ECE4450 L27: Buchla Lowpass Gates (Analog Circuits for Music Synthesis, Georgia Tech course)

[@stefansynths]

Your videos are a valuable resource to the DIY synth community! No one else does it like you!

[@jrodrigo1984]

Sir, you and Georgia Tech are doing a great work with this series.

[@Lantertronics]

Thank you for your kind words!

[@Tofu_Pilot]

Holy crap! For the love of all that is good, do so many of these. More! Please!

[@LenPopp]

I would love to see more lectures in this series. I've started making my own Eurorack synth, and I wouldn't have felt up to doing it without these videos.
Topics I'd like to see would be:
- coverage of more of the usual synth circuits, e.g. ring mod, noise, s&h
- how patch storage and programmability is done in analog synths
- analog drum machines

[@Mogwai06]

me too and so am I! good luck, brother!!

[@suitandtieguy]

Listening to this for the 20th time to try to get my head around wtf this thing does.
Thank you for your service!

[@Tofu_Pilot]

Gonna give us a 5U LPG, STG? You rock!

[@suitandtieguy]

@@Tofu_Pilot thanks for the kind words but if I do it will be a while

[@Meska_Statik]

yep, we whant more :)

[@krishna34674]

Please do more!

[@u-n-i-versus]

Yes please, do more of these. Unfortunately there are no classes like these where I live. Thank you professor for these valuable series

[@Lantertronics]

Will do!
There's no classes like these where anyone else lives either, because none of those places have anything like me. ;)

[@u-n-i-versus]

@@Lantertronics Haha, agreed ! Good thing we got the internet so that these teachings can spread all over the earth! Happy celebrations and Greetings from Greece

[@duckythescientist]

I was curious about the 220pF capacitor, so I threw the circuit into LTspice. In low-pass mode, the only difference I'm seeing is that it makes the response slightly flatter with about 0.7dB less of a peak (1.3dB compared to 2.0dB with R=200k).

[@Lantertronics]

You've largely confirmed a hypothesis of mine, which is that 220 pF cap is really intended to do its thing for the "combo" mode and just happens to tag along in the other modes.

[@torigurafu]

I'd be really interested in an analysis of different ring modulator/four quadrant multiplier circuits. Particularly the Buchla one with vactrols.

[@Lantertronics]

I've built that circuit (the one from the Music Easel). I've never fully wrapped my head around how it works. It's somehow using the response of one vactrol to linearize the other.

[@torigurafu]

@@Lantertronics Wow, that sound wild considering the variance/tolerance of vactrols.

[@charliehoyt9377]

I understood about 1/4 of this video but I watched the whole thing and now feel far more prepared for my concert on Jupiter. 👏👏

[@commanderkoen]

Yes please more of this. Your video's inspired me to start designing my own stuff and saved me from a lot of boredom during the lockdowns.

[@addictive_noise]

Thanks a lot! I'm actually trying these circuits since a few weeks using DIY vactrols, and this theoretical background is a real eye-opener!

[@NicolasGasnier]

Hi Aaron, thanks for putting this series of lectures on youtube ! This is really really interesting and I have learned a huge lot on analog synthesis. If you have the time, maybe a topic on analog organs would be much appreciated : from the sound generator to frequency dividers, registers and shapers (I have the eminent 310 in mind for example).
Regards

[@alfonsosantimone]

Nice stuff as usual Aaron! Keep 'em coming when you can! thanks a lot

[@galchinsky]

Just finished watching this and the guitar course. This was huge. Thank you

[@jstro-hobbytech]

I love how we have to assume ideal but in practice it never is a 1:1 result.

[@TheForestHedgehog]

Wow! I definitely want more. May be you be interested in Serge triple wave shaper based on Norton opamp? It's a bit esoteric circuit that I've been interested in analysis.

[@Lantertronics]

I'll do one as soon as I understand it myself.

[@TheForestHedgehog]

@@Lantertronics wow cool :))

[@funketude]

More. We demand more.

[@_indizivel]

Please keep up this great content!

[@RayMcNamaraMusic]

These are amazing lectures. Keep it up!

[@milestune9428]

wow! Thanks for putting these up!

[@Lantertronics]

You are welcome!

[@FloydAtema]

Loved it!

[@shean4]

More analysis like this please :)

[@ianbaxter3905]

These lectures are such a wonderful resource. Thank you for being so generous. I did wonder did I understand right - that in 'both' mode it's just a passive r-c filter?! Like a vactrol controlled tone pot?

