Synthesizer Build part-60: 4046 WAVESHAPER by Barton Music Circuits

This is the Barton Musical Circuits BMC33, 4046 Waveshaper from 2015. Not to be mistaken for a wavefolder. This module divides and multiplies an incoming signal by x8, x4, x2, x1, /2, /4, /8 and then you can mix these signals back together to create really awesome timbres. It's a Eurorack friendly design.

This analog circuit uses a CD4046 PLL (Phase Locked Loop) chip in combination with a CD4040 binary counter to create new timbres and waveshapes. It outputs only squarewaves. It's a really simple concept. You take a VCO signal, turn it into a squarewave by means of an opamp comparator and then multiply the signal x2, x4, x1 and x8 while also dividing it by /2, /4 and /8. Now you have 7 signals each an octave apart and each have a potmeter to set their respective levels which go into a little mixer and are output as one new signal.

It has a Slew switch which changes the capacitor of the filter inside the PLL chip, the CD4046. With higher capacitance the tuning will be more stable (especially at lower frequencies), but the tracking of the notes is slower which you can hear as a sort of glide or portamento effect between the notes. It makes a real difference. Makes it sound more SH101 or Acid like if you rapidly change notes. Some of the sounds it can produce can sound like what you get from a wavefolder although that's a completely different concept. The waveSHAPER can produce a lot of other sounds too.

You can alter this circuit and add CV inputs for each of the controls but I didn't do that. I saw a video by Analog Output who did this and he used little VCA's made with logic chips but that will only switch each channel on or off as far as I understood. Anyway, I'll leave the alterations up to you the builder of the project.

Btw, the output volume or amplitude of the output signal can be quite a bit higher than the input signal but it won't damage anything. You could add a overall level control on the output but that would make the faceplate design too big for my taste.

Here is the schematic I used for my layout design:

There is a PDF file available on the Barton Music Circuits website which contains this schematic plus a lot of extra info. You can download it by --- clicking here ---

If you want to hear what the module sounds like, there are two demo videos further down the article.

LAYOUTS:

Here are the layouts for this circuit. They are verified as always. I used a piece of stripboard that is 24 strips by 30 holes wide which makes it small enough for Eurorack but it will be 6 centimeters deep so it won't fit a Nifty Case for instance.

Wiring diagram:

Stripboard only:

Here are the cuts that need to be made and wirebridges to be soldered in first:

And finally the cuts as seen from the component side. You know the routine but I'll repeat it anyway; mark the cuts with a black Sharpie or Edding felt pen and then stick a pin through the marked holes and mark them again on the copper side. Then you can cut the strips at the marked locations using a sharp hand held 6- or 7mm drill, or whichever method you prefer.

Here is the bill of materials:

PICTURES:

Here are some pictures from the build proces. It was pretty straight forward and the layout turned out to be faultless but I made some silly mistakes when wiring it all up. I had the wire that grounds all the potmeters and sockets soldered to the -12V connection instead of the ground and I had the input and output reversed. Can you believe it? After 60 projects I still make these mistakes. It goes to show never to let your guard down and keep working precise and don't rush it, which was my problem.

Wirebridges put in and cuts made.

Stripboard built up. As you can see I did not include the 10µF capacitors over the power rails. They are in the layout but I usually only include features like that when I have problems with hum or ripple on the voltage lines. With this design you can leave them out. You don't need 100nF bypass caps over the chips either although you can include them if you want. They're not in the bill of materials.

Here's the panel design I made for it. I really got a taste now for using waterslide paper to make these panels. It looks so professional. Only I made a mistake.... I made a typo. The plus signs should be multiply signs. Aaaargh!!! Oh well, I'm not making a new one. ^___^  It came out looking great. The faceplate is 10hp or 5 centimeters wide.

Front and backside view:

I'm fresh out of knobs to put on the potmeters. I've ordered new ones but they haven't come in yet.

OSCILLOSCOPE SCREENSHOTS:

Here you can see how all these squarewaves of different frequencies are summed together and output through the mixer stage. Note how much higher in voltage the output signal is (in yellow) to the original signal (in blue). Both channels are set to 5V per division.

