Synthesizer Build part-50: UTILITY LFO for EURORACK.

This is the Ken Stone Utility LFO, the bigger version of project 47 with an extra feature that I added. I managed to make the stripboard even smaller than the 'Simple Dual LFO' so it fits even the 'Nifty Case' Eurorack skiff. The LFO has the following waveforms: Pulse, Square, Saw to Triangle to Rampwave and a Variable output which has a mix between Square and Triangle/Saw/Ramp waves. I later added a mini-mixer that adds the two variable outputs together to get even weirder waveforms.

An other LFO might not be the most exciting of projects but I think this LFO will be worth it because of the weird waveforms it can make and because I realized, now that I have my own Eurorack system, that modulation sources are important to have. To quote a popular YouTuber: Modulation is what makes Eurorack interesting. I even added a feature of my own later on. It's the ability to mix both variable outputs together to get a variable A+B output. That's at the bottom of this article.

The Dual LFO from project 47 is just the first two stages of the Utility LFO without the mixing stage. Because I actually use the Dual mixer in my Eurorack setup and I loved the idea of having the full Utility LFO available, I thought I'd build the whole LFO this time and try and make it as small as possible. It is 49mm deep and the panel is 9HP wide (4.5 centimeter). This is a bi-polar LFO meaning the waveforms go both positive and negative in voltage.

This LFO does not have a sync option but this is a really useful LFO for a Eurorack system because it has not only the normal waveforms you'd expect but the option to merge waveforms together which makes for some very weird modulation possibilities. And because this is a Dual LFO you could mix the 2 variable waveform outputs together in a Multiple and make even weirder shaped waveforms. That mixing needs to be done outside of this module though. I couldn't fit that inside this design. This LFO would pair really well with the Dual Voltage Processor for that reason.

I managed to get everything on an 18 by 24 hole wide piece of stripboard. Six potmeters and eight output sockets on the panel, and an extra little print for the two bi-colour rate indicator LEDs which I made separate from the main print just like on the Dual LFO and as mentioned before a second little print to mix the two variable outputs together. The panel I made for it is 9 HP wide (4.5 centimeter). You might be able to make it even smaller if you use smaller potmeters in the panel. Even though I included an L-Bracket in the layout, I didn't use one. The stripboard is actually hot-glued in place in between the two columns of potmeters straight to the back of the panel making sure no copper strips make contact with the metal of the panel. I did this to keep the overall depth of the module as low as possible.

I did not include a Eurorack power connector on the print although there is room enough left to put one in. Instead I made a powercord with a Eurorack connector at the end so it always stays connected to the stripboard. This is handier because eurorack ribbon cables take up space too and this is a smaller footprint solution with only three thin wires.

This is mainly a Eurorack project but naturally this circuit will work just as well in a Kosmo sized synthesizer. I optimized the circuit to run on +/-12V but it was originally intended to be run on +/-15V. You will get higher amplitude waveforms when you run this on a dual 15V powersupply so if that's a problem for you, you can change the 1K8 resistors I used on the waveform outputs back to the 1K's you see in the schematic. The original schematic uses +/-15V.

SCHEMATIC:

Below is the schematic I used for my layout. I put in bigger timing capacitors because I wanted one LFO running really slow and the other to about 20Hz. That is more useful for my modulation needs but you might want different values so I strongly advise you to do some testing with different capacitor values to get the LFO in the frequency range you desire.

The types of quad opamps and the one dual opamp used in this project are not critical. The schematic calls for TL074 and TL072 opamps but you can use anything with the same pinout. I used two LM324's and an NE5532 dual opamp. Btw, I did not include the transistor with the rate LED as seen on the schematic but I designed my own circuit for that so I could use bi-coloured LED's. It's just two opamp voltage followers (or buffers) feeding the LED's with the signal from the Pulse output. You can connect them to any output you wish but the pulse is the clearest for the LED's.

Here's the schematic drawing. Beware the opamp numbering does not follow the opamp order I used in the layout.

  

LAYOUTS:

Below are the layouts I made for this project. As ever they are verified. I used them for my build. I changed the order of the opamps used from the order on the schematic. I setup one LFO using all the opamps on the left hand side and the other LFO using all the opamps on the righthand side of the IC's on the stripboard. That made it more compact plus easier to keep the overview. Luckily I did not need to make any changes or do any troubleshooting. I built it and tested it and everything worked first go.

You need four 100K and two 500K linear panel potmeters to this project. Measure and test them before you use them. That can save you some troubleshooting later. If you plan on mounting the stripboard to the panel with hot-glue like I did then try to solder the hook-up wires of the righthand side (the side that's glued to the front panel) as far to the middle as possible so you can still get to them once the stripboard is glued in place. This won't be possible with all wires but try. You could also solder them straight to the back/copper side.

Wiring diagram:

Stripboard only view:

Here are the cuts and wirebridges as seen from the component side! As always, I advise to mark the cuts on the component side first with a black waterproof marker pen and then put a pin through the marked holes and mark them again on the copper side. Then you can make the cuts accurately and you can see where the cuts are when you're soldering in the components.

Bill of materials. 

The timing capacitors listed were chosen for my specific needs. I advise you to go by the schematic (47nF) or else test and determine the best values for your needs. You can use the Falstad simulation linked at the bottom of the article to test different values before building.

No bypass caps are included in this BOM because I didn't use any. They are on the schematic and you can put 100nF caps over the power connections on the IC's to ground if you want to. To do all IC's you'd need six 100nF ceramic caps (you don't have to do the LED driver IC).

This BOM does not include the components for the little mixer I added on further down the article. For that you will need 4 x 100K resistors, a 1K resistor and a 200K trimpot and a TL072 dual opamp.

