Synthesizer Build part-40: WAVETABLE OSCILLATOR (VCDO) By Electric Druid.

An amazing sounding digital oscillator with 16 waveforms and a sub-oscillator with 8 waveforms that spans 4 octaves. All but one of the parameters of this VCDO can be changed with external control voltages including the Bitcrush option which does not have a CV input in the original Electric Druid schematic but it has one in this build.  Only the Glide function doesn't have a CV input.

Warning: this is a big project. It needs two stripboards of the size I normally use (24x56) and my layout is definitely not Eurorack friendly. Everything needs to be shielded to prevent glitches in the main oscillator. Even the wiring of the control potmeters must be shielded.

It is possible to build a Eurorack friendly version of this VCDO on stripboard and the circuit will work fine on a dual 12 Volt powersupply but you can NOT cut these prints in half and connect them together like in other projects. You will need to make your own layout and much more compact than mine is now. However there is a smaller size layout available on the EB Facebook group files section. Check the link below the layout images under the heading 'Eurorack Layout' half way down this article.

ABOUT THE BUILD PROCESS AND PROBLEMS ENCOUNTERED.

Okay, not to put you off or anything but this is the most difficult build on this entire website so if you're a beginner or you don't have the right tools, especially a fine tipped soldering iron and good soldering skills plus a good oscilloscope, then please do not attempt this. By saying this I just want to avoid disappointment. As an alternative I would advise you to just order the Klang Stadt PCB and Panel from Frequency Central. That one is in the Eurorack format which mine won't fit in to.

I foolishly started out building this module like I did with all previous ones. Just build it up on stripboard, make a panel and then wire it up and test it. Well this turned out to be too light-hearted an approach because the main oscillator sounded like a scratchy vinyl record. I couldn't get it to sound right so I wrote to Tom Wiltshire (Electric Druid) about this problem and here's what he said about it

<Quote>

"It happened a bit on the first version of the PCB I did for the Frequency Central "Waverider" module. Eventually we tracked it down to the outputs being to close to the CV inputs. Keeping tracks and wires to those apart as much as possible helps a lot. On revision 2 of the Waverider PCB I routed the inputs on one side of the PCB, and the outputs on the other and that solved the problem. It boils down to noise getting into the CV inputs. That can come from many sources but from the chips own outputs was a big cause for us."

<End quote.>

So I started out fresh and re-built the entire module. This took me three days including designing a new layout. I now decided to shield everything and to keep the controls and the CV inputs on separate boards. This turned out to be the solution because it now works like it should. Instead of wires I used pinheaders to connect the two boards together. This would be the shortest route for the signals with less chance of noise getting into the connections. I had a blank single side copper clad circuitboard in my stock so I decided to cut this board to the same size as the stripboards and mount it inbetween the two stripboards and then connect it to ground. I cut holes in it for the pinheaders to go through and soldered upstanding copper edges around the holes to provide extra shielding for the pins. (The upstanding copper edges are a bit overkill and if you build this module, you don't really have to replicate that.)  

Here's a picture of how the boards eventually fit together. I stuck 4 transparent rubber feet on top of eachother and put it between the shield board and board two to act as spacers to prevent the upstanding copper edges around the pinheaders from touching the copper traces of board two. I also put some gaffa tape on the edges to insulate them.

SCHEMATIC:

[EDIT: As of Oct. 2023 the chip is available on back order.]

You can order the chip from Electric Druid. On that same page you will also find a link to the Datasheet with the schematics for this project. Download it and print it out.

NOTE: On the schematic, in the PDF, you will see one CV input circuit marked as "Spare CV Amount". On the page with the processor it is marked as 'Unused CV'. I don't know why it's marked like that but this is the Sub Oscillator CV Amount circuit which eventually goes into pin 18 of the processor chip. Just so you know.

If you're going to breadboard this circuit before building it up properly, don't leave any pins of the processor chip floating and make sure all the CV inputs get the voltages they need, otherwise it won't work properly.

