Classic 2 Op-Amp tri and square wave VCO - DIY Modular in a Week 1.2

[@cl3mens]

Thanks for this series! I built this circuit yesterday and got it to work fine, the expo converter does it's job. However, there seems to be some limitation built in as 5 V seems to be the maximum CV, so you get 5 octaves. Anything over 5 V just gives me the same note (rough C). It tracks across these 5 octaves but not too good between 4-5 V. I am sure I can fiddle around a bit more with the trimpots. Note to anybody else building this: DO USE a tuning pot as suggested (I connected a 100K pot as a voltage divider over my +9V and -9V rails.) I struggled a lot prior to adding that and just using CV from my keyboard, getting the scaling right but being slightly out of tune. I also added a simple BC547 amplifier to the triange and a 68K resistor to the square output and then a 22K to ground (the output signal is in the junction of these two). Made it play nice with the levels in my minibrute.

[@nicholasrichardson102]

curious what you figured out? I'm looking at building it with a different lin/expo converter to try and avoid this limitation but, having to redesign it because it has no hi freq trim ( I suspect this will be needed on this VCO)

[@jj74qformerlyjailbreak3]

I’m going to be up for days. Soon as amazon and micro-center get here. Tuesday Only thing I need now is an Oscilloscope Great stuff.

[@rautshsale1948]

after looking into this series, this seems to be the most comprehensive out there to build a basic complete system for relatively cheap. i just don't want to take an electronics degree before i start lol but feel like some basics would be a) useful to follow along, b) might make it easier to understand what it is that we are building (as opposed to blindly following instructions) and c) if/when something goes wrong, i'd have somewhat the ability to at least troubleshoot. but then again, every general electronics beginners video goes into so different topics, where i wonder if all of it is necessary to build modular. all this to say, what do you consider the absolute basics that one should know/learn before starting with this?

The thing is I learn as I go along aswell and some videos where I had an epiphany I talk more about the ins and outs and how the circuit works. And sometimes I just build it and see if it works. I talk a lot about that it is the mistakes you learn from and you will notice if you just start building that you will learn. You will learn while just sitting there watching schematics after schematics with all the same building blocks. And after a while you understand the difference between them and thus understanding the anatomy of the circuit. :) I would just jump in there. 😁

[@hoodiedude4204]

Awsome! But I would build a voltage controlled LFO instead an of a VCO with this. Its linear, doesnt have more than max. 5 octaves of range. Its really easy to mod this circuit to do Saw, reverse Saw, and PWM. it makes for a great LFO

It is done in one of the later episodes. So yeah. Good idea. :)

[@bondjovi4595]

Really great video. Lots of good info.

[@nicholasfaith8999]

Trying to adapt this for strip/Vero board. Do you know if there are any layouts for this for 12v (+/-)?

[@ottootto6396]

Hey, thanks a lot for the series! Made some of the other modules and they all work well. I just finished this one and it seems that the square wave isn't working. I am feeding it some square waves from the 40106 from a previous episode, but I just get a very quiet and really high pitched sound that does not react to me turning the pot. It does change a bit when I turn some of the pots from the 40106 (strangely also the pots on the outputs that are not connected). Triangle wave works fine and I am getting some cool sounds, but yeah.. missing the square wave. Any tips what to look out for? I just built the vco part and the input adjust. I double checked all the connections and tried different LM358's, but nothing seemed to help. Will probably make a new one tomorrow and see if the problem prevails. I am planning to build the exponential converter as a separate module with just an input and an output so that I can use it for other vco's too. Do you think that would work?