VIDEO DEMOs:

Here's a good demo video I found on YouTube by username Midiverse - TV. Although playing music inbetween the demo bits is not a good idea in my opinion:

And here's an other one by youtuber: Boogdish:

Okay that's it for article number 60. SIXTY!! I can hardly believe it. This site has become quite an archive for synthesizer projects and a lot of people seem to really enjoy it. Last month we passed the one million all time views!!

If you have any questions or remarks about this project then please put it in the comments below or post in the special Facebook group for this website.

Synthesizer Extra's No.5: PROFESSIONAL LOOKING PANELS using WATERSLIDE PAPER.

 An easy way to make your panels look really professional.

I've been doing this hobby for over 4 years now and all that time I always used black powdercoated aluminium to make my panels from and I always use a white acryllic pen to write all the labeling etc. 

It works fine but it doesn't look very professional.

For a long time I've seen people using waterslide decals to apply to their panels and it looks very slick. I wanted to try that myself so I ordered some "Water-based ink jet water transfer paper". That's what is says on the label. You can order this from AliExpress or your preferred webshop. If you Google it you'll find lots of sellers.

Make sure, if you use an inkjet printer like I do, to order transfer paper suitable for inkjet printers. It must say inkjet on the package and it must be transparent. If you use a laser printer then there's special transfer paper for that too.

There is also white transfer paper available so you can have white decals on a dark background but I'm not going any further into that.

First step: Design your panel layout.

I did my design in Photoshop. I like working with Photoshop because you can work with layers and the centimeter markings on the side are very accurate to how it will roll out of the printer.

There are also special layout design programs on the internet, like 'Schaeffer AG Front Panel Designer' which you can download for free.  There is also a free program called Inkscape which should work very well too. You can download that by clicking here. I have not worked with these yet although I intend to try them out soon.

You can find decal designs on the internet or make your own. Make sure you draw in dots for the places where you need to drill holes in the panel so you know where to drill them.

One tip I can give you is to make your panel design just a little bit smaller than the actual panel. Just a millimeter on the sides and have it start and end inbetween the holes in the panel where you screw it into the synthesizer case. That way the lacquer you apply later will seal those edges and prevent them from coming loose. 

Here's a picture to illustrate that point. You'll see in the light reflection on the top how the lacquer forms a protective layer over the edge which runs just under the mounting hole:

Btw, that panel had a typo in it, the plus signs should have been multiply signs but I still used it because it came out so well. This was the second panel I ever made using this method and it went perfectly.

Here is my first design for the Digisound-80 VCO, made in Photoshop and printed on A4 paper. (feel free to use it if you want):

I drew in the Octaves and Freq Fine control markings after measuring on the VCO where they should go so they actually indicate where the different octaves are and on the fine control where the notes are within the octave. Note the dots that indicate where to drill the holes for the potmeters and sockets.

Step two: Prepare your waterslide paper.

Now print your design onto the waterslide paper. Then cut it out nice and straight. I use one of those paper cutters with a rotating knife on a rails that you can put the paper under. It guarantees a straight cut. Round off the edges a little with scissors.

Now apply a few thin coats of clear acryllic lacquer onto the paper. Make sure there's no dust or hairs on the paper and let it dry for a day. If you use a laserprinter that uses toner then you don't have to apply the lacquer. However inkjet prints are not waterproof so they must be protected with lacquer. Make sure it is well dried before moving on.

Step three: Prepare the panel.

Take the design you made and print it out again but this time on a normal piece of paper. We are going to use this to drill the holes in the right place. 

Take your panel material, in my case white powdercoated aluminium, and apply the printed design to the protection layer of the panel with doublesided tape. You can use other methodes but I find this the easiest to do. Usually the panel material will have a protection layer against scratching, if it doesn't have that just tape it to the panel but make sure it can't move.

Now use a very thin drill to make the first pilot holes. I used a 3,3mm drill but that was too big and I couldn't place the drill accurately enough which caused me some problems when I put in the potmeters. 1,5mm will be better. So make sure you drill very accurately. Then drill the holes to the right size and take off the paper/protection layer. Make sure you de-burr the holes you just drilled. There must be no upstanding edges around the holes because that will cause air pockets under the waterslide paper. 

