Welcome! I'm located in The NL. On my site I publish records of my DIY Modular Synthesizer Project. I build using the 20CM high 'Kosmo' format panels. All layouts are made by myself, 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 'Home' bar below this text. If you'd like to support this website you can use this link: https://www.paypal.com/paypalme/modulareddy
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 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 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, no problem.
Here's the schematic by YuSynth. It's the same one as in chapter 7:
Here's the verified layout. I used this for my own build and it worked first time. I spent about 5 days making it. It wasn't easy to fit everything on a 24 by 55 hole stripboard but I managed it luckily. 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.
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. The layout below follows the schematic and has only one attenuated CV input, the other two are un-attenuated but if you want to add a level potmeter just copy the one from the CV-1 input. The Bill of Materials already has two 100K potmeters for this purpose listed. Once again I did NOT include any de-coupling caps and they are also not in the Bill of Materials so if you want to include them don't forget to order them with the rest of the components. You would only need de-coupling for U3 so one 100nF cap and two 22µF electrolytic caps are all you need. In the schematic there are also two 10 Ohm resistors in series with the positive and negative power rails. I'd leave them out anyway, unless you have problems with hum in the audio.
Wiring Diagram:
Print only:
Here's an overview of the cuts that need to be made. Follow it with great accuracy! This is viewed from the copper side of the print.
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 39 in total plus one jump wire. Here's a picture of the wirebridges installed and the cuts marked on the components side (something I always advise to do). Make sure you use single core copper wire, like transformer wire, for the wirebridges. If you use normal multithread insulated wire it will get very messy very soon, especially because there are 39 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. Don't forget to put in the jump wire at the top of the print (marked here in orange with black dots). That can be a normal piece of wire (insulated).
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 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.
After that put in the rest, I left plenty of room around the trim pots so you can accomodate different sized trimmers. I for instance 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. 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.
Here's a video of the filter in action, connected to my little sequencer so you have an idea of what it sounds like.
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.
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) here:
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.
Finally 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.
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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.
This was a little project I dreamed up myself and I designed the circuit too. This circuit outputs a Control Voltage and the height of that voltage is dependent on the brightness of the light falling on the LDR. It's quite a simple build. It consists of two opamps. The first one has the LDR (Light Dependent Resistor) 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 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.
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. 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, the brighter the light that shines on the LDR 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 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.
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. Here is the link to that item:
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.
Schematic drawing of the circuit:
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):
Print 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 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 socket 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 drilled a hole 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.
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.
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One of the best sounding VCO's you can build, with 4 waveforms including Sinewave. It has excellent 1V/Oct. tracking. With a newly designed stripboard layout.
This VCO is a brilliant design by Thomas Henry and he worked on it for a long time. He calls it his best design to date and it sure is that! VCO's of different designs, can sound different from eachother despite them producing the same basic waveforms. This difference is not really that noticeable with just the basic waves although there's a noticeable difference in the sound of the squarewave from this VCO compared to the Digisound 80 VCO. It starts to become more noticeable when you start playing with the Synchronization and the Frequency Modulation inputs. That's where this VCO really shines and I think that's why it is so popular in the modular synthesizer world. With the sync and FM functions the VCO-555 produces a very full sound, rich in harmonic content and very musical sounding. And it tracks very well over the octaves. You'll find out once you build this module and start experimenting with it. It's the VCO of choise for many hardened Modular Synthesizer aficionados.
As I mentioned, there is now a new layout for this VCO. The old layout worked fine too but the component placement wasn't that practical. This one is much better and it's verified. The old layout has been deleted.
This is a medium difficulty project. Not one I would recommend for beginners. Please read the entire article before you start building so you are aware of things you need to look out for.
ABOUT THE CIRCUIT:
I wasn't going to post the schematic here and instead linked to it on the Electro Music forum but then the forum had occasional accessibility problems so here's the circuit. (The link to Electro Music also has the original parts list if you scroll down.)
For the schematic below, just click on the image to enlarge it. Then right-click and 'save as...' Then you can zoom in on it:
The VCO uses no exotic chips. There's only two TL074's, a LM13700 and a TLC555. You can also use the ICM7555 (which is what I used) or the LMC555. Do not use a normal NE555 for this, you need the CMOS version. Although I'm told it will work with the normal NE555 these chips consume a lot more power and they can have oscillation problems under certain conditions (see my 81 LED chaser article.)
