ECE4450 L22: Moog Ladder Filters Analyzed (Analog Circuits for Music Synthesis, Georgia Tech course) 

The schematic at 3:31 is missing a cap to ground at the emitter connected to the current source. I was wondering how it would work, but that cap showed up in the small signal circuit equivalent at 11:47 . Also, the the double ladder, that cap isn't needed because it is replaced by the differential emitter coupling to the other side of the ladder.

By all means please post plenty for us non-students. Your lectures are awesome.

Hi Aaron, Thank you for the mention and you're correct about the use of the OTA in the Monowave. It was based on the Taurus ladder VCF, however the CA3080 was going obsolete, so swapping in an LM13700 and tweaking the bias gave me a "nice" sound. just a touch of distortion, no-one likes a super clean VCF, VCFs need character :) There's a whole bunch of other tricks you can do with the ladder filter that make it such a fabulous building block. Hope you and your loved ones are safe. Paula

I'm a EE major in the bay area and this is great! Building some synth DIY stuff and would love to see more videos posted for non-students. Thank you so much!

This is pure gold! Very good job on talking to an empty room!

This is my first RU-vid comment ever. I'm posting because I couldn't watch this without saying thank you. BSEET student in Oregon currently taking a transistor amplifier design class. This was exactly what I needed to connect my studies, my work, and my passion for synthesis! Thanks and here's hoping you share more!

I'm a hobbyist interested in homebuilt synthesizers, and my university doesnt offer much beyond extremely basic circuit classes. These videos are invaluable -- not just for understanding the particular circuits in question, but also for gaining a greater intuition for the operation of nonlinear circuits as a whole. Thanks so much!

Thank you for sharing. I hold a B. Sc. in electronics and have always been fascinated by this beautiful circuit and all its implications. Although I have seen analyses of the ladder filter before, I still learned something from your presentation, especially regarding the different implementations by Moog and others. Thank you, and stay safe.

I really enjoyed the way you did this lecture. Really wish my professors in college had a similar delivery taking care to just discuss the way YOU are conceptualizing everything, really makes it more understandable and fun.

Not in your class. I am hobbyist who taught himself electronics (I got a math degree from an engineering school so engineer speak is clear to me). I am very happy to see this filter broken down so anybody with a decent understanding of AC electronics can understand it. Very clear explanation! I can now not only see how it works, but I also now can can see how change it for different results.

Many thanks for sharing this video. The lecture is really interesting and very well done. This is a mix of "Control/System Theory" and Electronics and you explained all the concepts exactly as I would expect, even with the same notation I would have used! Again, many thanks for this lesson!

Awesome lecture! It's hard to find great content like this. Thanks!! As a software engineer getting into electronics by building a synthesizer, this was exactly the level of detail that makes things understandable. It would be amazing to hear the rest of the class! I can email cute pictures of quokkas if that helps. ;)

Thank you for publicly posting your lecture. It is exciting to watch and a pleasure to see such a friendly explanation for this great topic.

Hey Professor Lanterman, thank you so much for doing this, I'm in the last quarter of an EET Associates program and just finished a term on active filters and I was a little disappointed that we didn't get into this in the scope of my studies. I've been trying to understand this topology for years and you did a great job of explaining it! Now I'm off to see what other treats you may have in your post history...

my understanding of why in a ladder only the top and bottom of the ladder needs to be a tightly matched, thermally bonded, pair, is that the top and bottom pairs lock the bias current in both arms of the filter to be the same. Given the transistors were made in the same batch and are physically located in the same place, if the current through them is the same the temperature rise in them will also be about the same which keeps them "close enough" with modern transistors "weakly controlled" parameters are actually pretty consistent if the parts are from the same batch. I once sat and measured 2 dozen BC548's and their Hfe's all came out at exactly 220.

“Analog circuits for music synthesis “ looking at Moog! Wow, I had no idea this could be a course. I wish past me would know that this would be something I would be interested in in the future. I was a music major, and am a musician very interested in analog synthesis! Of course my music path did not send me in your direction. Later in life, I have found joy in learning electronics, and also playing analog synths like Moog synths. This is so awesome. I have zero idea of what you are talking about, but I can say that I truly appreciate that you have left this video here. I am sure that kids are learning this, and don’t appreciate it! I hope they appreciate how freaking cool this is. My guess is a lot of them are just rolling their eyes, and are just memorizing the exam answers. What an awesome course, and you are killing teaching this…. My degrees is music education, so I had a lot of education classes, and taught for 5 years. Great kid dude!

Hi! I study electronicl engineering at a South African university (Stellenbosch). It has been amazing coming across these lectures, since my university does not offer music synthesis courses. This is truly inspiring thank you!

EE for many years; very well-explained. Thanks!

vOUT = VOUT + vout. Thanks for the lecture!!! It was awesome!!!

Good to see you again Professor. I'm rooting for the powers that be to permit you to share as much as you'd like. :)

So cool to analyze the legendary ladder filter in a EE course! Awesome material Aaron and Georgia Tech!

Thanks for this, The moog 24 db low pass filter sound is what drove me to building my own synth circuits. Still haven't tackled this one, but I'm slowly gaining confidence. I have so much to learn, but how you explained the transistor ladder was very helpful.

Thank you so much for sharing these fantastic videos!

Excellent lecture on the Moog ladder! Thanks Aaron!

LOL, I will suppress the urge to email you a capybara.

Great lecture and very interesting! Hard to believe that was the first one you did in this format.

