Welcome to stripboard heaven! Here you'll find all the projects I used to build my DIY Modular Synthesizer. I'm using the 'Kosmo' size standard but I also build Eurorack sized modules. All layouts are made by myself and verified to work. The schematics they are based on come from all over the internet. If you're on a PC or MAC, there's a complete MENU in the sidebar. For mobile devices the menu is in the black 'Move to...' bar below this text.
An easy to build clock divider or binary counter with 5 outputs. A simple project and one that was missing from my collection of projects so here it is. For Eurorack or Kosmo.
This is a design from Barton Musical Circuits. With all the projects I have built so far I never built a Clock Divider. So I thought it was time to build one. This is a very easy to build design and I had it up and running within 2 hours not counting designing the layout.
I kept the layout quite thin and long so it can fit behind a small faceplate like a 4hp Eurorack panel.
Below is the schematic for this design, pretty straight forward. You have a TL072 dual opamp comparator with a fixed 110 mVolt signal on the inverting inputs and the clock comes in on the non inverting input. Any signal on the non inverting input higher than +110 mV will flip the comparator to high creating a pulse of +12V on pin 1, the output. That is then brought down to +5V by the voltage divider made up of the 120K and 100K resistors. That's why, if you want to run this project on +/-15V you need to change the 120K resistors to 150K resistors to keep that voltage the same.
The CD4024 binary counter/divider chip is then fed with that pulse on pin 1. It divides the input and presents it on the 5 outputs with every negative going pulse slope. The same happens with the second opamp when it is fed a Reset pulse. As long as the Reset input is high the divider will stop working. It will only start running again when the reset input goes low.
Because the input signal goes through an opamp comparator it doesn't matter what type of signal you use on the input. The comparator will change it in to a useable pulse wave.
You can actually clock this module with an audio rate signal, like any wave from a VCO and so use the divider as a sort of sub oscillator. (It will output a pulse wave). Each output will be an octave below the previous one.
Make sure you get your CD4024 from a reputable source. I couldn't get this circuit running at first but it turned out my CD4024 was a cheap fake from AliExpress or some such website. So be warned!
Here are the layouts I made for this circuit. As always the are verified:
Wiring diagram:
You can add up to two more steps to the clock divider because the CD4024 has 7 output pins. So you can add a /64 step (to pin 4) and a /128 step (to pin 3) if you wish. To do this all you have to do is run wires from those pins to two more sockets an LEDs making sure to solder in the 1K resistors. You can connect those resistors straight to the sockets and the LEDs. Make sure each connection has it's own 1K resistor otherwise you're going to pull down the voltage. For instance if you tap the LED off straight from the socket you're going to pull the output voltage down considerably. Look at how it's done on the layout and copy that.
Stripboard only:
The voltage regulator is there to feed the CD4024 with power. The CD4024 can be fed with anything from +3V to +15V and the voltage it is fed with also determines the voltage of the pulses it outputs. In my case I wanted my pulses to be a bit higher in voltage than +5V so I put in a 7808 voltage regulator that outputs +8V. You can also leave it out and feed the CD4024 with +12V but then your output pulses will also be +12V.
You don't have to include that ground strip at the bottom right. You can connect the ground lugs of all the sockets together with one long copperwire and then connect that to a ground point on the stripboard with one wire. That way you can keep the bottom strips free for mounting the board behind a faceplate, like I did (see further down).
Cuts and wirebridges seen from component side.
Mark the cuts with a Sharpie or Edding marker and then stick a pin through the marked holes and mark them again on the copper side. Now cut the copper strips at the marked positions with a sharp hand held 6- or 7mm drill bit.
And finally the Bill of Materials:
OSCILLOSCOPE SCREENSHOTS:
Here's a look at the signal coming out of the TL072 comparator (pin1). A nice big bi-polar squarewave. (Btw, I'm feeding the input with a triangle wave of +/5Vpp):
After this signal has gone through the diode it's been rectified into a positive squarewave:
After this wave has gone through the resistor(s) it goes into the clock input of the CD4024 with a voltage of 0 to +4.8V.
The picture below shows the amplitude of one of the outputs:
BIGGER VERSION:
I made a second layout for a clock divider with more outputs re-using the old layout but I put in a CD4040 chip. The chip is mounted upside down from what we normally see. Pin 1 is situated at the bottom right. This will give you divisions upto 1024 times (12 outputs) but the layout is not verified!!
I had confirmation that the layout does work, but it's not perfect.