Instead of the LM13700 you can also use the LM13600. I tested this myself and there's absolutely no difference between them.
I didn't put in the de-coupling capacitors for the chips. I almost never do because I have a good powersupply and no noise problems in the circuit. If you want to include them solder them in over the powerrails on the stripboard as near to the chips as possible. The connections are shown at the bottom of the schematic. You can use small ceramic 100nF caps for this. You can solder in the two 10µF electrolytic caps over the power rails on the stripboard too. One from plus to ground (- to gnd) and one from ground to minus (+ to ground). The exact position of the electrolytic caps on the stripboard doesn't matter. Put them where you have room. Note these caps are not included in the Bill of Materials below.
For temperature compensation the circuit uses a PTC Thermistor which I guess is the only exotic component in this VCO. PTC stands for Positive Temperature Coefficient, meaning that when the temperature goes up the resistance also goes up. This temperature dependent resistor has a nominal value of 2K. However, it's not necessary to use a Thermistor. You can get away with just using a 2K resistor, especially if the temperature doesn't change much anyway like if your synthesizer stays in the same location all the time. It'll just mean that it isn't as stable as it can be, but many people use this VCO without the Thermistor. If it does go out of tune you can easily adjust the Frequency Fine Control and set it right. It is handy to have a hacked tuner like the JOYO tuner attached to the VCO to keep an eye on the tuning.
Capacitor C4 (2200pF or 2.2nF) is the timing capacitor for the oscillator and therefore it should be a non-ceramic type like a Polystyrene or a Polyester or Silver-Mica type capacitor for temperature stability.
The VCO doesn't have an extra CV input because actually the Exponential FM input has that function. If you look at the schematic you'll see it is connected to the same pin as the 1V/Oct input and it has an attenuator too. The Frequency Coarse and Fine tune are on that same pin too.
The two PNP transistors Q2 and Q3 need to be matched. I matched them using the Hfe transistor tester on my multimeter and this is good enough. When measuring Hfe, give the transistors time to cool off after you touched them because the Hfe value will change with temperature. Some will tell you that the transistors need to be matched on the Base Emitter Voltage (Vbe) but I noticed that if you match them on Hfe, the other parameters will be pretty close too. Anyway it works fine this way.
The transistors need to be thermally connected to eachother on the print. Look at the pictures below to see how I did this. I covered them in thermal paste and bent some thin copper sheet around the bodies to keep them together. But you can just as well glue them together with some super-glue. That'll work fine too. On the layout below, the transistors are mounted in such a way that you can bend them towards eachother so the flat surfaces connect to eachother. If you do decide to use a Thermistor in this circuit you will need to find a way to also connect that Thermistor to these two transistors. It shouldn't be too difficult if you use some thin copper sheet or heat-shrink tubing. I advise to get one or more SMD Thermistors and solder legs to one and use that. I think it'll be easier to place with the transistors.
Some of the features of the VCO:
The VCO has four waveforms: Sine-, Ramp-, Triangle- and Squarewave. All the waves have an amplitude of +/-5V peak-to-peak.
It's got a Linear and an Exponential FM input, one Hard Sync input and a 1V/Octave input naturally for the keyboard. The FM inputs have attenuators. If you connect a signal to the Exponential FM input the pitch of the oscillator will change, with it being connected to the same input that also drives the 1 Volt per Octave control voltage. With the linear FM input this isn't as big a problem because it goes through special circuitry and it has a capacitor on the input, blocking any DC voltages but with Exponential FM the VCO pitch will change the moment you open the attenuator. Obviously you have to have some external way of influencing the pitch otherwise you couldn't, for instance, connect a sequencer to it.
There's also a potmeter for the Pulse Width which goes from 21% to 75% if you use the 330K resistor (R47) as seen on the schematic. I changed that resistor to a 190K one and now the Pulse Width goes all the way from 1.7% to 95%. You can also put in a 200K trimmer with a 47K resistor in series for safety so you can set the range you want. The layout below uses the 190K resistor instead of the 330K.
There are trimpotmeters for one Volt per Octave tracking (100 Ohm), High Frequency tracking, Ramp Wave connection (this makes sure the ramp wave has a smooth slope. If it is set wrong the ramp wave will have a step in it at the zero Volt level. There are two trimmers for the Sinewave. One for roundness and one for symmetry. The roundness trimmer will also change the amplitude of the Sinewave a little.