PICTURES:

Here are some pictures of the build proces and the panel I made for it. I had some fill-in panels left from when I bought my 'Nifty Case' Eurorack case and I used one of them to make my front panel. It was already cut to the right height so ideal for this project ^___^  All I had to do was cut off a piece that was 4.5cm wide (9HP) and spray paint it. I labeled everything with an Edding 400 marker pen.

Wirebridges and cuts. I made some minor changes to the layout after I built this so there are a few discrepancies between this picture and the current layout.

Stripboard ready for testing side A:

 

Panel, not yet labelled:

The finished module with the little 10 by 6 hole stripboard for the rate indicator LED's glued to the back of one of the potmeters. If you look closely at the sockets you can see I soldered all ground connections together with one copperwire going round them all. A wire goes from there to the ground connection on the stripboard.

The finished product:

Here's a little demo video I made showing the LFO in action in a little Eurorack setup. You can hear how the 'Pico Voice' VCO changes in sound as I connect the LFO to it. But then I get distracted by the Pico DSP effects module and the 2hp Freez, LOL. Oh well. You can hear the difference it makes anyway :)

(As you may have noticed, I really suck at making demo videos, LOL)

WAVEFORMS:

Here are some screenshots from the oscilloscope showing some of the waveforms. The one below shows the sharpest a sawtooth wave you can get. Pretty fast rise!

Cursor readings at LFO-B squarewave output:

Here is a collection of variable output readings from Variable output B:

To give you an idea of what can be achieved by mixing the two variable outputs in a simple passive multiple, here are eight images I put together to give you an impression. This should sound awesome with very slow running LFO's which is why I soldered a few more caps in parallel over the timing cap of LFO-B.

You can imagine that some of these waveforms, when put through a quantizer, would generate awesome melody- or bass-lines that can be easily manipulated with the LFO parameters. I tried to capture a little of that in the demo video I posted below.

Here's some technical data from the LFO:

LFO A: freq. range: 270mHz to 24Hz. 

LFO B: freq. range.: 41mHz (one full cycle every 24 seconds using a 650nF cap) to 2Hz.

Duty cycle of the pulsewave output goes between 2% and 98%. I made a mistake and used a 100K potmeter for the Shape but it needs a 500K potmeter. I only had one 500K pot so I put it in LFO B and the screenschots above are from that LFO. You can use a 100K for shape but that will significantly lower the range of the duty cycle (20 to 80%) also the slope of the Saw-/Rampwaves will be slower rising. It will also speed up the overall frequency of the LFO.

Maximum current draw = 20mA for both the positive and negative side.

The maximum amplitude of the waveforms is about +/-5V except for the Variable waveform output. When that potmeter is set to the mid point the output amplitude drops to about +/-2.5V because the potmeter acts as a voltage divider so in the mid position the amplitude is half of what it is when it is fully clockwise or counter clockwise. (We effectively have two 50K resistors on either side of the wiper of the 100K potmeter.) These may seem like low voltages but keep in mind that an LFO is usually attenuated anyway because if the changes are too big it just doesn't sound good on a VCO or in most patches. If you really need higher voltages you can make the 1K8 resistors on the outputs even bigger.

Here's the link to the Falstad simulation of this circuit. This is the Dual version with one speed potmeter at 100K and the other at 500K as it is in my LFO. You can change these variables by right clicking on them and choosing 'Edit':

--- CLICK HERE --- 

EXTRA FEATURE:

Okay as I write this it is four days since I posted this article and the cool looking results from the mixed variable outputs kept going through my mind. I really wanted to incorporate that into this design and now I found a way. I used an other small piece of stripboard on which I soldered a dual opamp and wired it up like the mixer in article 17 with 2 inputs. I knew there was no way to put an extra output socket on my panel so I sacrificed the squarewave output of LFO-B. That was the least useful of the outputs because I can get a squarewave anyway from the pulse output if I need one and I still have the squarewave of LFO-A. So I carefully soldered in the little mixer print which was just as big as the little LED driver and wired it all up and I re-labelled Square output B into 'Vari A+B'. I used a 200K trimmer to go over the inverting input of the second opamp and the output so I could adjust the gain and make it a little higher than the Variable outputs. I placed the little print above the sockets and used hot-glue to stick it in place. It is actually glued to the little LED driver board. This works perfectly! Now I have an output with two variable waveforms mixed together coming out of it.

Here is a picture showing how I added the mixer. I used two rigid copper wires to tap the signals from the sockets and lead them into the mixer. The non-inverting inputs of the opamps are connected to ground on the copper side:

Here's the layout of this little mixer. Mine is even smaller than this layout, but this will work fine. All resistors are 100K:

Here's the schematic for this little mixer:

DEMO VIDEO:

Finally I want to show you a little experiment I did using the new output. I put the Variable A+B signal through a quantizer (the 2hp Tune) and from there into the Pico Voice Wavetable Oscillator. The audio then went through the Pico DSP for some added reverb. You can really generate the weirdest melodies with this although this setup would benefit from the Voltage Processor because the negative phase of the signal does not produce any notes so it needs a positive offset voltage and the signal can do with some attenuation to get the notes closer together but I think you get the idea watching this short demo:

Okay, that's it for now. Article 50, wow I can hardly believe it. This journey started for me in October 2019 and I knew nothing about synthesizers then, but I was determined to get to grips with it and learn as much as possible. And what better way to learn then to build your own modular. So here we are more then 3 years and 50 projects later with a cool collection of builds helping hundreds of people to do the same. I'm really proud of what, not only I created but also of all the people who helped so much along the way with comments and directions. I'm not gonna name names but you know who you are, all of you. Thank you!! So many people told me they find the site a great help in their hobby and that's the biggest reward I could wish for. I am however going to wind down the DIY aspect of the hobby because having now built my own system and also haven gotten into Eurorack, I need to spend more time actually using it and figuring out how to use it all together. But I will remain available on Facebook and here to answer questions and help as much as I can to ensure you have a good experience using this website and get as much enjoyment out of it as I did.