One of the biggest mistake people including me did with this module is that one opamp is powered with plus and minus and one is powered plus and gnd. Check that first. The square is created with a comparator so check that opamp so you have a threshold voltage. And yes you can build the exp converter on itself and use with other modules. I did. that aswell. :)

[@ottootto6396]

@ While building the second one I figured out that I had mounted the transistor the wrong way around. Easy fix, so now I have two functional units. Patched up with the other oscs and my tesseract low coast I can get some pretty cool rythmic noise extratone kind of stuff. Really fun to just let it roll and see how it develops. Pretty excited to see what the next modules are gonna add. Good stuff :)

Awesome! Well if you follow the miaw series you’ll find a lot of modules that add much interesting functionality to your rig. Hope you find a few more nuggets to build. ;) share some sound and images on the discord when you have the time. :)

[@Sarahbuildsstepsequencers]

Kristian, I am wondering, does this circuit output both the square and triangle at the same time so that you could have them both outputting at once? I’m guessing so.

Yes it does.

[@copindesbois]

Hey ! i don't understand why i can't adjust frequency with the 100k potentiometer. I've done VCO, tested it with a CD40106 ( as you made in the video) but when i add the input adjust circuit, nothing happen when i turn the pot... i did exactly the same as the video.. any idea?? Thx!

[@jacksonshelton8055]

Is it essential to connect the VCO core op-amps to +VCC and GND, rather than +VCC and -VCC (dual rail)? In my experience with DIY noisemakers like a simple 555 timer oscillator, the output sounds pretty thin with just positive voltage, so I would think connecting the op-amps to a dual rail power supply (like a meanwell or other cheap dual rail 12 volt supply) would make it more suited for feeding into a recording device or amp (of course with a potentiometer as a voltage divider/attenuator on the output.) Some LM358 VCO schematics on the internet don't specify the supply method either, so I think it might work. I want to get started in DIY modular, but don't want magic smoke to appear.

It all depends on the circuit you make. This circuit uses the LM358 which isnt dual rail, and then it uses a voltage divider to create a "virtual ground" in between gnd and +12v. This is ofcourse not optimal in many cases. It could probably be made with a dual rail opamp instead. As long as the components arent too expensive, magic smoke are ok, and usually part of the game ;)

[@bashenko]

Thanks! I was looking for this video for a long time now :D

Great! Hope you like the other videos in the series aswell. :)

[@bashenko]

@ So we have this 'radio lovers club' here in Russia, and I've shared all your materials with the club. You did very great job.

[@Sarahbuildsstepsequencers]

Let’s say you use an LFO into you CV IN on this oscillator. Will it sound different if you use a triangle LFO as supposed to a square wave? Would a sine wave LFO work? Just curious.

A sine wave would modulate the pitc slowly, while a square wave “jumps” between two pitches. So yes it would sound very different. :)

[@Sarahbuildsstepsequencers]

Kristian Blåsol cool! Thank you!

[@HandsOfManos]

I'm confused, on the original circuit schematic pins 6 & 7 of the Input Adjust are connected to the 10k trim pot but it looks like on your illustration that it's just pin 7. Am I misunderstanding your drawing. Sorry if this was explained already.

[@benediktschnorr1718]

Hi, really great video! But I have a few issues: 1. Does this also work with 3V or 9V? 2. And if so, how can I connect any voltage source to the VEXPO input (without exp. converter), because connecting to V+ or Gnd doesn't work?

[@alebrenna441]

Hi Kristian!! I´m gathering stuff to start building some of your modules :) Let me ask you: The zener diodes for the coulored noise and the phobos ad/ar, how many W should they have? Also, in the Phobos, the 555 is the common one or the cmos (LMC555)? Last one: There´s a cap value missing in the excel file in the simple LFO, there´s 10nF, 100nF, 22uF and two more without value, would you mind checking? Well, I already said it, but, thanks a lot for the work you´re doing! It´s awesome!! Hope you´re comming with more MIAW soon!

The 555 is CMOS leveled I believe yes. The zener wattage is around 1w I think, just the normal cheap ones. I think I have fixed this compnent error before? I think you can ignore those. I have to check the schematics again, if unsure you can also just skim through teh schematics, there werent that many capacitors...

[@keithbuckel8399]

In the diagram at 12:03 what is the component you have coming out of pin 7. If its a trim pot, can I substitute for a fixed resitor?

[@guilhermeplatzer]

No.. this is to fine adjust the signal, a fixed resistor won't let you adjust the signal (so you will get a tuning issue)

[@alicewyan]

Those are nice stripboards! Where do you buy them?