You have to mount the 1K resistors straight to the sockets and LEDs otherwise the stripboard would get too big. I've had feedback that the output voltage is much lower with this design so use a 7808 voltage regulator. The CD4040 needs an inverted clock pulse so you need to put a transistor before the clock input. See schematic below. Make sure you use IC's from a reputable source, not from AliExpress.
Below is the schematic of a 12 step clock divider. I tested this setup on a breadboard and it works fine.
This is a different schematic than the one used for the stripboard layout in the picture above and that caused some confusion so I have now made a stripboard layout for this schematic too.
Here's the layout for the schematic above:
The manual switch progresses the clock one step per push. You can leave it out if you wish. I don't see the use of it but it only needs a switch and a diode.
I have put in one output stage as an example. Repeat those 11 more times for all the other outputs. The diodes in series with the 1K output resistors are BAT43 Schottky diodes. I didn't design this circuit so I don't know why they are Schottky's and I think 1N4148 would work just as well. I'm not sure why they're in there at all come to think of it. I think it's to protect the chip from reverse voltage.
This layout is NOT verified because I didn't build it using this layout. Only on a breadboard so the circuit does work, I know that. Please let me know if you built this layout, if it works so I can verify it.
I have had some feedback recently which showed some problems when running this at high speeds (as a sub oscillator). I suggest grounding each output by connecting a 100K resistor from each of the 12 outputs to ground. These outputs shouldn't really be left floating. Connect the resistors after the diode at the output sockets. With thanks to Neil for his feedback on this matter.
PICTURES:
Here are some pictures I took during building. The stripboard in the pictures may differ a little from the layouts because I later tidied up the layouts and put the components a bit closer together.
(My stripboard has one strip more than is shown on the layouts.)
I tried to keep the stripboard as shallow as possible so it can be mounted vertically behind a Eurorack faceplate with a depth of about 4 to 5 CM. In my personal case I built it for my Kosmo DIY synthesizer so I made a faceplate that is 2 CM wide and 20 CM high. The depth came out at 5 CM. There is room at the bottom to drill some holes to put in L-brackets to mount the stripboard behind a panel. I soldered the stripboard straight to the switch lugs of the sockets I used. Making sure the connections between each lug were broken and nothing made contact with it, not even ground.
I mounted the stripboard behind the faceplate by soldering the stripboard to the switch lugs of the sockets I used. The bottom 2 strips are not connected to anything. Make sure when you do this to break the contacts between the different sockets otherwise you will get in trouble. With this method my module came out at a depth of exactly 5 Centimeters.
(The soldering in this corner looks a bit 'how yer doin' but that's because things were soldered, de-soldered and re-soldered again. Believe me, overall the soldering is very neat. I've been soldering since the early 1980's. I know how to do it ^_____^ )
Here's a look at the finished module. I built mine in the Kosmo size because I already have one for my Eurorack setup.
I used a big voltage regulator because that's what I had in stock but you can use the smaller 78L05 or 78L08 versions in a TO92 package, like a transistor.
As you can see I bent the regulator over so it won't stick out at the side.
VIDEO DEMO:
Here's a little video I did while testing the module.
Okay, that's it for this one. A small project but one that was lacking from my website until now. This is a module that every synthesizer needs especially for drum related patches. If you have any questions or remarks please put them in the comments below or post on the special facebook group for this website.
The triple sloths by Nonlinearcircuits is a chaotic modulation source. It has 11 outputs that produce slowly changing voltages that follow a chaotic path. Great for generative patches and ambient music.
The module will fit in a Eurorack Nifty Case. I also made a layout for Kosmo sized modules.
This is a module I wanted to build for a long time and I finally got 'round to building it. This module produces random control voltages. We have 3 boards, Torpor, Apathy and Inertia. Torpor has the fastest changing voltages. It takes about 15 to 30 seconds to travel around 2 strange attractors, if you watch the plot on an oscilloscope set to X-Y display. Apathy takes about 60 to 90 seconds and Inertia takes about 30 to 40 minutes. Sloths cycles but it never repeats itself! It evolves.
Torpor and Apathy both have a potmeter. The potmeter doesn't change the frequency as you would expect but it changes the tendency of the waveform to be attracted to one or the other attractor. It nudges the waveform in a different direction you might say, that's why I labelled the potmeters 'Nudge'.
Inertia doesn't have a potmeter or a CV input. It just does it's own thing.