PCB Version.

I recently made some Eurorack friendly PCB's for this LFO including the Variable output mixer I added on.

Here's the KiCad schematic I made for this LFO:

To get your PCB, goto the Menu and click on the top option called 'PCB Service' to find these circuitboards.

If you have any questions please put them in the comments below or post them on the special Facebook Group for this website where there are some awesome people willing to answer your questions.

If you find these projects helpful and would like to support the website and its upkeep then you can buy me a Coffee. There's a button for that underneath the menu if you're on a PC or Mac. Or you can use this PayPal.Me link to donate directly. All donations go towards the website and projects. Thank you!

Synthesizer Build part-49: 8 STEP SEQUENCER version 2.0

A redesigned version of the 8 step sequencer (project number 8) with external clock input option and offset control that allows you to transpose the sequence upto 3.5 octaves up or down.

-- Please read the entire article before you start building!! --

I Have PCB's available for this sequencer with Kosmo sized front panels. See 'PCB Service' at the top of the menu.

The sequencer project I posted when I was just starting out on this modular journey has rapidly become a very popular project on my website. I was however never really happy with that design. It was a bit clumsy and it had no extra features and although it worked like it should, it was never as good as I wanted it to be. It always nagged me.

So because it is such a popular project now, and using the knowledge I gained in the three years I've been building modules, I wanted to offer people something better to build. Something that I was sure wouldn't disappoint anyone building it. I'm really happy with how it turned out and I love using it. This is one of the few sequencers that can actually deliver negative voltages if you want to. Because a sequencer doesn't have to be used to make melodies or bass-lines, it can be a modulation source aswell. It really is a step above the basic baby 8 sequencers without using Arduino's. So here it is; the 8 Step Sequencer version 2.0 

A NOTE FOR BEGINNERS: A sequencer does not actually produce any sound itself. It produces a stepped control voltage that can be patched into the CV input of a Voltage Controlled Oscillator and the VCO then produces the actual notes you hear. In a sequencer you can set each of these (8) steps manually to any voltage (and therefore any note) you want within 1 to 5 octaves.

This sequencer has a few advantages over the first one. 

01 External Clocking. The sequencer can be clocked by an external source. In order to make sure this external clocking would work as well as possible I decided to use some of the hex inverters with Schmitt-Trigger inputs in the CD40106 chip (that we use to provide the internal clock signal) as buffers. A Schmitt-Trigger input has hysteresis. This means there's a voltage difference between when the hex inverter flips from on to off. For instance it might jump to off when the input goes over 6 Volt and turn on when the input gets below 4 Volt (remember it's an inverter). That's a 2 Volt hysteresis and this means it will be less susceptible to noise on the external clock signal. This turned out to work just like I hoped it did. I used two of these inverters switched in series so the (external) clock pulse itself is not inverted. I did a test and installed a bypass switch to feed the signal past the two hex inverters and immediately the external clocking stopped working for some signals, proving it's a good solution.

There is one little downside. The external clockpulse needs to be quite high in voltage. A 5 Volt pulse won't be enough. It should preferably be 6V or higher. I tried clocking it with the Behringer RD-8 but it wouldn't work. But when the pulse is high enough in voltage it won't matter what wave shape you use, it'll work.  The Yusynth LFO with sync and FM input was able to trigger it if I used the triangle wave as external trigger. 

NB: One option to solve this problem: You can lead the trigger pulse through the Voltage Processor first and give it a little positive offset voltage. That way it will breach the 6V minimum threshold. 

An other option would be to use an opamp as a comparator so that if the trigger rises above a certain threshold the opamp goes high and low again when the signal trigger goes below the threshold. I found a comparator design that works. You could put this on a tiny piece of stripboard and solder it to the input lug of the external trigger input socket and connect it to the external clock input. I would use a toggle switch to go between internal and external clock in this case. Btw, I have now tested this design and it works provided you connect the 741 chip to positive and negative 12 V as shown in the layout.

The clockpulse will come out with a 180° phase shift but it will be a 0 to +10V pulse.

I used this design for the clock input of the PCB version of this sequencer and it works great. It takes any waveform and changes it into a useable clock pulse. 

I took this design from the input of the Waveshaper project. You can find the schematic in project 60.

I took some pictures of the input (in blue) and output (in yellow) from the scope screen. In the first picture I used a squarewave going in and in the second a triangle wave. As you can see they are both converted into a nice 0-10Vpp clock pulse:

02 CV OffSet. This sequencer has an Offset feature. That means you can transpose the whole CV output chain up or down by as much as 3.5 octaves without compromising the Volt per Octave tracking. With the previous sequencer we were limited in the lowest notes by the voltage drop of the diodes on the potmeters. So it was never possible to get to note C0 which is 0.0833 Volt. But now we can trim the offset down and that will drag the whole sequence down in voltage making it possible to get to the lowest possible notes without screwing up the volt/oct. tracking and without need for special Schottky Diodes. I did use Schottky diodes (which have a voltage drop of only 0.2V) but only because I re-used the old sequencer for this build and the diodes were already soldered to the potmeters.