You will need an oscilloscope to set these parameters, but a cheap 20 dollar one from eBay will do fine. Make sure you set it to DC when measuring.
At first I used multiturn trimmer potmeters for all but the 1V/Octave trimmer but I have changed that because I found it very tedious to tune the VCO with a multiturn trimmer for HF tracking. It's not necessary. I only use multiturns for the Sawtooth step and Sinewave symmetry.
When I built this module I had set all the trim-pots in the middle position before I soldered them in and when I started the module up, everything was perfect except for the tuning. Even the Sinewave was perfectly symmetrical right from the get go. So was the Rampwave :) Btw, the Rampwave is the reverse from what the 3340 VCO produces. It goes straight up and then slopes down. So I guess that is called a Sawtooth wave officially. I always get Saw and Ramp mixed up anyway so we'll keep caling it a Ramp wave ^___^
CONCERING THE COARSE FREQUENCY:
When I wanted to measure the range of the Coarse Frequency potmeter I discovered that its range was enormous. When I turned it from the middle position (50 on the decal) to one stripe before that (between 40 and 50 on the decal) I was already 4 octaves down. And turning it up it wasn't long before the frequency was so high I couldn't hear it anymore. I measured the frequency range and it goes from 18Hz to 28kHz. So I decided to tame it a little by increasing the value of R29 from 100K to 300K. This worked out pretty neat. Now every stripe on the decal is one octave up or down. I also tried a 500K resistor but that was too much because the VCO fell silent, so you can't increase it to any value you like. 300K would be the maximum I would advise to use.
I haven't implemented this change in the layout or the schematic because I want to leave it to you, the builder of this project, whether you want to change it or not. It's just a matter of convenience and the 555-VCO's you can buy readymade don't have this change. I myself did change both my VCO's but as a consequence the Coarse potmeter's normal position is now about 9 o'clock. That's the rest position as opposed to the normal 11 o'clock position.
Btw, a nice side effect of this change was that the tracking of the VCO improved a little also.
The Frequency Fine Control has a range of 1 Octave. From the 12 o'clock position half an octave down and half an octave up. I measured the frequency range on my scope and it was 570Hz over the full throw of the Finetune potmeter in the lower Octave range.
TUNING:
Before I started tuning I set the 'Frequency Coarse' potmeter in the 11 o'clock position to get in the right octave range, (this was before I changed R29) and the 'Frequency Fine' adjust was set to the 12 o'clock position.
Tuning the VCO is just a matter of playing a low C note like C2 and a high one like C5 and turning the trimmer for 1V/Octave and checking it against a good tuner or tuning app on your smartphone. The trimmer is just a 100 Ohm one and I used a normal type for this, not a multiturn trimmer, and it works fine. It's a matter of tuning the C notes and seeing if the higher note is a bit lower or higher than it should be and compare it with the low note. If the one is too high and the other too low and the middle note is spot on then you have to turn the HF Tracking trimmer a tiny bit and try to get them all in tune over a wide range of octaves. You should use all three tuning potmeters in the tuning process; the 1V/Oct., the HF Tracking and the Fine Tune potmeter on the panel. Changing the 1V/Oct. potmeter also influences the tracking. Once you get it right it'll track marvellously over a wide range of octaves. I was impressed. It tracked even better than the Digisound-80 VCO and I didn't even had the Thermistor installed, but it was a lot more difficult than tuning the Digisound-80 VCO.
I had my VCO in tune over 4 octaves in a timespan of about 10 to 15 minutes. After I installed the panel back into the synth, because I didn't use a PTC, the change in temperature did alter the tuning a bit but it was not dramatic.
What can be really helpful with tuning is to use a sequencer to play a string of C notes from low to high in a slow tempo. That way you can easily hear how the tracking tunes or de-tunes the VCO over the Octaves as you turn the trimmers. (Just an idea.)
12V vs 15V:
I have not tried this circuit on a dual 12 Volt powersupply yet. However there are some notes about this on the Electro-Music forum stating that for 12V you need to change these resistors:
R13 = 2K This is the 3K resistor in series with the Square- or Pulsewave output from pin 14 of IC4.
