Welcome to stripboard heaven! Here you'll find all the projects I used to build my DIY Modular Synthesizer. I'm using the 'Kosmo' size standard but I also build Eurorack sized modules. All layouts are made by myself and verified to work. The schematics they are based on come from all over the internet. If you're on a PC or MAC, there's a complete MENU in the sidebar. For mobile devices the menu is in the black 'Move to...' bar below this text.
This is just two Korg MS-20 filters behind one panel with switches to go between using them as individual filters or switching them in series. This is one of my early projects so the implementation is a bit clumsy with how I use the switches etc. but I'm keeping the article up for archival reasons plus this dual configuration actually sounds pretty awesome. But I wouldn't be surprised if you found a better way to make a dual MS20 VCF than this one.
I wasn't too pleased with the performance of the Prophet 5 lowpass filter so I decided to remove it and put a new filter in its place. I've seen lots of videos about the Korg MS-20 and really like the sound of it. I noticed that synthesizer has two nearly identical filters next to eachother; the highpass- and the lowpass-filter, so I wanted to emulate that in my own synth. So I set out to build two of the 'Late MS-20 filters' by Rene Schmitz, and fit them behind a single panel that was the size of the old Prophet 5 filter that I took out. It was a tight fit to put all the knobs and switches on but it worked out beautifully in the end.
The schematics and layout I used are just the same as the ones I used in article 12 of this blog, so if you want to build your own dual filter arrangement you can go to the Korg MS20 filter page and build TWO of those. Build both filters with the HP/LP switch but do not include the bandpass switch. You build two MS-20 HP/LP filters and put them behind one panel. Then, as extra, you add switches to the inputs so you're able to put them in series or use them independently of eachother. The wiring diagram for those switches is further down the article.
Here's a picture of what that looks like. You can see I have filter one on the left side and filter two on the right. Each has its own Cut-Off Frequency and Resonance controls and each has audio and CV-in level controls and each has it's own Highpass/Lowpass switch. Beneath those switches you see two more switches which enable me to switch both filters in series without using patch cables to connect them to eachother.:
The wiring of these two stripboards was a bit of a nightmare but I got it done in the end. I made some initial mistakes and had to re-wire some potmeters so that's why the wires look like such a mess. Luckily it doesn't affect the working of the filter.
In the first filter I used the LM13600 chip and in the second the LM13700 chip. And having them side by side is a good opportunity to compare them and the LM13600 is a bit tamer than the 13700. So if you have both chips in stock you can decide whether you want your filters to sound aggressive or a bit less aggressive. It's not a big difference though.
You can see in the pictures above that it's a tight fit but I did managed to include two volume or level potmeters for the audio inputs, which are not included in the original build but are very useful to have. I'm going to make sure that every filter I build in the future has input level control.
Beneath the HP/LP switches are the two switches that give you the option of using these filters as two stand-alone filters, so not internally connected, or if you want to put them in series so the output of filter 1 goes into the input of filter 2.
One other weird option would be to switch the output of filter 1 to the output jack but leave the input switch for filter 2 as is, so filter 2 has no input. Because these filters are self-oscillating you can now use filter 2 as an oscillator. Put the output into the 4 channel mixer described in article 17 and put the resulting wave through filter 1 or wherever you like. Connect a 1V/Oct voltage to the CV input. Just an idea, but you see there are endless possibilities. That is the beauty of modular synthesizers. :)
However, it would be better to use a single DPDT switch here and use it just to switch between two filters in series or both separate. That makes it easier to switch but that way you can not use one of the filters as stand-alone oscillator, but you won't use that function much anyway I'll bet.
Here is the wiring diagram for those two switches. By all means try and think of a better way to do this. This was one of my early projects so not everything is perfect. I still get confused by these switches when I use this module after 1,5 years of using it LOL
It would be better to use one double pole switch and connect the output of filter 1 to the wiper of one pole and the input socket of filter 2 the wiper of the second pole. With the switch set to the left the output of filter 1 goes to the output socket 1 and the input of filter 2 goes into filter 2. Set to the right the output from filter 1 goes into the input of filter 2 and the input socket of filter 2 is left disconnected.
