Monday, 19 July 2021

Synthesizer Build part-43: VACTROL VCF-1 by Skull & Circuits.

This is a bit of weird one among filters and because it uses Vactrols it doesn't sound like any other filter. It has some percussive qualities too if you feed the CV IN with an LFO.

After not having built anything for two months I decided to get going again and this filter seemed like a nice one to try. It's a very simple design and thus easy to build. Because it's such a small print and because it works on a dual 12V powersupply I made the layout more Eurorack friendly.  I have not tested this circuit on a dual 15V powersupply but I think it will work just as well on 15V.  
This project is more of an experimental one than one where the end product behaves in a way we expect from VCFs. What I mean is that the audio from this filter sounds different to all other filters and the CV IN behaves differently too. When I put an AD (envelope generator) signal on the CV IN, the resonance only comes up as the AD signal fades out, the opposite of how other filters behave and when I try to use a negative AD signal by putting it through the Dual Voltage Processor's Attenuverter, it doesn't give the expected result. Not even when I apply an offset voltage to the AD signal. So this is an experimenters dream. It works, but not like you expect. Just know that before you proceed to build it. ^____^

VACTROLS:
This is a Skull and Circuits design and you can find the original information by clicking here.
This is a 12dB LowPass filter, so a two pole instead of the usual four pole filters  This means the frequency rolloff won't be as steep as other (4 pole) filters. 
The Vactrols are something you'll need to make yourself. Well, you can buy them ready made but I advise to make them yourself because new ones can be hard to find and expensive and the ones from China will be fakes, I guarantee it. In the information link above is a video that shows you how to make your Vactrols step by step. I used two 5mm red LEDs (you need two Vactrols) and two LDRs no. 37 from a set with 10 pieces of 5 different types of LDR from eBay. They come in 5 little plastic bags and they are all numbered. I used the ones from the bag numbered 37. I had used those before on the Lopass Gate and they react very fast to light changes. The way your filter will turn out will be different from my filter. There are so many variables here that filters may turn out to be alike but never quite the same. This is mostly due of course to the Vactrols and the way you set the three trimmers.  I tried two different types of LEDs in my Vactrols. First I tried bright white LEDs but with those I needed to turn most of the trimmers completely clockwise or counterclockwise to get the filter to behave correctly. The second time I used normal red LEDs (5mm) and they worked better. Now I could use the trimmers more accurately to get the right sound. So I advise to use red LEDs for you Vactrols. The LEDs in the filter itself, mounted on the front panel, do not shine very bright in my module. I used two 3mm yellow LEDs and they only come on when the trim-potmeters are set to extreme positions. I can get them to shine brightly when I turn the trimmers a certain way but then the filter doesn't work properly. Again this is one of those things that will be different with your filter because of component tolerances and differences in the Vactrols etc.
Just out of interest, here are some measurements I took of my DIY Vactrol (out of circuit) with red LED:
OFF resistance = >200MOhm.  ON resistance with a +/-5Vpp signal = about 10K, with a 0/10Vpp signal = about 5K. This is with a 1K resistor in series with the 5mm red LED of the Vactrol.
Of course these values differ when the Vactrol is in circuit because there you can set offset voltage etc. which alters the resistance.

NOTE: This module pairs extremely well with the Voltage Processor and the Lopass Gate module. If you create a beat with an LFO into the CV IN of the filter but first put the CV through the voltage processor you can accurately control the sound and if you then send the audio through the Lopass Gate you can turn your beat into a sort of galloping beat. Connect a signal from the same LFO used for the VCF to CV1 of the Lopass Gate and use a faster LFO signal on CV 2 of the Lopass Gate. Used in this way the Vactrol VCF can be used to make some cool Techno kickdrum sounds.

LAYOUTS:
Here is the layout I made for this filter. As always the layout is verified. You can see it's small enough for a Eurorack module and I incorporated a Eurorack power connector to make life easier for those of you using that format. I myself didn't use the connector in my build but just soldered the power cable straight to the print like I always do.



Print Only. Note that the copper strip between pins 3 and 12 of the IC is NOT CUT! Both pins are connected to eachother underneath the chip:



Strangely enough I found that I needed to reverse the wiring of the Cutoff potmeter for it to work the right way around. I left it the way it is presented on the schematic, in the layout so you can decide for yourself whether you need to do that or not. 