The offset feature is a game changer for this sequencer in my opinion because we can make really cool basslines or melodies and transpose it up or down without any problems. Naturally the output is not quantized so you won't land on true notes every time when tuning or transposing the sequencer. It's always a good idea to have a quantizer in your rig but they are too complicated for me to build as a DIY project. However, you can buy a eurorack quantizer like the Doepfer A-156 QNT (which I have in my Eurorack system) for €119,- (and that's a dual quantizer with extra options!) On the other hand, without a quantizer we can tune by ear and to what sounds right to us, without being bound by set scales. So there are advantages too to not having a quantizer. I always tune my sequencer with the Joyo tuner which I hacked for modular use (click here for that project.)

The offset feature can also be very useful if you use the sequencer as a modulation source for instance to modulate the filter. You can drag the sequence down so some steps have a negative voltage and others a positive voltage and so create weird VCF responses. 

For those of you interested, the CV voltage (the sequence) goes into the inverting input of the offset opamp and the offset voltage goes into the non inverting input. Then in the second opamp the CV voltage is inverted back to normal again while the offset voltage now gets inverted. That's why the wiring of the offset potmeter is the other way around from normal. The output opamp has a 470pF capacitor over the feedback resistor to suppress little voltage spikes which I could see on my oscilloscope, just like in the Sample and Hold v2.0 project. The 470pF gets rid of that very effectively.

03 External Speed Control. I recently added an external speed control so you can influence the speed of the sequencer with an LFO or ADSR or any other CV source while still being able to set the overall speed with the speed control on the panel. I did this by simply putting a Vactrol over the Speed potmeter. It's really easy to do. Just add an extra input socket and make a Vactrol and connect the LED of the Vactrol to the socket using a 1K current limiting resistor to protect the LED in the Vactrol. Make sure you connect the plus to the audio lug of the socket and not the ground one. Also make sure you test the Vactrol before putting it in. My own Vactrol died on me a few days later but I used a 470 Ohm resistor instead of a 1K and that is too small as a current limiting resistor. Use 1K and a bright white LED. That should work fine for CV voltages upto +10V.

I did not add an attenuator for this function because I ran out of space on the face plate but you could of course do that if you wanted to. Vactrols consist of a Light Emitting Diode (LED) and a Light Dependent Resistor (LDR) wrapped together in some Heat-Shrink Tubing. They are really easy to make. There are enough videos on YouTube that show you how to make them. You can of course also buy them new. Now Vactrols are not very accurate in how they work so you can't set the speed exactly to a certain value with a certain voltage. This feature is meant to influence the sequencer in a musical way, like speed it up every x number of beats, to create some variation.

An other way to vary the sequencer speed is to vary the external clock speed when using an external clock. This would be a more exact option if, for instance, you are clocking the sequencer with an LFO with an external Frequency Modulation input, like the LFO in project 30.

Please only add the external speed control if you think you'll need it, otherwise save yourself the trouble.

SPEED CONTROL and the TUNE/RUN switch.

The sequencer has a speed control potmeter that will go from 1.34 seconds (746mHz) to about 185Hz. If you want that speed to be lower you can add a 4,7µF cap in parallel over the 10µF cap to bring that speed down to about 2 seconds which is slow enough and it will still be able to go very fast too. 

It also has the tune/run feature of the previous sequencer to make tuning each step easier. The old procedure was to just set the speed very slow and then stop the sequencer at each step so you could tune it. Then you would switch to Run to go to the next step and stop it again to tune that one. With this new version you can use the push switch to manually go through the steps to tune them.

I had some problems with stopping the sequencer in the beginning. The sequencer would continue running even after switching it to Tune but the solution was simple. When switched to Tune the clock input must be grounded (which I hadn't done). I used a 1K resistor for that, connected to the switch and to ground. This is why it is important to connect the wire that is in direct contact with pin 14 of the CD4017 to the middle pin of the Run/Tune switch. Otherwise this doesn't work. 

A word about tuning: it's not the easiest thing to tune this sequencer to an exact note due to the fact we have 7 Volt to deal with and a 100K potmeter to set it to an exact note. In the 1V/Octave standard the difference between two notes is only 0,1666 Volt. And between two half notes only 83,3 thousandth of a Volt. That sort of resolution is difficult to achieve with a normal potmeter. However it is not impossible. It takes little touches of the potmeter but, as you can see in the demo videos below, it can easily be done with a little patience and accuracy. This problem goes for all Baby 8 sequencers, not just this one and I use mine a lot and I've always managed to get it sounding really good and in tune. This is also why the CD4017 is powered with 8 Volt. If you gave it 12V the resolution would be much worse.  As I mentioned earlier, you could buy a cheap eurorack quantizer which would help a lot with accurate tuning but that's up to you. Or, an other really helpful tool to have is the Joyo Tuner, hacked for use with modular synthesizers. It's what I personally use to tune my sequencer.

MOMENTARY SWITCH

I had a lot of problems in the beginning, implementing a momentary switch into this design. With that switch you can advance one step each time you push it to switch between channels to make tuning easier. The problem was that I forgot to ground the clock input of the CD4017 when the sequencer is in Tune mode. I made some changes and I connected a 1K resistor to the 'Run/Tune' switch that grounds the clock input. After I had done that I thought I'd try to get the momentary switch working. I connected a momentary switch between +8V and the pin of the 'Run/Tune' switch that has the 1K resistor connected to it. But when I switched to Tune mode it still kept jumping several steps when I pushed the switch. I figured this must be due to contact bounce in the switch. To counter that I soldered a 100nF capacitor in parallel over the momentary switch and that did the trick. Now it works like it should. It's not perfect. Occasionally it will still skip a step randomly but that happens very rarely. Overall it works really well and it's perfectly useable. You can put in a bigger value capacitor like a 470nF if you want to be sure it works perfectly. (The PCB version uses 470nF)

SCHEMATIC:

Here is the schematic for this sequencer. I made it using Photoshop. 