Finally I want to show you a little video I made which demonstrates the sound of these two filters in series with eachother. I filmed this just after I had finished the build and I was still figuring out what the filter could do but it shows the added benefit of having two of these in series. It can do really deep and full sounding bass tones and it can also scream and distort and sound really weird. I am glad I fitted these and they are certainly a big improvement over the Prophet 5 filter although I will use the AS3320 chip inside it for a future build.
Plus all those knobs and switches so close to eachother look really cool I think ^_____^
Here's a look at the different sounds this filter can produce. (The phaser effects come from the special effects unit and not from this filter):
Okay, that's it for this one. If you enjoyed this article please check out the rest of my synth build and leave me a comment if you have any questions, or even to just say hi. Please also subscribe to my YouTube channel. That would be a great help. THANK YOU!!
Other websites that deal with the DUAL MS-20 configuration:
The iconic Moog Ladder Filter. This version is built with transistors only, not transistor array IC's. This is an early project of mine so please bear that in mind when reading the article.
A note before we begin: I have PCBs available for the Moog Ladder Filter using the CA3046 transistor array chips. Just go to the 'PCB Service' option at the top of the menu for more details.
Since this article was written I have made a new version of this filter, this time including the CA3046 transistor arrays and it works very well and no need to match transistors with that version. If you want to build this filter I would really advise you to use that layout instead of this one (although this one works fine too of course). You can find it in Chapter 39 (click here).
Before we start. Most people always want to know if it works on 12V. I tested the filter on dual 12V and it works just fine.
In this schematic the top and bottom transistors are applied in the form of a transistor array chip, the CA3046, but I couldn't get hold of that quickly enough and this early in the build I didn't really trust myself to design a layout including those arrays, so I decided to use all transistors and that works just as well. It makes the layout a lot easier. It is always mentioned that you must use matched pairs of transistors for this filter but really, that's a throw-back to the early seventies when transistors were not as consistent and reliable as they are now so if you have transistors from the same batch they will probably be matched well enough but put them through the transistor tester on your multimeter and match them on hfe value. The only place where the transistors must be matched well is on the place in the schematic where they use the CA3046; the top and bottom of the filter and the output on the side. I personally matched all my transistors by using the Transistor Curve Tracer I described in an earlier article on this website.
I built a second ladder filter as a test for the layout below and I used all unmatched transistors. The layout works fine but using unmatched transistors did not turn out well. I could not get the resonance trimmed correctly and there were enormous differences in volume when using the resonance potmeter. I used a squarewave for testing and the top of the squarewave had an angle to it instead of being horizontal. So you must used matched transistors!
This filter has a few quircks that you need to know about but which are normal for this design.
- The Resonance potmeter has only a small area of influence. For most of the throw of the potmeter you will hardly notice anything. This is normal for this design. That's why we need a reversed logarithmic potmeter for Resonance. To stretch out that last bit of the potmeter.
- When the Resonance is fully open, the output volume drops. This too is normal for this filter and even the original Moog ones have this. Yusynth also talks about this on his website.
- If the audio input level is too low you can loose the self-resonance on the bottom parts of a squarewave. (If you use a squarewave as input wave of course). Again, this is a known quirck of this filter type. It needs decent level of audio input.
The build is quite straight forward but you need to be very accurate. The 50K anti-logarithmic potmeter for the Emphasis or Resonance control was an other thing I couldn't get a hold of so I made my own by using a linear potmeter with a 5K resistor between pins 1 and 2. This works very well, In the layout I used a reversed logarithmic potmeter and I show the alternative that I myself used, next to it.
The input level potmeters are 50K logarithmic ones but if you don't have those just use linear ones. They don't even have to be 50K. You can use 100K or 1M or even 10K if that's what you have available. They're just audio input level pots so they act as attenuators or voltage dividers and the value has no impact on the working of the circuit. This goes for all the level potmeters in all the projects on this website unless it is mentioned otherwise on the layout.
The Frequency Cutoff potmeter however must be a 10K!
I made a layout for stripboard including the wiring. I used this layout to build a second filter and it worked straight away so this layout is verified. (All potmeters viewed from the front):
(Last revised: 24-June-2020: Corrected polarity of C3. 15-July-2020 added alternative for reversed potmeter.)
