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's a favorite among Psy-Trance and Techno producers! I'm reliably informed the hard sync in this VCO is regarded as being better than that of the Nord Lead. As is the FM function. That's saying something!

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. Some waveforms can be a bit lower in amplitude though. 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:

The KiCad version of the 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 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 :)

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.

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.

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

Synthesizer Build part-47: DUAL LFO for EURORACK.

A simple LFO with pulsewave (with variable pulse width) and a seamless transition between a Ramp wave, Triangle wave and Sawtooth wave using one potmeter. With LED rate indicators and Speed and Shape controls.

Well what more is there to say about this LFO. It's such a simple design that I could easily fit two of these on a small piece of stripboard and still have it small enough to fit a normal Eurorack case. The circuit is derived from the 'Utility LFO' by Ken Stone which is a larger version of this LFO. 

I now also have a project for the complete Utility LFO and it's even smaller than this one and a panel width which is only 1HP wider at 9HP.  Go to project 50 for that.  

This LFO is still useful on its own though because it is so small. It can easily be incorporated into other projects as an on-board LFO for instance.

The depth of this module is 55mm. I made the panel 4CM wide, that's 8hp, and I put the potmeters to one side leaving enough room to glue the print straight to the back of the panel at a 90° angle using hot glue. All the output sockets fitted nicely next to eachother at the bottom.

Naturally you can just as easy build this module in the Kosmo size and run it on 15V. If you do, you need to keep to the resistor values as they are in the schematic, not the layout because as I mention further down, I changed the 1K output resistors to 1K8 to get a nice +/-5V output signal. If you power this with 3 more volts you probably don't have to do that. Do some testing first to make sure though.

I tried my hand at using Falstad recently and tried to make a simulation of the complete Utility LFO circuit and it was surprisingly easy to do. 

So here is my very first ever Falstad simulation: --- CLICK HERE ---

Here's the schematic drawing of the dual LFO circuit:

The module consists of two of these circuits on a single piece of stripboard. I placed the LEDs on a separate piece of stripboard with a dual opamp, the good old TL072, and I used bi-coloured 3mm LEDs in red and blue. I drilled two 3mm holes to the left and in the middle of the first two- and last two potmeters for the LEDs and glued them in place with hot glue so the little print sits over the potmeters. See pictures below for illustration. Btw, you can use any dual opamp chip for this circuit as long as the pinout is the same; like the TL082, NE5532, LM358 etc.

LAYOUT:

Here is the layout I made for this Dual LFO. As always, the layout is verified. I used it for my build. I placed the Eurorack powerconnector on the left side for better access. In my build it's on the other side and very near the panel. Not a good place for a power connector but you only find these things out when you start building it. See, I make the mistakes so you don't have to LOL! (I hot-glued the print to the back of the panel with the righthand side closest to the panel.)

Stripboard only:

After doing the first tests I found the output voltages a bit on the low side. They were just +/-3,24V so I decided to experiment with the 1K resistors between the outputs and ground. I tried several values and I ended up using 1K8 resistors. That brought the output voltages to a nice +/-4,8V. Almost 5V so that's perfect for eurorack. If you want that voltage to be even higher in your LFO then experiment further with making the resistor(s) between the output socket and ground even higher in value.

I wanted to make one of the LFO's a bit slower than the other to give me a wider overall range so I used a larger capacitor for LFO number one. I used a 147nF and that made it perfect for my needs, between 0,2Hz and 10Hz. In the layout both timing caps are 47nF though.

 

TECHNICAL DATA:

Here are some measurement results for this Dual LFO:

Duty cycle of squarewave is 5% to 95% this varies a bit with the frequency but not more then 2%.

Lowest frequency: LFO-1 = 0,219Hz  LFO-2 = 0,653Hz (changed timing cap of LFO-1 from 47nF to 147nF)

Highest frequency: LFO-1 = 9,82Hz   LFO-2 = 34,2Hz

Output voltage is +4,8V or 9,6Vpeak-to-peak. That's after changing the 1K resistors in the schematic for 1,8K ones. Otherwise the voltage was just 3,2V and 6,4Vpp.

