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 for synthesizers =)

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.
Btw, it is not possible to have a clean signal come out of the module. In other words, the effect is never truly off. Even with the folding-potmeter set to minimum there's still a good bit of wavefolding going on so if you want to be able to have a clean output you can include a bypass switch or a Dry/Wet potmeter, but you'll have to figure out how to do that yourself. It's not included in this project. However it's very easy to do.
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 560nF 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:

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 doesn't help if you connect the input to ground with the built in socket switch, if there's no cable connected to the input. I tried it but it makes no difference. 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? Or you can use it as a quircky noise source ^____^

Here's a picture of the oscilloscope screen, probing the output without anything connected to the input. You can see how noisy the curve is:

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. However, going by the Falstad simulation at the bottom of this article, the value of those capacitors does not have a big influence on the shape of the waveform. I tried inputting 370nF caps and the output waves were practically the same as with 680nF caps.

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. Also, I only had one hand free to turn the knobs and play some notes on the keyboard, having the camera in my other hand:

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.

I made a Falstad simulation of the Metalizer and when you run it you can see it produces exactly the same waveforms as on the oscilloscope: 

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 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!

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.  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.

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

"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 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.) You can also use left over bits from the shield print to make the upstanding shielding if you want 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 gaffa tape on the edges to insulate them.

[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.

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 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. 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.



(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.


(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:

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  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.

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.

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 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 :)

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!

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.