Synthesizer Build part-28: WAVEFOLDER (Yusynth design).

Here's an alternative way to create awesome synthesizer sounds! It's a pretty easy project to build too.

After first experimenting with a wavefolder design I found on YouTube I decided to build the Yusynth version because I wanted this option in my synth. This circuit produces some awesome and very divers sounds and waveforms.

This is a really good sounding wavefolder with a VCA on the input so there will be no changes in audio level when you turn the 'Shape' knob. It has a different approach to wavefolding than the Triple Wavefolder and the Metalizer circuits which you can also find on this website. The addition of the diode ladder and the clamping diodes on the output opamp give this wavefolder a very distinctive sound which I personally really love. See the demo video further down the article.
The build was pretty straight-forward and it doesn't need to take up much room in your modular set-up either. This is a beginner to medium difficulty project but you do need to have a scope available to calibrate the circuit. A 20 dollar cheap one will do nicely. Make sure you use multi-turn trimmer potmeters for this. That will make it easier to calibrate later on. You can use normal trimmer pots if you have no multi-turn ones but it won't be as accurate. The schematic says to used matched pairs of diodes in the diode ladder but when I measured them they were almost all the same voltage drop. So as long as they come from the same batch I think you needn't bother with matching. The two transistors Q1 and Q2 need to be matched also but you can use the transistor tester in your multimeter. I recently built an adapter to change the pinout of my power supply bus system so I can test modules on dual 12 Volt and I'm happy to report the wavefolder works just as well on 12V as it does on 15V without any changes.

Here's the schematic I used from the Yusynth website:

Here's the (verified) layout I made for it and which I used for this project. These layouts have been updated on June 12th 2023. I made some cosmetic changes to them and colour-coded the wirebridges and removed the coloured bands from the resistors so the values are easier to read.

Wiring diagram:

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

Cuts and Wirebridges seen from the COMPONENT SIDE! As always, mark the cuts on the component side with a waterproof Sharpie and then stick a pin through the marked holes and mark them again on the copper side where the pin sticks through. Then cut the marked holes with a sharp 6 or 7mm handheld drill bit.

Bill of Materials:

This wavefolder works best if you feed it a triangle- or sine-wave from an analog VCO or waves from a Wavetable Oscillator. This is convenient because an analog filter works best with square-waves and ramp- or sawtooth-waves, they have the most harmonic content and triangle- or sine-waves don't work that well in a filter. So with the wavefolder we have a use for those triangle and sinewaves. Ramp- or sawtooth-waves will sound good too through the wavefolder but square-waves pass through the wavefolder unchanged.
Here's a video demonstration of the type of sounds I'm getting from this module using a triangle-wave only. There's also a very low frequency LFO ramp signal going into the CV input.:

CALIBRATING:
To calibrate this Wavefolder you will first need to set the two trimmers in their middle position. Turn the Shape potmeter all the way counter clockwise and Range all the way open (fully clockwise). Connect a sinewave from your VCO to the input and a scope to the output and turn the 1K trimmer (above the two transistors) to get the best looking sinewave possible.  It will probably not be a perfect sinewave but try to get the top and bottom part to look the same. Once you set this, turn the Range potmeter all the way counter clockwise and turn the 50K trimmer so as to just mute the signal, so the level is 0 when the Range potmeter is turned all the way left (counter-clockwise).
That's the calibration done.

Here are some pictures of the finished product:

This is what your soldering should look like:

Finally, here's a video I found on YouTube demonstrating the Wavefolder:

Okay, that's an other one done. A very worth while addition to the synthesizer. I can really recommend it and all you need to build it are some very common parts.
As always, please put any questions or remarks in the comments below.
Thanks for checking it out. See you on the next one!

Synthesizer Build part-27: QUADRATURE LFO Bergman edition.

A very quirky sinewave LFO with 4 outputs with a 90° phase shift to eachother. With extra waveform and an input for Frequency Modulation.

The quadrature LFO is something you won't find in many modular set-ups from the early days but it's a real little gem of a module to have in your set-up. It produces 4 sinewaves that are shifted in phase by 90° each. This can be used to create the 'Barber Pole' or 'Shepard Tone.' effect. "What's that?" I hear you ask. In short, it's an effect whereby it seems a tone is continously rising (or falling) without actually seeming to get any higher (or lower). See this Wikipedia Article for more on this effect. So that's one use. You could also feed four Voltage Controlled Panners with this LFO and have the sound go three-dimensionally around the room. Your imagination is the limit with this module which is why I was keen to experiment with this.