Current draw: positive: average 12mA max.: 18mA

                       negative: average -13mA max.: -18mA

Here's the Bill of Materials:

Here are some screenshots from the oscilloscope with some measuring data underneath the images. Some images may still show the lower output voltage but that's been fixed:

The following are screenshots from the oscilloscope showing two signals, one from each LFO, being combined in a simple passive multiple. A squarewave and a triangle wave each at different frequencies. The results are pretty cool looking:

In the top picture you see more of the waveform in the positive voltage region and very little below zero Volts. You can set that with the shape potmeters to your own liking or best sounding result. As you can see this makes the Dual LFO module much more versatile as a modulation source. Plenty to experiment with.

PICTURES:

Below are some pictures of the print. I took these before I changed the 1K resistors to 1K8 ones. In the top picture and the 3rd one you can see how I mounted the little print with the bi-colour LEDs. The print rests above the middle two potmeters and the LED's are bent backwards over the sides of the stripboard and go straight into the holes in the panel and are secured with hot-glue. The little print itself is not mounted in any way. It just relies on the LEDs to keep it in place.

This time, instead of spray-painting the panel I decided to keep it blank aluminium and I used an engraving tool to put the text on. That didn't work too well and it didn't look good at all so I printed some labels I made in Photoshop, laminated them with Scotch Tape and put some double sided sticky tape on the back and I put those on the panel. That looks much better. 

TRIGGER OUTPUT

A few days after completing this build I added a trigger output to this module. I connected it to the squarewave output of the second LFO (the faster one). I thought it might come in handy to have a trigger source. You can see in the picture below how I did that. It gives of both positive and negative trigger pulses of 5V and a length of about 4mSec.  If you're thinking of putting in a diode to only get positive pulses forget it. That won't work. It'll kill off the pulses completely. If you turn the Shape potmeter the positive and negative pulses will move further away or closer to eachother. Just like the rising and falling edges of the squarewave with different pulsewidths.

(The above drawing actually translates to a high pass filter with a cut-off frequency of 268Hz. So it filters out the actual square- or pulsewave and only lets through the initial harmonics of that wave, creating this spike pulse trigger response, but you can forget about this theory. This is not important.)

Here's a look at the final panel with trigger output. I just made some labels with text to put on the panel. Looks better than the engravings.

One other thing worth noting is that because we have two LFO's on one board, they will very slightly influence eachother. What I mean is, if you have one LFO running at almost twice the speed of the other, the faster one will adopt some multiple of the rythm of the slower one if you set the speed to some value close to that. That's a form of resonance and I won't get into the technicalities of that but it's quite easy to set an LFO at twice or 4 times the speed of the other because they share the same circuitboard. It's the same idea as when you have a group of people walking together and they all start to walk at the same pace. That's also a form of resonance. Don't think this will be an obvious thing to observe. The occurrence is very subtile.

Okay, that's number 47 done! A very useful little module and I saved a few bob by building it myself instead of buying a dual LFO module. Okay it doesn't have any fancy extra's like synchronization but that's okay by me. I think I'll mostly be using this as a clock source and some random modulation. That's why I made both LFO's run at different frequency ranges.

If you have any questions or remarks about this or any other project on my site please comment below or post in the FACEBOOK GROUP for this website.

If you find these projects helpful and would like to support the website and its upkeep then you can buy me a Coffee. There's a button for that underneath the menu if you're on a PC or Mac. Or you can use this PayPal.Me link to donate directly. All donations go towards the website and projects. Thank you!

Synthesizer Build part-40: WAVETABLE OSCILLATOR (VCDO) By Electric Druid.

An amazing sounding digital oscillator with 16 waveforms and a sub-oscillator with 8 waveforms that spans 4 octaves. All but one of the parameters of this VCDO can be changed with external control voltages including the Bitcrush option which does not have a CV input in the original Electric Druid schematic but it has one in this build.  Only the Glide function doesn't have a CV input.

Warning: this is a big project. It needs two stripboards of the size I normally use (24x56) and my layout is definitely not Eurorack friendly. Everything needs to be shielded to prevent glitches in the main oscillator. Even the wiring of the control potmeters must be shielded.

