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.

Synthesizer Build part-24: ADSR with 7555 (YuSynth design)

A great ADSR. Works very well and it's a very simple design, no trimmers to set. With verified stripboard layouts and now also in Eurorack format. There are also Eurorack Gerber files available for download for this project.

NB: Although I rate this as one of the best DIY ADSR's out there, there are some people having problems with this design. Even in my module the LED does stay on very dimly. Other people report problems with the envelope not returning to 0 Volt. In my case it works okay but I want you to be aware of this before you decide to build this. Should you have doubts then there is now an alternative to build.

Project 67, the Kassutronics Precision ADSR It also uses a 7555 chip, comes in eurorack size and works like a charm.

What does an ADSR or Envelope Generator do?

The Envelope Generator is generally better known as the ADSR which stands for Attack, Decay, Sustain and Release. These are the four amplitude phases a note goes through when you press a key on the keyboard. If we didn't have this ADSR in combination with the VCA, we would constantly hear the oscillator sound but we only want to hear it when we press a key on the keyboard right? So as soon as a key is pressed down, a Gate signal goes into this ADSR to tell it to produce an Envelope Signal. This envelope signal then goes to the VCA (Voltage Controlled Amplifier) where it opens up the VCA and so the amplitude of the envelope signal determins the volume of the sound coming out of the VCA.

The attack is the speed of the initial rise of the note, when you first press the key. Set it to zero and the sound is instantly there. Turn it open and the sound is going to take a while until it gets to full volume.

Decay is the time it takes for the note to go from the peak attack level to the sustain level. 

Sustain is the level of the note as you keep the key pressed down. It is usually set a bit less loud than the peak Attack level. (If we set Sustain fully open it will be on the same level as the peak Attack level and then it won't matter how you set the Decay because there's nothing to decay to.)

Then we have Release and that is the amount of time it takes for the note to fade out once you let go of the key. So the envelope generator produces a signal that determines the volume of the note over time and this signal is being used by the Voltage Controlled Amplifier (VCA) which interprets it as an output level. In some Minimoog synths it is also called the Loudness Contour.

Now of course the envelope output is a control voltage so it doesn't mean that you need to use it for the above mentioned purpose. You can connect it to anything that can be controlled with a control voltage like the filter cut-off or the pulse width of a squarewave or even the pitch of an oscillator. This opens up a miriad of options but let's not get ahead of ourselves here. If you're just starting out with synth building, you need the ADSR to open the VCA and the fancy stuff will come automatically with more experience. And this ADSR is great for beginners but also for seasoned builders in need of a good working ADSR. This is my ADSR of choise really.

My building experience:

This is the fourth Envelope Generator I present on my website and I think this one is the first that worked as it should straight away. No trimmers to set in the circuit either. I just used the schematic from the Yusynth website made a layout and built it. On the website he has two versions, an old and a new one. I built the new one. I can say without any doubt that this design is perfect if you want a good and reliable ADSR to pair with your VCA or to drive a filter. And because the circuit is so simple, even a stripboard version like this one would be robust enough to put in a rig you take on tour with you because, providing the panel is sturdy enough, there's practically nothing that can go wrong on the circuitboard.

This is the schematic. The opamp numbering on the schematic is different on the layout, I used the opamps in a different order but it works the same.

And this is the stripboard layout I made for it. It is verified, I used it for my build and it worked first time. Because it's so simple a design I didn't even test the stripboard after building it. I made a frontpanel and wired everything up and then I plugged it into my synth and it just worked. I would advise to change the 1M resistor (R6) on the Gate input, from a 1M type to a 100K type right from the start. Might save you some troubleshooting later on.

You can see the components are rather stretched out over the stripboard. This is something I did in all my early projects to make troubleshooting easier. There's a smaller version further down this article that can also be used for Eurorack systems. (There are also Gerber files for a Eurorack version available at the bottom of the article.)

Here is the stripboard only view: 

Bill of Materials:

If you want to add some extra outputs with buffers then below here is an extra layout that you can add to the ADSR to provide you with two extra normal outputs and two inverted ones. Of course you don't need to use the inverted output signal, you can use all four outputs for the normal signal. It doesn't matter what kind of signal is presented on the inputs, it will be replicated on the two outputs. (Two outputs for each input). This is an all purpose design so you can use this board for anything you like, even other projects like VCO's.

The wiring of the potmeters may look a bit strange with pin 3 left unused on three of the four potmeters, but I assure you that this is the way it should be wired up. Just follow the layout. It'll work fine I promise you. You can see in the schematic drawing that these pins are left dangling in the wind so that's what we do.