R27 = 22K This is the 39K resistor in series with the Sinewave Roundness trimpot to pin 16 of the LM13700.
R33 = 137K This is the 100K resistor over pins 6 and 7 of IC4.
That last one is a bit of a weird value for a resistor but the resistor values don't have to be spot on so you can also just put in a resistor closest to that value. It determins the gain of that opamp so a few K's more or less won't be a big deal. The circuit is quite forgiving anyway.
As for the Pulse Width Modulation resistor (R47). I already changed it from 330K to 190K and for 12V operation I guess it'll have to be changed to a lower value still. You'll have to do some experimenting with that to get it to your own liking. My advise would be to use a 200K trimmer with a 47K resistor in series and solder that in temporarily, set it so the pulse duty cycle goes from 1% to 100% or closest to that, de-solder it again carefully and measure the resistance and then put in a resistor of the measured value to replace the trimmer.
SYNCHRONIZATION:
The Hard Sync function works like a treat. If I connect a sawtooth signal from VCO-1 to the Hard Sync input of VCO-2 the second VCO will follow the tuning of the first VCO perfectly, even if that second VCO isn't tuned very well of itself. If you then force the second VCO out of tune by adjusting the Coarse Frequency control on VCO-2 you'll get some awesome distortion-like sounds that sound very musical. It totally blew my mind when I fed that through the Steiner-Parker filter. The VCO tries to stay in tune with VCO-1 and you can almost hear it struggling to do that. On the oscilloscope you can see the wave jumping in frequency as it tries to stay in tune and it does stay mostly within the main note played on VCO-1. But hearing the VCO struggle to do that is so awesome sounding. Unfortunately I didn't film this in the demo video below because when I filmed it I only had one VCO built, but you're going to get some great results if you build more then one Thomas Henry VCO-555.
I might make a new demo video soon, but in the mean time you can get an idea of the Hard Sync function by listening to the Fonitronik video I posted below my own demo video.
LAYOUTS:
Okay, below here is the layout I made for this VCO. The first VCO I built was made with a different layout. That layout was published in this article before and is still visible on the LookMumNoComputer Forum, but it had the transistors and the thermistor quite far away from each-other and it also had some jump-wires. I have since made a new layout and built a second VCO with the new layout to verify it and luckily it all worked first time. So here is the new and verified layout. Don't forget the 220nF capacitor between the linear FM input socket and its potmeter.
Wiring diagram:
(Last revised at: 17-Jan.-2021: Made cosmetic changes to layout and changed two trimmers from multi-turn to single turn (also updated in BOM. 25-jan.-2021: Slight cosmetic changes).
Here's the print only view:
And here's an overview of the cuts that need to be made, seen from the copper side:
Bill of Materials. Please note the decoupling caps and electrolytic caps you can see on the schematic bottom right, are not included in this BOM.
There's an extra 2K resistor included if you want to put a 2K in, instead of the 2K PTC Thermistor. I advise to order a batch of 100 2N3906 transistors so you can easily find a matched pair.
Here is a link to a UK retailer who has the PTC Thermistors listed. They are 3300ppm instead of the desired 3500ppm but I think it's close enough and will work fine. Choose the 2K version:
I have not tried these Thermistors myself (yet) but I plan on ordering some and testing them out. Until then I can give no personal guarantees that PTCs from this link will actually work. Order and use at your own risk.
Here's a demonstration video, demo-ing the waveforms and especially the Exponential FM option. I put it through the Steiner-Parker filter and I compare it with the Digisound-80 VCO. That comparison is not entirely fair because the DS-80 has no Exponential FM input, only a Linear one. Although, I suppose you could use the normal CV input as am FM input. That should be the equivalent of exponential FM but I haven't tried that. Btw, I forgot to mention the Steiner-Parker filter has a slow Triangle wave on the CV input which accounts for the 'Wah' sound you can hear. This video was made before I altered the Pulse Width Modulation so here you only hear it going from 25% to 75%..
