Synthersizer Build part-45: STEINER-PARKER DIODE FILTER for EURORACK.

This is the same Yusynth Steiner Parker diode multimode filter I posted in project 26 but with a new layout for Eurorack.

I'm busy setting up a Eurorack system dedicated to live performances, so I want to remake some of the modules I built earlier to make them fit the Eurorack 3U size. So here's the first one I converted, one of my absolute favourite filters, the Steiner Parker multimode diode filter with Lowpass, Highpass, Bandpass and Allpass. This is a Sallen-Key type filter with positive feedback so that you don't loose volume when you increase the resonance like you do with the Moog ladderfilter for instance.

I won't go further into how it works etc. You can go to the previous Steiner Parker article for more details.

I started out matching the diodes I needed by measuring the voltage drop but they all came from the same batch and the measurements were so close that I stopped matching and just put them in (and the filter works absolutely fine). The transistors however must be closely matched otherwise the filter won't be in balance. You can set the right balance with the 1K potmeter but that's only a fine control so make sure the transistors are matched. You can match them by simply measuring the HFE and look for two with the same values.

When you start out building, make the cuts in the copper strips first and then put in the wirebridges. Then you can put in the rest of the components.

About component values:

For the level potmeters I used 10K linear ones because that's what I had. You can use any value from 10K up, it doesn't matter for level potmeters. Keep to the recommended value for the Cut-Off and Resonance though. I used a 100K for the Cut-Off frequency potmeter and I changed R26 to a 100K to make the voltage drop over the potmeter the right value. This works perfectly fine. You can of course use a 47K (50K) potmeter but then use a 47K resistor for R26. (R26 is the 100K resistor in strip A to the right).

For the 1,5nF filter capacitors I would recommend using good quality polystyrene, polyester or silver mica types. These form the heart of the filter so don't use ceramic caps for those.

Btw, I left out the two 10 Ohm resistors in the + and -12V strips because this filter was designed for 15V but running on 12V so I wanted to avoid any further voltage drops. I also left out the bypass capacitors but if you want to include those just put a 100nF capacitor from +12V to ground and one from -12V to ground right above the location of the chip. There's room enough left. (I did put them in later, just to be sure, but they are not on the layout or the bill of materials.)

LAYOUTS:

Below are the layouts I made for this project. They are verified as always. I used these for my own build. I left out the second CV-IN and the second AUDIO-IN potmeters and jacks to keep the layout free from clutter. You just copy the first input if you want two of them (which I strongly advise you to do especially for the CV). The stripboard is 24 by 41 holes. The switch to choose between Lowpass, Bandpass, Highpass and Allpass is a normal 2 pole 4 way rotary switch. 

Instead of using a reverse logarithmic 50K potmeter for Resonance I used a 100K linear type with a 100K resistor soldered onto it to get the reverse logarithmic characteristic. (See layout below. Two 100K resistors in parallel make for one 50K resistor). This is the recommended alternative in the original Yusynth article and it works really well. Of course, if you happen to have a reverse logarithmic 50K potmeter then use that instead of the 100K pot + 100K resistor solution. Should you have problems with resonance coming in too soon, put a 10K resistor in series with pin 3 of the resonance trimmer potmeter to get the throw of the resonance panel potmeter more to the clockwise side. Thanks to Nick in the comments below for the heads up on that one!  Here's an image of the alternative wiring of the Resonance potmeter:

Wiring Diagram:

Stripboard only:

About trimmer T1: 

I changed trimmer T1 from a normal one to a multiturn trimmer which made it much easy to set. You need to set this trimmer so that the Cutoff frequency potmeter has the correct throw with full resonance at about 2/3 clockwise with the resonance potmeter set to almost self oscillation. I measured the resistance of T1 when I was done and it was about 640 Ohm.

This filter works best if it has a 1V/Oct CV permanently connected to it, although you can't play the self oscillation as you can with some other filters where you can use the filter as an oscillator. This filter's resonance is just too agressive for that.

