Welcome to stripboard heaven! Here you'll find all the projects I used to build my DIY Modular Synthesizer. I'm using the 'Kosmo' size standard but I also build Eurorack sized modules. All layouts are made by myself and verified to work. The schematics they are based on come from all over the internet. If you're on a PC or MAC, there's a complete MENU in the sidebar. For mobile devices the menu is in the black 'Move to...' bar below this text.
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.
LAYOUT:
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. I've added a Eurorack connector just in case you want to use that. The metalizer will work fine on dual 12 V too. You'll need to flow the 3 ground positions underneath the connector together with some extra solder.
Stripboard 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 method I used with the TB303 filter and the ARP2600 filter. That's the Ian Fritz method. You'll find a description of that method in the aforementioned articles.
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:
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. 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.
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:
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.
The famous Moog ladder Lowpass filter (YuSynth version) using two CA3046 transistor array chips so no need to hand match transistors. But this is not a project for beginners!
This is the second Moog Ladder Filter on this website. With the first one I wanted to avoid using the CA3046 chips because I was at the beginning of my synthesizer build project and at that time designing a layout including those chips was a bit too much for me but now, after more than a year of designing layouts from schematics I had confidence enough that I could make a layout that worked. Well, I was right. The layout I made worked perfectly first time.
This filter does sound a bit better than the first one I think. The resonance is better controllable and it just sounds like a professional filter allround.
This is a 4 pole Lowpass filter (24dB per Octave cut off slope.)
Using the CA3046 transistor arrays means that we don't have to hand pick and match transistors ourselves. The transistors in that chip are all matched and even though the chips were obsolete, you can now buy them again. There are also new manufacturers like Alfa Rpar's AS3046 which costs about 6 UK Pounds and is available on Electric Druid's website.
If you match transistors yourself and you don't do a good enough job, you might get a filter that self oscillates on the top half of a squarewave but not on the bottom half. That actually happened to me once too. That's why, if you build the all transistor version posted on this website (chapter 7), you need to be accurate with matching and that's also why this project is easier because there's no matching involved.
This filter is meant to run on a dual 15V powersupply but it will work on 12V too, but you'll need to make three resistor changes:
For Eurorack R24 and R27 need to be changed from 270K to 220K and R26 needs to be changed from 1K2 to 1K. These resistors are situated on the righthand side of the stripboard below the second CA3046 (U2).
Here's the schematic by YuSynth. It's the same one as in chapter 7. In the layout the numbering of the TL072 chip is reversed. I used pins 1,2 and 3 for the input and pins 5,6 and 7 for the output, instead of the other way around like on the schematic:
In the picture below is the verified layout. I used this for my own build and it worked first time. I spent about 5 days making and checking and double checking it. It wasn't easy to fit everything on a 24 by 56 hole stripboard but I managed it luckily. The first layout design had a jump wire in it but I made an updated version that got rid of the jump wire. Because of the complexity of the layout I would not advise this project to people who are just starting out in DIY synth building. It's not beginner friendly. There was no room left for any mounting holes so I connected the print to the panel using an L-Bracket and plenty of Hot-Glue. If you use a bigger piece of stripboard you will of course have room to use the extra space for mounting brackets.
Here's a Falstad simulation of the ladder filter I made myself: -- CLICK HERE --
There are three CV inputs on the schematic drawing and only one of them has an attenuator. In my build I gave two of them attenuators and the third CV input is un-attenuated. You can use that for a 1V/Octave input, but the self resonance won't track over the octaves. At least I don't think so. There's no specific 1V/Oct. input marked on the YuSynth schematic nor is there a trimmer for it. The Bill of Materials already has two 100K potmeters so you can have level control on two CV inputs.
Wiring Diagram (This is a 24 x 56 hole stripboard):
(Last revised: 23-Feb.-2021: Removed jumpwire and added a wire bridge. All layouts updated. 02-March-2021: reversed wiring of Resonance potmeter. 25-March-2021: Added de-coupling cap to U3 and two 22µF el.caps on powerrails. 16-7-2023: Removed colour coding from resistors.)
