an MCU that calculates the exp conversion to get rid of the unreliable transistor pair?

[@TheAudioPhool]

Absolutely! I'll go over that in the next video :)

[@mr-meek]

@@TheAudioPhool Would love to hear you talk about it! Thanks for the knowledge

[@robertcroft2591]

wow😲

Does anyone know why C1 on the schematic he linked should be polystyrene/polypropylene and (I'm guessing) not ceramic? What would be the difference if I plugged a ceramic one in there compared to the other two? Many thanks in advance. P.S.: love your videos, you're a great teacher :-) I suppose the next video would cover the expo converter? If that is so, I can't wait for it, I struggle to understand the functioning behind those circuits. Keep up the good work!

[@TheAudioPhool]

A few things! Firstly they tend to have better tolerance (i.e the capacitor will be fairly close to the rated value) more importantly though, the capacitance is stable over temperature, applied voltage and frequency range which is super important because otherwise the tuning of the oscillator will wander around over time making it impossible to play in tune! A ceramic one will work in a pinch of you just want to play with the circuit for fun, but if you want it to be stable over time then you need to get some fancy capacitor's :) I appreciate the kind words and yes the expo converter is up next as well as a midi to CV converter on a microcontroller which will be a lot of fun! Check out my Patreon if you want access to the update videos on that one which has a lot of the video stuff up there already if you can't wait ;)

[@JCHaywire]

Excellent, pithy, cogent content. Kudos! DE W0XO

[@TheAudioPhool]

Thanks!!

[@beasterfield321]

can you make sawtooth waves with out -9V??? I'm trying to design a gtr pedal and I only have +9V to work with.

[@TheAudioPhool]

If you have 9v and gnd then anywhere I've said -v in the schematic you'd have ground, anywhere I have ground you'd have 4.5v

[@beasterfield321]

@@TheAudioPhool I’ll give this a try!

[@jaszczurtd]

Just a quick (silly) question: what software you're using to draw schematics?

[@TheAudioPhool]

Depends which schematics you mean!

[@VandalIO]

Is there any perfect opamp out there ?

[@tzimmermann]

An ideal opamp is just a pure construct of the mind. You'll have to select the chip depending on your specifications. Each physical limitation of the opamp is listed in the datasheet. If you're in a regime where, for example, the gain-bandwidth product is way above what you need, the slew rate is high enough so you don't distort the output signal, you swing between less than a diode drop under the power supply (or you're using a rail-to-rail opamp), the input current is negligible, and the output equivalent load resistance is high enough, then you can consider the opamp as "ideal", which allows you to perform simple calculations. I mostly designed simple audio filters lately, so these are the things I have in mind, but there are other limitations to take into account (noise, total harmonic distortion...). Read the "Understanding Operational Amplifier Specifications" application report by Jim Karki if you need more info. Note that sometimes, we can use the limitations to our advantage. I recently saw an implementation of a diodeless deadband function by Buchla which he uses profusely in his timbre modulation (see Aaron Lanterman's video on the subject), and you absolutely can't comprehend how it works if you consider the opamp as ideal!

[@biswajit681]

I request you to please make video on smps control loop

[@TheAudioPhool]

I'll make a note. Thanks for watching :)

[@winsrrow8125]

Recomended generic JFET transistors?

[@TheAudioPhool]

I used a j111. Schematic is in the description:)

[@winsrrow8125]

@@TheAudioPhool thanks, could u share a list with the common components u use? Im interested in following ur videos and currently i only have resistor/cap/inductors, some 2n2222/2n2907, lm358-tl082. No JFET, power transistors...

[@lmello009]

6:17 If my memory serves me right you could ground the lm311 positive supply so that its output range is -15v to approx 0v ps: you could teach at uni

[@TheAudioPhool]

Lm311 has an open collector so you have to set the output with a pullup/down resistor whatever you do! Really handy for level shifting :) Thanks for the kind words!

[@lmello009]

@@TheAudioPhool I proposed a vco as a miniproject, one of the student groups made the triangle/square circuit with a diode-based waveshaper for sine. They only forgot to probe and take a picture/export the square wave on their final report but I saw the whole thing working! I told them to pair two bjt transistors with an opamp current source circuit and asked my fellow workshop colleague if he could make a thermal to-92 coupler out of a spare alluminum sheet - the exp converter worked as expected and that was their nicest result. We had only 3 afternoons of reposition classes at the lab, they were green as an avocado after 2 years of online classes but it was worth it.

[@TheAudioPhool]

Sounds like a great project! Well done!!

[@doughale1555]

… and by driving that capacitor feedback opamp with pulses you get a stairstep.

[@funkbungus137]

oh shit yeah, busting the lid off the industry with some op-amp truth lol. awesome.

[@TheAudioPhool]

Truth bombs yo 😎 💣💥 🤯

[@StationGarageSt]

Feeling rather dazed, albeit enlightened. I do fair bit of car electrical diagnostic work. Hobby breadboarding too. Neanderthal man in the presence of such Circuit Wizardry!

[@TheAudioPhool]

Haha! Thanks so much for watching :) glad you enjoyed it

[@gyrgrls]

Can we differentiate between ideal and practical integrators? 🤣

[@simonkormendy849]

Actually, no electronic device is 100% perfect, it is currently not humanly possible to make electronic components that are 100% perfect, even a simple copper wire isn't 100% perfect.

[@subtitles1492]

get rid of the dramatic hand clapping, it’s distracting. your teaching is excellent as it is and does need no Pewdiepie emulation. 😀 1:03 1:10 1:35 …

[@simonkormendy849]

Actually, no electronic device is 100% perfect, it is currently not humanly possible to make electronic components that are 100% perfect, even a simple copper wire isn't 100% perfect.