Stripboard only. Beware that some stripboards are sold with 56 instead of 55 holes horizontally. The layout is 55 holes wide:
Here are a few pictures of the finished circuitboard:
As you can see in the pictures, I added two trimpotmeters which are not on the stripboard layout above. These are two 200K trim pots and they go over pins 1 and 2 of each opamp, to make the gain adjustable. It says in the schematic to 'adjust the value of the feedback resistors according to audio level'. These trimpots make that possible without having to use the soldering iron. It's a bit awkward with the wires but I had to put the potmeters on the print where there was room enough to accommodate them and the wires. Plus I added them as an after thought, so after I made the layout. At least they are all neatly in a row. :-)
For clarity I made a second layout which includes these alterations. If you decide to replicate this then don't forget to remove (or not solder in) the original resistors over pins 1 and 2; the 56K on IC-1 and the 120K on IC-2 because these are replaced by the trimmers, as the layout below shows. Lay-out is verified not only by me but I heard from many people who built this filter successfully using this layout.:
I lowered the Control Voltage input resistors from 100K to 5K6. In the schematic they are 100K but after installing the filter in my synth set-up I noticed that the CV hardly had any effect at all when I connected a LFO to it, so I lowered these to 5K6.
After finishing the build I tested the filter on the oscilloscope first and set all the trimmers to the right positions. It's easy enough to do, you just watch the scope for the best response. Then, after installing the filter you can adjust the trimmers to get the best sound out of it. This filter is self-oscillating, meaning that if you have nothing connected to the inputs and you turn Frequency Cut-off and Resonance all the way up the filter will oscillate of its own. There's no 1V/Oct. input though so resonance won't keep track with the notes on the keyboard. An other frequently occurring problem is that the self resonance only occurs at the top of the squarewave and not the bottom part. When you start it up it will self oscillate on both the top and the bottom but as soon as the transistors warm up, about 20 seconds, the bottom oscillations disappear. This happens when the transistors are not perfectly matched. Using the CA3046 transistor arrays will solve this and that's why I made a second Moog Ladder Filter project using the CA3046 chips. You can find that in chapter 39
The first all transistor filter I built didn't have this problem so if you're careful with matching the transistors you should be fine. Please note that the input volume is also an influence on this. If the level is too low you can also have the bottom oscillations disappear.
Here are some oscilloscope images to illustrate what I mean:
Self oscillation when filter is just switched on:
And here's the situation after about 20 seconds. The bottom oscillations are gone. The filter still sounds pretty cool though:
This is something I only discovered a short while ago but well matched transistors or using the CA3046 chip should solve this issue. The first Ladder Filter I built using all transistors didn't suffer from this problem because I was careful to match the transistors accurately.
MATCHING TRANSISTORS:
I used to advise people that matching transistors on their Hfe value was good enough but I have found an easy way to do it properly which I advise you to use. This is the Ian Fritz method. We set up a small differential amplifier on a little breadboard and measure the voltage between the two emitters. If the transistors are matched that voltage should be zero. Here's a schematic of the test setup:
The diode is a 1N4148 or any silicon diode will do really. It's voltage drop ensures both transistors get the same base-collector voltage. Make sure the 100K resistors have exactly the same resistance value!
Beware this setup uses a dual 12V powersupply.
VIDEO DEMO:
Here's a video showing the test results on the oscilloscope so you have an idea of what the waveforms should look like. In this first filter I built and which I demo in this video the transistors seem to be reasonably well matched because I do retain some self oscillation on the lower parts of the squarewave:
A demonstration of the sound of the filter:
I recently made a Falstad simulation of the ladder filter and it works reasonably well. It shows the resonance and the trimmers work as expected. It even shows the amplitude getting smaller with resonance and self oscillation. You can view the simulation by --- CLICKING HERE --
Here's a look at my PCB for the filter. This is what is actually in my synthesizer and I build it from a different layout that I made earlier especially for the Eurocard format of stripboard:
Here's the panel I made for it:
As you can see in the picture, I've installed a bypass switch for this filter. It's great to have this filter in series with the Korg MS-20 or the ARP2600 filter but sometimes you want to be able to easily switch to one filter. With a bypass switch there's no need to constantly connect and disconnect patch cables so this is really helpful. The switch only works with audio input 1 and it sends the signal straight to the output jack and disconnects the in- and output from the in- and output jacks at the same time. Here's the wiring diagram for the bypass switch:
Okay that's it for this project. Way more synthesizer build articles to find on this website and while you're here leave a comment please!