Bill of materials:



TRIMMING THE CIRCUIT:
Trimming this circuit is a matter of trial and error. You need to set the trimmers in such a way that you get a good deal of self oscillation when the Resonance potmeter is set almost completely open and you need to get the right range for the Cutoff potmeter. I can not give you a procedure to help you do this. You will have to figure it out yourself but it's pretty straight forward. Just put a squarewave or rampwave signal on the audio input and connect an LFO signal (+/-5Vpp) to the CV input and then connect the output to your VCA. Changing R7 from a 47K resistor to a 100K trimmer helped a lot in getting this filter trimmed. It was suggested in the text of the original Skull and Circuits article about this VCF and I also saw they implemented it on the PCB so that's why I put in a trimmer for R7 in the layout. It might be a good thing to use multiturn trimmers instead of the single turn ones I use in the layout. I used normal trimmers on my print but it can be fiddly to set these correctly. I might replace mine with multiturn ones too. You might think it would be a good idea to put an attenuation potmeter on the audio input but I tried that using the passive attenuator on my mixer but it didn't help at all. The filter only worked if I had the potmeter fully open so there's no need for an audio input level potmeter. As you can see in the schematic, the audio is attenuated by a factor of almost 18 times by the 1K and 56 Ohm resistor voltage divider right at the audio input. Then it is boosted up again in the output opamp.
The whole upper portion of the schematic dealing with the Cutoff and CV input goes straight to the LEDs of the Vactrols so you can see that he whole filter hangs on these Vactrols. The Offset and Range trimmers control the Vactrol LEDs and determin when the LEDs turn on and how sensitive they are.

Schematic drawing:



Here are some pictures from the build proces. In these pictures the third trimmer is not yet put in. I tested it first with R7 as a normal 47K resistor. I later changed it for a 100K trimmer.
The print:


Print mounted behind the panel not yet wired up:




Video of the first test. You can see here that connecting an AD (or Envelope) signal to CV IN results in the opposite reaction to what normally happens. Using a negative or inverted AD signal doesn't fix this issue. Not even with a positive offset voltage applied. That just proves that this is a very quircky filter and all the more interesting for it ^__^  I've heard better results than mine from other people who built this VCF, so it depends a lot on how your vactrols turn out.




Okay, that's it for now. I hope you found this article useful and if you did maybe you would like to contribute to the upkeep of this website and to keep these projects coming. If you do, you can buy me a coffee. There's a button for that underneath the main menu if you're on a PC or Mac. Otherwise you can use this PayPal donation link.  All donations will be used to buy components for future projects. Thank You!

If you have any questions or remarks you can put them in the comments below or go to the Facebook Page for this website where we have an awesome little community of cool DIY synthesizer enthusiasts that are more than willing to help you out with any problems you might encounter.

Tuesday, 13 April 2021

Synthesizer Build part-42: 8 RANDOM GATES by Yusynth.

 Creates 8 random gate outputs from one gate input signal which can be as high in frequency as an audio signal. Lots of creative possibilities with this module.

There is an other random gates project on my website already. That one is included in the Noise Module article and it creates random pulses on one output. With this module we have 8 different outputs which trigger in a completely random order. It needs a squarewave on the input that can come from an LFO, the gate out from a sequencer, the clock pulse from a sample and hold or even the pulse wave output from a VCO. The pulse width doesn't matter for the functioning of the module, it can handle any pulse wave. I tested connecting it to a VCO but the output is nothing very useful. It's just a lot of clicks and even putting it through a filter didn't make it sound any better. So as a sound source it isn't that good but that's not what it's designed for anyway. There are a lot of other ways you can use this module. To trigger drum modules for instance.

ABOUT THE CIRCUIT:
The module is fed with only positive voltage so no dual powersource needed. It works fine on both +15V or +12V. You can feed the gate-in with signals that have a negative cycle to them. It will simply ground the negative part of the cycle through diode D1. The output gate signals have an amplitude of 8 Volt when powered from a +15V powersupply.
This build consists mainly of wirebridges. My layout has 37 of them. All the output stages are made on separate pieces of stripboard with just 4 strips of 10 holes. They are soldered straight to the output sockets. I did this to save space otherwise I would have had to make a separate print with all the outputs on them. This way saves space and also hookup wire. The three 100nF capacitors you can see on the layout are meant to be de-coupling caps but where they are positioned is really too far away from the chips to be effective. So instead of putting them where the layout shows them, solder them straight over the plus and ground pins of the IC's (top right and bottom left of each chip).

Here's the layout I made. First the wiring diagram:


(Last revised: 14-April-2021: Added missing 1K resistor to output prints.)