Eurorack 12V vs 15V.

I tested this circuit on a dual 12V powersupply and it works the same as on 15V. The maximum amplitude of the sinewaves stays the same too (+/- 7,5 Vpp). I think this is due to the zener diodes. They keep the amplitude constant. The maximum amplitude of the Trapezoïdal wave however will be lower at +/-10Vpp maximum. You can of course turn the amplitude of the waves down with the Output Level knob to, for instance, the Eurorack standard of +/- 5Vpp. No problem. So this is, in the way it works, a very Eurorack friendly module. For Eurorack you can cut the stripboard in half along the cuts in the copper strips, in the middle and fold it over. Then connect the top 3, strip J and the bottom ground copper strip together again with wire and you have a print small enough to fit behind a Eurorack panel.

How I came across the Trapezoïdal function:

I found this module with the schematic on the Yusynth website and set out to make a layout. Once again it turned out I made a faultless layout but it was with building it up that I made a mistake that turned out be an asset later on. This design uses two 5V Zener Diodes and somehow I had managed to stick one of them in the wrong hole on the stripboard so it was not connected correctly. This resulted in the output being Trapezoïdal instead of Sinusoïdal. Not knowing I had made this mistake, I posted about this on the Synth DIY Facebook page and people allerted me that it had to be the Zener Diodes that were at fault and they were right. After correcting the mistake everything worked fine but I then got remarks that I should include this waveform option in the final design of the module. So I did. I adapted the stripboard layout and added a switch to go between the two waveforms. If you want to build it as originally intended, without the switch, then just don't cut the copper between the two connection points for the switch on the stripboard, so the zener diode is connected again.

One more very important thing to note: YOU MUST USE POLYSTYRENE OR POLYESTER CAPS FOR THE TWO 10nF CAPACITORS!!  I've had several people build this module and then it didn't work because ceramic caps were used. They need to be high quality non-ceramic ones or it simply won't work.

Bill of Materials:

LAYOUTS:

Here are the new layouts. I have deleted the old ones I made because I don't want anyone using them. As always the layouts are verified. I added more cuts to the right of the stripboard to make the copper strips a bit shorter and to prevent short circuits with anything touching the side of the board. 

Wiring diagram:

The current limiting resistor for LED D4 (bottom right) is a 12K and not a 1K2 like the other three. I did this because otherwise the white LED would be much brighter than the other ones. So it's not a mistake, it should be 12K for any white LED you use.

Stripboard only:

Red wirebridges are connections to +15V, Pink ones are connections to -15V, Green ones are connections to ground and the blue ones are internal connections between components.

Cuts and wirebridges as seen from the Component Side!!

As always, mark the cuts with a Sharpie or Edding pen and then put a pin through the marked holes and mark them again on the copper side. Then cut the strips at the marked holes with a 6 or 7mm sharp hand-held drill bit.

THINGS TO KNOW AND SCHEMATIC:

The LFO needs a few seconds to start up, when you first switch it on. If the 'Rate' potmeter is turned all the way counter clockwise it won't start up at all. With Rate set to 1Hz it takes a good 20 seconds to start-up and before the LED's light up. So make sure it's not on minimum when you switch on, or you could have a long wait on your hands. Turn Rate all the way up and it'll start up almost immediately.
The normal sinewave output goes from -7.2V to +7.2V with a frequency of about one cycle per 30 seconds to about 140 Hz. You can set the lowest frequency you want available with the trimmer on the stripboard (T1). I had a warning from someone on YouTube not to set the trim pot all the way down because his went up in smoke. I had no such problems when testing this print but I just thought I'd mention it here. Anyway, he must have done something wrong because that shouldn't even be possible.
The Trapezoïdal wave has a higher amplitude and lower frequency so beware of that when you switch between them. It's maximum amplitude is -14,4 to +14,4 Volt and maximum frequency is 52Hz compared to the Sinewave's 140Hz. So you can roughly say the Trapezoïdal wave is double the amplitude and half the frequency of the Sinewave. That means both waves go high enough in frequency to be in the audio range so you can hear them. That opens up a wide range of uses for this LFO. One of my favourites is to have the CV control the Cut-Off frequencies of multiple filters and then feed the Quad LFO FM input with a ramp wave from an other LFO so you get a sweep. Sounds very cool!
The amplitude of the waveform(s) can be set by the dual gang 100K potmeter so you can set it at any level between zero and the maximum I just mentioned. The direction of the phase shifting between the 4 outputs can be turned around by the DPDT switch. You can see the direction it has by four 3mm LEDs on the panel. I didn't have an Orange LED so I used Red, Yellow, Green and White LEDs and the white one is quite a bit brighter than the rest so that's why it has a 12K resistor as current limiter and all the others have 1K2 resistors. This keeps the brightness perfectly in balance with the other three LEDs. One little drawback is that the LEDs only come on when the dual-gang output level potmeter is at the ten o'clock position or higher. At the lowest levels the LEDs don't light up. That's just how the circuit works.
Instead of the LM13700 you can also use the LM13600 and the TL074 can also be a TL084. From testing I also came to the conclusion that the 10nF caps don't necessarily need to be matched so closely. But remember they can NOT be ceramic capacitors. They don't work in this circuit. The two PNP transistors do need to be matched but you can use your multimeter's transistor tester for that and matched them to within 2 points of their hfe or amplification factor.