The first filter I built and not one of the best in my opinion. Skip to an other project. I'm keeping this up for archival purposes.
[EDIT] Before we start: I'm writing this about 7 months after I published the article below and I can tell you now that I removed this filter from my synth. I couldn't get it to self-oscillate and I was not impressed with the sound of it. Maybe that's due to the fact that I was just starting out with synth building when I made this and I made some mistakes, but if you have the AS3320 chip I advise you to use it for the Digisound 80.6 lowpass filter. That is an amazing sounding filter!
I'm keeping this article up because this website is an archive of all my builds and that includes the ones that were not a succes (That's only this project anyway. The rest all works fine.)
Okay on with the original text:
I've considered many filter designs, and there's a lot to choose from if you search for schematics on the internet, but I've picked out 3 filters that I want in my synthesizer. Two of those are LowPass filters and one has the choise between Lowpass and Highpass. That's the Korg MS20 filter We'll get to that one later.
Now we will concern outselves with the Sequential Circuits Pro One (and many others) Lowpass filter based on the AS3320 chip. I went to the ElectricDruide website and found a page full of filters and amongst them I found this circuit:
There are also versions which are re-configurable with the flick of a switch but they were a bit too complicated for my taste and I thought this would be a great project to start with. Well, it was a good project to learn from but the result was nothing to write home about.
I made a layout on stripboard which you can find in the picture below. All potmeters viewed from the front.:
(Layout revised 15-Feb-2021)
Print only:
Bill of Materials:
The first version I made of this had capacitors that were 220pF instead of the 150pF as seen in this schematic. I thought that would give me more control over the low frequencies and I was right, LOL! It brought the top cut-off frequency down to about 200Hz. Way too low. So I soldered in the 150pF and everything worked after that.
The three inputs in this schematic have different values but I did some testing and the 120K resistor worked the best on the input so I put those in all 3 inputs. I think you should also do this if you decide to build this filter because these schematics reflect the circuit that is used in the synthesizer itself and that's why the inputs have different values because they receive signals with different amplitudes. In our synth all the VCO's produce signals with a set amplitude of 10V peak to peak, therefore the input resistors need to be the same value.
There's not much more to say about this. The opamp in the schematics can be any low noise audio type. I used the TL072 for that because I have a lot of those in my components collection and they are the opamps most used in synthesizer projects. But you can also use the TL082 or NE5532.
You can use this filter with a dual 12V powersupply without any changes except for the current limiting resistor to pin 13. Change it from 1K5 to 1K2 for -12V operation.
This filter sounds like a lowpass filter should although it is not as versatile as the Moog or Korg filters. For one, this filter is not self oscillating (at least, the one I build isn't) so you can't make it scream but it does produce that resonant synthesizer sound, if you know what I mean. It's just a different filter to the Korg or the Moog Ladder Filter which is an other filter I've put in my synth build. It's more a filter to round off certain sounds you've created on your synth, to make them fuller. I don't know, you have to listen to it to know what I'm on about. It should be capable of self oscillation if you read the text that goes with the schematics. The fact that mine didn't self oscillate is probably due to my inexperience at the time I built this.
EDIT 20-March-2020: I just finished work on the Digisound 80.6 lowpass filter using the AS3320 chip and it sounds fenominal. If I were you I would build that filter instead of this one.
Here are some pictures of the PCB and the panel I made:
The filter is the one on the right. The other one is the VCO. I had yet to add the text to the panels.
You can see the inputs for oscillators one, two and for noise on the left and below that the resonance control voltage input (for the LFO for instance). That input has a level control and there's a switch for internal or external resonance control. On the right is the audio output. The top potmeter is for the Cut-off frequency and the one below is, as mentioned, for resonance.
