Friday, 22 May 2020

Synthesizer Build part-33: DIGISOUND-80 ENVELOPE GENERATOR with AS3310.

A fantastic ADSR with 3 different types of envelopes and extra outputs including an inverted one.

This Envelope Generator or ADSR is a very luxurious one because it produces three different types of envelopes. The following description is from the original text for this module:
First there's the 'Damped' mode. The object of this mode is to more closely simulate the piano envelope which has a sharp attack, a brief initial decay, a long release and finally a very short release as the damper is applied to the string. So it's an ADRR response and in this mode the end of the gate pulse causes the final short release to occur. In other words releasing the note has the same action as applying the damper on a piano.
In 'Normal' mode the ADSR functions as any ADSR would with the duration of the Sustain period being equal to the duration of gate signal being present and the key being pressed down.
The 'Automatic' mode is particularly beneficial when envelopes are being initiated from non-keyboard sources like an LFO or from a clock signal. A short pulse will now generate a complete ADR envelope and, by adjustment of the time constants, this type of envelope can be made to approximate the ADSR type envelope. Usually these external sources would only generate a limited AD type of envelope.

Further features of this envelope generator are:
- Independent trigger input for re-triggering and generating multiple peak envelopes in the Damped and Auto modes.
- Gate and Trigger pulses within a range of +3V to +15V are acceptable.
- Wide range of time constants. Typically 2 milliseconds to 20 seconds. If longer times are needed you can increase the value of C9.
- 0 to +10V peak attack output
- 0 to 100% Sustain level.
- Low control voltage feedthrough which means low residual voltage when the envelope cycle is completed thus ensuring that the VCA is off.
- Manual gating facility.

Features I added:
- Extra buffered envelope output.
- Extra inverted envelope output (0V to -10V).

Dual 12 Volt operation:
This envelope generator is designed to run on a dual 15V powersupply but I tested it on a dual 12V supply and it works just as well with only a very small loss in envelope voltage. On 12V the envelope is about +9V so no problem running this on +/-12V. One change should be made however; the current limiting resistor R25 should be changed from a 750 Ohm to a 470 Ohm according to the datasheet of the AS3310. However I test ran it on dual 12 Volt without changing the resistor and it worked perfectly fine.

I had build this envelope generator some time ago and I've been using it in my synthesizer for all that time but I didn't write an article about it until now because there was something wrong with it. In the 'Normal' mode, which is the one you'll be using most I think, the Decay was oscillating. It kept on being triggered for as long as a gate signal was present. The only way to stop it was to turn up the Sustain level so it matched the Attack level and then you wouldn't hear the constant up and down oscillation of the volume level.
The frequency of this oscillating Decay could be changed by changing the Decay time. Short time equals fast oscillations, long time equals slow oscillations so you could almost think this was meant to be but I can not believe it was meant to work like this in the 'Normal' mode.
So I was using this ADSR with Sustain turned up but it annoyed me that is wasn't functioning quite right because this is an awesome ADSR and I wanted to do an article on it. So I asked on the Synth DIY Facebook group what could be causing this. I was told it was due to capacitor C7 and that I should remove it. They were absolutely right. Removing C7 did the trick, at least in the 'Normal' mode but when I switched to 'Damp' or 'Auto' mode the ADSR was hanging. It wouldn't go into the  Release state. So for these two modes capacitor C7 needed to be in place.
By happy coïncidence I had used a vintage double pole 3-way switch to switch between the different modes and I had one pole left unused. So I connected the capacitor to that switch in such a way that it was connected in 'Damped' and 'Auto' mode and disconnected in 'Normal' mode. This worked fantastically and now it behaves just as it should do. Should you want an oscillating Decay in 'Normal' mode you could easily add a switch to connect C7 again. Now you have the choise between the two. (This option I leave to you. It is not documented anywhere in this article).
All these changes have been drawn into the layout and into the new schematic that I made.
I used a SPDT toggle switch to go between manual gating and inputting gate signals. This is marked in the schematic as a gate input socket with internal switch, which you can of course also use instead of an external switch.

One little thing you need to be aware of with this ADSR is that I you need to switch to Auto mode whilst holding down a key on the keyboard. If you don't do that, then the ADSR only gets triggered (in Auto mode) if you push the manual trigger button but not by the keyboard. I think that's meant to be though because Auto mode is for external sources so that would make sense. If however you switch to Auto mode whilst holding down a key then it will work with the keyboard. Any key you press after switching it on will keep sounding until you press an other key and it will keep sounding until you switch back to Normal mode. Once you get used to this it's actually not a problem at all. Just something to be aware of.