[@guilhermeplatzer]

Thanks for the videos! I assembled this, but in low frequencies, the square wave loses its square shape. Do you know what can i do?

[@SomeOne-pd6vm]

that's normal for analog VCOs (: both my Mother 32 and my Korg Minilogue XD do this, as do almost all other analog synths (but I only own those two)

[@leonidgribanov8930]

First of all thanks for all the tutorials! I've built this VCO, however, I have a problem that only when connecting jack to the triangle output, the signal disappears (when connecting oscilloscope instead of jack it shows up normally as a triangle). Any advice on what might be the problem?

Did you add the buffers in the circuit? Without those the I put of other module might draw too much power. And of course power to the buffer opamp.

[@qualmos]

Hello thanks for this video. i am a newbe when it comes to electronics at this level. I have only tried to build the vco-part. I can't make it work. I have used constant DC to feed the vco. Just to hear a tone. Question: do you need the VEE if you only are going to do the vco-part? Thanks in advance

Did you make the voltage divider? It is important for the oscillation.

[@tuomasmaki3427]

Hi kristian Great videos and tutorials :) I am newbie with all about electronics, but maybe i can built some moduls whit these instructions. My question is: I made earlier a power supply by thomas henry desing and it is - 15v gnd +15v. Can i use that with these moduls or do i need 12v version?

Most of the modules should work with 15v. Just check all ics so they can handle 15v if you use 15v and ground or if you use dual voltages that they can handle 30v. Some pots might have dead zones as the voltage is outside of the voltages that affect the sounds.

[@spot2028]

Getting started on this. Do you have any thoughts or tips on the thermal coupling of the transistors and matching them? And, in the whole scheme of the overall system, do you think it is worth making the exponential converter section? Reading the comments and watching your other video it seems a bit of a hassle. Thanks!

If you want to use any other kind of mainstream commercial product to control the vco ie a sequencer then you need the exp converter. Actually it isn’t that complicated. I made it complicated by doing all the “parts” on different pcbs. I did another one on a single pcb and that was fine to work with. Tuning it is still a hassle of course. I didn’t care about the thermal coupling and matching. Maybe that should be done but for my needs right now it wasn’t worth the work.

[@spot2028]

@ Well then, I have the parts, so I guess I'll be building the whole thing :). Would you happen to know if it's difficult to convert midi to cv? I guess I mean "build-able?" I have seen midi to cv units for sale for not too much. But I really enjoy making this stuff! Thanks so much!

First. Check in the panels folder for the 1.2 panel with the looong name. That will give you an idea what you can do with linear and exp cv in (no cv amount on exp in) and lo/hi (lfo). Also I will make a midi-cv module aswell. Look at the page of Niklas Rönnberg (find link in colored noise or AR videos) his midi interface seems great!

[@spot2028]

@ Awesome! Will do, thanks so much!

[@spot2028]

@ Ok, sorry to keep asking questions. Please understand I'm on a pretty steep learning curve with this stuff!! After looking at the panels, I have two main questions: 1) What is the difference between the Rate, Frequency and CV amt pots? Are they in the schematics or are they mods you put in? 2) Are the Linear and Exponential CV in's just the inputs shown on the Input Adjust schematic? In other words, both inputs go into the LM358 per the schematic? Thank you very much!

[@gauravsharma5601]

I am actually trying to simulate your VCO part on proteus ISIS but I find very less amount of voltage drop just beyond the capacitor point. Has anyone got the idea ?

[@petercarlson3271]

where did you get the jacks from for so cheap. all I can find are ones for around $2 each

You can actually buy quality jacks from thonk.co.uk called thonkiconn which are almost standard in all modules today. If you buy 50+ you get them for 0.21£ which is a good price. If you want even cheaper I found similar (but stereo and not breaking) on lcsc.com for 0.08$ if you buy 50 or more. Those are not as good quality though but they work. They are a bit “stiff”. Hope that helps.

