Synthesizer Build part-53: RINGMODULATOR with AD633 for Eurorack.

This is the MFOS Ring-Modulator based on the AD633 analog multiplier chip and it sounds awesome. It's very small and will easily fit a Eurorack system so naturally no problem for a Kosmo system either. This ring-modulator is perfect for creating bell sounds and all sorts of timbres.

This is the first article in which I did not actually build the project myself. I was asked by one of our Facebook members, Justin Andrews, to make a stripboard layout for a schematic that he found. It sounded like an ideal little project for the website so I set out to make the layout. Justin built it up and it worked like a charm first go. The AD633 is a small DIP 8 Analog Multiplier chip and they can be a bit pricey. They cost about €22,- each. The MFOS article states they are cheap but they seem to have gone up in price. Make sure you get them from a reputable source though, not from AliExpress for a few dollars. Those will be 100% fakes! I looked around and it seems they are no longer in production but there are still electronics webshops who have them in stock so they shouldn't be hard to find.

The other chip in this circuit is a single opamp, the LF411. I don't know why this type was chosen over the normal µA741 and I suppose you can use a 741 if you wish. The pinout is the same. Only the actual opamp connections of the chip are used not the offset controls. The 43K resistor is a bit of a strange value. You can get away with a 47K too I reckon. Not even the 2,2µF input caps need to be specifically that value. They are DC blockers and in that function you can use 1µF upto 4,7µF without any problems. Together with the 100K resistors these caps form a highpass filter with a cutoff frequency of 1.6Hz if you use 1µF for the caps. It's even lower with higher values so no influence on the sound what so ever whatever value cap you use.

Here is the link to the full article on the Music From Outer Space website.

SCHEMATIC.

Here's the schematic for this project. As you can see it can hardly be simpler and there are no trimmers to set so no calibration necessary. If you read the article linked above you'll see that right at the top Ray Wilson says not to build this project as it has been superseded by newer ones but that doesn't mean this design doesn't work of course. Far from it in fact. It works very well. It's just very basic in its setup.

Both inputs, the Carrier and the Modulation input, are AC inputs. They have an electrolytic capacitor in series with the inputs so this ring modulator is only for audio range signals, not for CV. In the MFOS article it is stated in the Bill of Materials that these should be ceramic capacitors so in fact bi-polar, but I would just put in electrolytic capacitors. That always seems to work just fine and they are used in many other projects for the same function without any problems.

The circuit has two settings: Modulate and Multiply. Justin's experience was that the Multiply mode had a more choppy sound with more artifacts and harmonics. You can see in the scope screenshots at the bottom of the article why that is.

The circuit needs signal at synthesizer levels to work well. The input is meant for 10Vpeak-to-peak signals so if you want to use it for lower level signal you are advised to amplify those first to at least a few Vpp before they enter the ring modulator. 

The circuit is designed to run on +/-12V but I don't see why it wouldn't run normally on +/-15V either.

There is an updated version of this ringmodulator called the Sonic Multiplier which is more difficult to build and has a quad opamp in it and uses an internal sinewave generator with an LM13700. I have not made layouts for it but here is the link to that project on the MFOS website:

---  CLICK HERE  ---

LAYOUTS:

Here are the layouts I made for this project and they have been verified. Beware the size of the stripboard is only 16 strips by 26 holes. I see I made one little oversight in the layout design. It would have been better if I had put the power connector at the bottom instead of at the same side where the faceplate is meant to go. But it still works fine of course :) 

Beware the negative 12 Volt is the top connection and the positive 12 Volt is bottom connection of the power header.

Wiring diagram:

Stripboard only view:

Below are the cuts and wirebridges as seen from the COMPONENT SIDE! As always, mark the cuts on the component side and then stick a pin through the marked holes and mark them again on the copper side. Then you can cut them with a sharp hand held 6 or 7mm drill bit.

Bill of Materials. I typed this bill of materials in Notepad so it's a bit small:

PICTURES.

Here are some pictures of Justin's work. He did a great job and made a really cool faceplate for it too, in Eurorack size. 

The finished module. Justin used waterslide decals for the faceplate artwork and sealed it in with a coat of clear lacquer:

Oscilloscope screenshots:

Here are some scope screenshot combining different waveforms in both Modulation and Multiplication Mode so you can see the difference in processing. I put multiple images together in one to save some space.

DEMO VIDEO.

And finally a demonstration of the ring modulator in action.

So that's all for this article. Not much of a write up but then again there's not really much more to say about this Ring Modulator. It does its job and it does it very well. If you have any questions or remarks you can put them in the comments below or post them in the special Facebook Group for this website.