Torpor and Apathy have CV inputs, Most of the time a CV input signal will be added on top of the output signals of the module but it can also have the effect of changing the path of the voltages.
You can use an output from one stage to input into an other stage to get even weirder voltage paths.
We have an X, Y and Z output for each stage. Each of these outputs are taken from a different part of the circuit and the Z output is simply the inverted version of the Y output. The two extra Z outputs at the bottom are made up like this: V (Z3+) = Vz Apathy + Vz Inertia - Vz Torpor if greater than 0 otherwise it's 0V.
V (Z3-) = Vz Apathy + Vz Inertia - Vz Torpor if smaller than 0 otherwise it's 0V.
Beware that the voltages summed together can add up to + or -10V so attenuation on those signals would be a good idea.
The X outputs are the lowest in voltage. They stay between +/- 2.5Volt. It will cycle around the 0V line.
The Y outputs vary around +/- 5Volt. They will stay positive for a while and then go negative for a while.
The Z outputs are the same as the Y outputs only inverted.
With testing the Sloths on one board, I found the X output voltages of the Apathy and Inertia circuit much higher than +/- 2V. So I tried putting in voltage dividers but when I then mounted the board behind a panel the X voltages were suddenly too low. Really puzzling.
I ended up taking out the 1K resistors to the X outputs of the two problematic circuits and putting in 10K trimmers on the copper side. That solved the problem because I can now dial in the voltages from the X outputs. I connected pin 1 of the trimmer to pin 1 of the TL074 (the signal source). The wiper of the trimpot went to the X output strip and pin 3 of the trimmer went to ground which is the strip below the output. See picture below.:
LAYOUTS:
Below are the layouts I made for this module. As always they are verified. I used them to build my module. We have a stripboard for each of the three stages and one for the extra two Z-3 outputs that mix the Z outputs from all 3 modules together.
Here is the overall layout showing all boards (Kosmo size layout further down).
[EDIT] on Nov. 6th 2024 I made a slight alteration to the layouts. I routed the LED output through the left over opamp so that is doesn't pull down the voltage of the Z output.
Here's a close-up of the two boards with alterred X-outputs, with trimmers. There was no room for normal trimmers so I put in multi-turn ones on the layout below. This will allow you to set the X output voltages to your liking.
There's not much room for the 1µF capacitors but it doesn't matter if the underside of the caps stick out above the resistors a bit as long as the leads are not touching other components. I put in higher value resistors as current limiters for the LEDs because the 470Ω ones recommended in the schematic made the LEDs shine awfully bright. I thought 1K8 would be better, and they are. All non inverting inputs (+) of the opamps in the TL074 are grounded so the strips that connect pin 3 to 12 and pin 5 to 10 must not be cut underneath the chip.
Here's the Torpor board:
Here's the Apathy board (version without trimmer on X output):
Here's the Inertia board (version without trimmer on X output):
And finally the extra Z outputs board:
You tap the Z inputs from the Z-outputs of the three boards.
I didn't make any layouts with just the cuts and wirebridges because these are such small boards that you can easily see where the cuts need to be made and where to put the wirebridges.
Do be aware that the Apathy board has an extra cut in it above the TL074 chip. All boards differ from eachother slightly so do pay close attention when working on them.
Here is the Bill of Materials. There are some very high value resistors needed for the Inertia board and I used Bi-polar capacitors on all boards so you need to order these new instead of putting them together by putting capacitors in parallel. I did leave room to do that at the top of the stripboards but it's easier to just order Bi-polar caps. I did have to make my own 100M resistor by putting ten 10M resistors in series and I used three 33M resistors in series to make the 68M resistor. My local electronics store didn't have them. I only had the 2 Watt versions of those so they took up a lot of space. I should have just used six 10M resistors in series for that one too. For the 1µF caps I ordered ten 1µF WIMA MKS box capacitors with 5mm distance between the legs. They are not polarized and work very well here although they are a bit bigger than round 1µF bi-polar caps, but it fitted well enough.
KOSMO SIZE LAYOUT:
Here's a layout I made later just in case you want to build this for a Kosmo sized setup. In that case you can have all three Sloths on one piece of stripboard and it gives you a little more space to place the capacitors too. Again I made a slight alteration to the previous version in that the LED output is now routed through the left-over opamp so it is buffered and can't pull down the Z output voltage.
This layout is also verified. I've just finished building this version too.
Use the extra Z outputs board posted above to add to this main board.