Here's an other video (by Fonitronik) with a very cool demonstration of this VCO. If you look closely you can see that the Coarse potmeter on this VCO is also set to the 11 o'clock position to hit the right octave (confirming that it is the exact same VCO). There is some reverb on the signal in this video so it sounds a bit fuller than the clean audio you get from this VCO. This video also demonstrates the awesome Hard Sync function:
Here are some pictures from the build proces. I always start by making the cuts and then I put in all the wire bridges. You can see the cuts marked in black on the component side. There are 33 wire bridges to put in. They differ a bit from the layout because since the first build I made some cosmetic changes to the layout:
Here you can see how I bent the two transistors Q2 and Q3 towards eachother and then thermally connected them together with some thermal heat-sink compound and some thin copper. I left some extra copper on there which I can use to connect the Thermistor to. I have ordered a few of them.
As you can see from the pictures below it is quite an easy build. Just over 40 resistors, 4 IC's and some other components. If you work methodically you should be able to easily copy this design and have yourself a fantastic VCO for a fraction of the price they cost new.
In the picture below you can see progress of the third VCO-555 I'm building. Here I used super glue to connect the two matched transistors together and I neatly bent the legs so it all fits in place nicely.
Here's a look at the finished product:
Here's a look at the panel I made for it. On the right you can see a 1V/Oct. output socket. It is connected in parallel over the 1V/Oct. input without any buffering. It's just a wire connection. I use that to 'daisy-chain' all my VCO's together and so keep the Dual Buffered Multiple free for other things. This feature is also included in the Digisound-80 VCO in article 18. Do not use this output as a CV input because it has no resistor in series. So that wouldn't work and could even damage your MIDI to CV converter.
Here's how it's installed in my synth. A Digisound-80 VCO flanked on both sides by a Thomas Henry VCO (the second and third TH VCO-555 I built.). Note the fine tune buttons. It's the first time I used knobs with a number scale on them, like the ones LMNC uses only smaller, and they fit very well here. I used big knobs for the Frequency Coarse potmeters and they leave only the numbers of the decal visible. I somehow like that, but that is just a personal consideration and may change in time:
Finally a look at some scope images of the VCO. At the top we have the Duty Cycle of the squarewave with the potmeter fully counter clock-wise and then fully clock-wise. The somewhat limited range of the PWM was the only drawback of this VCO and it was naging me so I changed resistor R47 from a 330K to a 190K (after experimenting with a trimmer) and now the PWM has a nice range all the way from 1% to 95%. You can see the exact values in the image below. At the bottom we see the Sinewave and the FFT readout of that Sinewave. The Sinewave has a bit lower amplitude than the rest of the waveforms if you want it to be a pure Sinewave. You can turn the amplitude up by turning the 'Sinewave Roundness' trimmer but then the Sinewaves gets a slightly pointy curve at the top and bottom. On the picture below you can see the best compromise between the two. The bottom right picture shows the Fast Fourier Transform (FFT) of the Sinewave. This shows the main peak in the middle at approx. 100Hz and then the harmonic frequencies as the peaks to the right of the middle. As you can see it's not a perfect Sinewave but that's not really important. What's important is how it sounds and it sounds great! Little imperfections can actually make the Sinewave sound better. It's not like we're dealing with an FM Broadcast transmitter where the Sinewave needs to be as clean as possible.
Okay, that's another one done.
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This is the Fonik Buchla Style Dual Voltage Processor. A very useful module for altering Control Voltages with four different functions. Offset, Attenuation, Inverter and Lag control.
I wanted a Voltage Processor module in my synth for a long time and I was thinking of copying the ARP2600 VP, but that one is fairly limited in its options and when I saw this design I thought it would fit much better in my system. This module lets you alter the offset of a control voltage by 0 to +5V or -5 to +5V. It lets you attenuate and invert a control voltage by means of a Attenuverter and it has a Lag control that is a direct copy of the Lag control from the ARP2600, with a 1 MOhm potmeter and a 470nF capacitor (The ARP used a 100nF cap). This alters the slew rate of, for instance, a Squarewave and rounds off the corners turning it into a Sharkfin Wave. In fact it adds a 90° phase shift to the signal. Besides control voltages this module can also handle audio signals.
This module will work fine on either a dual 12V or a dual 15V powersupply so no problem for you Eurorack fanatics =).
The circuit is primarily meant for control voltages but it can handle audio signals just as well. Even at very high frequencies it won't distort the signal. With audio you can use the Lag control to turn a Triangle wave into a Sinewave although with less amplitude. It won't be perfect but it's possible. It can also turn a 0V to +10Vpp signal into a +5/-5V signal by adding a -5V DC Offset voltage to it. The other way around works too of course, turning +5/-5V into 0V to +10Vpp signal. Very useful.