Here's the schematic I made the layout from:

I made a Falstad simulation of this circuit and it shows the start-up time really well. When you drag the 'RATE' potmeter to the left (faster rate) it will start up quicker. If you drag it the other way it will take quite a while.

---- CLICK HERE for SIMULATION ---

Here's a picture of the finished panel:

Here are some screenshots from the oscilloscope:

Here you can see the beautiful and absolutely perfect sinewaves this LFO produces:

Here's the feature I added myself. Trapezoïdal waves. You can see the amplitudes differ a tiny bit from eachother but that's not a problem in normal use. It's the same with the Sinewaves btw.

Fast Fourier Transform (FFT) image of the sinewave at 11Hz. As you can see, it's a near perfect sinewave at this frequency. Almost no harmonic spikes to the right of the main wave. When the frequency gets higher the sinewave becomes a little less perfect but that's only visible on a oscilloscope's FFT readout, not with the naked eye:

Here's what happens when you add a Ramp wave from an LFO to the FM Input. You get a frequency sweep:

Finally a little video showing all the different aspects of this module.

Here's a video of the first test I did with the Quadrature LFO. The patch is set up as follows:
3 VCO's are feeding 3 filters with a squarewave. The Steiner, Korg and the ARP filters. The Steiner-Parker receives two sinewaves from the Quad-LFO, one on CV-1 and one on CV-2 which are 90° separated in phase. The FM input of the Quad-LFO is being fed by a 0 to 10V ramp wave from the other LFO. Each filter output goes in a different channel of the mixer where they are summed and the output then goes through the CaraOK effects unit set to preset 61 which is a chorus effect. From there it goes to the speakers. The "da-daa-dang da-daa-dang" drone you hear is produced by the waves from the Quad LFO. :)

Here's an other short sample of the Quad LFO. It's being fed by a slowly rising ramp wave and two of the outputs are going into the Steiner Parker filter. The ARP and the Wavefolder are also in the mix:

Just for my own record keeping, here is an image of the state of readiness my synthesizer is in now. I have 8 free power-buss connections left so plenty of room to build more modules in the near future.

Okay, that's it for this one. With special thanks to the folks over at the Synth DIY FaceBook Group for all their help in the initial troubleshoot.
As always, if you have any questions or comments please put them in the comments below. 

Synthesizer Build part-22: RING MODULATOR (Yusynth design).

An excellent ring-modulator to serve as an extra source of weird sounds. This one is simple to build and works very well.

Next to the filter and the FM and Sync capabilities of a VCO, I think the ringmodulator is one of the most important ingredients for sound shaping in any synthesizer and an often overlooked one. No synth should be without one. The ring-modulator was something I always wanted to include in my DIY synthesizer and I was thinking of doing it the old fashioned way with audio transformers but they are very expensive. So I went looking for designs that used semiconductors and came across the Yusynth design. I ordered some MC1496N IC's from a shop near where I live because I didn't want to wait for components from China, what with the Corona virus going on etc. and I wanted to be sure I got real MC1496's and not fakes, which is so often the case with IC's from China. The MC1496 is a chip you will find in many vintage synthesizers and also in the Macbeth studio systems Dual Oscillators for Eurorack (a favourite of Colin Benders). They have a built in ringmodulator that uses this chip. Anyway, I got the chips the next day and I set out to make a stripboard layout.