Sloths one board with extra Z outputs board. Cuts and wirebridges.
SCHEMATIC:
Because this is a kit that Nonlinearcircuits is selling to create income, I'm not going to post the schematic here. Instead I'm going to link to it on the Nonlinearcircuits website, because I don't want to negatively impact their revenue.
The link opens the Triple Sloths page and if you scroll down you'll find a green button marked 'build instructions' and if you click that you can download the PDF which also has the schematic in it.
If you do not want to build it on stripboard you can order the complete kit from nonlinearcircuits instead, with PCB's. That module will be 8hp wide. The one I made is 14hp wide because I needed more space to put three stripboards vertically behind the panel. The kit does require you to solder SMD parts unless you get a singel 4hp Sloth module which is through hole.
You can have a look at the schematic for the Torpor circuit in this Falstad simulation I made:
If you are having trouble finding bi-polar capacitors, you can make your own. Below here is the schematic for a bi-polar cap made up of polarized capacitors.
The equivalent value of a cap made like this is the same as the value of one of the polarized capacitors, provided you use two caps of the same value. So for instance if C1 is 100µF and C2 is 100µF then the equivalent value of the bi-polar capacitor you created will also be 100µF because each of the two caps is used for one phase of the signal. One for the positive side and one for the negative side.
It might be a good idea to use Schottky diodes for D1 and D2 because of their lower voltage drop and I can not guarantee this method actually works. I just thought I'd mention the option but I haven't tried it myself.
Bi-polar capacitors are used a lot in audio speaker cross-over filters, so that is one place where you can start looking if you want to buy them new. I tried to Google them and had no problem finding them online. Just use the search terms: bi-polar, bipolair or audio capacitors.
OSCILLOSCOPE SCREENSHOTS:
Below are some screenshots I took during testing. You can see the random voltages at work. Yellow is X and blue is Y. You can see that Y has a higher voltage than X. The last one shows what happened when I put a triangle wave on the CV input of the Torpor module. The signal was added on top of the voltage. The first three screenshots below were are from the Eurorack version with the separate boards.
Here are some screenshot I took when testing the Kosmo sized stripboard with all three Sloths on one board. These are taken from the X outputs of the three boards.
This is over a timespan of 2 minutes. Yellow is Torpor, blue is Apathy and purple is Inertia. You can see the voltages are not all within +/-2V so I experimented with putting in voltage dividers but that didn't work out well.
This one is the same as the one above only with a timespan of 4 minutes.
Again you can see here that the voltage of the Apathy and Inertia X outputs is much higher than the Torpor X output. I don't know why this is the case because I checked and double checked. I switched IC's etc. but I couldn't find anything wrong.
Here's a series of three screenshots with the X,Y and Z outputs of each circuit after I put in the voltage dividers but before the board was mounted behind a panel. Here's the Torpor:
Apathy X,Y & Z:
Inertia X,Y & Z:
You may notice that there's not much difference over time in the waveforms, especially the last two but that occurs over time and in very small amounts. Try experimenting with feeding slow LFO signals into the CV inputs of Torpor and Inertia. You can use one output of Sloths to go into the CV input of another Sloths.
Z3 plus output:
Z3 minus output:
PICTURES:
Here are some pictures I took when building the Kosmo version:
I made the 100M and 68M from 10M resistors in series. I put small pieces of heatshrink tubing on the soldered ends where the resistors connect to eachother to prevent accidental short circuits. Then I hotglued the resistors in place.
I didn't have a 39µF bipolar cap so I put in a 22µF (in the Inertia part) and added two polarized 10µF caps with diodes attached like I showed earlier in the article. I'm not sure if it has an influence. The capacity meter doesn't pick up the extra capacity because of the diodes but at least it is working normally.
With the 100M resistor made up of ten 10M resistors in series I added a center tap point that I connected to a copper strip that was not in use. I wanted to add a switch so I could half the resistance to make the Inertia part of the circuit work a little faster if I wanted to. That didn't work out though. It did go faster after closing the switch but the output voltage also shot up way too high. So do not replicate my experiment.
Here you can see how I mounted the Z outputs board. It is just floating. The main Sloths board is mounted by putting two sets of copperwire through the ground strip at the top and twisting and soldering them together and then soldering them to the ground connection wire or the sockets. The socket grounds are all connected together with one copper wire going through all the ground lugs of the sockets.
Here's a look at the finished panel mounted in the synth:
Below are some pictures from building the Eurorack version.