The ADSR triggers with a gate signal with a threshold of 3 Volt. The output envelope is 10Vpp. There's a manual trigger button on the panel (which is useful for testing). The envelope generator has two outputs. There's a normal output and an inverted output with a switch that lets you choose between +10V to 0V or 0V to -10V. There's also a switch to change the duration times with 'Fast' and 'Slow' settings. Use a DPDT ON-ON switch for the Fast/Slow function and a SPDT (ON-ON) switch for the Inverter voltage function. In Fast mode the duration for Attack, Decay and Release can be set between 1mS and 1Sec. In Slow mode they can be set from 5mS to 10Sec. These times are generated by the 1µF and 10µF electrolytic capacitors C4a and C4b. In the text on the Yusynth website it says to use Tantalum caps for this but I used normal Electrolithic Caps and this works just fine. I hate Tantalum caps anyway, they always blow up on me, LOL. If you want longer times you can install bigger caps. You could even take a 3 position switch and add a third cap of, for instance, 47µF to generate really long times. I haven't tried this myself so I can not guarantee it works but I don't see why it shouldn't.
There's a LED to indicate the level of the envelope. The LED remains lit very dimly if there's no Gate signal present and the ADSR is at rest. This is normal for this circuit. It simply indicates the ADSR is ready to fire.

Make sure you use three logarithmic 1 Mega Ohm potmeters for Attack, Decay and Release. Otherwise it will be difficult to set the parameters accurately. For Sustain we use a normal linear 10K potmeter.

It's interesting to note that all the 1 Mega Ohm potmeters control time parameters (Attack time, Decay time and Release time) while the 10K linear potmeter controls a level. The Sustain level.
You can run this envelope generator on a dual 12 Volt powersupply without any changes only the envelope output levels will go from 0 to 8 Volt instead of 0 to 10 Volt.

EURORACK LAYOUTS:

I recently made layouts for Eurorack in both the 10 pin and the 16 pin versions. In the 16 pin version the Gate input is connected to the eurorack-connector's gate pin but also has a separate input socket. If you want to disconnect the Gate signal from the eurorack-connector if you're using the normal input socket, then you must solder the gate connection from the eurorack-connector to the switch of the gate input socket instead of using the wirebridge as shown on the layout for the 16 pin version.

(Remember there are also eurorack Gerber files available at the bottom of this article.)

I've had confirmation that this layout works. So it is now officially verified.

Eurorack 10 pin version:

A very observant reader drew my attention to the fact I had forgotten the connection from pin 6 of the 7555 to pin 14 of the TL074 so I had to tuck that in later and that's why it runs underneath the chip socket of the TL074.  You can also choose to make that connection directly on the backside (copper side) by soldering a small wire inbetween those points, that's up to you.

I used Schottky diodes in this design because that works much better. I advise to always use Schottky diodes in Envelope Generators because it will help with cutting down any DC offset voltage at the output.

Stripboard only:

Cuts and wirebridges seen from component side. Mark the cuts on the component side with a black Sharpie or Edding pen and then stick a pin through the marked holes and mark them again on the copper side. Then cut the strips at the marked positions with a sharp hand held 6- or 7mm drill bit.

Bill of materials, will also work for 16 pin version except you must use a 16 pin Eurorack power connector obviously ;)

Eurorack 16 pin version. The diodes are marked as 1N4148 in the layouts below but use Schottky diodes instead! Like mentioned in the 10 pin version and the BOM above.

Stripboard only:

Here are some screen shots from the oscilloscope. These are from the 'Kosmo' sized ADSR but that shouldn't matter in the end result of course:

The normal envelope:

Inverted 0V to -10V:

Inverted +10V to 0V:

Here's a image showing the fastest rise time this ADSR can reach. It's just under 1 milliSecond or 980µSec.

TROUBLESHOOTING:

If you experience problems with this ADSR like the LED is always on and the VCA does not close then here are some tips for you suggested by people in the comments and on the Facebook group.:

Put a 100 Ohm resistor in series with diodes D4 and D2 (to the release and decay potmeters)

Put a 4K7 resistor in series with the LED. (This didn't help for me, my LED is always a tiny bit on)

Replace all 1N4148 diodes for schottky diodes.

Reduce the value of C3 from 10nF to 4,7nF or even 1nF.

Use a 500K potmeter for Release if you have trouble accurately setting the release time.

Replace the 1M resistor R6 with a 100K resistor. R6 is located at the Gate input

Well, that's all there is to say about this project really. A very satisfying build because everything worked as it should right from the start. The panel potmeters work over their complete throw, unlike some other E.G.'s I built, and you can set all the parameters very easily. If someone would ask me what ADSR to build I would certainly recommend this one. You can easily add on extra outputs if you so desire. You can add a TL074 for instance and wire up some extra outputs and/or inverted outputs. That's easy enough to do.
Okay, to close off, here are some pictures of the finished product. I made a copper bracket to keep the print in place behind the panel. That way I could use just one M3 bolt. I soldered all wires straight to the copper side.

Finally: there are now Gerber files available for this particular module (for Eurorack) which I uploaded to MediaFire from where you can download them for free. 

Just click here: --- DOWNLOAD GERBERS ---

EURORACK VERSION WITH LOOPING OPTION:

Now there's also a Eurorack version of this ADSR that has a looping function included. Paul Darlington, a member of the EB Facebook group, came up with this brilliant addition to the schematic. Here's a link to the files he posted on Github: --- CLICK HERE ---

You are not allowed to use these files for commercial purposes! They are published under Creative Commons 4.0 license. 

Here's a picture of the faceplate of Paul's ADSR module:

Okay, that's all for this article. If you have any questions or comments please leave them in the comments below or post them on the special Facebook Group for this website.