The circuit consists mostly of 47K resistors but you can actually alter the value of those and use for instance all 91K resistors. I actually did this as a test with the second part of this dual module and it didn't change the working of the circuit in any way. Just make sure you use the same value for all 7 resistors. Don't make them lower than 47K though.
This circuit was designed by Chris MacDonald and modified by Peter Grenader and then further improved by Matthias Herrmann who added the Lag (Glide) control function. The only thing I did was adding the Offset switch, changing the potmeter values from 50K to 100K, changing the value of the Lag Capacitor from 1µF to 470nF and adding the 470 Ohm resistor before the Lag potmeter to eliminate noise issues.
The original schematic and a PCB design can be found in this original PDF and I made a new drawing from that schematic which is posted below. Like I just mentioned, they use 50K panel potmeters in the schematic but I didn't have those so I used 100K potmeters. Again, this made no difference what so ever. You must however use a 1 MegaOhm potmeter for the Lag control because this, together with the capacitor, forms a simple lowpass filter and these values are important to get the correct frequency response. The original schematic uses a 1µF capacitor for the Lag control but with testing I found out that this is way too much. So I changed it for a 150nF in the layout but that turned out to be not quite enough. (The original ARP2600 Lag control uses a 100nF capacitor.) In my own build I experimented with different values and I ended up using a 270nF and a 180nF in parallel to make a total of 450nF and that works fine. So I set the capacitor value on the layout to 470nF. I found that this gives the best Lag control response. Of course, if you don't have a cap of that value available, you can use an other one with a value close by. Anything between 300nF and 700nF will work fine and you can put two (or more) in parallel to create the value you want.
The trim potmeters are for setting the attenuverter mid point, but they don't have too much of an impact so you don't have to use multiturn potmeters for those. The normal ones will do fine. I added a switch to the offset control so you now have a choise to offset a control voltage from 0 to +5V or from -5 to +5V.
A little quirck I found, at least in my build, is that there can be a lot of noise on the output if the Lag potmeters are set fully closed (counter clockwise). Because this was the case with both sides of the Dual Processor I figured this was a fault in the circuit design so I added a 470 Ohm resistor between the Lag potmeter and R6. The value is low enough not to influence the Lag filter and it gets rid of all noise issues that I had.
The schematic drawing doesn't include any de-coupling capacitors but they are included in the layout. Just four 100nF ceramic caps on the power rails as close to the chips as possible. If you experience hum on the audio output you could even put some 10µF to 47µF electrolytic capacitors on the power rails. There's room enough left for that. Make sure they are rated 25V or higher and put one on the +15V to ground (negative pole to ground) and one on the ground to -15V (negative pole to -15) rails. I leave that up to you but for my module it wasn't necessary to include them. (The electrolytic capacitors are not included in the layout, only the de-coupling caps.)
Here's the schematic drawing which I re-made from the original, from the above linked PDF file. The Dual Voltage Processor consists of two of these circuits side by side with only the Ground as a common link:
Here is the verified stripboard layout I made for it. It's the same layout once repeated and mirrored to make it a dual module. You can easily cut the stripboard in half and fold it over, connecting the traces that need to be connected, together with some copper-wire to make it a Eurorack size.
Print only.
Bill of Materials:
Here's a video with a quick overview of the different functions.
I watched a demonstration video about the ARP Odyssey and in it they showed the effect that the Odyssey's Lag control had on the filter cut-off control voltage. It made the filter make these 'Wah' sounds. And I'm very chuffed to see that the Lag control in this module has the precise same effect on a filter.
Here are some pictures from the build process:
In the picture of the panel (below) the 'Lag' control is still called 'Glide'. That's what it's called on the schematic but I chose to use the same term that ARP uses in the 2600. I think it's a more accurate description because it actually creates a phase shift of about 90 degrees (see also the article about the ARP Envelope Follower). So that makes the signal lag behind the original in a small way.
The picture below shows one side of the dual module wired up and the other side has not yet been wired up. The LEDs of that side are still mounted on the print (which was necessary for testing) instead of in the panel.
When the panel is in 'rest' position so to speak, all potmeters should be set fully counter clockwise and the switch set to 0/+5V. That way, any signal you put in will come out unchanged. You can then alter it by turning the controls.