Here you can see the 'Inertia' board with the 100M resistor I had to make from ten 10M resistors in series. I made the 68M from three 22M resistors. These were big 2 Watt resistors. In hindsight it would have been better to have used six 10M ¼ Watt resistors in series.
Here are the three boards together. I soldered powercables to them for testing. When they were mounted behind the panel each board got power from the board beside it with simple daisy chained wire connections. You could use pinheaders but you'll need the extra high version.
One thing I noticed when testing, which is important to know, is this: I connected the Torpor module to my bench powersupply and it would only produce sinewaves but they weren't random. This turned out to be a fault in my powersupply. When I connected it to my synthesizer powersupply it worked normally.
Here you can see the backside of the module. Three boards tucked in together with the extra Z outputs underneath. The two outer boards are connected to the faceplate through the potmeter that is soldered straight to the stripboards. The Inertia board has no potmeter and it is mounted inbetween the two others and secured with hot glue.
Wiring these stripboards up was very time consuming. It took me almost a whole day. Because there is almost no access after the boards are mounted behind the panel, you have to solder the wires to the boards first. Put in all the sockets and ground them all. Then put in the boards and solder the wires to the sockets. To save space I soldered three wires to a Female Eurorack powerconnector and soldered the wires to the Torpor board. The other three boards get their power from the board to the left of it with again three wires. Be careful that non of the components touch the copper strips of the neighbouring boards. I put in gaffa tape and hot glue to protect some areas from short circuits.
Here's the finished module with the faceplate made with the waterslide paper method. Again I made a mistake. I forgot the two CV inputs. Well, there was room enough to put them in they are just not labeled. I called my module Sloth, not Sloths for no reason really :-D
Btw, these knobs are temporary. The ones I'm going to use are slightly larger but they are still in the mail.
When you start designing your panel layout make sure to offset the sockets a little from the potmeter positions. Don't put them straight underneath the potmeters because the stripboards will touch them. Put them slightly to the left. I did make that mistake and I had problems getting the boards to fit.
And like I said before, don't forget to put in the CV inputs. ^_____^
DEMO VIDEO:
First a little demo I filmed myself with the following patch: Sloths Torpor X output goes into the 2hp Tune quantizer which turns the voltage into random notes following a chromatic scale then the 1V/Oct signal from the 2hp goes into the Digisound 80 VCO and from there into a 2164 Lowpass filter which has the cutoff controlled by Sloths Torpor Y output. Although that didn't come out very pronounced.
Here's a little demo of the Kosmo sized Sloths in action with the Torpor and Apathy X outputs controlling the filter cutoff of the TH State Variable Filter and the Lowpass Gate.
Here's a cool video I found on YouTube explaining how this module works:
TIP: lead the output of one of the sloths (the faster one like Torpor Y output) into the signal in of a Sample and Hold to get random stepped voltages like the Turning Machine produces.
Okay that's another one done.
If you have any comments or questions about this module then please put them in the comments below or in the special Facebook group for this website. Beware that comments are moderated and don't appear until I approved them.
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A fantastic sounding VCO with 5 waveform outputs and an amazing hard sync sound! Quite easy to build too. This is a Kosmo project, not Eurorack. At least not this particular article. But this VCO will run fine on a dual 12V powersupply.
PCBs for this VCO are in stock again, with newly designed boards.
Finally a new VCO project on my website. These are always the most popular projects as I can see in the data I get from Google. And this is a really nice one too.
It's a favorite among Psy-Trance and Techno producers! I'm reliably informed by a top Dutch psytrance producer that the hard sync and FM functions of this VCO are better than that of the Nord Lead. He regards this VCO as his secret weapon creating unique sounds not heard on other albums (see demo below).
It has no less than five waveform outputs. The usual ones: Square/Pulse (with PWM), Sine wave, Triangle wave and Sawtooth wave and then there's the Rampoid wave. This is a mixture of the Triangle and the Sawtooth waves and there's a potmeter to go between the two which makes for some really cool wave shapes. See the scope pictures below.
One little side note though, this VCO is known for being difficult with tuning. It'll tune fine but the tracking over the octaves is not very precise. It's good enough to make the VCO useable of course but you will spend some time tuning and it won't be perfect. Just so you know!