LAYOUTS:

Below are the layouts for this project. They are all verified as usual. Not only by me but I had confirmation from a number of people who built this module successfully using the layouts below.

I'm going to give you a whole collection of layouts detailing the different steps. The Bitcrush section of this module was designed by Mike Desira, whom most of you will know from a lot of synthesizer DIY related Facebook groups. He has been a great help to me, not only in this but many other projects too. On my panel I have a Bitcrush switch to go between internal and external sources. I still had that in there from the first version so I thought I might aswell use it again. I personally prefer it to mixing the Bitcrush signals together. The layout shows both versions for the Bitcrush option, without switch and in dotted lines with switch. Mike did away with the switch in his design. Instead you do need to open the internal Bitcrush potmeter for the CV potmeter to work. The signals are mixed together in an opamp and inverted. 

Here's a schematic drawing of Mike's solution. On the right is the version with a switch to go between internal or external bitcrush as indicated with dotted lines on the layout wiring diagram. 

EDIT: Until the 8th of June 2021 I had a second inverter stage in the Bitcrush circuit but this turned out to be a mistake so I have corrected the circuit and all the relevant layouts. So if you built this VCDO before the 8th of June 2021 and your Bitcrush section isn't working, check it against the new layouts and make the necessary changes. It's a matter of changing two resistors and a wirebridge to bypass that second opamp. The second opamp must be properly connected to ground, which it is in the layouts.

 

The de-coupling capacitors are mostly not included in the layout. I soldered those straight to the pins of the IC's on the copper side. So get yourself some small ceramic 100nF caps and solder them on, on the copper side, to pins 4 and 8 of the TL072's. The processor chip has a 100nF cap in the layout already. 

I also put 100nF caps over all the inputs of the processor chip. With the previous version of this board, when I was troubleshooting it, I soldered 100nF caps over the inputs and this seemed to improve the input signals a lot. Before I did that the signals had little spikes on them when viewed on my oscilloscope and after I put in the caps these spikes were gone. So I used this idea in this version, eventhough these caps are not in the Electric Druid schematic. They are included in the bill of materials. The de-coupling caps, soldered directly onto the chips on the copper side, are not included in the bill of materials.

Here is the wiring diagram for this project. The wires coming from the wipers of the top right five potmeters to pins 1, 2, 3, 7 and 8 of the processor must be shielded wires. The outer shielding must be connected to ground but only on one side. If you connect both sides to ground there could be current flow in the outer shielding and that would create a lot of hum! (Ground loops) The easiest solution is to connect the outer braiding of each wire to the grounded pin of the respective potmeter it's connected to.

(Last revised: 9-June-2021 Removed second inverter stage from the Bitcrush section and tied off the second opamp to ground. 12-June-2021: Reversed polarity of top capacitor (+5V to Gnd) )

The two stripboards are mounted with the copper sides towards eachother. The pinheaders are soldered straight to the copper sides of the stripboards. In between them is mounted the blank single-sided copperclad circuitboard (shield board) with holes for the pinheaders to stick through. It will help with soldering on the female pinheader sockets if you bend the pins 90 degrees. Makes it easier to solder them in place. But be careful, they are fragile. 

Drill two holes at the bottom of this shield board, at the same distance as the mounting holes of the two stripboards, for the M3 mounting bolts to go through. Make sure the copper side of the shield-print is facing the copper strips of stripboard two and facing away from the main board with the processor on it. We will mount the shield board with the non-copper side touching the copper strips of the Main Board and the copper-side towards the copper strips of board two and we don't want any short circuits :)

Here's the main board. You can leave out the 10K resistor over the output of the 7905 voltage regulator. This resistor is there because some regulators only work well if they are presented with a load on the output but the circuit itself is enough of a load usually:

(Last revised: 23-April-2021: Corrected mistake with C2 (330pF) which went to pin 3 instead of pin 1 of IC-1 like it should. 9-June-2021: Removed colour-code striping from all resistors for clarity. 12-June-2021: Reversed polarity of top capacitor (+5V to Gnd))

Board Two with the CV Inputs on them and the Bitcrush circuit by Mike Desira. (Updated corrected version):

(Last revised: 8-June-2021: took out 2nd inverter stage for Bitcrush option.)