Making the cuts accurately:

Here's a layout of all the cuts you must make and the wirebridges you need to solder in. This is viewed from the component side. Mark the cuts on the component side, with an Edding pen, and then stick a needle through the marked holes and mark them again on the copper side. Then you can cut them with a hand held 7mm dril bit. The cuts are all over the place so concentrate and be accurate otherwise the filter won't work. Don't forget the cut underneath the wirebridge at position S-19:

Bill of materials: Buy a batch of 100 BC547 transistors if you don't have any, so you have enough to choose from when looking for a matched pair. If you want to include de-coupling capacitors then order two extra 100nF caps because these are not included in the BOM. Order good quality polystyrene or silver mica or polyester types for the three 1,5nF filter caps.

Here's the schematic drawing by Yusynth:

Here are some pictures of the build proces and the finished product. Notice I had to put two capacitors in parallel to create a 680nF capacitor. I didn't have one in stock.

I soldered all the wires directly to the copper side of the print and mounted the print with the component side pointing backwards of course, otherwise you can't get at the trimmers. I put some Gaffa tape over the pins of the 4 way rotary switch to avoid accidental contact with the print or wiring.

 

A look at the finished panel. I managed to fit everything in nicely. I had this piece of powdercoated aluminium left over so that was perfect for this project. I made the 3mm mounting holes wider to give me some room to move the module sideways to fit the rest of the modules (which are yet to come ^___^)

Finally a word about hum. This filter is susceptible to hum especially when using a switching powersupply. I have no problems with mine in my DIY synth because it uses linear powersupplies but my Eurorack filter did suffer from this. I solved it by putting two 1000µF/25V electrolytic capacitors over the powerrails. This provides enough capacitance to suppress the hum. It worked fine for me. See picture below. The overall depth of the module is 45mm with these caps installed. Still below 5 CM.

There's a forum post about the hum problem here -- CLICK HERE --

Okay that's it for this one.  

If you have any questions or remarks please comment below or post them in the Facebook group for this website where we have a great little community willing to help anyone encountering problems with the projects.

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. To quote the YuSynth website: "If feeding the GATE IN with a high frequency pulse coming from a VCO, each GATE output becomes an individual coloured digital noise source usable for sound effects. The colour of the noise will directly depend on the frequency from the VCO. White noise is obtained for frequencies above 30kHz".. 

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.

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.

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: 

  --- CLICK HERE TO OPEN SIMULATION ---

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.

Synthesizer Build part-39: MOOG LADDER FILTER (YuSynth Design).

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! ^___^

In case the video doesn't show up on mobile devices here's the link to the video below:  https://www.youtube.com/watch?v=rIlgBagLW-0

KNOWN QUIRCKS OF THIS FILTER:

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.

-- CLICK HERE --

ADDING A 24dB/12dB MODE SWITCH:

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.

Synthesizer Build part-30: LFO with SYNC and FM INPUT (Yusynth).

A very useful LFO with synchronization and Frequency Modulation input, using the ICM7555 IC. This is an other Yusynth design.

I seem to be building a lot of Yusynth designed circuits lately but that's because I know they work so well. This LFO is no exception. This is a medium difficulty project. I wouldn't advise it for beginners. Just take a look at the layout and you'll know what I mean.
This LFO circuit uses the well known ICM7555 chip as main oscillator and two TL074's (or TL084's or any other equivalent) to produce the different waveforms. The 7555 is the CMOS version of the NE555, Do NOT use an NE555 in this circuit! 

The LFO has 4 outputs, one for Sine-, Triangle-, Squarewave and Ramp wave. It has a switch for two frequency ranges. The normal setting (x1.0) goes from about one cycle per 14 seconds to about 100Hz. Then there's a x0.1 setting that divides this roughly by ten so you get (in my case) one cycle per 60 seconds to 18Hz but this can be set with a trimmer on the print so you can set it to your own liking. 
Because the layout is pretty chaotic looking, you need to go about this build very methodically. Mark out all the cuts you need to make first. I've made a special layout with just the cuts on it, to make it easier for you to do this accurately.