[Edit: Dec 2025: I just want to add to that last remark that I just finished building this VCO using all PCB's and using a Texas Instruments CD4046 and I got it in tune over 5 octaves with +/-3 cents so that ain't half bad. I used just the V/Oct trim and the fine tune pot on the panel to get back on the exact notes and if the high octaves were a bit off I used the HF-trim, which on this VCO actually works. I also built a 4046 Super VCO with the suboscillator from the VCO Maximus and that one tuned very well too.]
When I was researching the VCF-1 filter (project 56) I found the 'Birth Of A Synth' website with all of Thomas Henry's projects on it and in the list was this VCO. I came across this design before and I always wanted to build it because the TH VCO-555 was also such a good design but also because of this VCO's famous Hard Sync sound.
The finished module.
The 'Birth of a synth' website also lists another VCO, the VCO-1 but if you look at the schematic it's just a scaled down version of the X4046 so I went with this design.
SCHEMATIC:
Below is the schematic for this VCO. The CD4046 is an interesting chip to use for a synthesizer VCO. It has an onboard voltage controlled oscillator and two types of phase comparators. The IC has been used in some very cool Eurorack modules too, among them the Wiard Wogglebug.
The 4046 produces 2 halfs of a sawtooth wave coming out of pins 6 and 7 depending on the state of the VCO output of the chip (which is a squarewave). When it's high, pin7 is ramping. When it's low pin 6 is ramping. So instead of picking the signal from the output of the chip, Thomas Henry picked them straight from pins 6 and 7. These are then combined to form a composite sawtooth wave and that's why we have to set a trimmer to match them up to eachother to form one wave. The triangle wave is made by inverting one of the sawtooth halfs and applying an offset voltage to it to glue them together to form a triangle wave. This has the side effect of creating those spikes you see at the top and bottom of the triangle wave. Once we have the triangle wave it isn't too difficult to turn it into a sinewave by using the tried and tested transistor pair converter method. The squarewave is made by sending that sinewave into an opamp comparator which flips polarity everytime the sinewave goes over a threshold voltage set by the PWM opamp. Varying this voltage produces a change in the dutycycle of the squarewave.
The opamp used in the exponential converter, with the inputs of the VCO, is again an interesting one, the LF442. This is a modernised version of the LM1458. It has the same input characteristics of the LM1458 but only draws one tenth of the current. In addition the well matched high voltage JFET input devices of the LF442 reduce the input bias and offset currents by a factor of 10.000 over the LM1458. This ensures very low voltage drift and it also has very low equivalent input noise voltage for a low power amplifier. Seems like a good choise then ^___^
New LF442's are very difficult to find and I struck it lucky when my local electronics shop still had two of them in stock but as an alternative, the 4558 will do nicely or the TL072. They all work fine in this VCO. I tested them myself.
Here are the main features of the X-4046 VCO:
Exponential control and modulation.
Linear modulation.
Five unique waveform outputs: triangle, sawtooth,pulse with pulse width modulation, sine and variable rampoid. All waves are roughly 10Vpp through zero. (+/-5V)
Frequency range goes al the way from roughly one cycle every 24 seconds (41.7mHz) upto around 16.4kHz. so this VCO is also usable as a LFO.
And as the article in 'Birth of a Synth' states; one of the finest hard sync effects ever heard from a VCO.
The original schematic has the circuit running on a dual 15V powersupply but I changed it to dual 12V power for this project.
THIS VCO WILL RUN ON BOTH +/-12V OR +/-15V. I first built my VCO to work on +/-15V but I also tested it on +/-12V and it works just as well. Even the tracking wasn't much different when I switched to +/-12V so because most people build for 12V (Eurorack and Kosmo) I revised the schematic. Some waveforms were a bit lower in amplitude though. Most notably the sinewave which dropped quite a bit so for that reason R18 and R19 going from Q4 and Q5 to the opamp were changed from 10K to 15K. Also the output for the pulse wave needed to be increased so I changed those output divider resistors to 2K2 for both. The changes are made in the schematic and layouts.
Schematic:
LAYOUTS:
Below are the layouts for this project. As always they are verified. I used them for my build and I can tell you it worked flawlessly right from the get go. Not a single mistake! All I had to do was trim the waveforms into the right shape and the VCO was up and running. Oh and tune it for octave tracking of course. I have adapted the layout for use with +/-12V.
Here's the wiring diagram. We have 7 potmeters, 10 in- and output sockets and a toggle switch to wire up. It took me an afternoon and the next morning to get it done. I used 1M potmeters instead of 100K for all but the Frequency Coarse and Fine controls. The value of the panel potmeters makes no difference except the 'Skew' potmeter. That one should be 500K or higher. (I also used a 1M for that one) but I later used a 100K in my Eurorack version and that works fine too.