It is possible to build a Eurorack friendly version of this VCDO on stripboard and the circuit will work fine on a dual 12 Volt powersupply but you can NOT cut these prints in half and connect them together like in other projects. You will need to make your own layout and much more compact than mine is now. However there is a smaller size layout available on the EB Facebook group files section. Check the link below the layout images under the heading 'Eurorack Layout' half way down this article.

ABOUT THE BUILD PROCESS AND PROBLEMS ENCOUNTERED.

Okay, not to put you off or anything but this is the most difficult build on this entire website so if you're a beginner or you don't have the right tools, especially a fine tipped soldering iron and good soldering skills plus a good oscilloscope, then please do not attempt this. By saying this I just want to avoid disappointment. As an alternative I would advise you to just order the Klang Stadt PCB and Panel from Frequency Central. That one is in the Eurorack format which mine won't fit in to.

I foolishly started out building this module like I did with all previous ones. Just build it up on stripboard, make a panel and then wire it up and test it. Well this turned out to be too light-hearted an approach because the main oscillator sounded like a scratchy vinyl record. I couldn't get it to sound right so I wrote to Tom Wiltshire (Electric Druid) about this problem and here's what he said about it

<Quote>

"It happened a bit on the first version of the PCB I did for the Frequency Central "Waverider" module. Eventually we tracked it down to the outputs being to close to the CV inputs. Keeping tracks and wires to those apart as much as possible helps a lot. On revision 2 of the Waverider PCB I routed the inputs on one side of the PCB, and the outputs on the other and that solved the problem. It boils down to noise getting into the CV inputs. That can come from many sources but from the chips own outputs was a big cause for us."

<End quote.>

So I started out fresh and re-built the entire module. This took me three days including designing a new layout. I now decided to shield everything and to keep the controls and the CV inputs on separate boards. This turned out to be the solution because it now works like it should. Instead of wires I used pinheaders to connect the two boards together. This would be the shortest route for the signals with less chance of noise getting into the connections. I had a blank single side copper clad circuitboard in my stock so I decided to cut this board to the same size as the stripboards and mount it inbetween the two stripboards and then connect it to ground. I cut holes in it for the pinheaders to go through and soldered upstanding copper edges around the holes to provide extra shielding for the pins. (The upstanding copper edges are a bit overkill and if you build this module, you don't really have to replicate that.)  

Here's a picture of how the boards eventually fit together. I stuck 4 transparent rubber feet on top of eachother and put it between the shield board and board two to act as spacers to prevent the upstanding copper edges around the pinheaders from touching the copper traces of board two. I also put some gaffa tape on the edges to insulate them.

SCHEMATIC:

[EDIT: As of Oct. 2023 the chip is available on back order.]

You can order the chip from Electric Druid. On that same page you will also find a link to the Datasheet with the schematics for this project. Download it and print it out.

NOTE: On the schematic, in the PDF, you will see one CV input circuit marked as "Spare CV Amount". On the page with the processor it is marked as 'Unused CV'. I don't know why it's marked like that but this is the Sub Oscillator CV Amount circuit which eventually goes into pin 18 of the processor chip. Just so you know.

If you're going to breadboard this circuit before building it up properly, don't leave any pins of the processor chip floating and make sure all the CV inputs get the voltages they need, otherwise it won't work properly.

LAYOUTS:

Below are the layouts for this project. They are all verified as usual. Not only by me but I had confirmation from a number of people who built this module successfully using the layouts below.

I'm going to give you a whole collection of layouts detailing the different steps. The Bitcrush section of this module was designed by Mike Desira, whom most of you will know from a lot of synthesizer DIY related Facebook groups. He has been a great help to me, not only in this but many other projects too. On my panel I have a Bitcrush switch to go between internal and external sources. I still had that in there from the first version so I thought I might aswell use it again. I personally prefer it to mixing the Bitcrush signals together. The layout shows both versions for the Bitcrush option, without switch and in dotted lines with switch. Mike did away with the switch in his design. Instead you do need to open the internal Bitcrush potmeter for the CV potmeter to work. The signals are mixed together in an opamp and inverted. 

Here's a schematic drawing of Mike's solution. On the right is the version with a switch to go between internal or external bitcrush as indicated with dotted lines on the layout wiring diagram. 