I must say I absolutely love this LFO. It has quickly become my goto LFO for modulation duties. It's particularly hand for modulating the LowPass Gate because the speed can be modulated with an ADSR for instance so a sound can start off sounding continuous with the LFO driven into audio range by the Envelope Generator and then lowering in frequency, fading out into a pulsating beat created by the Lowpass Gate. It's awesome :)

STRIPBOARD LAYOUTS:

Here's the stripboard layout I made for this LFO. I built mine using this layout so it's verified. All wire bridges connecting to ground are coloured green. Btw, you can use other values for the 50K panel potmeter. It's just a voltage divider level pot. You can use 10K or 100K or 1M, whatever you have available.

Naturally, instead of having a switch to go between Saw and Inverted Saw (Rampwave) you can install two output sockets and have both available at once. That's up to you.

Instead of the 50K resistor at the top right, you can use a 47K one.
Wiring diagram:

Print only. Beware that some stripboards are sold with 56 instead of 55 holes horizontally. The layout is 55 holes wide:

Here's the overview of where the cuts need to be made. I usually mark them with a black Sharpie on the component side, because that way they are easier to identify from the layout, and then I stick a pin through the marked holes and mark them again on the copper side. (That's why I'm showing both sides here). Then I cut the copper side with a 6mm or 7mm drill bit (or a Dremel-tool) in the marked places.

Bill of Materials:

Here's the schematic I used for the layout:

You can see in the schematic that there's a fifth output, underneath the saw output. This is an inverted version of the sawtooth wave and I installed an extra switch to give you the choise between Saw or Ramp. (The un-inverted version is actually a Ramp (rising voltage) and not a Saw, but whatever.)
All waveforms are bi-polar, they have the zero volt line as their mid point so they have a negative and positive phase.
Here is the result of some measurements I took from the LFO:

In the x1.0 setting:
Frequency Range = 1 cycle per 14 seconds to 100Hz
Squarewave amplitude = +5 to -5 V.  Duty Cycle = 26% to 86%
Sinewave amplitude = +5.3 to -5.3 V
Triangle wave = +7 to -7 V
Sawtooth wave = +7 to -8 V

In the x0.1 setting:
Frequency Range = 1 cycle per 60 seconds to 18,7Hz
Amplitudes are the same.
Squarewave duty cycle = 18% to 98%

The synchronization pulse threshold = +2,9V.

As you can see, a fantastically broad range of options and synchronization works very well. When you put a high amplitude sawtooth wave on the CV input the resulting frequency sweep can reach well in to the 400Hz (in x1.0 setting). The LED indicates the frequency rate and is connected to the squarewave output so it will react to changes in duty cycle by being on longer or shorter.

Calibrating the circuit:
You can set the Frequency range by turning the Rate panel potmeter all the way counter clockwise and then use trimmer T1 to set the lowest rate.
Trimmer T2a and T2b are used to set the sawtooth wave in such a way that the positive phase has the same amplitude as the negative phase. In other words you set it so the zero volt line runs right through the middle of the wave. There are two of them because one is used in the x1.0 setting and the other in the x0.1 setting, so only one of those trimmers is active at any one time. Therefore you need to set this twice.
Trimmer T3 is used to set the Sine symmetry. Turn it so that the top of the wave has the same curve as the bottom of the sinewave. This potmeter also influences the duty cycle of the square wave, so you need to set the duty cycle panel potmeter in the middle position and trim the Sinewave so it looks good and then look at the Squarewave and make sure the panel potmeter for duty cycle can be used over its full throw. To make things even more complicated, this trimmer also has an effect on the shape of the Triangle wave so it's a bit fiddly but you need to go between all of these three parameters and find the right setting. You'll get the hang of this soon enough though. It sounds more difficult than it really is. You just have to find the setting that looks the best for all three waveforms. A multi channel oscilloscope will be of great use here.
If you can not get the waveforms right you need to change the 1µF and 10µF capacitors for some other ones with the same value. Yusynth says to use Tantalum caps here but I tried those and it only made things worse. But you may have a different experience. You need to be able to experiment, an other reason why this is not a beginners project.