In the layout of board two you can see 10 Schottky Diodes. These, together with the 4K7 resistors, are there to protect the inputs of the processor chip from voltages that exceed the +/-5 Volt limit for CV voltages.

The two voltage regulators are the big TO220 packages and they don't need heatsinks. The current going through them is so low they won't even warm up. You can also use the smaller 'L' types that look like a little transistor but I used the big ones because that's what I had in stock. If you use the big ones, make sure the backsides don't touch eachother, otherwise you'll get a short circuit.

Here's an overview of the cuts, wirebridges and the positions of the pinheaders. I used a double row of pinheaders to make sure I got good contact and to make sure it doesn't get loose. Mark each cut on the component side of the print with a felt pen or a Sharpy. Then stick a needle through the marked hole and mark it again on the copper side. Then make the cuts. This is the most accurate way to do it and prevents errors.

MAIN BOARD, CUTS and WIREBRIDGES - COMPONENT SIDE:

BOARD TWO, CUTS and WIREBRIDGES - COMPONENT SIDE:

(Last revised: 17-March-2021: Corrected a cut at the powersupply pinheader. 9-June-2021: Tied off second opamp of Bitcrush section because that stage has been removed.)

And finally a view of the cuts and the position of the pinheaders seen from the copper side of the print where they actually need to be soldered on and, obviously, where the cuts need to be made.

MAIN BOARD, CUTS and PINHEADERS - COPPER SIDE:

BOARD TWO, CUTS and PINHEADERS - COPPER SIDE:

(Last revised: 17-March-2021: Corrected a cut at the powersupply pinheader.)

Bill of Materials:

Note: the pinheaders are not included in the bill of materials. You can order them in strips of 40 pins long. Make sure you get both the male and female versions and order ten strips of 40 pins. They cost pennies and are always handy to have in stock.

Here's the link to a listing on AliExpress that has the same ones I used. These are female ones but the male ones are also listed on the same page. I'm afraid I could only find the Dutch site version. Order some of both:

--CLICK HERE --

EURORACK LAYOUT:

There is a smaller size layout available in the files section of the 'Eddy Bergman Projects Discussion and Help' Facebook page made by Markus Möbius. He used it to build his VCDO and based it on my layout but just made it more compact and he used single rows of pinheaders. His VCDO works fine. Look for the file name ED_VCDO.diy  It's a DIYLC project file. The layout doesn't have any potmeter and socket connections so you have to reference it with mine to get that sorted out.

DEMO VIDEO:

Here's a demo video with a look at the functions and the different sounds/waveforms you can get from this digital oscillator. When you start mixing the two outputs together, you can get some awesome sounds. If you then put it through a filter it starts sounding really amazing. That's in the last bit of the video. Btw, the mixing together of the Main Oscillator and the Sub Oscillator is done with the 4 channel mixer/passive attenuator from article 17.

For some reason my YouTube embedded videos don't show up on mobile devices anymore. Please go to my YouTube channel if you can't see the video here.

Here's an other video, not by me, that I found on YouTube with a 12 minute demo of the Frequency Central Waverider module, which is the same as the module I built here. The subtitles are in what I think is Spanish though.

TIP: Try connecting the Triple Sloths (proj 61) to some of the CV inputs and a slow sample and hold on the V/Oct input and let it generate its own music.

PICTURES OF THE BUILD PROCESS:

Here are some shots I took whilst building the latest version of this module. In the top picture you can see the green ground wire soldered to the shield print. This is connected to the ground of the powersupply. You can also see I put some tape over the copper edges to insulate them electrically should they touch the copper of board two. If you use upstanding edges then look out not to make them too tall. If they are taller than the pinheaders they will touch the copper strips of Board Two and cause short circuits!. So make sure they are not too tall and use tape over them to be extra sure they can't cause short circuits.