Step four: Apply the waterslide paper to the panel.

Now take a nice big bowl and fill it 2/3rds with slightly luke warm water. Put one drop of washing up liquid in in the bowl. This decreases the water tension. (Don't make the water all bubbly from the soap because then you can't see what you're doing). Put the waterslide paper into the bowl. It will immediately curl up. Carefully roll it out with your fingers and make sure it is completely in contact with the water. The paper will straighten out. Wait about 20 seconds until the image layer can be moved over the back paper. In other words until the image can be slid off of the paper. 

MAKE SURE the image doesn't come off while it is still in the water!! Or all the glue will wash off. That's why I say 20 seconds in the water is about right.

Put a little water on the panel with your fingers to wetten it a little. Make sure the panel has been de-greased and free of fingerprints. (A little alcohol does wonders in cleaning the surface beforehand).

Now take out the waterslide paper and place it over the panel. Grip it carefully with your fingers on the top side of the panel and then slide the back layer down from under the image layer. It is important that you don't move the waterslide paper too much once it is applied to the panel because this will impact on the stickiness of the paper. The slippery stuff underneath the image layer is actually the glue so you need to make sure this is not washed away by too much movement.

There are special 'decal setting solutions' available for purchase, that will cure the layer and make for a good bonding between panel and image layer. I don't own any of that myself but I might try this later, however you don't really need it. 

Now carefully squeeze out the water underneath the waterslide image by using the backpaper as a squeegee. Carefully move it over the image layer and squeeze out any water underneath. Be careful not to crease it! This takes a bit of practise but it doesn't have to be perfect. The image layer may still look a bit rippled but that will disappear when it dries up. Make sure there are no folds though. When the water has been squeezed from under the paper, you can use a fine cloth to dry the surface of most of the water. Be very careful though. If you don't trust yourself, leave the water on top or carefully use some tissue paper. I put it on the central heating in my room and it was dry within an hour. 

Step five: The final touches.

When the panel is dry, cut out the parts that are covering the holes you drilled with a very sharp knife. Take your time with this, don't rush it. You can ruin it otherwise. Use a very sharp knife to clear the holes and make a scissor action (cut) against the metal so you don't pull on the image layer. After that you must coat it again with a few layers of clear lacquer and when that is dry you can put in all the knobs, switches and sockets. . When you put in anything that needs screwing down, and that's everything, make sure there are rings underneath so the screwing action doesn't cut into the waterslide material. This is a bit problematic with sockets because they don't come with rings, so be careful when you tighten them. (You can apply some extra layers of lacquer in those areas to protect the paper if you think it's necessary.) You can hold the screw and turn the socket or potmeter from behind the panel, do what you think works for best for you.

And that's all there is to it. Anyone with a computer and a printer can do this. I do advise to make a practise piece first and use it to hone in your skills. I went directly to making a panel and although it looks okay there are some creases here and there that are visible when the light hits it, but here is my first result:

VIDEO TUTORIALS:

I found a few video tutorials on YouTube that show the proces from beginning to end. These are all about guitar pedals but it works the same as with synthesizer panels. 

I urge you to watch these before you start, so you have a good idea of what's involved.

--- CLICK HERE FOR TUTORIAL ---

--- CLICK HERE FOR ANOTHER TUTORIAL ---

Okay that's it for this one. I hope this is of use to you. If you have any questions or remarks please put them in the comments below. They won't appear directly, comments are moderated, but everyone of them is answered by me. You can also post your questions in the Facebook Group for this website.

Synthesizer Build part-59: BASS++ DRUMVOICE by THOMAS HENRY.

Finally a new drum related project and this is a really good one. This circuit creates all sorts of percussive sounds from Bass drum and Tom-Toms to Woodblock and a lot in between. 

Once again a Thomas Henry project. They're just so good and I wanted to build a drum related module for a long time to expand on the 808 Kickdrum from Juanito Moore. This is a relatively simple circuit to produce such a wide variety of drum sounds. 