EDIT: Until the 8th of June 2021 I had a second inverter stage in the Bitcrush circuit but this turned out to be a mistake so I have corrected the circuit and all the relevant layouts. So if you built this VCDO before the 8th of June 2021 and your Bitcrush section isn't working, check it against the new layouts and make the necessary changes. It's a matter of changing two resistors and a wirebridge to bypass that second opamp. The second opamp must be properly connected to ground, which it is in the layouts.

 

The de-coupling capacitors are mostly not included in the layout. I soldered those straight to the pins of the IC's on the copper side. So get yourself some small ceramic 100nF caps and solder them on, on the copper side, to pins 4 and 8 of the TL072's. The processor chip has a 100nF cap in the layout already. 

I also put 100nF caps over all the inputs of the processor chip. With the previous version of this board, when I was troubleshooting it, I soldered 100nF caps over the inputs and this seemed to improve the input signals a lot. Before I did that the signals had little spikes on them when viewed on my oscilloscope and after I put in the caps these spikes were gone. So I used this idea in this version, eventhough these caps are not in the Electric Druid schematic. They are included in the bill of materials. The de-coupling caps, soldered directly onto the chips on the copper side, are not included in the bill of materials.

Here is the wiring diagram for this project. The wires coming from the wipers of the top right five potmeters to pins 1, 2, 3, 7 and 8 of the processor must be shielded wires. The outer shielding must be connected to ground but only on one side. If you connect both sides to ground there could be current flow in the outer shielding and that would create a lot of hum! (Ground loops) The easiest solution is to connect the outer braiding of each wire to the grounded pin of the respective potmeter it's connected to.

(Last revised: 9-June-2021 Removed second inverter stage from the Bitcrush section and tied off the second opamp to ground. 12-June-2021: Reversed polarity of top capacitor (+5V to Gnd) )

The two stripboards are mounted with the copper sides towards eachother. The pinheaders are soldered straight to the copper sides of the stripboards. In between them is mounted the blank single-sided copperclad circuitboard (shield board) with holes for the pinheaders to stick through. It will help with soldering on the female pinheader sockets if you bend the pins 90 degrees. Makes it easier to solder them in place. But be careful, they are fragile. 

Drill two holes at the bottom of this shield board, at the same distance as the mounting holes of the two stripboards, for the M3 mounting bolts to go through. Make sure the copper side of the shield-print is facing the copper strips of stripboard two and facing away from the main board with the processor on it. We will mount the shield board with the non-copper side touching the copper strips of the Main Board and the copper-side towards the copper strips of board two and we don't want any short circuits :)

Here's the main board. You can leave out the 10K resistor over the output of the 7905 voltage regulator. This resistor is there because some regulators only work well if they are presented with a load on the output but the circuit itself is enough of a load usually:

(Last revised: 23-April-2021: Corrected mistake with C2 (330pF) which went to pin 3 instead of pin 1 of IC-1 like it should. 9-June-2021: Removed colour-code striping from all resistors for clarity. 12-June-2021: Reversed polarity of top capacitor (+5V to Gnd))

Board Two with the CV Inputs on them and the Bitcrush circuit by Mike Desira. (Updated corrected version):

(Last revised: 8-June-2021: took out 2nd inverter stage for Bitcrush option.)

In the layout of board two you can see 10 Schottky Diodes. These, together with the 4K7 resistors, are there to protect the inputs of the processor chip from voltages that exceed the +/-5 Volt limit for CV voltages.

The two voltage regulators are the big TO220 packages and they don't need heatsinks. The current going through them is so low they won't even warm up. You can also use the smaller 'L' types that look like a little transistor but I used the big ones because that's what I had in stock. If you use the big ones, make sure the backsides don't touch eachother, otherwise you'll get a short circuit.

Here's an overview of the cuts, wirebridges and the positions of the pinheaders. I used a double row of pinheaders to make sure I got good contact and to make sure it doesn't get loose. Mark each cut on the component side of the print with a felt pen or a Sharpy. Then stick a needle through the marked hole and mark it again on the copper side. Then make the cuts. This is the most accurate way to do it and prevents errors.