Stripboard only. As you can see I re-used an idea I implemented in the first Moog Ladder Filter project namely to make the gain of the in- and output opamps adjustable with trimpotmeters. So I replaced R5 (56K) with a 100K trimmer and R32 (120K) with a 200K trimmer. Take particular care with the orientation of the transistors! As you can see on the layout the middle ones are rotated 180° in relation to the other transistor pairs. These transistor pairs do not need to be matched. The matched pairs are all contained within the transistor array chips. However, it can't hurt to check their Hfe values and choose transistors that have simular values. Again, this is not necessary but it's something I did myself.
Here's an overview of the cuts that need to be made. Follow it with great accuracy! I'm giving you a view from both sides of the print because I personally always mark the cuts on the component side first and then stick a needle through the marked hole and then mark and cut it on the copper side where the needle comes through. That's my procedure and it guarantees that all the cuts are made accurately. It also helps should you need to troubleshoot later. The first image also has the wirebridges on the component side. Put those in after you finished the cuts.
Here are the cuts and wirebridges marked on the component side. The green ones are connections to ground, red are connections to positive voltage rail and purple to negative voltage rail:
And here are the cuts marked on the Copper Side:
Bill of Materials.
BUILDING PROCEDURE:
Make sure you go about building this filter very methodically. It's certainly not one of the easiest builds on this website. Mark out the cuts accurately and then cut where indicated. Then put in all the wire bridges. There are 40 in total. Here's a picture of the wire bridges installed and the cuts marked on the component side (something I always advise to do). This is a picture of my print made using the old layout. I have now updated the layout, as mentioned before, and got rid of the jump wire in exchange for one extra wire bridge. Make sure you use single core copper wire, like transformer wire, or tinned copper wire for the wire bridges. If you use normal multistrand insulated wire it will get very messy very soon, especially because there are 40 of them. Break open an old transformer, get the wire out in as long pieces as possible, sandpaper the wire because there's a layer of insulating lacker on there that needs to come off. Then you can use it.
Then put in the flat lying resistors first. In this picture I forgot the 680 Ohm resistor R34 and the 22 Ohm is a 220 Ohm so I had to replace that one. So beware you get these right ;) Mark off every component you solder in on a paper print-out of the layout to keep track of your progress. This print also doesn't have the two 10 Ohm resistors on the powerrails because I left those out in my build.
After that put in the rest, I left plenty of room around the trim pots so you can accomodate different sized trimmers. For instance, I use a lot of old de-soldered trimmers I got from old circuitboards and they are usually a bit bigger than what you get these days, but it will all fit.
CALIBRATING THE FILTER:
The trimmers can be normal types. No need to use multiturn trimmers. You need to connect this filter to an oscilloscope and keep an eye on the output signal while inputting a squarewave from your VCO. Then set the trimmers to good resonance response and good signal amplitude over the full throw of the panel potmeters. Then connect it to the VCA and trim again for best sound. It's a matter of experience but it's really not that difficult. You just need to use your logic. I can't really give you a procedure for calibrating.
Beware that the Resonance only works at the last bit of throw on the potmeter. That is why you need a reversed logarithmic potmeter, to stretch out the resistance in that area of the potmeter and get more fine control over Resonance. This is a normal characteristic of the Moog Ladder Filter and there's not really anything you can do about it. All Moog Ladder Filters have this. You could say it's a design fault.
Here's a video of the filter in action, connected to my little sequencer so you have an idea of what it sounds like. You might see occasionally that the self oscillations on the lower part of the squarewave disappear, but this is due to the fact that I have the volume set quite low (itchy neighbours ;-) ) Play with this filter at full volume and you'll blow your mind. It sounds so good! ^___^
This filter has some weird characteristics that occur in all Moog Ladder Filters. For one, if you turn the Resonance (sometimes called Emphasis) fully open, the volume drops a bit. You can see that happening in the demo video above. The second quirck is that the Resonance potmeter is only effective in the last little bit of the throw of the potmeter. That's why you need a reverse logarithmic potmeter. To stretch out that last fully clockwise bit of the potmeter. But don't worry, you can still dial in the Resonance very effectively and to compensate for the drop in volume there's a volume control potmeter on the audio input. So if you set that three quarters open, you can give it a little extra when you open up the Resonance. Anyway, if you set the resonance first then the volume will stay the same when you turn the Cut-Off Frequency potmeter. So it's not too big a problem really. That's probably why Bob Moog didn't address this issue.