Here's the schematic I used to make the stripboard layout:

Just two IC's and 4 transistors. The core of the circuit consists of a VCO built up from the first of the two OTA opamps in the LM13700. This is called the Shell VCO. The VCO's pitch is influenced by the little Envelope Generator consisting of the 2,2µF capacitor and the Decay potmeter fed from IC-2a. This opamp takes the Trigger pulse and with the Sensitivity control, which is an offset control really, turns it into a useable Envelope signal. The VCO also has it's own manual pitch control and there's an external CV input with a level control (Range) and this is where the real magic lays because if you input a VCO signal into this CV input all sorts of weird sounds result. The VCO output goes through the second OTA which functions as a VCA with a buffered output. There are DC blocking capacitors (2,2µF) to get rid of any offset voltages.

Then there's an Impact section which provides the beat, so to speak. It creates the initial hit of the stick on the drum which you can control in tone and intensity. This is fed from the same trigger pulse as the Envelope Generator.

I did not have any 2,2µF electrolytic caps in stock so I used 3,3µF or 4,7µF caps in those places where they are used as blocking capacitors. The value of those isn't that critical. However C11 is the capacitor that determins the Decay length and for that I used two 1µF caps in parallel. With the wide tolerances they have that came to 2,3µF when I measured them together so that was ideal. 

C2 is an other critical capacitor. It determins the frequency range of the VCO so keep to the indicated value for that one. You can make that cap switchable with other values to change the base frequency of the VCO. I leave that up to you.

If you want to know more or you want a more detailed explanation of the circuit then I urge you to read the original article on the Birth of a Synth website.

MODIFICATIONS:

Because it is such a simple circuit people have been modifying this circuit in all sorts of ways. Some of these modifications you can check out via this link to the electro music forum:

One thing you can do is add an extra socket so you can input external envelope signals. Have it normalled to the built in E.G. and then break that connection when a patch cable is inserted.  I think a good place to insert that signal would be between the output of the opamp (pin 1 of the TL072) and the junction that connects to all the diodes. 

An other thing is to add a built-in noise generator by means of a transistor with the collector-leg cut off. This would be handy for snare like sounds.

You can also add a switch to choose between different values of timing cap (C2) to be able to change the frequency range of the VCO.

With the circuit being this simple it will be easy to add to it and make it your own. I will leave that up to the individual builder. This article just deals with the original version.

LAYOUTS:

Below is the series of layouts I used. They are verified as always and this project was yet an other hole in one. It worked straight away, no trouble shooting required. I kept the layout small enough to fit behind a Eurorack panel. Just 24 strips with a width of 41 holes.

Wiring diagram:

Here's the stripboard only view:

The cuts and wirebridges:

And finally the cuts only view. Seen from the component side. 

Mark the cuts on the component side with a waterproof Sharpie or Edding pen and then stick a pin through the marked holes and mark them again on the copper side. Then cut the copper at the marked positions. Be very accurate here. There's not much room for errors.

Here's the Bill of Materials:

PICTURES:

Here are some pictures from the build process:

The finished stripboard:

Because this circuit is a bit difficult to understand and therefore the function of the 9 different knobs is also not easy to understand I decided to make a faceplate with a sort of block diagram on it so I could show which knob controls which part of the circuit. This would make the faceplate a lot bigger but it would also make the user understand which part of the circuit he was influencing.

It was not easy to design a flowchart or block diagram that was simple enough but also true to the functioning of the circuit and it took me about 4 drafts before I was happy with the design.

Here's the resulting faceplate:

Everything in place ready to be wired up:

And here's the final result. Each section of the circuit has its own colour knobs. The trigger pulse is visible through the yellow LED inside the triangle:

VIDEO DEMO:

Here's a little video of me trying the module out for the first time. Don't expect too much from this. I was just fooling around with it. I had a pulse wave on the Trigger input and a sawtooth from my VCO (which was connected to the sequencer) going into the CV input.

I recorded the audio of this video separately with a Zoom H8 to get the best bass tones which my phone would never pick up.