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!

Synthesizer Build part-9: THE LFO or LOW FREQUENCY OSCILLATOR.

Before we start, this article is about my first attempt at building an LFO based on the AS3340 chip and it didn't work out very well.  This article is here for personal archive purposes not as a build project.

If you want to read about the LFO that did work then click here to go to chapter 13

So: THIS IS NOT A PROJECT PAGE! DON'T BUILD THIS! It's just posted here for archive purposes for myself.

The LFO is an indispensable  part of any synthesizer. It is mainly used to modulate other parts of the synth like the filters or the VCO's or as a source for clock pulses.
The LFO I build for my synth project is nothing more then a cut down version of the VCO based on the AS3340 chip. I left out a few things, like the high frequency track and Hard- and Soft sync options and I added an inverter for the saw tooth wave. (I was just getting into synthesizer building when I made this so I made some stupid decisions.)
The low frequency is achieved by using a 100nF capacitor from pin 11 to ground instead of the 1nF used in the VCO. You can experiment with this by using different values of caps on pin 11. In fact I made a switch in the LFO panel with a choise of a 270nF for extra Low Frequency and a 100nF for normal LFO use. The total reach is about one wave every 8 seconds to 20 waves per second.
The reverse sawtooth wave offset voltage must be set to zero volt using an oscilloscope.
Here's the layout I drew for it. The schematic is just the same as the AS3340 datasheet schematic.

Note that there is no squarewave output on this LFO. When testing this design I got so much ringing on the downward slope of the squarewave that I deemed it unuseable for LFO use. I therefore made a separate squarewave oscillator using the CD40106 design from the 8 Step Sequencer from the previous article. I made it on a piece of stripboard that simply hangs from the 100K frequency potmeter which is soldered straight to the PCB. One plus point of this approach is that you can have the squarewave going at a different frequency to the other two waveshapes which could be useful for triggering drum modules etc. Be careful that the squarewave oscillator doesn't touch the panel. When I first build it the contacts from the potmeter touched the panel and the CD40106 literally went up in smoke! My whole attic stank of magic smoke for a day! So put some gaffer tape on the contacts or the panel to be safe.

As you can see in the picture the LFO has a CV input and an FM input to control the waveforms with other modulation sources so you can create more weirdness :)
This LFO has a weird quirck that I actually like a lot. It has a bit of a beat when it dies out. When the wave dies out it doesn't do so quietly but it pops a little. I'm not sure why this is but I don't mind it. The waves consist of a negative and positive voltage part so the middle of the wave is around the zero volt line. That might have something to do with it as most of my modules work with signals from zero to plus ten volts. I don't know, but if you do please let me know what causes the plopping sound in the comments below. :) Btw, don't let this withhold you from building the LFO. It works fantastically.

[EDIT-1: Friday the 13th of December (that figures, LOL)]
I changed an output jack for a new one because it kept getting loose and I switched the panel back on and boom, up went the CD40106 again! Magic smoke (nothing magic about it in my opinion but there we are ^__^ ). So I tried fixing the ringing issue with the squarewave from the AS3340 with as result that now only the triangle wave is still working. It's going from bad to worse with this module so I think I'm going to scrap it and build one of Yusynth's LFO's. Luckily it's not a vital part of the synth but naturally you have to have a good and well working LFO in your setup. I saw a Yusynth design that can be synced to other signals which is really cool because the LFO then engages when you hit a note on the keyboard. That's what I want. So more on this later.

EDIT-2: Friday 27th of December-2019]
I tried the Yusynth LFO, in fact it was an improved design because the original has some issues with the sync pulse. A fellow member of the Synth DIY Facebook group provided a layout and schematics and I build it but I can not get it to work. I can't figure out what I did wrong but I'll get it working one day.
In the mean time I've build an LFO from a schematic I found on the MusicFromOuterSpace website.
This one has no sync option but it is a very cool LFO and a very simple design, with sine-, triangle-, sawtooth-, ramp- and squarewaves. The transition from saw to triangle to ramp is continous by means of a 50K potmeter. The wave amplitudes are +5V to -5V but I added a few opamps with DC-offset functions so I also have outputs for the sinewave and the saw-triangle-ramp waves that go from 0V to +10V.
I had a lot of trouble getting this one to work to untill I checked my symmetrical powersupply and noticed it had +1.4V and -20Volts. So it's obvious it doesn't work that way. (Btw, that is not the cause of the synchronized LFO not working.)
I'll be adding a new article about the MFOS LFO as soon as I built the panel and have it all installed so I can make some pictures or video to illustrate the article with. Stay tuned.

Okay, that's it for this one.