If you plan on building this ADSR you might just build it first like it was intended with C7 connected to pin 7 of IC1-B and without connecting C7 to the second pole of the 3 Way switch. In the stripboard layout it's simply a matter of connecting the 10nF cap between pin 2 of the LM358 and the strip directly underneath the LM358 which connects it to pin 7 via a wire bridge. Then it's back to how it was originally. Should you encounter the same problems I had then you can make the same alterations I did and have it function perfectly that way. Instead of a double pole 3-way (rotary) switch you can use a single pole one and if you need C7 to be disconnected in Normal mode, just use a little toggle switch for that. Double pole 3-way switches can be expensive unless, like me, you have some lying about in your junk box.

Here's the new schematic drawing that I made and used for my build with C7 connected to switch S1-B. (That's the only difference to the original schematic) :


This is a re-drawn version of the original Digisound-80 schematic, without any changes. You can use the "J" and "K" keys on your keyboard to quickly switch from one picture to the other so you can easily see the changes (only on a Mac or PC).:


Here's the verified stripboard layout. The changes I made are implemented in the layout but if you connect the lower pin of C7 one strip higher, you can do away with switch S1-B and everything is back to how it originally was, so the changes (if needed) are very easy to make.
BEWARE! All IC's are mounted with pin 1 to the lower right!
Wiring diagram:


Print only:


Bill of Materials:



CALIBRATION:
There are two trimmers in this circuit, RV2 and RV6.
RV2 is used to set the maximum Sustain voltage to the same value as the peak Attack voltage so no sudden voltage change occurs when the attack cycle is finished or so that the Sustain voltage can never be higher than the peak Attack voltage. The best way to set this is to use an oscilloscope but you can do it with a voltmeter too. I advise to check out the original text (second link below) and read the calibration instructions there. They are on page 4.
RV6 is more for polyphonic systems and for normal use it can be left in the middle position.
So, that all the calibration you need to do ^__^

Here's a screenshot of the oscilloscope that illustrates the oscillating Decay problem I had in the beginning:


Here are some screenshots of the different modes of this ADSR:
This is the Damped mode with short and continuous key pressing:


You can see that every time you let go of a key an almost instantaneous release kicks in and kills off the note.
Here's the 'Automatic' mode with the same quick key presses:


Here you can see that letting go of the key will not stop the envelope. It will go through its complete cycle even if no gate signal is present. If you press a key before the cycle is finished it will start at the beginning again as you can see at the right side of the waveform in the screenshot above. This way you can create multiple peaked envelopes by re-triggering the ADSR.

Finally here's a shot of the normal ADSR mode:


I'm really glad I was able, with the help of the Synth DIY group, to get this envelope generator working like it should. Even with the oscillating Decay I thought it good enough to keep it in my modular setup but now it's working like it should it is a real little gem.
I don't think you can build a better ADSR with the AS3310 chip.

Here are two pictures of the module, one taken after I installed it in the synth and one after I just finished the build. You can see that I put in a lot of output jacks for the envelope. It's always useful to have a few extra I think. The top two outputs are switched in parallel over the ADSR output and the bottom two are switched in parallel over the extra output on the stripboard. Below the inputs for Gate and Trigger there are two more sockets. They are Gate and Trigger outputs. They are each switched in parallel over their respective input sockets. I later added a yellow LED to have a visual indication of the envelope. The LED is soldered over one of the extra ADSR output sockets using a 15K resistor as current limiter so as to not influence the envelope voltage and to make sure the LED doesn't shine too bright:





Here's a link to the Electro-Music Engineer PDF article by Charles Blakey about this module:
http://www.digisound80.co.uk/digisound/other_documents/doc_files/1981-12_EM_Eng_CEM3310.pdf

Here's the original Digisound article in PDF form, about this ADSR:
http://www.digisound80.co.uk/digisound/modules/80-18_files/80-18.pdf

In the original Digisound modular synthesizer this is actually a dual ADSR:
http://www.digisound80.co.uk/digisound/modules/80-18.htm

Okay, that's number 33 done. If you have any questions please post them on the Eddy Bergman Projects Discussion and help Facebook Group, or the comments below or contact me directly.
If this website is of use to you please consider buying me a coffee ^___^
See you on the next one!

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.
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:


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 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 change them all for resistors of the same value:


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:







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.

Thursday, 7 May 2020

Synthesizer Build part-31: NOISE MODULE.

A very easy to build noise module with 5 different sorts of noise, two of them being 'Grainy' noise with adjustable graininess.