This module can replicate that late 70's 'Peewww peeewww sound made famous by Kelly Marie in her song 'It feels like I'm in love' . Remember that one? (LOL)

It's capable of much more than can be seen in this demo video, if you go to the 'Birth of a Synth' website Bass++ article and listen to the sound sample posted there, you can hear what this module is really capable of.

Okay that's an other one done and again a Thomas Henry design. They are just so good. They always deliver.

If you have any questions or remarks about this project then please put them in the comments below or post on the special Facebook Group for this website.

Synthesizer Build part-58: VCA-1 by THOMAS HENRY.

 A very good working VCA and Mixer using the AS3080 IC. Very easy to build and with a Line Out option too.

Having built the VCF-1 and the X-4046 VCO designs by Thomas Henry I thought I might as well build the VCA-1 aswell. By coïncidence I needed a new VCA in my DIY synthesizer anyway because the transistor based VCA from way back in the beginning when I started this Modular journey is now starting to act up after working flawlessly for 3 years. It was about time for a new and updated VCA and one with a little more options too. This project is another one from the Birth of a Synth website where I got the others from too.

I built and tested this VCA to run on a dual 12V powersupply so perfect for Eurorack too. It's designed for +/-15V but either voltage will work fine. No component changes needed.

If you're new to DIY synthesizer building and you're not sure about the function of a VCA and what it's for, then please go back to project 10 on this website and read the first bit of that article. That will explain it for you. Then come back here and build this one ;)

This VCA is not only a Voltage Controlled Amplifier. It's also a 3 channel mixer and it has a Line Out option (all in mono though). I did put in 3 inputs in the layout but I only used one in my own module. I didn't have the room for 3 because I needed this VCA to replace my old one and that one is only 4 CM wide. You could easily add even more channels just by putting in more 100K resistors connected to pin 2 of the TL074, and having your inputs come in through those resistors.

This project was yet an other hole in one. It all worked flawlessly at the first try, just like the X-4046 VCO. I LOVE Thomas Henry designs. They just work so well.

Here's a look at the finished product on the test bench:

I made a few changes in the way I'm using this VCA as opposed to how Thomas Henry intended it to be used. TH had the ADSR coming in on an unattenuated input and an extra CV input with attenuation. I turned that around and I have given the ADSR a level control and the extra CV input has no level potmeter. I also put in an extra bi-coloured LED because I used a quad opamp instead of a dual plus a single opamp and just like with the State Variable Filter I had one opamp left over. I connected that to the ADSR input so we have a visual indication that the VCA is receiving an envelope signal and if that signal is positive or negative in Voltage and how strong that signal is, going by the brightness of the LED. Actually a very useful feature to have.

SCHEMATIC:

Here's the schematic I used to make the layout. As mentioned, I made some changes in the type of opamps I used. I also only used one input instead of three. As you can see it's a very simple circuit and it works very well with the AS3080. I used a TL074 for the opamps so the opamp pin numbering on the schematic will be different from the layout.

LAYOUTS:

Below are the layouts I made for this project. As ever they are verified. I used them for my build and it again worked straight away, just like the VCO.  Again, the LED was an extra I put in myself and it's not in the schematic. It's fed by an opamp buffer connected to the ADSR input with a Bi-Coloured LED on the output and a 2K4 resistor as current limiter. It's a useful addition.

Wiring diagram:

Stripboard only view:

This layout was small enough to have a few strips left unused which gives up plenty of room to connect some L brackets to mount the stripboard to the faceplate.

Cuts and wirebridges (component side view). I did not bother to make a layout with just the cuts on it because they are easy enough to see on this combined view:

And here's the Bill of Materials. 

You can order AS3080 chips from Electric Druid. 

You can also order them from Thonk.

Testing was pretty straight forward. I connected my scope to the Max. output and put a VCO signal on the input (yellow line) and an LFO signal on the ADSR input (blue line) to serve as envelope signal. The scope showed a beautifully responsive VCA reaction as you can see on the screenshots below. 