A ringmodulator takes two signals and multiplies them. If you input just one signal you won't get anything out because if you multiply by nothing (zero) the outcome is nothing. So both inputs need a signal going in for this to work. (That's why you can use Ring-modulators as crude VCA's when switched to DC mode) One is called the Carrier wave and the other is called the Modulator wave. You can modulate the amplitude of the carrier and so get AM modulation. You can get the most beautiful results from this circuit. It can produce very cool bell like sounds or very gnarly AM modulated sounds. You can spend hours experimenting with it. I myself usually combine the output from the ringmodulator with the output from one of the VCO's going straight into a mixer so I can add both signals up and then send that through a filter and/or the lowpass gate and boy do you get phat sounds like that!

Click here to go to the original Yusynth article.  

Schematic for single ringmodulator:

Here is the (verified) stripboard layout I made from it. The original schematic is for a double ring modulator but I only built one. But it's just the same circuit repeated. I used this layout for my build so it is tried and tested. Note that the electrolytic capacitor on the AC output jacks has it's polarity reversed from those on the AC inputs.

Stripboard only:

Bill of Materials:

There different types of 1496 chips for sale, like MC or LM, but the letters in front of the numbers don't matter. They just indicate which firm produced the chip. They will all work fine in this circuit as long as they're 1496's.

TUNING THE RINGMODULATOR:

You can find the tuning procedure on the Yusynth website. I'll describe the procedure here:

There are two trimmers to adjust: A1 and A2. These trimmers are used for cancelling the input signals. The settings are quite simple, you will need a signal generator that delivers a sinewave signal with a 10V peak to peak (+/-5V) output amplitude. You can also use a VCO in your synthesizer to do this. 

The Yusynth website talks about audio amplifiers but it's easier to use a VCO with sinewave and a VCA from your synthesizer to do this and make sure you connect an oscilloscope to the output signal with a frequency counter enabled so you can set your VCO to 1kHz.

Here is how to proceed :

1. Set your audio generator (or VCO) to 1kHz and set the output level of the generator to 10Vpp.
2. Connect the output AxB of the module to an audio amplifier or your VCA. Be sure to set the input potentiometer of the amplifier to a low value: the output level of the module is 10Vpp and most of the audio amplifiers expect an input level that doesn't exceed 1Vpp. If you use a VCA it'll be okay. (We need a line level output signal so we can listen to it through speakers but if you connect an oscilloscope you can just watch the signal)
3. Connect the signal generator to the input A with a capacitor (AC-INPUT). There, you must hear the 1kHz signal at the output AxB.
4. Adjust the trimmer A2 so that the 1kHz signal can no longer be heard at the output.
   
5. Disconnect the signal generator or VCO from input A and then connect the signal generator to the input B  with a capacitor (AC-INPUT). There, you must hear the 1kHz signal at the output AxB. Adjust the trimmer A1 so that the 1kHz signal can no longer be heard at the output.

Now the module is ready to operate. A last check can be done by connecting the 1kHz signal to both inputs A and B (AC inputs): there you must hear a signal which is twice as high in frequency (2kHz).

It will be a bit of a balancing act to get these signals on the zero volt line on your oscilloscope. Turning one potmeter might create an slight offset voltage that you can trim away with the other trimpot. If all is well you should easily be able to tune the ringmodulator in a few minutes.

If only one input is used there should be no output (because something times zero = zero) and if there's a signal on both inputs you'll get the two signals multiplied out of the output. That's why a ringmodulator can also be used as a crude VCA.

When I first tested my ringmodulator I kept measuring a negative offset of -9V on the output if I stuck a signal into input B. It turned out that my TL072 was faulty. I stuck a new one in and all was well.

PICTURES:
Ring modulation is a very interesting way of combining two frequencies and can get very complex very quickly if you use waves that have a lot of harmonic content like squarewaves. More on the theory involved is here on this Wikipedia page about ring modulation.

This is one of only two ringmodulator designs on this website because this one is just so good. You don't need to fiddle with audio transformers and diodes. The chip might be difficult to get for some people but my local electronics store had them in stock. They don't sell many of them.

I didn't think I could fit any more modules in, but this one was just small enough to go into the wood panel above the modules, next to my Sample and Hold module. Here's a look at the finished panel and how I fit the stripboard behind it with a little copper L-Bracket I made myself and soldered onto the stripboard.

Ignore the sawdust specks in the bottom picture, LOL. I took it just after putting the module in and the synth was covered in fine dust.
Okay that's another one done. This is getting to be quite a big and powerful "sound design machine." It's about time I made a new case that I can put on top of this synthesizer so I can keep building ^___^

If you have any questions please leave them in the comments below!