Okay that's an other one done. If you have any questions please put them in the comments below or on the EddyBergman Facebook group. Please read the whole article before asking questions.
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A combination of a Voltage Controlled Amplifier and a LoPass Filter using Vactrols. It has three modes and sounds amazing!
This module is not like your conventional Lowpass Filter. It's a combination of a VCA and a VCF. It helps if you're trained a bit in your modular synthesizer knowledge to get the best out of this module. As a beginner you might be better of building some normal filters first and leave this one for later. But then again, if you're feeling adventurous, then hop to it. You will certainly learn a thing or two as I did. Plus it's quite easy to build.
A little bit of history:
When modular synthesizers were first being developed there were two people who became prominent in this world in the United States. Don Buchla on the West Coast and Bob Moog on the East Coast of the States. While Bob Moog preferred a more conventional way of playing the synthesizer by using a black and white piano style keyboard, Don Buchla chose to go an other route and developed a touch sensitive device that would react to the pressure human fingers would impose on it. Buchla didn't even like to call his instruments synthesizers since that name connotes imitating existing sounds and/or instruments. His intentions were to make instruments for creating new sounds. He wanted unrestrained artistic expression un-bound by the conventional chromatic scale used in western music. A completely different approach to modular synthesis but one that sounds out of this world if you get it right. However, piano style keyboards are instantly recognized by musicians as something they can work with, and therefore the Moog system became the most widely adopted system in the world. This module is one from Don Buchla's stables, in fact the first one from his design philosophy on my website. (Hopefully not the last one because I really like the West Coast approach.) The addition of the resonant feedback loop and the refinement of the original Buchla design goes to the credit of Thomas White. The module I built is the Thomas White version as presented on the website modularsynthesis.com. Click here to visit that webpage.
Here's the link to the NatualRythmMusic website which features the same project.
(I'm not associated with any of those websites.)
Resonant Lopass Gate:
To be honest with you, I had never heard of Resonant Lopass Gates before I held a poll on Facebook to see what people would like me to build for future projects. This was one of the options that was mentioned. It instantly intrigued me because I didn't know what it was. So I asked for schematics, did some research and started building one.
This module consists of three parts and there's a 'Mode' switch to switch between them. There's a voltage controlled amplifier or VCA and a lowpass filter (12dB) and the option to have both on at the same time. The VCA is nothing more than a voltage controlled attenuator and with the switch in VCA mode that is what you get. Now if you set the switch to 'Both' mode, you get the same VCA function but unlike a pure VCA not all frequencies are attenuated equally. Depending on the height of the Control Voltage the filter cuts off parts of the high frequency content of the input signal. If we now switch to VCF mode we have the full function of the lowpass filter including resonance (and it can self-oscillate) and the CV voltage determins the cut-off frequency of the filter. The VCA part is no longer working in this mode but we still get a mixture of changing cutoff frequencies and changes in amplitude driven by CV voltage and the CV input also affects the amount of resonance that is put on the audio signal. It's very complicated and I can't explain it very well but it makes for a very special sounding module. Because it works best with a constantly changing CV input, the module produces more of a percussive, pulse like sound. At least, that's where its strenght lies. (See demo video lower down the article for sound samples) The CV inputs can be anything from a Gate signal to an Envelope signal or an LFO. You can experiment with what sounds best. I think it's better to have signals going into both CV inputs at the same time. The CV 2 input has an inverter connected to it in the form of opamp U2-A, The more you turn it clockwise the more the CV signal gets inverted. This is one of the changes that has been made (by Thomas White) from the original design as described in the 'modularsysthesis' article in the link below here, which I incorporated into the redrawn schematic. It works very well. The CV-2 control contributes a lot to the funky sound of this module.