Stripboard only view:
I had some difficulty in placing the matched transistor pair Q4 and Q5 near to the opamp they need to be connected to, so I had to use some jump wires for that. The jumpwires are not shown in the layout. Instead I have marked the places where they need to go with 2 orange circles with the number 5 meaning this point needs to be connected to pin 5 of IC-4 and 2 yellow circles marked with the number 6 which needs to connect to pin 6 of IC-4. I used shielded wires and I connected the outer braiding of the wires to the ground strip underneath IC-4 (strip X) and these points are also marked with green circles with numbers in them. (Only ground the wires at one end)
However, you don't have to use shielded wires. Normal jump wires will work fine too. I just played it safe because the wires pass right over IC-1 but you can save yourself the trouble.
Here's a look at all the cuts and wirebridges that need to be put in place before you start putting in the components. There are 45 wirebridges to solder in:
A close-up of where the two jumpwires need to go. This image doesn't show the whole stripboard just a zoomed-in bit to show where the wires must go.:
Cuts only view, seen from the component side. As always, mark the cuts on the component side first with a waterproof Sharpie or Edding400 and then put a pin through the marked holes and mark them again on the copper side. Then cut the copper strips at the marked places. That way you have the least chance of making mistakes.
And here's the Bill of Materials. For the PTC I used the same one as I used on the 555-VCO. See project 37. That article has links to the webshop where I got them from They are 3300ppm instead of 3500ppm but that 200ppm difference you can ignore. It works just fine. If you don't have a 2K PTC then just put in a 2K resistor instead.
BOM has been updates as per 14-5-2026. I noticed there were a few items missing.
BEST CHIPS TO USE:
It is mentioned in the article that certain 4046 chips are better for tuning than others. I used a Texas Instruments CD4046. It was good enough for me but if you want the best chip for this circuit the ones to get are: National CD4046, Fairchild CD4046 or the Motorola MC14046. This last one is the best one you can get. They are pretty difficult to find though so you'll probably end up doing as I did a go with the Texas Instruments CD4046 and take the tuning difficulties for granted. You'll still end up with a fantastic and very useable VCO. Actually, the stripboard version took a bit of time to tune but I later made eurorack PCBs for this VCO and they tuned just fine with Texas Instrument IC's. You can have the occasional bad chip in a batch though, so if you struggle to get it tuned change out the 4046 for another and try again.
I've had some feedback that the Philips HEF4046B chips work very well in this VCO and they're easy to source in some parts of the world.
THE BUILD PROCESS:
As I mentioned before I had to use jump wires on the stripboard and because the wires pass right over, or near, the CD4046 I chose to used shielded wires. I connected the shielding to the bottom right ground strip (X). The outside shielding of the wires must only be grounded at one end. At first I used unshielded wires and actually it will work just as well so you don't have to used shielded wires. I just played it safe.
The transistor pairs need to be matched because one of the pairs makes up the current mirror for the 1V/Octave tracking and the other pair determins the shape of the sinewave. It's a classic triangle to sinewave converter design. I matched them by measuring the Hfe on my multimeter and choosing two that have the same value. You really should use the Ian Fritz method though. See the TB-303 filter project for an in depth explanation of how that works.
Just like in the 555 VCO, Thomas Henry uses a 2K PTC for temperature compensation. Luckily I still had a few left so I didn't need to order any. I recently ordered ten more because they are out of production. So when the shops are out of stock, that's it. No more PTC's. At least, not these ones.
After I had finished making the stripboard, I made the front panel and put in all the potmeters and sockets. I made a special mounting bracket for the stripboard out of plexi glass. I took a small strip of it and bent it at one end in an L shape, using a heat-gun. then I glued small squares of plexiglass to the top and bottom ends so the stripboard could sit inbetween them. Then I hot glued the stripboard to the bracket. It works very well. Here's a front and back view picture to illustrate:
Here are some more pictures from the build process:
I had already started putting in some components before I remembered to take a picture of the stripboard with just the wirebridges.
Stripboard finished but chips not yet mounted in their sockets. In this picture you can see the jumpwires and because this was in the testing phase they are normal not shielded wires. I later put in shielded to see if there was any difference but there wasn't so you can just use normal jump wires.
Everything ready for wiring up. That took me an afternoon plus the next morning. All the socket grounds are connected together through one copper wire which then connects to ground on the stripboard.