There is an alternative schematic by Harald Antes that addresses this drop in volume problem but it is too complex to implement on this layout and this size stripboard but I'll give you the link (which a longtime member of the EB Facebook group kindly posted). There are Gerber files included so you can just order a PCB and build it that way.
Making the above mentioned version would be a whole other project in itself. Maybe something for the future. However, if you take a look at the schematic he does suggest a way to switch between the 'Poles' of the filter. I tried this and installed a DPDT toggle switch (ON-ON) and connected it so that I had the choise between 24dB (4 pole) and 12dB (2 pole) and all I can say is, spare yourself the trouble. It adds absolutely nothing to this filter. The only difference is that in 12dB mode the filter's self oscillation on top of the input wave disappears. It still sounds pretty cool but in no way different from the sound you can get in the normal 24dB mode. So don't bother. I just tried it so you don't have to.
But just in case you want to try it yourself here's how to connect the switch. Compare it with the original layout to see which two wire bridges you need to remove and replace with the switch. Do not mix up the wires. The dotted wires go to the bottom side of the ladder and the normal coloured ones go to the top side of the ladder. Don't mix them up! Be accurate. Btw, if you want to make the filter switchable between 24dB and 18dB instead of 24dB and 12dB connect the dotted green and the pink wires to the dots with the same colours. Each of the poles can be tapped off from the collector of the transistor in that pole.
[EDIT] I recently changed the connections to the ones I indicate on the layout turning it into a 18dB filter and this sounds a bit better. You get a little bit of self-oscillation in the signal this way but I just know I will only use this filter in 24dB mode because that sounds the best.
Here are some pictures of the finished module:
A view behind the panel:
Okay, that's it for now. If you have any questions please put them in the comments below or ask on the special Facebook Group for this website.
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.
A fun little project to make your modular synthesizer react to light. It has offset and level controls and CV smoothing plus an external LDR input.
Let me start by saying that this module needs to be connected to a VCO to work so it's not a stand-alone thing. This circuit outputs a Control Voltage and the height of that voltage is dependent on the brightness of the light falling on the LDR, the Light Dependent Resistor.
This was a little project I dreamed up myself and I designed the circuit too. It's quite a simple build. It consists of two opamps. The first one has the LDR input and the Offset control but it inverts the CV voltage. Then the second opamp inverts the CV voltage back to normal and feeds it to the output socket via a level potmeter. There are two 3mm LEDs on the output to indicate if there's a positive or negative voltage present and the brightness indicates the voltage level.
The Smooth switch is there to suppress the 50Hz or 100Hz hum you get from LED (or other) light fittings. They flicker so fast you can't see it but the LDR reacts to it. The switch simply puts a 10µF electrolytic capacitor over the LDR smoothing out the control voltage.
This circuit works on +/-12V but it will work equally well on +/-15V. It consumes very little current. On 12V the maximum current I measured was 5.6mA. 1.6mA of that is consumed by the LEDs if one of them is on. So you see, it hardly draws any current at all. It will also work on 9V although the CV voltage will be less high obviously. The offset feature needs a dual powersupply in order to transpose the CV voltage down so you'd need two 9V batteries to create a dual 9V powersource. I haven't tried it on 9V but I get questions about it but I don't see why it wouldn't work. You might need to adjust some of the resistor values or experiment a bit to get the best out of it. That's up to you.
There's a link to a 3D printed front panel for this project in the comments below.
HOW TO USE IT:
This circuit doesn't generate any sound itself. It just outputs a Control Voltage. You can connect the output Control Voltage to the CV input of a Voltage Controlled Oscillator (VCO) to get the Theremin effect. You can also put it through a Sample and Hold first and then into a VCO. In that way you will get stepped tones. An other option is to lead the CV through a Quantizer first, to get it to output true notes that adhere to the 1V/Oct standard and so try to make melodies with light. Of course you can also use the CV to affect the Cut-Off frequency of a filter. Your imagination is the limit :)
The CV voltage and therefore the tone will get higher as the light that shines on the LDR gets brighter, and lower when it gets darker. The exact way it reacts can be set very accurately using the offset control, without limiting the dynamic range of the notes. (The same idea as with version 2 of the 8 step sequencer).