In the box, on the wiring diagram above, you can see the schematic drawing of the output stripboards. I left out the 1K resistors in series with the output in my original design. I had simply forgotten it but I have now updated everything and the 1K resistor is now included. It helps to protect the transistor against short circuits, smooths the output voltage a bit and also determins the output impedance.
The 270 Ohm and the LED together with the 1K resistor to ground form a voltage divider that determins the voltage of the outputed Gate signal. That voltage is normally 8 Volt but if you want it to be higher you can make the 1K to ground a higher value like 1K5 or lower for a lower output Gate voltage.

Here's the main stripboard. It's only 24 by 48 holes but you could try to redesign it and make it even more compact so it would fit in a Eurorack system. For instance, if you connected the outputs straight to the correct pins of the chip instead of using the wirebridges you can save about 8 or 9 holes in width. Certainly enough room to make it fit a Eurorack system. And because it's a "Random" gates generator, the correct order doesn't really matter does it?


And here's a close-up of the little output stripboard that is soldered straight to the output socket: (If you print this one, choose the A6 format to save some printer ink.)
You need to make 8 of these output prints. Some cuts are a bit hard to see but the top two strips are cut at position 5 and there's an other cut at position C8.


(Last revised: 14-April-2021: Added missing 1K resistor to output prints.)

Here's the Bill of Materials:



Here's the schematic by Yusynth. You can find the original YuSynth article by clicking HERE.


As you can see it's actually quite a simple circuit. It mostly consists of connections between the three IC's. It is mentioned on the YuSynth website that this module needs a bit of time before it starts behaving correctly. When you first start it up it will probably not fire on all cilinders and display a repeating pattern with only about 4 or 5 LEDs lighting up and after at least ten cycles this will change into a random pattern using all the outputs. However, since I changed the new CD4070 I had in there for a used vintage CD4070 from the 1980's that I had lying around, the module works good right from the start. 
The module that I built was at first prone to hanging. It would suddenly stop being random and get stuck in a 4 or 5 LED pattern. Only by changing the input gate frequency or pulling the Gate-In cable in and out a few times would I get it working again. It turned out this was also due to the IC's I was using. I don't know if it was a fake chip or if it was damaged but I changed IC-3 for an old stock CD4070 that I once de-soldered out of an organ circuit board and the problem was solved immediately.
So make sure the chips you're using come from a reputable source!

MODE SWITCH:
There's a mode switch that lets you choose between two settings. In the ON position the output stays high until it detects the next pulse, so the pulses don't have any dead time between them. In the OFF position the output pulse stops on the negative slope of the input gate pulse, so the output pulses will have the same length as the input gate pulses.
There's also an option to advance the pulses manually with a momentary switch (normally off). This switch is connected to the internal switch of the Gate input socket so it will only work when there is no cable connected to the gate input socket.

Some screenshots from the oscilloscope. The first one shows how extremely fast the risetime of the output gate signals is. Just over 123 nanno seconds! That's 0 to 8 Volt in 0.000000123 seconds. This means theoretically that it could handle signals upto 40MHz! (Agreed, this knowledge is of no use in the synthesizer world but it fascinates me personally because I also have a background in radio technology and transmitters.)


Here's what the output sequence of one of the random gates looks like. A non-repeating sequence of pulses with an amplitude of 8V. 



Here are some pictures of the build proces:

Wirebridges. In this picture there's a little wirebridge missing connecting pins 7 and 8 of IC2 (CD4051).


Here's the finished print. Like I mentioned earlier, the de-coupling caps are much to far away from the chips to be effective so get some small ceramic 100nF caps and carefully solder them straight over the plus and minus connections of the chips on the copper side. I myself left it like this and it works just fine because I don't use a switchmode powersupply but a linear one, with a big transformer. 


Here's the main board with the 8 output prints. My output prints are missing the 1K resistor in series with the output sockets (I had forgotten those) but they are included in the layouts. That 1K resistor helps to make the output waves smoother. I could see that on the oscilloscope images. It also protects the transistors by limiting the current going through them should the output be shorted. (Although damage will be very unlikely even without the 1K resistors because the pulses are so short).


Finished panel backside wiring:


Frontal view of the mounted panel:


And here's a little test video showing the module firing randomly on all cilinders :)


TIP:
If you want a fast pulse train with random gaps in it, then connect 4 outputs from this module to the 4 inputs of a mixer, like the mixer/passive attenuator module on this website. At the output of the mixer you will get a pulse train with random gaps in them. It's cool to use this on the cut-off of a filter to add some random spice to the sound.
If you then set the switch on the random gates module to 'Stay high until the next gate pulse' you have sort of a random voltage generator, although there will still be random 0V gaps in the output but that makes it unique :)
You could even make a little TL072 mixer print and include it in this module. Choose how many inputs you want (less than 8 of course) and connect those mixer-inputs to whichever outputs you choose and then make an extra output socket on the panel that carries the output from the mixer and label it "Pulse Train". It's just a thought but there are many ways to adapt this design to your own needs.