I have only drawn two of the output steps coming out of the CD4017, with the LED, the potmeter and the diode connecting to the CV Rails. You need 8 of those to complete the 8 steps of the sequencer of course. The CV Rails is just a bare copper wire where the outputs of each of the 8 steps are soldered to. From there a wire then connects the CV Rails to the offset opamp on the stripboard.

The addition of the offset feature means that when the sequencer is switched off, there would normally still be an offset voltage on the CV output! I have routed the CV output through the same switch as the one we use to switch the sequencer on and off. So when we switch the sequencer off the CV output is also interrupted. That's why we need a dual pole switch for the on/off.

ALTERNATIVE SPEED CONTROL:

I found a better way to do the speed control on the sequencer. Instead of just a 100K pot and a 10µF cap, use a 500K potmeter with a 10K resistor in series and then use a 4,7µF cap like in the picture below:

This gives a better and smoother speed control. This is not implemented on the stripboard layout so you'll have to make these changes yourself.

The connections of the rotary switch follow one step behind the connections of the potmeters. So step 1 is reset by the pulse from step 2 so be very accurate in that. I got that wrong in the previous version. 

There are two diagrams on the layout below explaining where all connections go for the potmeters and for the rotary switch.

In the schematic I use normal 1N4148 diodes but in the layout they are named as 1N5819 Schottky diodes. Go with the 1N4148 diodes. I only have Schottky's in the layout because that's what was already in there from the previous version of this sequencer. Schottky diodes have a lower voltage drop than normal silicone diodes but now that we have the Offset feature the voltage drop is no longer an issue.

It is totally unnecessary to include transistors in the output steps to feed the LEDs. I just put 10K resistors in series with the LEDs to keep their current draw to a minimum and because opamps don't draw any current at all the LEDs do not pull down the voltage when they are on. The LEDs are fed with 8V from the outputs of the CD4017 and with the 10K resistors they are still bright enough. It is however important that you do NOT use any LEDs that draw a lot of current like blue LEDs or bright white LEDs. Those may draw the voltage of the CV output down. Not only that, in the long run they can heat up the CD4017 so much that it fails. The outputs from the chip can't deliver more than 6.8mA maximum with a 15V power supply. (see datasheet)

(The PCB version runs on +/-12V and uses a 7805 to feed the CD4017 and the potmeters (5 octaves) and it has 4K7 resistors on the LEDs.)

The current draw of this module is incredibly low. The +12V part only draws 6 mA in normal use and with the internal clock at full speed it draws 10 mA. The negative side, -12V, only draws 0.73 mA! That's 730 µA! Regardless of the clock-speed. That's nothing! So you can easily run this module on two 9V batteries and use it as a stand alone sequencer should you wish to do so, and your batteries will last for months. (use 2 batteries to create a dual voltage supply)

The Gate output produces gate signals that are exactly half the length of a single CV step. In other words they have a duty cycle of 50%.

HERE IS A FALSTAD SIMULATION OF THIS CIRCUIT: --- CLICK HERE ---

LAYOUTS:

Below is the layout I made for this project. If you built the first version of this sequencer earlier, then it's really easy to replace just the stripboard with this new one. You only have to make two extra holes in the face plate for the external clock input socket and for the External Speed CV input (or three if you want to include the 'end of cycle' trigger output) and all you have to do is reconnect the old wiring to the new stripboard,

In this layout I connected only the first 3 steps to show you how it should be done. You can easily repeat these connections for the other 5 steps. I did this to prevent the layout becoming a mess of hook-up wires. Follow the numbering in the text at the bottom right to connect the potmeters and rotary switch pins to the correct pins of the CD4017. Of course you could include the left over two pins from the chip to make it a 10 step sequencer but 10 steps don't sound right. Normally you got 4 steps to a beat so 8 steps sounds better. If you do want to make it a 10 step sequencer you will need a rotary switch with 11 positions! Otherwise, if you use a 10 step switch, the CD4017 will be reset at step 9 instead of 10. In case of a 10 step sequencer you don't need a reset pulse because the CD4017 only goes to 10 steps so it will reset itself.

This sequencer is equipped with an ON/OFF switch so you can easily introduce it into a jam session by flicking the switch. That way you can leave it patched up and have it instantly available when you need it. The ON/OFF switch for this module is located behind the voltage regulator and that is done on purpose. If you put it before the regulator the sequencer would shut down very slowly because the 470µF capacitor discharges very slowly. So you would hear the sequence getting slower and slower and the notes going out of tune and fading out if you switched off. With the switch behind the voltage regulator the switch-off (or on) is instantly done. The regulator itself doesn't use any current when not in use and this has the added bonus that the sequencer starts up immediately too if you switch it on.

If you want to include 'Mute' switches for each step then I indicated on the layout the best place to put them (after the diode of each step). If you mute a step there will still be a gate signal for that step present on the Gate output.  

Wiring diagram:

If you don't want to include the External Speed control, just leave it out. 

I show only 3 of the 8 steps in this layout to avoid it becoming too cluttered with hook-up wires. It's already a mess of wires. Just repeat the LED, Diode and Potmeter combinations five more times. The list at the bottom right tells you where to connect each step. This layout also contains an LED pinout diagram.

All potmeters are viewed from the front!

(The connections of the rotary switch follow one step behind the connections of the potmeters to the CD4017. That's why there are two columns of connections on the lower right.)

Please be aware of the wiring of switch 1a and 1b. The switch interrupts power to the CD40106 and CD4017 chip and also the CV output.

THE LAYOUT BELOW IS THE SAME LAYOUT AS ABOVE ONLY THE POTMETERS ARE NOW SEEN FROM THE BACKSIDE! I thought this might be helpful for some people when wiring up the panel.

