Synthesizer Build part-5: TIPS FOR SYNTH BUILDING and GENERAL KNOWLEDGE

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:

LINK ONE

LINK TWO

SOME EXTRA TIPS:

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!

Synthesizer Build part-4: THE ENVELOPE GENERATOR or ADSR

This was the first Envelope Generator I built but I no longer use this design myself since I discovered the Digisound 80 ADSR and the Yusynth 7555 ADSR both of which are much better designs with the Digisound design also using the AS3310 chip (or the CEM3310). So my strong advise is not to build this particular design. "Why is it posted here then", I hear you ask. Well, because this website is an archive of the synthesizer I built and that includes all the lesser designs too. But you get ample warning if I advise against building. It's mostly the early projects that can be a bit problematic. The design below is simply the datasheet circuit of the AS3310 chip, which is not the best design by a long shot.

Original text of this article:
The Envelope Generator is generally better known as the ADSR which stands for Attack, Decay, Sustain and Release. These are the four phases a note goes through when you press a key on the keyboard. The attack is the speed of the initial rise of the note, once you press the key. 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 a bit less loud than the first instance of the note being played. 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 resonance or the pulse width of a squarewave. 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 later.

I decided to build this ADSR using the chip series that I plan to use for the most important components of my DIY synth, the AS33xx series of chips. The AS3310 is the ADSR chip and it costs way less then its CEM counterpart. It's about €6,- 

So I looked up the datasheet and used the circuit that was presented there. I made the following stripboard layout for it. This layout is verified, I used it for my build. (All potmeters viewed from the front.):

(Last revised: 16-March-2020: Removed direct potmeter connection to 5Volt. Revised potmeter wiring. Trigger when not used shorted to Gate via internal switch in trigger input socket.)

Print only:

This design works very well and does the job it needs to do. It has a few little quircks though. The potmeters for instance. I used normal linear type potmeter and that works but it would be better to have reversed logarithmic or anti-logarithmic potmeters because the difference between 1 second and 10 seconds on the Release for instance is only a few degrees of turning the knob. But once you're used to this it's not really a problem. The Sustain potmeter is at its maximum at about 2/5th of its maximum throw. If you turn it further the Sustain level rises but the attack won't be able to reach it. So if you have Attack set to, for instance, one second, it will rise normally and after one second it will suddenly jump to the Sustain level. I've got some oscilloscope pictures below to illustrate this.
The external trigger input is normally shorted out through a switch in the Trigger input socket. So if there's no trigger cable attached, the trigger for the chip is provided by the Gate signal through the 3nF capacitor. The AS3310 needs a simultaneous gate and trigger signal to function. So if you plug a cable into the trigger input but you don't provide a trigger signal, the Attack parameter of the ADSR will not work! So this is not a malfunction, this is how it's supposed to work.

I added a few extra's to this design. First there is the option to output a signal that is twice the voltage of the normal output (10Vpp instead of 5Vpp). You can use this, together with a passive attenuator in the mixer panel, to drive a filter's resonance or other parameters of the synth. Then there's also an inverted signal output, to add to the options of driving parameters of the synth. This goes from 0V to -10V.
All this takes place at the opamp on the lower left of the circuitboard. You can use the old favourite TL072 for this or the TL082. Pins 1,2 and 3 together with the two 100K resistors form the 2x amplification. You can use other resistor values as long as you use 2 resistors of the same value. Then the input signal is split at the non inverting input and goes, via a 100K resistor to the other side of the chip where the opamp is set up as an inverting buffer. Both opamp outputs have their own output jack socket. The normal 5V ADSR output is a separate socket (of course).

And finally I added a manual trigger option, at first I added it so I could put a gate signal on the gate input for test purposes, but then I thought this would be handy to have anyway so I added the switch to the final panel. I decoupled the manual trigger signal from the gate input socket with a Schottky Diode so no voltage goes into the circuitry that delivers the normal gate signals so as not to damage it (although this is probably not necessary). I used a Schottky diode because their voltage drop is only 0.2 Volts so it doesn't detract too much from the usual 5 Volt gate signal.