Okay, that's an other one done. If you have any questions or remarks please put them in the comments below or post on the special Facebook Group for this website where we have a great community of synth enthousiasts willing to help you.

If you successfully built this module and you're using it in a cool way that others might enjoy, please make a video, put it on YouTube and contact me with the link. I'll add it to the article with full credit given.

If you're enjoying this content and find this website useful and would like to help support it and keep it running you can buy me a coffee. There's a button for that underneath the main menu if you're on a PC or Mac. Otherwise you can use this Paypal.Me link. All donations go towards the purchase of new components for future projects. Thank you!!

Monday, 22 March 2021

Synthesizer Build part-41: METALIZER by YuSyth.

A module out of the wavefolding stable only this one sounds really sharp and metally, hence the name. It's quite an easy build too although it does need two pairs of matched BC547 transistors. It's more or less a quadruple wavefolder with a Voltage Controlled Amplifier on the input which is controllable with two attenuated CV inputs.

This Yusynth module was something I hadn't come across before because it is not on the YuSyth main website, at least not in his projects menu which is where I normally look. Someone posted a link to this module on Facebook and I thought it would make a perfect little project.
Yves Uson (YuSynth) designed this Metalizer for the Arturia MiniBrute and MicroBrute and he says it's now one of the most characteristic features of those two monosynths. I think this will be a great addition to any modular system. It's like a Heavy Metal guitar pedal =)

When I started building this project I went about it much too hasty and I had made about six or seven mistakes when I first tried to test it. I had forgotten cuts, misplaced wirebridges, used the wrong transistors in the wrong place, the whole shabang. But luckily, over time, I've become quite good at troubleshooting and I recognized the mistakes pretty fast when going through the schematic and comparing it with the layout. The final mistake was a cut I had forgotten that connected the -15V to the base of transistor Q2 which generated a enormously loud buzz. I detected that by using the 'Highlight Connected Areas' function of DIYLC, the layout making software I use. Once I cut that copper strip the module sprang to life. It sounds pretty cool  It's much like the other wavefolders on this website but this one has more harmonic distortion and much more complex waveforms. It sounds buzzy-er, gritty-er more metal like, sometimes more ring-y if you know what I mean. 
If you read the 'Triple Wavefolder' article you might remember me speaking about having a VCA on the input to control the input level and with that the number of folds the waveform undergoes. Well, this Metalizer has a built-in VCA on the input that is controlled by the CV-1 and CV-2 inputs. Also, the audio level doesn't change if you turn the 'Wave Folding' potmeter which is a problem that the triple wavefolder does have.
The waveforms that come out of this module look like some three year old kid took a pencil and scratched on a notepad in a fit of rage and anger ^____^
Tip: this Metalizer is particularly useful if you make drone like, continuous sounds with your modular synth. Having it produce a constant noise and modulated by a slow sine or triangle wave from an LFO can produce some very cool results especially if you are into more heavy, distorted sounds. You can also vary the frequency of the VCO going into the Metalizer by connecting the VCO to a slow LFO signal too and have the two interact that way. Enough ways to experiment with this awesome module.
Like the other wavefolders, this module works best if you feed it a Triangle- or a Sinewave. 
The module is meant to work on a dual 15 Volt powersupply but will work fine on a dual 12 Volt supply.

The build proces was quite straight forward. One of the things you need to look out for is the 680nF capacitors. Those are values that are not often used in synthesizer projects. I think this is the first one on this website that uses 680nF. The only ones I had were some very big ceramic ones but I didn't have enough so I had one capacitor that I made up out of two caps mounted in parallel. I didn't account for the size of those capacitors in the layout but if you order new 680nF caps they will fit fine in the space allocated to them in the layout. The new ones are much smaller than the old stock I had. I later found out that the exact value of those capacitors is not that critical. You can use anything between 680nF and 1µF as long as it's non-polarized.
You might think 'I'll put a level potmeter on the input so I can control the volume' but don't do that! That function is already covered by the built in VCA so keep to the design as shown on the layout and schematic.

Here is the link to the schematic in the YuSynth article. It also has PCB layouts, if you want to make your own PCB for this module, and it has the panel design which I more or less copied for my own panel.