NOTE: The position of the Gate output wire as I built it here will mean that when you set the sequencer to 'Tune' you won't get a gate signal output if you push the momentary switch. If you do want a gate output when in tune mode then de-solder the wire that goes to the gate output socket out from the stripboard and solder it to the middle pin of the 'RUN/TUNE' switch or to the right hand side of strip L (pos. 22 to 38). That way you'll always have a gate signal when the sequencer moves from one step to the next. I don't think it's necessary to make this change but I just want to mention it here.

Wiring procedure:

When you are ready with the stripboard and ready for wiring, make the face plate first and put all the potmeters, sockets. LEDs and switches in. Then wire up the potmeters with the diodes to the CV rail (a bare copper wire) that connects with a wire to the stripboard. Wire up all the LEDs too. Now loosely connect the stripboard to the faceplate and then you can wire everything up to the stripboard very easily.

The mysterious grey component at the bottom middle is an L-Bracket to mount the stripboard to the faceplate. But you can use any method you want to connect the stripboard to the faceplate. In my build the stripboard is mounted parallel to the faceplate with one M3 threaded stand-off. The wiring also helps to keep it in place nicely.

TIP: You could connect a socket to each of the 8 stages (before the potmeter) and so use this as a trigger sequencer too.

Stripboard only view:

Below is a close-up of the stripboard. The voltage regulator and the big 470µF electrolytic capacitor plus the other two 10µF caps are quite crammed in together on the top left of the board but it shouldn't be a problem. The voltage regulator doesn't even get warm in normal use so it doesn't need a heatsink. You could also use the smaller 78L08 types that look like a TO-92 package transistor. 

You do need the big 470µF cap in there otherwise the pulsetrain could be audible on the voltage rail. In fact, I myself used a 2200µF/16V cap in that position to be on the safe side. (The light blue edges of the caps indicate the negative pole.)

Cuts and Wirebridges:

Below are the cuts and wirebridges seen from the component side. As always, mark the cuts on the component side first using this layout and then stick a pin through the marked holes and mark them again on the copper side and cut the strips by hand with a sharp 6 or 7mm drill bit. That way you have the least chance of making mistakes. Check the cuts afterwards with the continuïty mode of your digital multimeter or a strong magnifying glass.

Bill of materials.  This is a new version including a Vactrol for the external speed option.

In my own sequencer I actually have two Gate Out sockets, just connected together. I found it useful in some patches to have two so order 5 sockets it you want to include that option.

Pictures:

Here are some pictures of the stripboard during the building proces. My stripboard had one little error in it which was spotted by one of our awesome Facebook members and that was that the copper strip connecting pin 8 of the CD4017 to ground had a cut in it. I built it with that error included and strangely enough it worked normally but I have now corrected it. I made an other error in the top picture, the connection to +12V for the TL072 chip has been forgotten. (Holes N-41 and O-41 in the picture below) You can see it's added in the picture below it:

OSCILLOSCOPE SCREENSHOTS:

Here's a picture of the 'End of Cycle' trigger pulse that resets the CD4017. You can see how enormously fast this pulse rises and falls, within 280 nanoSeconds. (Ignore the yellow line above it.) 

In itself it's not too strong a signal so the signal is routed through two of the left over Schmitt Trigger inverters of the CD40106. This makes sure we'll get a strong 8V end of cycle pulse output. 

Here's an example of a CV output sequence with potmeters set to various notes.  As you can see the maximum output voltage is around 7 Volt (or 7 octaves) when the potmeter(s) are fully set clockwise and goes all the way to 0V with the potmeter(s) fully closed and a little negative offset applied. You can easily set or adjust this just by ear. 

And this is a scope image of the clock pulse generated by the CD40106 as it enters the CD4017:

DEMO VIDEOS:

Finally, here's a little demo video showing the sequencer in action connected to a Thomas Henry VCO-555 and the Steiner Parker filter.

If you can't see the video above, here's the link:  https://youtu.be/lcsw4txNoj 

And here's a video of me trying to replicate the intro from Vangelis' Spiral. I always loved that sequence. The sequencer is again connected to a Thomas Henry 555-VCO and the Steiner Parker filter. Plus a little echo from the FX Unit:

To get this sound connect the sequencer CV out to the Exp. FM Input of the Thomas Henry VCO-555 (attenuator fully clockwise). Take the Sawtooth output and patch it to the input of the Steiner-Parker filter set to Lowpass. From there into the VCA and add some echo with preset 59 of the CaraOK FX Unit. Just add a little of the echo. Play with the VCF Cut-off to get the variation in the sound.

To program that pattern, tune your steps as follows:  F2, C2, F3, C3, F4, C4, F5, C5

And finally a test with Vangelis' Dervish-D intro. Make sure you use a fast envelope on the VCA because the notes need to sound punchy.

The note progression for this sequence is: C#3, C#3, C#4, G#3, B3, G#3, F#3, E3

CLOCKING AT AUDIO RATES or the SEQUENCER as WAVEFORM GENERATOR:

I was watching one of Sam Battle's (LMNC) videos and he talked about using a Baby 8 sequencer as a waveform generator. If you clock this sequencer at audio rates you will in fact get an other oscillator with a waveform that is cut into 8 steps (or less) and adjusting each step will change that part of the waveform and with it the overall sound of the oscillator/sequencer. The sequencer is clocked by a VCO so the clock frequency will change with the note you play so it will track over the octaves and the CV out from the sequencer can go straight into a filter.