All sorts of facts you need to know and an bit about how I made my synthesizer cabinets. A glossary explaining terms you hear a lot in the synthesizer world.
My first synth cabinet:
I'm not going to get too deep into this because every individual will make their own cabinet or case to their own taste I think. This cabinet represents the vintage 70's look that I wanted for my synth and I'm very happy with it.
If you are going to build all, or almost all, of the projects on my website you're going to end up with an amazing synthesizer (that I call the "Bergman-Berlin") that can rival the big Moog systems of back in the day and will cost you far less money. You can build as many oscillators as you wish (my system has five) and a variety of filters and other sound manipulators and noise generators and mixers that will make this an amazing sounding synth. There are examples enough in the demo videos on this site. Here is a picture of my synthesizer as it now is, at the end of October 2020:
Here are some pictures from different stages of building the first cabinet:
Almost finished, just one more panel to fit but already working very well. You can see I incorporated a 'Keyboard Garage' in the case so I can push the keyboard underneath the synth if I'm not using it, to free up space for other things.
I made no drawings and I measured everything as I was building it. That's the way I usually approach woodwork. The drawing is in my head. I did make two cardboard templates for the side panels to make sure I got those exactly the same. I measured the current draw with all panels that I have build so far switched on. All together it drew 250mA. That's less than an old fashioned bicycle lamp. :) I also installed a temperature sensor that is directly in contact with the heatsink of the LM317 that regulates the 15 volt output and it runs up to about 60°C. That's perfectly fine and normal. It can handle double that and the temperature stays at 60° and doesn't climb.
The panels I use are made from aluminium (or aluminum if you're in the States ^^ ). They are 20 centimeters high so you could say I use the LookMumNoComputer Kosmo format. I bought 2 sheets of 1 meter long and 1.5mm thick and they are powder coated in gray/black. This powder coating is something I can really recommend because it's hard to scratch. If you just spray-paint your panels they will scratch very easily. You can write on the powder coating with a white acrylic pen. The one pen I bought had too wide a tip and I sharpened the tip with a razorblade but in the end it was un-useable. I ordered a pen online with a 0.7mm tip and that works far better. But if you laser-engrave your panels then you don't need all this anyway.
One IMPORTANT TIP I want to give you is the following: When you make your front panels for the modules set up a standard for their measurements right from the beginning. What I mean by that is decide on a fixed width for all of them. Choose for instance, 10CM for the bigger projects like the VCO's and 5CM for the smaller ones. Use those widths throughout the synth and don't do what I did and make them just the smallest size they can be.
Here is why: You're going to build more panels/modules (eventually) than will fit in your synth cabinet and if they have a standardized width you can easily exchange them. For instance you might need more LFO's so you can take out a VCA and put in an LFO panel because they are the same width. I can not do that as easily because all my panels are designed with different widths.
The thickness of the panels I use is 1.5mm That is thick enough and won't bend or flex when connecting patch cables. It also leaves enough room for the thread of the sockets and potmeters.
IF YOU BUILD THE MODULES ON THIS WEBSITE YOU WILL END UP WITH A MODULAR SYNTHESIZER THAT CAN RIVAL THE SOUND OF A BIG MOOG SYSTEM FOR JUST A FRACTION OF THE PRICE PLUS THE SATISFACTION OF HAVING BUILT IT YOURSELF!
Make sure the panels you are going to use are at least 1.5mm thick aluminium!! If they are any thinner than that they will bend or flex if you put a cable into a socket on the panel. So keep that in mind!
This cabinet is 1 meter and 11 millimeters wide, 38 centimeters high and deep.
If you are building your own synthesizer I would be very curious to see some pictures so if you can link to that please leave the link in the comments. That'd be awesome!
POTMETER PIN NUMBERING:
To avoid confusion here is the way we number the pins of a potmeter:
Pin 1 is the Counter Clock Wise part (the left pin if you look at the potmeter with shaft facing you)
Pin 2 is the middle pin.
Pin 3 is the Clock Wise part (the righthand pin if you look at the potmeter with shaft facing you).
Here's an illustration of this:
WHAT DOES "U" AND "HP" MEAN IN SYNTHESIZER MEASUREMENTS?