Here's the layout, wiring diagram:


Print only:



THINGS TO LOOK OUT FOR:
Beware, the first two pairs of BC547's need to be matched. Q1 and Q2 is one pair and Q3 and Q4 the other. I matched them with my transistor curve tracer on the oscilloscope but you can use the Hfe transistor tester on your multimeter (if it has one). You can also get dedicated transistor testers for cheap on eBay that'll do the job nicely too. Just test them and pick the ones that have similar readings.
An other thing to keep in mind is this: if you look at the output of this module when there is nothing connected to the input you're going to see a very noisy squarewave-like waveform on the scope. This is normal. As soon as you plug in the input everything will be back to normal. It's just a design flaw but harmless although you will hear this noise if you have the output connected to the audio in the rest of your synthesizer. So when no input is used the output must be disconnected or the Metalizer channel of the mixer must be muted. You know what I mean, right?

Here's a picture of the oscilloscope screen, probing the output without anything connected to the input:



ABOUT COMPONENT VALUES:
The potmeter values in the circuit are not critical because they are just used as voltage dividers here so you can use any value you happen to have lying around. I would advise to keep them in the 50K to 1M range though. That should work fine. The value of the 680nF capacitors can also be varied. Values between 680nF and 1µF will all work fine as long as they are not polarized so if you use 1µF caps they can't be electrolytic capacitors. They must be non polarized. The output capacitor of 10µF is an electrolytic capacitor but its value can also be varied. Anything between 4,7µF and 10µF will work just fine. Make sure the minus pole is towards the output socket.
Luckily there are no trimmers in this circuit so there's nothing that needs tweaking or tuning. 

Here's an overview of the cuts and the wirebridges. Mark the cuts with a Sharpy (water proof felt pen) on the component side of the print first. Then stick a needle through the marked holes and mark them on the copper side. Then cut them with a hand-held 7mm drill bit. 


Cuts only, viewed from the COPPER SIDE:


Bill of Materials:



Here are some pictures of the finished product: Note the enormous size 680nF caps I had to use because I didn't have anything else in stock.




Here's a little demo video that I made of the very first test of this module. So this was the first time I had it switched on and connected to a VCO:


Here's an other demo video I found on YouTube (not by me) which shows the Metalizer in action with a sequencer attached. The Metalizer is the second module from the left, marked "Metawave" (the one lying flat on the table):



Here are some screenshots of the oscilloscope showing the characteristic waveforms that come out of the Metalizer. They are very spikey sharp waves with loads of harmonics. If you put a conventional Lowpass Filter after the Metalizer you're going to get mid to high frequency sharp sounds out of it that sound pretty cool but there won't be much variation when you turn the 'Folding' knob on the Metalizer. In my opinion it's better to use this on its own, not in combination with a filter unless those sharp sounds are what you're looking for. They sound very musical. Almost like an FM synthesizer. The waves in the pictures below were all generated by putting a Triangle wave on the input and then probing the output.





Okay, that was article number 41. I will take it easy for the coming time because I have run out of some essential components and materials like the powdercoated aluminium strips I use to make my panels from and some electronic components. I'm even out of Hook-up Wire. I used a shielded cable with 8 wires inside as a source for hook-up wire. I had 68 meters of it and it's now all gone. That means there's over half a kilometer of wire in my synth now, LOL. So I need to replenish my stock and I also just acquired a VC340 Vocoder (such a cool piece of kit!) so I need to take it easy on the wallet too, LOL. You know how it is with this hobby, LOL :)

If you have any questions or remarks about this project please put them in the comments below or post them in the special Facebook Group for this website where we have a very cool little community willing to help you with any questions you might have.

If you like what you see and you would like to support my projects and the upkeep of this website then you can buy me a coffee. There's a button for that underneath the main menu if you're on a PC or Mac. Otherwise you could use this Paypal Me link. All donations go towards the purchase of new components for future projects. Thank you very much!

Friday, 12 March 2021

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.  The Glide function doesn't have a CV input but that's not needed anyway. 

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 is what he said about it:

"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."

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 print in my stock so I decided to cut this print 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 stick through and soldered upstanding copper strips 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 prints eventually fit together. I stuck 4 transparent rubber feet on top of eachother and put it between the shield print 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 gaffer tape on the edges to insulate them.


SCHEMATIC:
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.

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. The easiest solution is to connect the outer braiding of each wire to the ground pin of the respective potmeter.


(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 print (shield print) 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 print 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:


(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 version without second inverter for Bitcrush option; 8-June-2021):


(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.

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 BangGood that has the same ones I used. These are female ones but the male ones are also listed on the same page. Order some of both:

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.


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.



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 on my budget.

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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.