MAIN BOARD, CUTS and WIREBRIDGES - COMPONENT SIDE:

BOARD TWO, CUTS and WIREBRIDGES - COMPONENT SIDE:

(Last revised: 17-March-2021: Corrected a cut at the powersupply pinheader. 9-June-2021: Tied off second opamp of Bitcrush section because that stage has been removed.)

And finally a view of the cuts and the position of the pinheaders seen from the copper side of the print where they actually need to be soldered on and, obviously, where the cuts need to be made.

MAIN BOARD, CUTS and PINHEADERS - COPPER SIDE:

BOARD TWO, CUTS and PINHEADERS - COPPER SIDE:

(Last revised: 17-March-2021: Corrected a cut at the powersupply pinheader.)

Bill of Materials:

Note: the pinheaders are not included in the bill of materials. You can order them in strips of 40 pins long. Make sure you get both the male and female versions and order ten strips of 40 pins. They cost pennies and are always handy to have in stock.

Here's the link to a listing on AliExpress that has the same ones I used. These are female ones but the male ones are also listed on the same page. I'm afraid I could only find the Dutch site version. Order some of both:

--CLICK HERE --

EURORACK LAYOUT:

There is a smaller size layout available in the files section of the 'Eddy Bergman Projects Discussion and Help' Facebook page made by Markus Möbius. He used it to build his VCDO and based it on my layout but just made it more compact and he used single rows of pinheaders. His VCDO works fine. Look for the file name ED_VCDO.diy  It's a DIYLC project file. The layout doesn't have any potmeter and socket connections so you have to reference it with mine to get that sorted out.

DEMO VIDEO:

Here's a demo video with a look at the functions and the different sounds/waveforms you can get from this digital oscillator. When you start mixing the two outputs together, you can get some awesome sounds. If you then put it through a filter it starts sounding really amazing. That's in the last bit of the video. Btw, the mixing together of the Main Oscillator and the Sub Oscillator is done with the 4 channel mixer/passive attenuator from article 17.

For some reason my YouTube embedded videos don't show up on mobile devices anymore. Please go to my YouTube channel if you can't see the video here.

Here's an other video, not by me, that I found on YouTube with a 12 minute demo of the Frequency Central Waverider module, which is the same as the module I built here. The subtitles are in what I think is Spanish though.

TIP: Try connecting the Triple Sloths (proj 61) to some of the CV inputs and a slow sample and hold on the V/Oct input and let it generate its own music.

PICTURES OF THE BUILD PROCESS:

Here are some shots I took whilst building the latest version of this module. In the top picture you can see the green ground wire soldered to the shield print. This is connected to the ground of the powersupply. You can also see I put some tape over the copper edges to insulate them electrically should they touch the copper of board two. If you use upstanding edges then look out not to make them too tall. If they are taller than the pinheaders they will touch the copper strips of Board Two and cause short circuits!. So make sure they are not too tall and use tape over them to be extra sure they can't cause short circuits.

I also made cuts in the corners of the upstanding edges so I can bend some of it out of the way when connecting the two boards together. They obstruct the view of the pinheaders making it difficult to align the two boards correctly. After connecting the two boards I can bend the copper back up and leave it like that.

In the next picture you can see the preparations I took before soldering on the pinheaders. I applied some solder inbetween all the holes and on the pins themselves too. This way I had only to touch them with the soldering iron and the solder would flow and connect them to the copper strip. Then I would add some more solder to make sure the connections were nice and stirdy and I checked the continuity between the strips to make sure there were no short circuits.

In the middle picture you can see the shield print as I call it, mounted inbetween the two stripboards. All the orange wires in the bottom picture are shielded wires. The outer braiding of these wires must be connected to ground but only at one end of the wire. If you connect both ends to ground you can get ground loops with all sorts of problems. I connected the shielding of the wires to the ground connection of the potmeters they are connected to. On the other side of the wires I cut off the outer copper braiding and put a little piece of shrink tubing on to prevent little individual wires from the outer braiding sticking out and contacting other components by accident. (You never know). The prints are connected to the panel by two copper L-Brackets with thin M3 bolts through them, 3 centimeters long. The order of mounting is as follows: Bolt goes through the main board first, then the shield print, then a plastic spacer, then the L-Bracket, then a plastic ring to prevent the L-Bracket from touching the copper of Board Two and then through Board Two. Then I put a ring and a nut on it.