When you're just getting into the modular synthesizer hobby you will hear/read terms like 'this module is so and so U high and so and so HP wide. What does that mean?
Well U stands for RU which means 'Rack Units'. It comes from the 19 Inch rack system. 1U equals one Rack Unit which is 1.75 Inch or 4.445 centimeters high. Eurorack modules for instance are practically always 3U high which is 5.05 Inches or 12.85 centimeters. There are also horizontal modules in Eurorack that are 1U high. Some rigs have an extra 1U row to accomodate them.
HP stands for Horizontal Pitch and is a unit for width. 1HP is 0.2 Inch or 5.08 millimeters.
So the Kosmo panels I use are 4.5U high and a 10 centimeter wide panel would be 20HP.
Now there must be some rounding off of numbers going on in these standards because if I multiply 4.445 centimeters with 3 (for 3U) I get 13.335 not 12.85 centimeters. So I'm not sure what's going on there. Maybe there are some differences between USA and UK standards. I don't know.
DUCKING and SIDECHAINING:
What does Ducking and Side Chaining mean? Ducking is a term for lowering the volume of some sound source so an other sound can better be heard over top. So the sound is ducking underneath the louder sound. This is a technique often used in percussion setups where, for instance, you need a kick drum to be heard over a bassline so the trigger signal that triggers the kick-drum also goes in an envelope generator which produces an inverted envelope that closes a VCA with the Bassline signal going through it. So as soon as the Kick drum is triggered, the Bassline is silenced somewhat so you can hear the Kick better. That technique with the VCA being triggered by the Kick drum is called side-chaining.
LEGATO:
This is a term you hear a lot when talking about synthesizer or sequencer playing. Legato means that notes are played without the Envelope Generator being triggered by a Gate signal. The new notes you play will blend in with previous notes until the Envelope Generator's Release phase has died out and the synth falls silent or until a new Gate pulse is fired. There is usually a special setting on a synth or sequencer that makes this possible. Legato is usually achieved on a keyboard by not lifting the fingers from the keys completely before playing a new note. The sequencer in the Keystep by Arturia for instance can be programmed to play Legato. It will then play the notes you programmed in but without giving off Gate pulses for each note.
March 2020 the second stage: Here are some pictures of the second stage of the synthesizer. This is a much simpler case and it is 20 by 20 by 100 Centimeters so it sticks out at the back a bit. This was necessary to accommodate the power buss system. I made some trunk locks on the sides so I can clamp the top section to the main synthesizer. This works just perfectly. I did have to solder these locks though because the locks themselves were connected to the main plate with the screwholes just by three flimsy bits of folded-over metal. So if you put any force on that they would bend and let loose over time. So I heated them with a blowtorch and soldered them from the inside. This worked really well because I used a bit of flux on the metal and this made the solder flow into all the little seems so it is very neatly soldered.
I made the width of the second stage too short by 1 centimeter so I had to use extra pieces of wood to connect the locks to.
EXTRA INFO: ABOUT THE STRIPBOARD I USE:
For everything I build and publish on this website I use standard stripboards of 24 strips high and 56 holes wide. The layouts I make are usually 24 by 55 so you have one hole extra room in case you make a mistake. You can order those stripboards from AliExpress for a very reasonable price. However, sometimes the pre-drilled holes are not quite in the middle of the copper strips which makes it difficult to solder components but this doesn't happen often and is the compromise you have to be willing to make. I have built my entire synthesizer with these 24x55 stripboards and all the layouts I publish use this size as a starting point. That's 6,5 by 14,5 Centimeter. Here's a link to where you can order them:
Here are some extra tips about general topics, not necessarily relevant to my projects but just things I want you to keep in mind.
ABOUT WIREBRIDGES:
All the projects here require wire bridges to be soldered in. Don't make those wire bridges out of electrically insulated multistrand wire, because it will get messy very fast on your stripboard if you use that. They take up a lot of room and create big solder blobs on the copper side. Avoid doing that if you can. Instead use single core copper wire, like transformer wire. Use sandpaper to clean off the insulating lacquer layer and reveal the bare copper and then you can easily solder them in place. I always neatly bend them to the right size too with a pair of neadle nose pliers. The picture below shows the stripboard for the Moog ladder filter (chapter 39) and imagine doing these wire bridges with normal electrical wire. It would be a mess.
