Sunday, 10 May 2020

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 LFO 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 print 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 print 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.
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 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.)
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's a nice project to do if you're stuck at home.

Here is the (verified) layout. Wiring diagram:



Here's the layout for the main print. 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)


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 print. Note: component numbering does NOT follow the numbering in the datasheet schematic. 



And here's a close-up of the second print with the extra outputs and rate indicator LED. You can use this print 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:


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



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:


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 soldering.

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.

28 comments:

  1. A good blog always comes-up with new and exciting information and while reading I have feel that this blog is really have all those quality that qualify a blog to be a good one. thesis writing service

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    1. Thank you! I get a lot of visits from the Thesis writers. Glad to be of service. :)

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  2. Dit is een leuke om helemaal zelf te ontwerpen met een Arduino, die chip van Electrodruid is een PIC controller. Meeste functionaliteit is makkelijk te doen, behalve die S/H, nog geen idee hoe dat zou moeten werken.

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    1. Klopt, dit kun je zo helemaal in een Arduino programmeren. Die chips die hij op zijn website verkoopt bij inderdaad gewoon door hem geprogrammeerde PIC controllers. Voor S&H moet er toch wel een 'randomize command' beschikbaar zijn in de programmeer taal? Maar ik heb geen verstand van Arduino's, ik heb me er nog niet in verdiept hoewel dat wel tijd wordt. Kan een hoop werk besparen in deze hobby :)

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  3. Eddy, vraagje. Waarvoor gebruik je eigenlijk de hogere ranges tot 50 en 100 Hz. Zo snel kan je gehoor toch nooit meegaan ?

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    1. Je kunt die hogere frequenties gebruiken in, bijvoorbeeld, een ring-modulator. 50 tot 100Hz is net hoorbaar als een diepe bass. Zo kun je een ander geluid verpakken in een laag frequent draag golf. Ik heb dit echter nog niet geprobeerd dus ik weet niet hoe het klinkt maar dat is in elk geval één van de opties.

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  4. ok, thanks. De Arduino werkt namelijk niet echt boven de 20 Hz. Omdat ik de PWM optie gebruik met een low pass filter.

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  5. Wat wel leuk is, heb al 40 verschillende waveforms en realiseer me net dat je er ook een ADSR mee kan maken.

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    1. Oh cool zeg. Je moet je eigen project samenstellen joh, en publiceren. Zijn vast een hoop mensen in geïnteresseerd.

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  6. Zal ik doen tzt, moet er nu nog 1 geheel van maken. En even goed nadenken over de knoppen lay-out.

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  7. https://github.com/rolf-electronics/Modular-Synthesizer

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  8. Als je de LFO wil nabouwen i.i.g het schema staat op GitHub

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  9. ELECTRIC DRUID, gebruikt een microcontroller naar ik inschat draait die op een aantal MHz, hooguit 10. Ben de LFO aan het ombouwen naar een type met een Teensy 4.1 ipv de Atmel328P van de Arduino Nano. Die Teensy 4.1 draait op 600 MHZ ! Daat gaat een veel betere resolutie opleveren en max frequency tot zeker 500Hz, hoewel ik geen idee heb wat ik daar mee kan.

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    1. Tsja, Rolf. Ik denk niet dat je in deze toepassing veel hebt aan extra resolutie. De golfvormen werken perfect zoals ze uit deze LFO komen. Maar goed, jij bent nogal goed in dit soort dingen dus leef je uit zou ik zeggen. Er komt vast iets heel vets uit ^___^

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  10. Denk dat digitale filters bouwen met zo een ding pas echt leuk wordt, tons of possibilities. Maar eerst snel die LFO afbouwen :)

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    1. Haha ik zie dat we nog wel wat leuks kunnen verwachten van jou in de toekomst ^___^

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  11. Nou voor de LFO had je wel gelijk. Qua resolutie niet heel veel mee opgeschoten en hogere frequenties is ook beperkt omdat er natuurlijk een laagdoorlaat filter (Sallen-Key) achter zit. Dat was ik even vergeten. Dus nu eerst maar de LFO in elkaar solderen. En daarna een Steiner Parker, want de knoppen heb ik al op een blindplaat. Daarna maar eens kijken wat ik nodig heb om het een beetje musicaal te laten klinken, de synthesizer heeft nog altijd een hoog pieptoon gehalte.

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  12. Heb nog wel een vraagje, wat is een praktisch aantal aan LFO's en clock generators in een synthesizer

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  13. Hey Eddy,
    first i have to say BIG THANKS for all of your great tutorials!
    Your website is my number one resource for modular diy projects.
    I‘m in the process of building your vclfo10 modul.
    And i ask myself, if it would kill my lfo-chip, if i feed a typical eurorack signal (from -10v to 10v) into the modul inputs (like the frequency, level and sync in cv inputs

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    1. I'm not sure about the sync option but the CV inputs have attenuators on them so they will be alright. I usually feed it either +/-5V or 0-10V and that works fine. Maybe you can find some info on that in the datasheet for the VCLFO chip on the electric druid website.

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    2. Thank vou. The electric druid schematic says -5v to +5v for the frequency and level cv input jacks.

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    3. Okay cool. So you need to bring the voltage down a bit to +/-5V.

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  14. Hi Eddy! I build this great project, but I have only constant voltage on output :( I checked connections 2 times.

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    1. Hmm that's weird. There must be a mistake somewhere because the layout is verified.

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