When you turn the INITIAL potmeter past the 1 o'clock position the audio signal will reach its amplitude limit. In that case the VCA will also not shut completely. (The audio will not distort though) You can look at the Initial potmeter as the 'Gain' control on other VCA's. You use it to open the VCA so you have continuous sound without any keys being pressed on the keyboard. The further you turn it clockwise the louder the audio will be.

Here you can see the negative voltage rejection on the ADSR input. As soon as the blue line goes through the zero Volt line and higher, the audio will come on. The LED will shine blue when there's a negative voltage presented on the ADSR input and the VCA will just stay closed.

CALIBRATING THE VCA:

This is simple. There's only one trimmer and you use it to trim away any DC offset on the audio output. What you do is you connect an oscilloscope to the Max output. Set the AC/DC switch to DC. Then you put an audio signal on the input and an LFO signal on the ADSR input, like the screenshot's above. Then you turn the trimmer until the signal is centered around the zero Volt line. In other words, the zero Volt line goes straight through the middle. 

That's all.

PICTURES:

Here are some pictures of the finished module:

So that's it for now. Three in a row this month and three very good Thomas Henry projects for you to sink your teeth in.

If you have any questions or remarks please comment below or in the special Facebook Group for this website.

Synthesizer Build part-57: X-4046 VCO by THOMAS HENRY.

 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.

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 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!

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.

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 comparitors. The IC has been used in some very cool Eurorack modules too, among them the Wiard Wogglebug.

The opamp used in the exponential converter, with the inputs of the VCO, is also 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 ^___^

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)

And as the article in 'Birth of a Synth' states; one of the finest hard sync effects ever heard from a VCO.

THIS VCO WILL RUN ON BOTH +/-12V OR +/-15V. I 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 there's no problem building this for Eurorack. There's a video on YouTube showing a stripboard eurorack version being built. He uses lots of small pieces of stripboard with the potmeters soldered straight to them.

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.

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 needs to be 500K or higher. (I also used a 1M for that one).

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. You can also just put in a 2K resistor instead of the PTC.:

It is mentioned in the article that certain 4046 chips are better for tuning than others. I used a Texas Instruments CD4046 but that one is impossible to get tuned accurately. 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.

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 as I always do just by measuring the Hfe on my multimeter and choosing two that have the same value. If the Hfe is the same you can be pretty sure the Vbe will be pretty similar too.

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.

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 :)

TUNING THE VCO:

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. The sinewave took a bit of time to get right but it's just a matter of trial and error. You need to set the offset voltage for the Triangle and Sawtooth waves so that the zero Volt line goes nicely through the middle.

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.

Tuning the VCO to track with the octaves is less straight forward but just a matter of using the V/Oct trimmer in combination with the Frequency controls on the front panel. The HF tracking has very little influence. I found it quite difficult to get this VCO in tune but that's a known characteristic of this VCO.  It's not a fault in the schematic or layout.

I turned the Frequency fine control to get note C3 in tune and then I checked notes C2 and C5 and I turned the V/Oct. trimmer to get them closer to the true note. Then I checked all the octaves again.

I again set C3 in tune with the Freq control and turned the V/Oct. trimmer to get the others (C2 - C5) closer to where they need to be. I used the HF tracking to get better results on the higher octave but it has little influence.

I repeated this proces until I got reasonable results. I managed to get C3 to C5 in tune but C2 was about 20 cents too low. I just left it at that because it sounds just fine for my needs. I'll try and get it tuned better later. You really need to take your time for this.

What is very important here is the make of your 4046 chip. 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 not so good (and that's the one I had in stock and used).

These are the test results Thomas Henry himself got when tuning his VCO to track over the octaves:

Source: Birth of a Synth website.

OSCILLOSCOPE SCREENSHOTS:

Here are the standard waveforms. The spikes you see on the triangle wave are a characteristic of the VCO. They are very fast and way beyond the human hearing range so no problem at all.

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.

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!

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 little test video in which I try the famous Hard Sync function of the VCO. I must say this VCO paired with the State Variable filter is a killer combination. I'm using a sawtooth wave from the Thomas Henry 555 VCO into the Hard Sync input.

Okay that's if for this project.

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