The idea behind the external LDR input is to make it possible to bring the LDR to the light-source instead of having to shine lights on the panel itself (with the built in LDR). This makes it much more flexible. You can just take the LDR in your hand and point it at things and use it as an instrument. The whole circuit works so much better when you use this option. Try it!!
If you feel you need more output voltage then change the 100K feedback resistor over pins 6 and 7 of the IC. Double the value to double the gain. 147K should be enough to go really high but normally it shouldn't be necessary to change it. Obviously you are limited by the height of the power supply voltage but with 1V/Octave you really don't want your CV output to exceed 8 Volts.
You can experiment with light sources and where you put the external LDR and let your imagination run wild. You could build a whole light operated synthesizer with this project as a starting point. =)
LDR:
I can not give you a part number for the LDR to use in this circuit. I ordered a set of 5 different LDRs with 10 pieces of each, from eBay. The link to that has expired but here's an other one to a set of 70 with 7 different values. That will last you a long time. Handy for making Vactrols too to have this in stock:
I used the one marked 5537. That's a very fast reacting LDR. But to make sure, test them with the resistance meter on you multimeter and choose one that reacts fast to light changes.
Here's how you can make an external LDR that you can move around and point at light sources. Simply take a female jack socket like the ones you mount in panels and solder an LDR over the audio and ground contacts. Use some hot glue to make it nice and stirdy. Now you can connect it to a patch cable and connect the other end of the cable to the external LDR input. Flick the switch to 'Ext.' and you're in business. =)
External LDR. Just put some hot glue around the LDR leads to stiffen it up a bit. The external LDR worked really well when I tested it. Of course you can shorten the leads of the LDR or bend them at 90° so it can lay on a table and catch the light from above. It's all up to you.
Schematic drawing of the circuit:
LAYOUTS:
Here is the verified layout. As you can see you can build this on a very small piece of stripboard. Don't be fooled by the wiring of the Offset potmeter. It looks like it's wired the wrong way around but remember that the opamps are wired as inverters so the offset voltage is turned the right way up in the second stage. (All potmeters are viewed from the front with shaft facing you):
Stripboard only:
Bill of Materials:
TAKE NOTE OF THIS:
There are a few things you need to beware of when building this project. I built in the option to connect an external LDR to the panel instead of using the built-in LDR with a switch to choose between them. The socket for this External LDR input must be mounted in such a way that it is completely isolated from the panel if you are using a metal panel. The socket is connected directly to +12V, if it touched the panel it won't short out because there is still a 10K resistor between it and ground but it won't work as an input anymore. So connect the socket to some plastic and make a big enough hole in the panel to glue or screw the socket behind the opening without it touching the panel itself. (See pictures below to see how I mounted it to the panel.)
DO NOT CONNECT ANYTHING ELSE THAN AN LDR TO THE EXTERNAL LDR INPUT! It has +12V on it and may damage sensitive electronics. So make sure you label that input clearly! Maybe it's wise to use a different kind of connector for the Ext. LDR. That way you can't put in a patch cable by mistake.
The same caution must be taken with the LDR that is mounted in the panel itself. Make sure it makes no electrical contact with the panel when you glue it in place with hot-glue. Check it with a continuity meter after glueing it in place.
Here's a short video I made of the very first test I did. This thing can really make a VCO squeel!!:
Here are some pictures of the build proces and the end product:
In the picture below you can see how I mounted the 'External LDR' input socket. I used some white plastic and mounted the socket in that and then I drilled a hole in the panel, wide enough to take the socket with plenty of room around it, so it wouldn't touch the metal of the panel. Then I hot-glued it all in place and it works very well like this:
Here are some oscilloscope screenshots showing the maximum amplitude of the light pulses I got with testing. It was more than 20Vpp when I ran the module on +/-15V but you can turn that down with the level control.
Here's an image which shows the 100Hz hum you can get from flickering lights (the small ripple in the lower parts of the waves):
Here's the effect the 'Smooth' switch has on that. It not only gets rid of the ripple but also dampens the pulses. You can lower the value of the smooth capacitor a bit to 4,7µF but no lower than that otherwise the ripple won't be surpressed.
Okay, that's it for now. If you have any questions please put them in the comments below or visit the Facebook Group that was setup especially for this website.
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.