It's a really fun thing to experiment with. I'll link to the video in question below here, where Sam explains how this works. The video should start at 9:25:

https://youtu.be/wmqCtuT1PDE?si=yxJVTJrG-m7D-4QJ&t=565

Here are some pictures of the PCB version of this sequencer, which you can find in the webshop. Just click on 'PCB Service' at the top of the menu.

KORG SQ-1

TIP: Finally here's a little tip for all you who want to take sequencing a little further. Buy a Korg SQ-1 sequencer. It costs less than €100,- and will give you 16 steps or 2x8 steps and a miriad of options. This is of course not a module but a stand alone sequencer but it is very small and runs on 2 AA batteries. The case is made of metal and the thing weighs over a kilo! It outputs quantized CV voltages and you can set the voltage range to upto 8V. A lot of performers use an SQ-1 in their live sets. It also works very well with the modular synthesizer I've built from all these projects.

If you want to know more about this easy to use sequencer then just Google "Korg SQ1" or even better do a search on YouTube and you will find a sea of videos on this machine that will tell you all you want to know. 

Okay that's it for the Sequencer V2.0. As always, if you have any questions or remarks about this or other projects please comment below or post on the Facebook Group for this website.

If you find these projects helpful and would like to support the website and its upkeep then you can buy me a Coffee. There's a button for that underneath the menu if you're on a PC or Mac. Or you can use this PayPal.Me link to donate directly. All donations go towards the website and projects. Thank you!

Synthesizer Build part-48: PASSIVE MULTIPLES and SWITCHED PASSIVE MULTIPLES.

The simplest modules you can build but they will be the ones you use most often because each modular synth needs at least a few of these.

This will probably be the shortes article on this website and the simplest of projects but I just thought I'd mention these multiples here because recently I built a few for my Eurorack case and some newcomers to this hobby might not be aware of them. They are so useful to have in your setup.

Multiples are passive devices because they do not require any power source. They just split up signals so you can have 'multiple' sources of the same signal (hence the name). You put the output of an audio or CV source into one of the sockets and then you can tap that signal from the other sockets to turn one output into multiple outputs.

There are two versions of these that you can build.

The straight forward passive multiple that consists of just a number of 3,5mm female sockets connected together. Usually it's between 8 to 10 of these underneath eachother. You can add a switch in the middle so you can split it into two rows of half the number of sockets. That way you can use if for more than one signal source.

Then there's the switched multiple. That's the same idea only now each socket has a 2-way switch next to it, with a middle off position. Each switch has their left pins connected together underneath eachother and the same for the right pins and the middle pin of each switch goes to a female jack socket. (see schematic image below)

This will allow you to put one of two signals on each of the outputs or switch that output off. This can be very handy in live settings where you want to switch between two sequencers for instance. So you need toggle switches with a middle off setting for these. At least, that's the best way of doing it. ON-OFF-ON switches. You can use ON-ON switches but then you can't switch anything off.

There are also buffered multiples like the one in project number 25 on this website but they require opamps so they are not passive in any way.

Here's a schematic overview of the multiples. The length of these is dependent on the space you have available on your panel. For Eurorack it's usually 10 in a vertical line for a passive mult or 8 if there's a switch in the middle. And for a switched mult it's usually also 10. For Eurorack that is. For a Kosmo sized panel there's room for much more sockets.

Here is a picture of the mults I made and built into my Eurorack case. This was rather hastily done on a sunday afternoon so it looks a bit rubbish (so what else is new) but that doesn't matter to me as long as it works. My switched mult (on top) uses dual pole switches because that's all I had so there's some redundancy built in because single pole switches are really all you need.

The bottom one has a switch in the middle so I can use it as one 8 socket multiple or two 4 socket multiples.

If you want to build Buffered Multiples with opamp buffers then you can go to this article here.

Buffered Multiples are often used to connect more then one VCO to a 1V/Octave signal, because with those signals it is important that the voltage on the input is reproduced accurately on the outputs, in other words it's not dragged down however many VCO's you connect to the multiple. Passive Mults with many things connected to them can draw the voltage down a bit wich would de-tune a VCO.

Okay that's all. Just a simple little item but one you will have to build at least once. The good thing about them is they need no circuitboards and you can use off-cuts of panel material to build a few of them.

Okay, until the next one!

Synthesizer Build part-47: DUAL LFO for EURORACK.

A simple LFO with pulsewave (with variable pulse width) and a seamless transition between a Ramp wave, Triangle wave and Sawtooth wave using one potmeter. With LED rate indicators and Speed and Shape controls.

Well what more is there to say about this LFO. It's such a simple design that I could easily fit two of these on a small piece of stripboard and still have it small enough to fit a normal Eurorack case. The circuit is derived from the 'Utility LFO' by Ken Stone which is a larger version of this LFO. 

I now also have a project for the complete Utility LFO and it's even smaller than this one and a panel width which is only 1HP wider at 9HP.  Go to project 50 for that.  

This LFO is still useful on its own though because it is so small. It can easily be incorporated into other projects as an on-board LFO for instance.

The depth of this module is 55mm. I made the panel 4CM wide, that's 8hp, and I put the potmeters to one side leaving enough room to glue the print straight to the back of the panel at a 90° angle using hot glue. All the output sockets fitted nicely next to eachother at the bottom.

Naturally you can just as easy build this module in the Kosmo size and run it on 15V. If you do, you need to keep to the resistor values as they are in the schematic, not the layout because as I mention further down, I changed the 1K output resistors to 1K8 to get a nice +/-5V output signal. If you power this with 3 more volts you probably don't have to do that. Do some testing first to make sure though.

I tried my hand at using Falstad recently and tried to make a simulation of the complete Utility LFO circuit and it was surprisingly easy to do. 