My faceplate design. Just white acryllic marker on black powdercoated aluminium, sealed with a clear lacquer coating, which is why it's so reflective :)
The finished VCO undergoing testing. I have a special power output on the side of my synth that I can use to test new modules. Very handy to have :)
CALIBRATING THE WAVEFORMS:
Calibrating the waveforms of this VCO is really straight forward.
For the different waveforms you just adjust the trimmers until the waveforms look good to you. Set the triangle wave first. Use the trimmers to connect the two halfs of the waveform. After that you can set the sinewave. Triangle connect does exactly what it says, it connects the upward slope to the downward slope. Very straight forward to set. One trimmer is for the upward slope and the other for the downward slope. You'll see frequency spikes appear on the top and bottom of the triangle wave. This is normal. They are so high in frequency that they can't be heard so ignore them.
You need to set the offset voltage for the Triangle and Sawtooth waves so that the zero Volt line goes nicely through the middle.
The Triangle wave is made up of two sawtooth waves put together so the Ramp or Sawtooth wave is half a Triangle wave and therefore double the frequency of the other waveforms. (One octave higher)
TUNING THE VCO:
Tuning the V/Octave tracking of the VCO is a straight forward process of going between high and low notes. I always use the C2 and C5 notes.
Use the Triangle wave for tuning.
- Press key C2 on your keyboard and use the front panel coarse and fine tune potmeters to tune to C2.
- Now press C5 and see if you are higher or lower than C5.
- If you're lower, trim the V/Oct up a little bit. Don't make big changes and remember if you tuned up or down.
- Now both notes will be higher so press C2 again and use the front pots to tune to C2 and then press C5 again and see if you're closer to it.
Repeat this process until both C2 and C5 are in tune.
If all is well the notes inbetween shouldn't be too far off either. You'll always be a few cents off on C3 and C4 but that's normal with this VCO.
If the notes in between are way off then you can bet your CD4046 is to blame. I tried altering all the components in the tuning circuit but nothing influenced it except capacitor C3 and the CD4046.
If you can't get the VCO in tune before you're at the end of the throw of your V/Oct. trimmer, you can lower the capacitance of C3 (10nF). Put in a cap of around 8.5nF.
I tested different CD4046 chips and I found they have different characteristics over the octaves.
I made a graph to illustrate this:
The red line represents the curve I got with a random CD4046 and the purple curve are the results I got with another CD4046, both from Texas Instruments. You see, you have to try a few chips if you can't get it in tune correctly. The purple curve represents a good result for this VCO.
Changing the value of the 390 Ohm resistor won't help with tuning at all. Believe me, I tried that.
Lowering the value of R15 (10K) won't help either. One other cause can be if your transistor pair isn't matched. That would upset the exponential converter too.
The make of your 4046 chip is important. Look at the text under the Bill of Materials for a sum up of the best chips for this circuit. Motorola works best, Texas Instruments is said not to work so good but I found that this depends on the individual chip, as I mentioned before. The TI chips in my VCOs work fine and I've got them in tune over 5 octaves with just a few cents between them but a few chips in my batch were unusable.
These are the test results Thomas Henry himself got when tuning his VCO to track over the octaves:
Here are the standard waveforms. The spikes you see on the triangle wave are a characteristic of the VCO as I mentioned in the schematic section. They are very fast and way beyond the human hearing range (80kHz or over) so not audible what so ever.
When I looked at the sawtooth wave I saw it had a bit of a wobble on the oscilloscope. However this changed to rock solid once I started playing the keyboard. Consequent versions I built of this VCO using PCB's all had this wobble but it goes away once you start playing the VCO with a keyboard.
Here are some screenshots of triangle and sawtooth waves in the Hard Sync function for which this VCO is (rightly) well known. It sounds awesome!
Here's a look at a recently finished project, the 4046 SUPER VCO with the suboscillator from project 69:
DEMO VIDEOS:
Here's a test video showing the VCO in action through the Thomas Henry State Variable filter of the previous project.
Here's a video showing how top psy-trance producer Jake Jakaan (Alienatic) uses this VCO to make his signature awesome alien sounds, making full use of the Hard Sync and FM functions. He's using one of the 4046 Super VCO's I built for him but it's the same VCO as in this project.
Here's the video where someone is building this VCO on small pieces of stripboard connected straight to the panel by means of the potmeters.
Okay that's if for this project.
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