[@vullematti4447]

Everything's working for me, except buffers, which is quite sad since I can't build the rest without buffers (Things on the output changing my pitch) ://

That is strange. Buffers are really simple circuits, and not much should be able to go wrong. Check so you have power to the opamp. And wiring of course. And one last thing could be a faulty opamp. So except those three I dont know what could be wrong. Hope it helps. :)

[@vullematti4447]

@ Double checked all of these haha, do You think it could come from my single rail 5v supply ?? (I didn't made the exponential part, only the VCO and the Buffers)

It depends on what opamps you use.

[@justinharris1199]

what cap did you use for C2?

[@AdamTheAd-vanc3d]

For some reason this expo converter never worked for me ???.

I have just built it. I haven’t calibrated it. But now I have a multi turn pot so I can try. I’ll try to get the time to test this tonight.

[@AdamTheAd-vanc3d]

@ Ok kool be intresting to see how you get on with it. The circuit topolgy looks similar to other expo converters . Maybe i just needed to tweak some values here and there. Currently im ising the Roland jp8/system 100 style expos with really good tracking up to 8 octaves +.

So I got it to work. But I am NOT good at tuning this. But the functionality is there. I’ll do a live video tonight discussing this and going through a few things I did to this Vco.

[@AdamTheAd-vanc3d]

@ Ok brilliant . I can only think you may have to tweak the ie: swap trimmer value i had to do this in my expo converter. kzbin.info/www/bejne/fKrHmImiaLRgd9k . It looks more complex but the basic topolgy is the same. What time will you be going live . I will look out for notification . Also see kzbin.info/www/bejne/jHS4e4efj7ODf8k

Sorry for late reply, because of bad sounds in the live sending I did a quick video instead, which you can find here: kzbin.info/www/bejne/ZonMZGiMr7iMl9E

[@gabrieldai2]

can it be hard synced?

[@alb2935]

Thanks so much!

[@aabs7978]

Please connect the circuit to the potmeters.

[@TheBishoptutu]

Hi Kristian Who does the screen printing for your face plates you use, are they available for purchase. Nothing worse than a crappy looking deck.

There is a Dropbox folder associated with the MiaW and all panels are there. (Link in every description). These can just be sent to a laser cutting firm that can cut these out and etch them for you.

[@TheBishoptutu]

P.S. Love your vids

[@JurekPrzezdziecki]

Using Vref based just on a voltage divider is way too far from precise effect. You want to stabilize the part of the circuit responsible for tuning the frequency. You want your circuit to not drift especially when other parts of your circuit share the same power supply. Always use precise voltage reference points chip like LM4040 or REF01. More complex circuit than more problems you will get otherways.

Thanks for the info. This module was more about being “cheap” and easy. I agree it is not stable at all. I hope to find a much nicer and more stable design in later episodes. The cem3340 is always a good starting point. ;)

[@nicholasrichardson102]

@ I just built a 3340, wonderful VCO. my bench supply was having an issue (I never plug modules into my rack until I know the are safe) but, something wasn't connecting right and it was mostly making a weird hissing, high pitched noise, and dropping out/locking up when turning the knob. when I realized what was wrong its been fine.. gotta change some resistors (they were supposed to be 1% but, its not close enough to make my square symmetry right

[@wodrummer91]

Whenever I try and build this module (with the exponential converter) it always gives off magic smoke from the lm358s. Any idea why? I have triple checked all my wiring and it seems fine

all of them!? Start by checking (a fourth time) so the power is correct as some are connected between +V and GND and some between +V and -V.... U1 and U2 (input summer and exp converter (one unused)) between V+ and V1. U3 and U4 used in the VCO core should be connected between +V and GND... I have built two of them now, and although I got magic smoke from the first one, that was a pot that I had connected the wrong way. So it does work if you follow the schematics. Error checking is 90% of the work on some modules. I have spent countless hours watching my circuits, just to find I missed one leg, after checking 3-4 times?!?!?!?

[@wodrummer91]

@ thanks for the help. Turns out it is was a bad connection in the power supply