Thanks! Found the channel today. Great!

Thanks for the explanation, really apreciate your work.

Interesting analysis, had to refresh my frequency domain studies from my college classes. The Moog Voyager uses a trick from the modular to realize a highpass filter response. The Voyager doesn't implement the highpass architecture in the patent or the 904B module. They just use an opamp to subtract the unfiltered audio from the output of the ladder filter (with zero resonance). The passband of the filter output is out of phase with respect to the unfiltered audio; so the pass band frequencies cancel, but the frequencies above the passband remain... and you have a highpass filter. Yes I have schematics.

this is an awesome class, I wish you could release the entire series so we all can learn the great and fun EE class! It is fun to connect the theory learned from book with the real application. Thank you for the offering!

incredibly well explained and easy to understand. Thanks

This was even more understandable than in your awesome lecture series 👍🙂 thanks for uploading The difference between current controlling and voltage controlling just continues to mess with my brain. 🤷‍♂️

This is great. Thanks for posting it here

Invaluable. Thank you.

This is amazing!

10000% lovely, thank you very much

Thank you very much for sharing.

wooo! upload more ???

The non-linearity of the ladder is supposed to be cancelled out because it's a differential set up. But why they chose to use a TCA instead of an instrumentation amplifier is an interesting question!

Great explanation; thank you for sharing! I would love to have seen the rest of the course

wow thanks a lot!

Very cool, wish this was offered back in my day :-)

Would love to attend the course run by Aaron 😍

Robert Moog was brilliant

Awesome lecture, thank you :)

This is brilliant and explains a lot! Not sure whether it would be relevant to your course materials, but I would love to find a video tutorial on J/P Fets & N/P channel MOSFETS in circuits.

At 20:30 or so I realized I'm still dropping '-' signs in math, which I had a problem in EE school... LOL Thank you for sharing the maths exposition.

Thanks.

Its fantastic! I want more :)

This is fantastic! I'd love to have the full course. :D

thx for sharing ;)

That´s a masterclass! Thank you so much. How would you go about implementing a FET (or MOSFET) transistor ladder? Would it be even possible?

Great!

Hi Mr Lanterman, thank you so much for sharing this with us, this is exactly the content that helps me understand more about these circuits. I'd love to take part in one of your classes - have you ever considered doing some sort of online class? I've got an EE degree but I found that many of the essential stuff for music synthesis is not tought anymore in todays classes, sadly! I'd totally help fund you via patreon or direct donations if that would enable you to put more time towards recording videos like this one. Once again, thank you so much for this valuable content!

i'm not part of your class, but thanks a lot, that was interesting :)

Hey Aaron, I really appreciate your video. If you could explain, im curious why when you do the small signal model of the half circuit, you choose to call the emitter of the input BJT an AC GND. Wouldn’t that pin just be floating because the current source would be an open circuit?

This is fascinating, I would seriously consider moving to Georgia state to take courses in analog synthesizer design.

Very well explained👍could you please explain how that pnp with its base grounded converts a vairiabe voltage to a variable current?

The diode-connected transistors in the TB-303 make me wonder if it would be possible to rig up a ladder filter with ganged potentiometers such that one extreme is fully diode-connected and the other is like the classic Moog design, a kind of mooginess control.

To manufacture analog equipment , the Design process can NOT use the approximations assumed in 11:10/35:06 r]pi , r]o = infinite. 1st stage design uses r]pi-type , r]o-type at I]bias -type - - -testing of the circuit becomes CRUCIAL to eliminate the many units that are faulty. A more refined design uses hfe]LO ,hfe]HI values AND - - - most importan transistors hfe must be measured REPEAT ONLY hfe]measured !

At RPI I saw the same capital/lowercase bias/small signal notation used in ECSE courses.

fantastic! now I can finally start to understand how the ladder filter works! I've always wanted what the circuitry is actually doing so I can start making some of my own and- *wait what the hell is this guy talking about*

Behringer has an implementation of the 904B high-pass out now. I assume that they have lifted the design straight off.

Thanks a lot, professor. You made it really clear to me, but still, looking at the equations, i don't get why we can't just replace transistors with resistors? And why won't that be Ibias dependent? In fact, increasing current through simple RC filter can also change it's cut-off frequency to some extent, am I right?

I'm not your student but I wish to send you a cute kitty for sure. thank you

Stumped - is there a video series of the full course?

I am not sure how, but your presentations appear to be unclogging a forty-year 'wtf! Transistors do what? & how? hole flow wtf? you're kiddin' me.." that sort of deal seems to fade each view. It is actually since 1969 when Wendy Carlos' "Switched-on Bach" blew my brain apart to want to learn how this works...... Now, a 8 stereo/2x8 mono inputs by same outputs VCA cross-point Matrix Mixer forces me to understand so I can build it and be able to route anything to anything at will, something I missed on the Buchla racks available to me for 10ish years back then. Thanks!

awesome job. however, i did improve the Buchla wave folder / timbre ... not being a professor. my profile has a video of it. this drawing from Robert looks a bit different. www.synthfool.com/docs/Moog/modular/moog_904b.gif

course, quokkas produce the least cute sound on the planet sounds like a cackling witch from hell, even more unnerving from 20 feet up a tree.

I think I saw The Roots Of Unity open up for Living Colour in the 90's

You have to be slower and more detailed on math expressions. And explain every expression's member. That is most interesting and complex part.For me it looks greek.