I also made cuts in the corners of the upstanding edges so I can bend some of it out of the way when connecting the two boards together. They obstruct the view of the pinheaders making it difficult to align the two boards correctly. After connecting the two boards I can bend the copper back up and leave it like that.

In the next picture you can see the preparations I took before soldering on the pinheaders. I applied some solder inbetween all the holes and on the pins themselves too. This way I had only to touch them with the soldering iron and the solder would flow and connect them to the copper strip. Then I would add some more solder to make sure the connections were nice and stirdy and I checked the continuity between the strips to make sure there were no short circuits.

In the middle picture you can see the shield print as I call it, mounted inbetween the two stripboards. All the orange wires in the bottom picture are shielded wires. The outer braiding of these wires must be connected to ground but only at one end of the wire. If you connect both ends to ground you can get ground loops with all sorts of problems. I connected the shielding of the wires to the ground connection of the potmeters they are connected to. On the other side of the wires I cut off the outer copper braiding and put a little piece of shrink tubing on to prevent little individual wires from the outer braiding sticking out and contacting other components by accident. (You never know). The prints are connected to the panel by two copper L-Brackets with thin M3 bolts through them, 3 centimeters long. The order of mounting is as follows: Bolt goes through the main board first, then the shield print, then a plastic spacer, then the L-Bracket, then a plastic ring to prevent the L-Bracket from touching the copper of Board Two and then through Board Two. Then I put a ring and a nut on it.

Here's a look at the panel I made for this module. The mix-up of colours of the knobs is intentionally done, I assure you =). The yellow is for control functions and the red knobs are for CV Input levels. Make sure when designing a panel, that you make the two wave selection potmeters, those connected to pins 3 and 7 of the processor chip, your main controls on the panel. Not the frequency controls as is usual with normal VCO's. This is not a normal VCO ^___^. I took my inspiration for designing the layout of the panel from the Klang Stadt version from Frequency Central.

Here's the Wavetable Oscillator next to my two Thomas Henry VCO's. A killer combination!

Here's how I prepared the potmeters on the panel before I connected them to the prints. I soldered in all the 1K resistors and 100nF capacitors and made all the ground connections for the potmeters when I still had access to them. Then I soldered in the wires with the prints laying loose on top of the panel starting with the shielded wires first because they are the bulkiest. 

I made two L-Brackets from some thick copper sheeting I had lying around. You can or course use any metal to make your own L-Brackets or even buy them ready made. Make sure non of it contacts the prints' copper side. I used home made plastic rings to insulate the print from the L-Brackets.

Here's a picture of how I made the first version of this module with much too long wiring and unshielded prints. This did not work so don't copy this!!

TUNING THE VCDO:

Tuning was quite a difficult operation. This is mainly due to the fact that the oscillator quantizes the incoming 1V/Oct signal. But this does have the advantage that once you get the tuning right, it'll be rock solid over many octaves (I got it tuned over 7 octaves in about 15 minutes). 

Because the tuning trimmers are a bit fiddly I put in two of them on advise from Mike Desira. One for normal tuning (20K multiturn) and one for fine tuning (2K multiturn). I also used the Offset control potmeter in the tuning process. This is a normal 20K potmeter, not a multiturn. 

Before you start tuning, set the frequency potmeters on the panel in the 12 o'clock position. 

It was a trial and error kinda process but, like I said, after about 15 minutes I had the VCDO tuned over 7 octaves. You just need to try this and develop a feel for it. I can't give you a procedure for tuning. Make sure you use all the potmeters in this process. The Offset, the tuning trimmers and also the main Frequency control on the panel (not the finetune one).

At one point I had it tuned and tracking nicely only the lowest few notes were way off. I used the offset trimmer and retuned until I also had those low notes in tune and then it suddenly was tracking fine over the 7 octaves of my M-Audio keyboard. You just have to experiment until you get it right.

This is an amazing sounding oscillator. It's got 16 different waveforms in the main oscillator and an other 8 with 4 different octaves in the sub oscillator. You can connect both to a mixer and mix the two signals together and you get some awesome results!! All parameters can be externally changed with control voltages, except for the Glide control. You don't really need CV control on that.