MORE TIPS and INFO:
Measure the value of every component before you solder it in place. Most multimeters these days have transistor, resistance and capacitance modes so this should be no problem. It might save you a lot of time in trouble shooting later on.
Get an oscilloscope if you don't have one already! You are going to need one very soon if you go on building modules. Get a cheap one from eBay like a DSO138 for about 20 dollars. You can also look at the second hand market. Very good analog cathode ray oscilloscopes can be had on eBay for very little money. I myself decided to invest in a good digital scope and at that time the Rigol DS1054Z was just coming on the market and was praised to the hilt by Dave from the EEVblog on YouTube so I got one of those. I've never regretted that because it's a tremendous help to me and it has 4 channels.
Don't use lead free solder. I know, environment etc etc. The stuff is CRAP! Get the good old 40/60 or 37/63 Tin/Lead solder at a thickness of 0.6 or 0.5 mm. You can thank me later ;)
Why is output impedance important? Output impedance is a combination of the normal DC resistance and the AC resistance of any module that outputs audio signals. This is usually determined by a resistor in series with the output socket. Why is the value important? If you have a high output impedance and you use long cables, the capacitance of this cable combined with the output resistance (impedance) forms a lowpass filter that can cut off some of your high frequency audio. Don't ask me for details, you will have to Google that but this is one reason why output impedance is a thing. Normally we have a HIGH INPUT impedance because the inputs go into opamps which have an infinitely high resistance and we have a LOW OUTPUT impedance around the 1K Ohm mark among other reasons because of what I mentioned above. Now long cables are not usually used between modular synthesizer modules but they are used in amplifiers. I just want you to know about this, as part of you electronics knowledge.
Don't put those cheap Chinese Volt and Ampere meters into your power supply. I know these digital displays look cool and it's handy to know how much current your system is drawing but these meters introduce a shit-load of noise onto you powerrails. If you do want a measuring system in your powerrails, use analog meters with pointing needles instead. They look even cooler, especially when back-lit, and don't have internal circuitry that can introduce noise into your system.
Why does a filter have a Volt per Octave input??
There are two reasons why a filter has a V/Oct input. The first is that some filters can be used as sinewave oscillators if you set the resonance fully open so the filter begins to scream or gives of a loud whistle like tone. That tone can be made to follow the chromatic scale if you input a V/Oct signal and usually you also have to tune the filter using a trimmer somewhere in the circuit.
The second reason why filters have a V/Oct input is so that they open up more, become brighter, as you play higher up the keyboard. If the filter wouldn't do that then at a certain point your high notes wouldn't come through or they would be very much attenuated. So the higher the note you play, the higher the Keyboard CV voltage is and the more the filter opens up.
Beware that there are situations where you don't want this behaviour, for instance if you're building a patch to make a Bass-Line. You want the filter to be low and dark so in that case you don't input keyboard CV voltage.
WHAT IS THIS BUSINESS ABOUT CERAMIC CAPACITORS AND WHY YOU MUST NOT USE THEM AS TIMING CAPS IN OSCILLATORS.
Ceramic capacitors come in a number of classes. Class 1 ceramic caps are also know as NPO or COG caps. These are the low value ones, upto about 1nF. They are relatively stable in keeping their value when the temperature changes.
Class 2 SMD caps are usually higher values ones (1nF and up) and have an EIA code which gives you the lowest usable temperature, the higherst temp and the tolerance value in a "letter, number, letter" code. For instance X6R would mean -55°C to +105°C tolerance +/-15%.
Now the fact that these caps change their value with temperature makes them unsuitable for use in oscillators where you need stability to make sure they stay in tune.
But an other thing you probably didn't know is that these caps also change their value depending on how much voltage you put on them! Yes, I bet you didn't know that.
Now if you want to know more about this I advise you to watch the video below from the man that taught me almost all I know about electronics. Dave Jones from the EEVBlog:
Any questions or remarks? Put them in the comments below please. Comments containing links will be deleted!