So here is my very first ever Falstad simulation: --- CLICK HERE ---

Here's the schematic drawing of the dual LFO circuit:

The module consists of two of these circuits on a single piece of stripboard. I placed the LEDs on a separate piece of stripboard with a dual opamp, the good old TL072, and I used bi-coloured 3mm LEDs in red and blue. I drilled two 3mm holes to the left and in the middle of the first two- and last two potmeters for the LEDs and glued them in place with hot glue so the little print sits over the potmeters. See pictures below for illustration. Btw, you can use any dual opamp chip for this circuit as long as the pinout is the same; like the TL082, NE5532, LM358 etc.

LAYOUT:

Here is the layout I made for this Dual LFO. As always, the layout is verified. I used it for my build. I placed the Eurorack powerconnector on the left side for better access. In my build it's on the other side and very near the panel. Not a good place for a power connector but you only find these things out when you start building it. See, I make the mistakes so you don't have to LOL! (I hot-glued the print to the back of the panel with the righthand side closest to the panel.)

Stripboard only:

After doing the first tests I found the output voltages a bit on the low side. They were just +/-3,24V so I decided to experiment with the 1K resistors between the outputs and ground. I tried several values and I ended up using 1K8 resistors. That brought the output voltages to a nice +/-4,8V. Almost 5V so that's perfect for eurorack. If you want that voltage to be even higher in your LFO then experiment further with making the resistor(s) between the output socket and ground even higher in value.

I wanted to make one of the LFO's a bit slower than the other to give me a wider overall range so I used a larger capacitor for LFO number one. I used a 147nF and that made it perfect for my needs, between 0,2Hz and 10Hz. In the layout both timing caps are 47nF though.

 

TECHNICAL DATA:

Here are some measurement results for this Dual LFO:

Duty cycle of squarewave is 5% to 95% this varies a bit with the frequency but not more then 2%.

Lowest frequency: LFO-1 = 0,219Hz  LFO-2 = 0,653Hz (changed timing cap of LFO-1 from 47nF to 147nF)

Highest frequency: LFO-1 = 9,82Hz   LFO-2 = 34,2Hz

Output voltage is +4,8V or 9,6Vpeak-to-peak. That's after changing the 1K resistors in the schematic for 1,8K ones. Otherwise the voltage was just 3,2V and 6,4Vpp.

Current draw: positive: average 12mA max.: 18mA

                       negative: average -13mA max.: -18mA

Here's the Bill of Materials:

Here are some screenshots from the oscilloscope with some measuring data underneath the images. Some images may still show the lower output voltage but that's been fixed:

The following are screenshots from the oscilloscope showing two signals, one from each LFO, being combined in a simple passive multiple. A squarewave and a triangle wave each at different frequencies. The results are pretty cool looking:

In the top picture you see more of the waveform in the positive voltage region and very little below zero Volts. You can set that with the shape potmeters to your own liking or best sounding result. As you can see this makes the Dual LFO module much more versatile as a modulation source. Plenty to experiment with.

PICTURES:

Below are some pictures of the print. I took these before I changed the 1K resistors to 1K8 ones. In the top picture and the 3rd one you can see how I mounted the little print with the bi-colour LEDs. The print rests above the middle two potmeters and the LED's are bent backwards over the sides of the stripboard and go straight into the holes in the panel and are secured with hot-glue. The little print itself is not mounted in any way. It just relies on the LEDs to keep it in place.

This time, instead of spray-painting the panel I decided to keep it blank aluminium and I used an engraving tool to put the text on. That didn't work too well and it didn't look good at all so I printed some labels I made in Photoshop, laminated them with Scotch Tape and put some double sided sticky tape on the back and I put those on the panel. That looks much better. 

TRIGGER OUTPUT

A few days after completing this build I added a trigger output to this module. I connected it to the squarewave output of the second LFO (the faster one). I thought it might come in handy to have a trigger source. You can see in the picture below how I did that. It gives of both positive and negative trigger pulses of 5V and a length of about 4mSec.  If you're thinking of putting in a diode to only get positive pulses forget it. That won't work. It'll kill off the pulses completely. If you turn the Shape potmeter the positive and negative pulses will move further away or closer to eachother. Just like the rising and falling edges of the squarewave with different pulsewidths.

(The above drawing actually translates to a high pass filter with a cut-off frequency of 268Hz. So it filters out the actual square- or pulsewave and only lets through the initial harmonics of that wave, creating this spike pulse trigger response, but you can forget about this theory. This is not important.)

Here's a look at the final panel with trigger output. I just made some labels with text to put on the panel. Looks better than the engravings.

One other thing worth noting is that because we have two LFO's on one board, they will very slightly influence eachother. What I mean is, if you have one LFO running at almost twice the speed of the other, the faster one will adopt some multiple of the rythm of the slower one if you set the speed to some value close to that. That's a form of resonance and I won't get into the technicalities of that but it's quite easy to set an LFO at twice or 4 times the speed of the other because they share the same circuitboard. It's the same idea as when you have a group of people walking together and they all start to walk at the same pace. That's also a form of resonance. Don't think this will be an obvious thing to observe. The occurrence is very subtile.

Okay, that's number 47 done! A very useful little module and I saved a few bob by building it myself instead of buying a dual LFO module. Okay it doesn't have any fancy extra's like synchronization but that's okay by me. I think I'll mostly be using this as a clock source and some random modulation. That's why I made both LFO's run at different frequency ranges.

If you have any questions or remarks about this or any other project on my site please comment below or post in the FACEBOOK GROUP for this website.

If you find these projects helpful and would like to support the website and its upkeep then you can buy me a Coffee. There's a button for that underneath the menu if you're on a PC or Mac. Or you can use this PayPal.Me link to donate directly. All donations go towards the website and projects. Thank you!