Here's an overview of the 16 waveforms from the main oscillator. The waves all merge and flow over into eachother so there's no stepping between waves so really you have a lot more waveforms inbetween these, but these are the 16 main waves:

And here are the 8 waveforms from the sub-oscillator. Each of these waves is present in 4 different octaves. (The last image on the bottom right is aan example of a Bitcrushed wave with Bitcrush set half way.) The waves from the sub-oscillator do not merge from one to the other. As you turn the Sub Oscillator knob you'll get a waveform at the lowest octave and as you turn more clockwise the octaves will go up in 4 steps until it reaches the 4th octave and then it switches to the next waveform, again at the lowest octave. Then the cycle repeats. So this all happens in definite steps.

You can find the original DIYLC Layout file in the 'Files' section of the EddyBergman FaceBook group.

Okay, that's it for now. All in all not so much a difficult build but a very labour intensive build number 40. I will take it easy with the building for the coming months now. I really need to build a new case because I already built 7 modules for which I have no space. I'm also out of a lot of vital components so I need to replenish my stock which will take some time.

If you have any questions, please put them in the comments below or post them in the special Facebook Group for this website. There are a lot of expert people there who can help you, or at least try :)

DISCLAIMER: The author of this article does not accept any responsability for the correct functioning of this, and any other, module/project on this website. What you build, you build at your own risk. All project layouts are thoroughly tested before publication, it's up to you to replicate them and the author can not be held responsable for any mistakes made.

Synthesizer Build part-32: ELECTRIC DRUID VCLFO-10 with extras.

A truly awesome LFO with 16 waveforms and 8 different controls. I added 2 extra outputs for 10Vpp and a frequency indicator LED.

This Low Frequency Oscillator was one I had on my wish list for a long time. Last month I decided to buy the chip, it was only 5 Pounds anyway, and it arrived precisely a week later from Tom Whiltshire of Electric Druid in Portugal.
I downloaded the Datasheet PDF with all the schematics etc on it but I found parts of the schematic a bit confusing. The Frequency and the Level controls have their own opamps and they both have two potmeters connected which looked a bit weird to me. So I asked on the Synth DIY Facebook Group what the deal was with those two potmeters. It turns out both the Level and the Frequency controls can be connected to an external control voltage so one potmeter is connected to an input jack and serves as the input level control or attenuator and the other potmeter is for manual setting of the Frequency and the same for Level. So after I had that straight I set about making a stripboard layout. Now, I noticed there was no rate indication LED in the schematic. I always find it handy to have a frequency indicator LED on the panel, so I designed a second board and included a rate indicator LED on it, together with two extra outputs that have a DC offset of +5V so the outputs are 0V to +10V. That is the level I use most on my synthesizer so I needed to have that included. This does mean that the Noise level through these outputs has a +5V DC offset so use the +/-5V output for noise.
I made a second stripboard layout and made a mounting hole in it, on the upper right corner, so the second print can be stacked on top of the main circuit board, using a 3 cm M-3 bolt  and a bit of plastic tubing as a spacer to keep the two prints from touching eachother. The layouts worked like a charm and everything worked fine when I tested it.

 

If you find that you wired up the potmeters the wrong way around, you can easily correct that by connecting pin 2 of the VCLFO chip to ground. That reverses the working of the potmeters. Make sure the two level potmeters are wired like on the diagram though. They are not influenced by pin 2 of the chip.
The main stripboard has its own plus and minus 5V power supply included, so everything can be powered from a single dual 12 Volt power supply. I used the big 7805 and 7905 in TO-220 package because that's the only ones I had available but you can use the smaller L versions. This circuit hardly draws any current at all so they won't run warm and don't need heatsinks. I did not include any de-coupling capacitors or electrolytic caps on the power rails (except for the -5V because that was indicated in the schematic). You can put those in though, if you think you need it. Use two 100nF ceramic caps, one from +12V to ground and one from ground to -12V.