Here's the schematic drawing that I re-made from the schematic on 'modularsynthesis. It has all the changes that are suggested in the linked article implemented. (Click on the image to enlarge it and then right-click and 'Save as' to save it to your computer. Then you can zoom in on it.) :
I did not use any de-coupling capacitors on the two IC'S but if you want them included, or if you're having trouble with noise from the powersupply, than just put a 100nF ceramic cap between the plus and ground and one from ground to minus 15V and as close to the chips as possible You can also put some 10µF/25V electrolytic caps on the power rails to suppress any hum. The 'Deep' switch is a normal SPDT toggle switch (ON-ON). If you turn it on, the sound will be deeper with less high tones. It has the effect of turning the 'Offset' knob counterclockwise. You can set the amount with the trimmer Tp2. The MODE switch needs to be a 3 pole ON-OFF-ON switch and I have colour-coded the connections so you can easily see what goes where. The 3 by 3 diagram represents the bottom pins of the switch. You can see it all connected in the layout below. The switch needs to have a middle position and in that position none of the 3 connections in the schematic are made, so they are all open. This is the 'Both' mode and is how it should be although it may look a bit weird at first. You can also use a 3 position rotary switch of course but it will have to be a 3 pole, 3 position rotary switch. I myself used a vintage 6 pole 3 way switch I had in my junkbox. I had four of them and used two of those in earlier projects. One in the Digisound 80 ADSR and one in the Steiner-Parker filter.
About the Vactrols: The layout I made for this module worked rightaway but I did some experimenting with the Vactrols. I ordered a batch of VTL5C4 vactrols and they have now arrived but the Vactrols I made myself seem to work so well that I'm hesitant to replace them. I made mine from 5mm red LEDs and LDR's that had an 'off' resistance of over 200MOhm and with a bright white LED shining on them the resistance was about 200 Ohm. I later soldered a 3mm red LED in parallel over the vactrol LED on the left to dim it a little, because I found out that sounded better. I made some Vactrols earlier and used bright white LEDs in them but although they did work, the LEDs hardly came on because the maximum voltage over them was about 2,7 Volt which was too close to the threshold voltage of those LEDs. The red LEDs will shine full on with that voltage which works much better. (So because the LEDs in the Vactrols are part of the circuit and not connected directly to a powersupply they don't require their own current limiting resistors.)
The picture below is the wiring diagram. The module is meant to work on a dual 15V powersupply but it will work fine on a dual 12V powersupply (Eurorack) . I did notice a bit less self-oscillation in the resonance when I tested it, but it still sounded amazing and you can still get that cool sharp synthesizer sound out of it. You might be able to get the resonance back up with the 20K trimmer but I didn't try that. One other thing, I built this module using two TL074 chips, not the TL084 as mentioned in the layout. It doesn't really matter which of the two you use where. It's up to you. As always the layout is verified. I used it to build my module and I already had confirmation from others who built this successfully. All potmeters are viewed from the front with the shaft facing you.
Print only:
Bill of Materials:
How to calibrate this module:
There are two trimmers on the board, the 20K trimmer directly influences the voltage that the Vactrols get so it plays a part in determining the sound. So you need to set it for best resonance, at least that's what I did. The influence it has is not that obvious though.
The second one is for the 'Deep' switch and determins the 'deepness' or the low frequency emphasis of the circuit. It's a sort of tone control and the effect it gives is like turning the Offset knob down. You can set it to whatever you like best.
Here's a video demonstrating the sounds you can get from this module (listen with headphones to get the best effect). When I say "In 'Both-Mode' you don't get Resonance" what I mean is that you don't get self-oscillation in 'Both-Mode'. Resonance still works.:
TIP: Try altering the pulse width of the squarewave going into the Lopass Gate. You'll get some really cool sounds that way.
Here's a video demo-ing the Erica Synths Lopass Gate (LPG) which is based on the same schematic as this one. Go to 1m22 to skip the intro nonsense:
Here are some pictures from the build proces. The two black thingies at the bottom left of the stripboard are my home made Vactrols:
I used a vintage 6-pole 3-way switch but unfortunately I drilled the holes for the screws in the wrong place but since they were 3mm holes I put some 3mm LEDs in them and connected them to a free pole of the switch so that the yellow LED goes on when the switch is set to VCA mode and the red one goes on when switched to VCF mode and both go on when in 'Both' mode. =)
Here's a sketch of how I connected the LEDs to achieve that. In 'Both' mode they are a bit dimmer because of the 0,6V voltage drop of the extra diodes but you hardly notice that. It works perfectly fine:
It would be very cool to have three or four of these Resonant Lopass Gates in a modular synthesizer set-up and to use them partly as VCA's with a twist. You can do some really cool things with this module, I know that. But I myself haven't figured out yet in how many ways you can use this.
Okay, that's it for now. As always, put any questions you might have in the comments below or on the facebook group.
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