[@Lantertronics]

Yup, it's a two pole instead of one pole on a tone control on electric guitar, but it's really just a two-capacitor passive RC filter.

[@Linguae_Music]

Thank you Aaron

[@AMTunLimited]

Fun fact: the term for a brand that has turned into the name for everything of it's type is a "genericized trademark"

[@Lantertronics]

I liike it!

[@massimookissed1023]

There is another term: _"genericide"_
where your brand name becomes the generic name for the _thing,_ and it becomes impossible to renew any trademarking on that name.
Google is worried that the verb _to google_ could become the generic word for Internet searching,
and Lego comes down like a ton of plastic bricks on anyone using the name Lego to describe non-Lego plastic interlocking bricks.

[@AjinkyaMahajan]

I thought Music Synthesis was purely digital after the birth of MIDI using custom ASICS, timers, Waveform shapers, oscillators, DSPs. As of the analog side, only data converters like ADCs, DACs and OTAs were used. It was a great addon to my knowledge base.
Is there any book or other resources to refer exclusively for Analog circuits for music application??
Also, please cover Lock-in Amplifiers in a future video.
Cheers ✨✨

[@Lantertronics]

Alas, lock-in amplifiers are an RF thing and beyond my current areas of expertise.
As far as books go, I recommend finding a copy of "Musical Applications of Microprocessors" by Hal Chamberlin. It has an excellent chapter on analog circuits.

[@AnalogDude_]

3,150us$ and 2.800us$ for a pedal ... that's madness, not?
Pluto, hahaha ... that made me laugh.
Yeah, i would like to know the the importance of tuning a filter, what's the goal of tuning? how does that relate to 1Voct.
Would you do a video on that?
Wish you would have been my teacher, it's a pleasure to listen to you.

[@Lantertronics]

Heh, yeah those prices are crazy. You should see the prices on a Yamaha CS-80! It's like old guitars; they're that price because they're old and rare. You could buy modern clones much cheaper.
In the case of tuning the filter, it's largely for predictability, in particular if you can tune the filter cutoff to a 1/v per octave standard (or whatever the standard is) to match your oscillator, the filter can track the pitch so each note will have a similar harmonic structure. Regarding a video, the one to watch is my video on exponential converters:
th-cam.com/video/ZWJhApUmfEU/w-d-xo.html
As always, thank you for your kind words!

[@AnalogDude_]

@@Lantertronics lol, i have watched that before and that's the one i have in front of me right now.
at my school i was among the best in maths and physics, but that was some time ago, it's like starting over again.
wiki: baby.
however, you would love the pcb's i design.
did you see that video the TH-camr: Fran published a few days ago on transistors from the 60ties?

[@Lantertronics]

@@AnalogDude_ I haven't seen her video yet but I'll check it out; I love Fran's videos.

[@AnalogDude_]

@@Lantertronics These guys where absolute hero's in my view.
How do you come up with the idea? that adding impurities to Germanium or Silica you can create a (semi) conductor and come up with the mask design of a transistor.
even the idea that you can grow crystals! ... by pulling a rod.

[@AnalogDude_]

​@@Lantertronics Hmmm, professor, how much current can you pull from a TL072 ... and a CD4000 series IC, since they pretty much source power / current from the internal power rails albeit via transistor's / FET's it should be limited only by the power supply of the circuit, right? i often use a certain circuit "made" by Don Buchla and I'm really curious to know how much power you can pull with a opamp, at home i use the Mitsubishi M5218A ... and if I'm correct they should deliver 20 mA.
i got one for ya.
Korg_700s_Service_Manual.pdf
Would you do a video on this Filter? it's different than all ... and it sounds cool.
mylarmelodies: Vintage Synth Lab VCF-74 Eurorack (Korg Minikorg 700s) Filter Demo
th-cam.com/video/Z_Bec49So5E/w-d-xo.html

[@dr.feelicks2051]

Sola powa’d lasa beam gitaw✌️

[@jstro-hobbytech]

We would be best friends if not for the 2000km between us. I play at this stuff but you own it. You need to record some original music Dr Lanterman. You play guitar as well. I like adding snobby progressive riffing to the whip whoops haha

[@cjvanstraeten1169]

Nice videos i like it how you explain different items ..but the thing i miss is a lecture about the resonant potentiometers on filters ..how is it possible to create these squitchy sounding filters and when do you get this ..resonance i know ..like Xc is equal XL but how does it work in analog filters in synth ??..thanks for sharing your knowledge

[@Lantertronics]

If you have capacitors and inductors you can get a resonant circuit -- but if you're restricted to just using capacitors you need to use active elements to get resonance, basically via feedback. I have a couple of videos talking about the kind of sound you're talking about. One about four-pole filters:
th-cam.com/video/DRWZ39ae2_k/w-d-xo.html
And another about two-pole filters:
th-cam.com/video/f8ITRgPgzmY/w-d-xo.html

[@kvfleckenstein]

Is your class available online?