SYNCHRONIZATION POTMETER:

There is an extra 100K trimmer in the layout with which you can set the Synchronization mode between Sync Off, sync-ing the LFO, the Sample and Hold or both. Instead of a trimmer, as seen on the layout,  you can also make this a feature on the front panel and connect a potmeter to the same points as where the trimmer now sits, and of course you then leave out the trimmer. That way you can change the sync setting on the panel itself. This is what I later did. Beware these extra's are not listed in the Bill of Materials. I used a 100K potmeter but you can use any value potmeter or trimmer for this function because it is just a voltage divider connected between +5V and ground. (Use a value of 10K or higher.)

Looking at the panel-potmeter front-on with pins pointing downwards, connect the left pin to ground, the middle pin (wiper) to pin 8 of the chip and the right pin to +5 Volt.

It took me 5 and a half hours to solder the stripboard components in place and to wire it all up. The whole proces of designing the layout, designing and making a panel etc. took a whole weekend so it was a nice project to do because at the time I, and everyone else, was stuck at home in Covid Lockdown anyway.

Here is the (verified) layout. Wiring diagram:

The +5V and -5V points on the left side of the stripboard are simply indicators, so you know that voltage is available at that point. You could say they are test points you can check if you are troubleshooting this board (which of course I hope won't be necessary. ;) But nothing needs to be connected to those points. Sorry if that's a bit confusing.

This circuit will run fine on +/-15V too. The voltage only feeds the IC's and the regulators and they can all take it without problem or without any changes needed.

Here's the layout for the main stripboard. Beware that some stripboards are sold with 56 instead of 55 holes horizontally. The layout is 55 holes wide!!

In this layout the synchronization mode is set with a 100K trimmer at the top of the stripboard. As I mentioned before I myself exchanged that for a panel mounted potmeter later. The sync mode depends on the voltage on pin 8 and the trimmer or potmeter sets that voltage.

There is no capacitor on the input of the 7905 voltage regulator, it doesn't need one to work but if you want you can put a 1µF electrolytic cap over the input to ground. Easiest way to do that is to connect it to holes B-11 and C-11 with the negative pole in position C-11 (-12V)

The Zero Adjust 100K trimpot is used to set the symmetry of the output signal. You must use an oscilloscope to adjust this. Set it so the LFO output signal's positive amplitude is the same as the negative amplitude.

Make sure you get the cuts right in the stripboard. Especially those in the power rails at the top otherwise you'll have a direct short circuit between ground and -12V. Always measure continuïty over the power connections to rule out short circuits before you connect it to power for testing.

Here's the Bill of Materials for the main stripboard. Note: component numbering does NOT follow the numbering in the datasheet schematic. 

OFFSET AND LED INDICATOR BOARD:

Here's a close-up of the second board with the extra outputs and rate indicator LED. You can use this board for other projects too, if you need to add a DC offset voltage to a certain output. I chose 150K resistors for around the opamps (R3,4,5 and 6) because I have a lot of them but you can use any value from 47K to 500K instead of the 150K's as long as you use the same value for all four resistors:

The DC Offset trimpot must be set to a +5VDC Offset to get a 0V to 10Vpp output signal. Use an oscilloscope connected to the output socket to set this. I don't have a schematic drawing for this part but it's a really straightforward opamp offset circuit with the offset trimpot connected to the non-inverting (positive) input of the opamp. The signal goes in at the inverting input and then it goes through a second opamp stage to invert it back to normal again. Then the second output (at the bottom) is simply fed the signal of the first output via an opamp buffer. The second opamp of the chip on the right is not used and properly connected to ground to 'park' it so to speak.

Here's the Bill of Materials for the extra board:

You don't have to use this extra board for 0 to 10 Volts outputs of course. If you find you need more Bi-Polar outputs of +/-5V then set the trimmer to 0V offset and it's done. 