One other thing which I became aware of through reader feedback; if your output levels are very low and transistor Q1 gets hot then you might be using fake chips. I've had feedback where this problem turned up and changing the chips for ones from a reputable source fixed the problem. So once again, make sure your chips aren't fakes from China.

The x1.0 and x0.1 frequency range settings.
Calibrate the LFO in the frequency setting that you think you will be using most. If you get the waveforms right in the x1.0 setting then the sinewave may not look ok in the x0.1 setting.  That's a little quirck of this LFO and difficult to get right but I usually only use an LFO in the 10 second to 10Hz range, so if all is well in the x1.0 setting, then that's good enough for me. The duty cycle range of the squarewave varies too, according to how the frequency range switch is set. It's really only the sinewave that I personally can not get right in the lower frequency setting. It rises normally and then drops off so it's more like a sine version of the ramp wave. But that's the only thing I can't get right. I found that adding a 0,1µF electrolithic capacitor in parallel over the 1µF cap helps in getting it all looking good. This however will vary from build to build with component tolerances etc.

12V vs 15V:
This LFO will work on a dual 12V powersupply but the frequency will go down by a large amount but you can turn that up again with the trimmer T1 on the print. The amplitudes of the waveforms will go down to between 2 and 5 Volt so that is significantly lower. The LFO is not really meant to work on +/-12V but it will work. However, if you need to address this problem I advise to make an extra print with a TL074 quad opamp chip and set these opamps to a gain of 2 and have all the waveforms go through it. That will double their amplitudes. You can also give them a DC offset voltage to keep them all at a positive voltage if that's what you need. However, if you're a beginner and don't know how to do the above mentioned extra's then don't worry. Don't bother with it for now. Just build the LFO and run it on 12V. LFO outputs are usually attenuated anyway so the lower amplitude signals will still be very useable. This will be a module you will use a lot! I guarantee it.

Here are some screenshots of the waveforms. You will need to try and trim the negative spike in the top of the Triangle wave away while keeping the sinewave looking good. I don't think it's possible to get rid of it completely but you won't hear it in normal use.

As you can see from the screenshots this is a bi-polar LFO. Meaning the output voltages go both positive and negative.

The result of introducing the synchronization pulse. The waveform resets at the rising edge of the sync pulse and will remain high until the pulse falls away. Short trigger pulses will work best here:

Here's what happens when you put an inverted ramp wave (from high to low) on the FM Modulation input (CV IN). You get a frequency sweep that can be quite high in frequency, but you can set the level, and with it the maximum frequency, with the FM Level potmeter. You can see that the amplitude drops a bit in the higher frequencies for some of the waveforms:

Some pictures of the finished module:

I am thinking of adding a second print, like I mentioned earlier, with just a single TL074 on it to use the 4 opamps to give the 4 waveforms a +5V DC offset so they go from 0 to 10V and stay in the positive voltage range. Edit: There's now a Dual Voltage Processor project on this website that can be used for this purpose too.

To conclude this article I made a little test video showing off the 'Synchronization' feature of this LFO, which was the main reason I wanted to include it in my modular synth. As you can see it works very well:

Here's a Falstad simulation of this circuit which I drew myself. It's not working quite like it should but it gives a good indication of how the circuit works: -- CLICK HERE --

Okay that's article number 30 done! Quite a milestone for me I must say, to write 30 articles in so short a time. As per usual, please put any remarks or questions in the comments below, or post them in the Facebook Group for this website.