[@AnalogDude_]

in the case of PWM'ing a led what frequency would you suggest?

[@Lantertronics]

Usually your best bet is just to go with the defaults in whatever microcontroller library you are using.

[@AnalogDude_]

@@Lantertronics hmm, micro controller, somehow misses the point of a analog synthesizer.
i haven't programmed a micro controller for something like 5 years or so. accept a hello world thing in a arm32 bluepil, not so long ago.
it kinda sucks, 3v333 hardware and
scaling down a 10 v.p.p. signal. haven't looked into that yet.

[@Lantertronics]

@@AnalogDude_ Ah, sorry, I didn't realize the context of your question. If you're using an analog signal to drive the brightness of an LED you can just drive it directly. PWM is only really necessary when you're driving it with something fundamentally digital.

[@AnalogDude_]

@@Lantertronics there might be a way to achieve this without "software", have to look into that. will keep you updated. currently i don't have a multi meter, mine died.

[@Lantertronics]

@@AnalogDude_ Check out the various circuits Buchla uses to drive the LEDs in Vactrols; you can just use them to drive regular LEDs.

[@Mogwai06]

@ approx. 15 minutes in, when its stated that Buchla very likely added the first stage (opamp and the two 15k resistors) in order to keep the 'LPF' and 'Gate' modes from being too jarringly different, does that mean that the gain of 2 thats added was basically to bring the 'Gate' mode level up closer to the level of the 'LPF mode' output?
As in if you were switching from using the 'Gate' mode and switched to the 'LPF' mode, the 'LPF' mode output wouldve been way louder?
I hope that makes sense. thats what i think you meant anyway. thanks!

[@Mogwai06]

my bad... i got a horrendous habit of asking questions in the middle of a video because ill totally forget what i was going to ask or to even ask at all

[@jstro-hobbytech]

What's your opinion on the whole Klon diode thing. From its worth to you as a guitar player and as a scientist minus perceived (or otherwise) historic worth. I personally think the klon is overrated but I like a more 1994 cynic, Paul Masvidal sound.

[@Lantertronics]

The idea that there's some special batch of 1N34A Germaniums that Bill Finnegan found is kind of absurd. There's silicon based Klons that sound awfully close to the Germanium Klons, given adjustment of other things in the circuit so the diodes kick in at the same point. The main interesting thing about the Klon is the way some of the undistorted signal is mixed with the distorted signal.

[@jstro-hobbytech]

@Lantertronics thank you for the level headed answer that I couldn't have said better myself. There's a whole channel I found dedicated to it and the guy has no ee knowledge at all. Spends a fortune on diodes and gear but never shows a schematic, waveforms or any empirical data of any kind but has a ton of subs.
I just sold my spark amp and regret it now because I'd like to have done a teardown. It's the best practice amp ive ever had but I got a helix for free and I just run it into my 2.1 jbl studio monitors now. The hunt for tone has never been a concern of mine as I've always dedicated my time to being able to play what I hear in my head. It took a long time. I'm 44 and I can confidently say I'm there without any bs or boasting. I'm going to record an ep soon with a cover and 4 originals and never release it. I plan to pay a professional engineer to take the compositions and reamp and master them as a gift to myself. A buddy is going to play drums and add some diy synth from circuits we love. I'm going to cover "US and Them" or pigs from the animals album with a tasteful combination of shredding and synth in lieu of vocals. Haha. The cover song will melded into the ep as it's going to be one large piece of music. I'm going to try to get one of my favorite musicians to contribute a few riffs. He's not super famous so it can't hurt to ask.

[@MoraFermi]

A question from an interested by-stander: Is there a way to approximate a TCA with a normal op-amp?

[@Lantertronics]

I assume you mean OTA? Alas, there's no way to approximate an OTA with an op-amp. You immediately run into something like a parameter mismatch error in computer programming: the OTA has 3 input pins and the op-amp only has two. There's a "programmable op amp" with a 3rd input pin for changing slew rate -- that's not an OTA, but is an interesting chip used in the filter in the Polivoks, but that's a specialized thing.