WAVEFORMS:

This VCLFO produces 16 waveforms in 2 sets of 8. I have made a little compilation image of oscilloscope images I took of the waveforms and some sample and hold results. The blue line is the original +/- 5V output and the purple line is the one I put in myself with 0 to 10Vpp. You can see that the noise has a +5V DC Offset on the purple line. When you start testing this circuit after completing the build, it's possible you don't see a waveform but just a flat line. That means your offset voltage is too high or too low, so all you need to do then is set the offset voltage with the trimmer on the main stripboard. Then check the 10V outputs and set that offset with the trimmer on the small print. I advise to use multiturn trimmers for those, but you don't have to. Make sure your oscilloscope is set to DC mode for measuring these waveforms.

Each of the waveforms produced can be sent through a sample and hold unit which is built into the chip and as the chip can also produce noise you can also get random tones produced by this LFO if you connect it to the CV-2 input of one of your VCO's. The sample rate of the S&H can be set with a 10K panel potmeter and if you turn it to zero the S&H switches off automatically.
The VCLFO has a synchronization input and it can be frequency modulated by means of a Frequency CV input with attenuation potmeter. There's even a separate input for the Level control which is a volume control changing the amplitude of the waves.
There's also a control on the panel for 'Distortion' which bends the bottom or top part of the wave with the middle setting being the clean, undistorted wave.
The LFO has 4 frequency ranges and they are:
8 seconds per wave to 12,5 Hz
4,6 sec/wave to 25 Hz
2,6 sec/wave to 50 Hz
1,2 sec/wave to 100 Hz
You set the frequency range with the LFO Range potmeter and then you can set the Frequency within that range with the Frequency potmeter. There's a smoothing switch included in the circuit which rounds off the corners of the waves and makes them smoother (obviously, LOL). This is to prevent the sharp edges of some waveforms from causing clicking sounds when you're using the LFO as a Tremolo.
The possibilities are endless with this LFO and with the chip only costing 5 UK Pounds, like I mentioned, you should really get this one.

Here are some pictures of the finished panel and of the stripboard and wiring. I admit the panel is a mess but it works for me:

In the picture below you can see I made a change by adding an extra potmeter (the one with the yellow knob) with which you can set the Synchronization mode between synchronizing the LFO, the Sample and Hold or both.

And here's a little video I shot using the LFO in a reasonably complicated patch. I've got 3 VCO's feeding squarewaves into 3 filters and a triangle wave into the wave folder. Each filter receives an LFO signal from a different LFO. The Electric Druid VCLFO-10 is feeding a quad pulse into the Steiner Parker filter. All LFO's are synced from the main LFO which is the Music From Outer Space LFO. You can also see the Mixer/Passive Attenuator in action with the bright blue clipping LED coming on occasionally and the Digisound 80.6 LPF sounding really good!

If you're interested in recreating this patch then here is the basic set-up I made. The eventual sound is, of course, dependant on the settings of all the potmeters and little changes can make a big difference but this at least is the foundation of this patch:

ORDER THE CHIP:

Here is a link to the product page of the Electric Druid VCLFO-10 from where you can order the chip:  https://electricdruid.net/product/vclfo-10/

If you have any questions about the chip or simply want to say thanks to Tom Wiltshire, drop him a line on his website. He's a really nice guy and he'll appreciate your feedback.

Okay, that's it for now. I have now finished the second stage of my synthesizer and so I have no more room to put new modules unless I build a third case. That will no doubt happen but not right away, what with summer coming it's going to be too hot in the attic to spend all day in there wood-working or soldering. I also built up a Eurorack system in early 2022 which took a big chunk out of my budget, which wasn't/isn't too big anyway, but that's all in the game right?

As always, if you have any questions please post them on the EB Projects Discussion and Help Facebook group, or in the comments below or contact me directly via Facebook.

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

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

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

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

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

STRIPBOARD LAYOUTS:

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

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

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

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

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

Bill of Materials:

Here's the schematic I used for the layout:

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

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

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

The synchronization pulse threshold = +2,9V.

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

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

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

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

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

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

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

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

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

Some pictures of the finished module:

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

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

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

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