This is a module I adapted from the MFOS Noise Cornucopia schematic by Roy Wilson. I needed a good noise source in my synth and this one seemed perfect. The original schematic has a random gates section which I didn't need but which you can easily add on if you want it. But I left that out. (I made a separate layout for the Random Gates Generator section which you can find further down the article) I also changed the transistor used to generate the noise and I changed the way the transistor is integrated in the circuit. My way is simpler and generates 200mV worth of noise right at the emitter of the BC547.
This was a one day build for me. I spent the morning adapting the design and making a stripboard layout. Then I built it in the afternoon and by 8pm I had a good functioning noise module built into my synthesizer. The layout I made worked right from the start. No troubleshooting needed.
In the layout below the transistor is shown as a schematic symbol, and not as it's normally shown in the TO-92 package, to make it clear that the collector is not connected. In fact, you need to cut off the collector leg completely to stop it working as an antenna. I've put the pin-out of the BC547 in the layout to make this extra clear. You don't need to choose a BC547 that gives you the best noise results. Any BC547 will work fine. That's an other reason why I changed the transistor arrangement from the original 2N3904 with capacitor. This works much better. Should you experience hum or something, from the power supply, then you can put a 10µF or a 22µF electrolytic cap between the base (ground) and the emitter (+ to emitter).

Here is the verified layout.

(Last revised 16-May-2020: Added grounding wires to output jacks and pinout to noise transistor.)

Print only:


Bill of Materials:



Here is the altered schematic, made from the original Noise Cornucopia design:


I changed the 500K trimmer, used to set the amplitude of the noise, for a 200K panel potmeter so you can use it as a level control. In my panel I used a 500K panel potmeter but that really is too high a value. When I turn the potmeter 1/3rd open, the amplitude reaches it's maximum at 10V peak-to-peak and the rest is just clipped, so it's better to use a 200K potmeter. If you only have a 100K potmeter you can try changing R5 from 10K to 4K7 to get the gain right, and then it should work with a 100K potmeter, but I haven't tried this so no guarantees there.
The opamps used here are not critical. The schematic says to use TL074 and TL072 but I used the TL084 and TL082. I think you could even use an LM324 instead of the TL074. As long as they are low-noise opamps (LOL, low noise, in a noise module??)
This module is designed to work on a dual 12 Volt powersupply but it will work equally well on 15 V.

The 'Grainy' noise is a real asset to have. It's very useful because of its harsh sound. It sounds a bit like the noise you get from old TV sets. You can set the 'Graininess' with the 100K panel potmeter. If you look at the scope image in the video you can see that most pulses from the Grainy Noise go into negative voltage. The more you turn up the Graininess, the more pulses you get that go positive and that's what is used to create random gate pulses. In fact only the positive noise pulses are used in the Random Gates generator and the negative ones aren't used because that diode has been left out. See the original Noise Cornucopia Schematic for that. The Highpass grainy output is a bit low in amplitude. That's not just in my build but other example videos show the same thing. To change that you really should put it through an extra opamp and give it some extra gain but I didn't bother with that. I don't think I will be using that output much anyway. If you change the resistor to ground you also change the highpass filter so I don't think that is advisable to make it louder.

I've made a separate layout for the random gates section of the MFOS Noise Cornucopia design, for those interested in adding this on.




Here's a video I made with sound samples of the different types of noise:




And finally some pictures of the finished product. As you can see the finished module is very small. In fact it is only 3 centimeters wide so it won't take up much space in your modular set-up:





Okay, that's number 31 done. A very satisfying build because everything worked right from the get go. Any questions or remarks? Please put them in the comments below or post your questions on the EB Projects Discussion and Help Facebook Group.
See you on the next one.

Sunday, 3 May 2020

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

A very useful LFO with synchronization and FM 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) 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.

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 colored green:
Wiring diagram:



Print only:



Here's the overview of where the cuts need to be made. I usually mark them with a black Sharpy 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, to identify them, 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 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 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.

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, 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.

Here are some screenshots of the waveforms. Don't mind the negative pulse in the top of the Triangle wave. I have since managed to trim that away with one of the trimmer potmeters.



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, but that's for later.

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:



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 usual, please put any remarks or questions in the comments below, or message me on Facebook. Now I need to wait for new supplies because I've been building so much lately that I'm running short even on resistors. Just look at the blog archive, and you'll see I've posted at least 4 articles per month in the last half year. ^___^  If you like what you see here you can support me by buying me a coffee. There's a button under the menu for that and it would really be a great help!
But anyway, thanks for checking out my website and see you again soon I hope.