Here's a look at the panel I made for this module. The mix-up of colours of the knobs is intentionally done, I assure you =). The yellow is for control functions and the red knobs are for CV Input levels. Make sure when designing a panel, that you make the two wave selection potmeters, those connected to pins 3 and 7 of the processor chip, your main controls on the panel. Not the frequency controls as is usual with normal VCO's. This is not a normal VCO ^___^. I took my inspiration for designing the layout of the panel from the Klang Stadt version from Frequency Central.

Here's the Wavetable Oscillator next to my two Thomas Henry VCO's. A killer combination!

Here's how I prepared the potmeters on the panel before I connected them to the prints. I soldered in all the 1K resistors and 100nF capacitors and made all the ground connections for the potmeters when I still had access to them. Then I soldered in the wires with the prints laying loose on top of the panel starting with the shielded wires first because they are the bulkiest. 

I made two L-Brackets from some thick copper sheeting I had lying around. You can or course use any metal to make your own L-Brackets or even buy them ready made. Make sure non of it contacts the prints' copper side. I used home made plastic rings to insulate the print from the L-Brackets.

Here's a picture of how I made the first version of this module with much too long wiring and unshielded prints. This did not work so don't copy this!!

TUNING THE VCDO:

Tuning was quite a difficult operation. This is mainly due to the fact that the oscillator quantizes the incoming 1V/Oct signal. But this does have the advantage that once you get the tuning right, it'll be rock solid over many octaves (I got it tuned over 7 octaves in about 15 minutes). 

Because the tuning trimmers are a bit fiddly I put in two of them on advise from Mike Desira. One for normal tuning (20K multiturn) and one for fine tuning (2K multiturn). I also used the Offset control potmeter in the tuning process. This is a normal 20K potmeter, not a multiturn. 

Before you start tuning, set the frequency potmeters on the panel in the 12 o'clock position. 

It was a trial and error kinda process but, like I said, after about 15 minutes I had the VCDO tuned over 7 octaves. You just need to try this and develop a feel for it. I can't give you a procedure for tuning. Make sure you use all the potmeters in this process. The Offset, the tuning trimmers and also the main Frequency control on the panel (not the finetune one).

At one point I had it tuned and tracking nicely only the lowest few notes were way off. I used the offset trimmer and retuned until I also had those low notes in tune and then it suddenly was tracking fine over the 7 octaves of my M-Audio keyboard. You just have to experiment until you get it right.

This is an amazing sounding oscillator. It's got 16 different waveforms in the main oscillator and an other 8 with 4 different octaves in the sub oscillator. You can connect both to a mixer and mix the two signals together and you get some awesome results!! All parameters can be externally changed with control voltages, except for the Glide control. You don't really need CV control on that.

Here's an overview of the 16 waveforms from the main oscillator. The waves all merge and flow over into eachother so there's no stepping between waves so really you have a lot more waveforms inbetween these, but these are the 16 main waves:

And here are the 8 waveforms from the sub-oscillator. Each of these waves is present in 4 different octaves. (The last image on the bottom right is aan example of a Bitcrushed wave with Bitcrush set half way.) The waves from the sub-oscillator do not merge from one to the other. As you turn the Sub Oscillator knob you'll get a waveform at the lowest octave and as you turn more clockwise the octaves will go up in 4 steps until it reaches the 4th octave and then it switches to the next waveform, again at the lowest octave. Then the cycle repeats. So this all happens in definite steps.

You can find the original DIYLC Layout file in the 'Files' section of the EddyBergman FaceBook group.

Okay, that's it for now. All in all not so much a difficult build but a very labour intensive build number 40. I will take it easy with the building for the coming months now. I really need to build a new case because I already built 7 modules for which I have no space. I'm also out of a lot of vital components so I need to replenish my stock which will take some time.

If you have any questions, please put them in the comments below or post them in the special Facebook Group for this website. There are a lot of expert people there who can help you, or at least try :)

DISCLAIMER: The author of this article does not accept any responsability for the correct functioning of this, and any other, module/project on this website. What you build, you build at your own risk. All project layouts are thoroughly tested before publication, it's up to you to replicate them and the author can not be held responsable for any mistakes made.