Here's the E.G. mounted in my synth. You can see that I doubled the output sockets. There's 2 outputs for normal 5Vpp ADSR and 2 for either 10Vpp or Inverted -10Vpp I also installed a Gate output and a Trigger output. The Trigger output is connected to the Gate output via a 3nF capacitor and the Gate output is simply switched in parallel over the Gate input. I will however install a opamp buffer for the gate output in the near future.:

Here are some oscilloscope screenshots showing the function of each variable:
This is the normal envelope CV at 10Vpp.

Varying the Decay time:

The picture below shows the quirck I mentioned earlier where the Sustain level is set higher than the Attack can reach and so after the Attack cycle has finished the Decay is skipped all together (because there is no Decay if the Sustain level is higher than the Attack level) and the envelope jumps to the Sustain level. You can clearly hear the jump in volume in the audio. You can use this to your benefit though because it sorta has a percussive quality to it. Anyway, if you don't want this, just turn the Sustain down a bit. Problem solved. You can also limit the maximum resistor value of the Sustain potmeter by adding a resistor or trimmer to pin 3, but you'll have to experiment to find which value works best.

Lowering the Sustain level:

Increasing the Release time:

And finally switching between the inverse envelope (which was set to 0 to -5V in my ADSR but to 0 to -10V in the stripboard layout) and the 10Vpp envelope.

Okay, that's it for this one.
I hope you enjoyed this article and leave a comment please if you found this helpful! Much appreciated! Also, any questions? Put them in the comments or contact me on Facebook. I'm a member of the 'Synth DIY' Facebook group and the LMNC Discussions FBgroup and also the "Synth DIY for non engineers" Facebook Group all under my own name Eddy Bergman.
Stay tuned for more build reports and click 'follow' to be notified of new posts to this website.

Synthesizer Build part-3: TRIANGLE TO SINEWAVE CONVERTER

This article has been re-written at 11-11-2020.

After I had finished the VCO I wanted to add a Sinewave option to it. The first design I had posted here was a bit sketchy so I now present a new layout here. This layout has been made using the schematic of the Thomas Henry CEM3340 Deluxe VCO, which has a sinewave output. Btw, you can find that schematic in the 'files' section of the 'Synth DIY for non engineers Facebook Group'.

This circuit needs the Triangle input wave to be +/-5 Volt peak-to-peak. You can input a Trianglewave of 0V to +10Vpp but then the input must first go through the 1µF electrolytic capacitor to take away the offset voltage. The Triangle to Sinewave converter will not work properly if you input a 0/+10Vpp Trianglewave without first filtering out the DC offset voltage.

I altered the feedback resistor (Rf on layout) from 10K to 15K to get the amplitude correct with the waveform standard of my synthesizer project which is 0 to +10Vpp. This had the effect that the +/-5V output got a negative offset voltage. What I should have done is change the other 10K that goes from the + input to ground into a 15K also, so everything is in balance again but I put a 1µF capacitor in series with the output of the +/-5Vpp sinewave. The negative pole of the electrolytic capacitor is facing the direction the signal is coming from because I had a negative offset voltage to deal with. Make sure you match the 10K resistors so they all have the same value and if you change the feedback resistor to a 15K make sure you change the other 10K to ground also. Match the transistors too. (Matching them on hfe is good enough). If after all that you still have an offset voltage on the output (unlikely) then you can put a 1µF cap in series with the +/-5V output.

The output amplitude on a dual 12V powersupply is +/-4.2Vpp or 0 to 9.4Vpp. For a dual 15V power supply it is +/-5Vpp or 0 to 10Vpp.

Here is the new stripboard layout. This converter offers a +/-5Vpp output and a 0/+10Vpp output. 

Here is the schematic drawing. I did not include any de-coupling capacitors but if you want to include them then just add two 100nF ceramic capacitors to the voltage rails as close to the chip as possible. One going from +15V to ground and the other from ground to -15V.

Here are two pictures from the oscilloscope. One without offset from the +/-5Vpp output and one with offset from the 0/+10Vpp output. If you look closely at the pictures you see that the scope is set to 2V per division and therefore that the amplitude of the sinewave is 8V. But now that I changed the feedback resistor Rf, that has changed to 10V (even a tiny bit over):

As you can see they are beautiful sinewaves and you can set the symmetry and distortion very accurately with the trimpots on the stripboard. 

It will be easy enough to mount this little stripboard on one of the M3 bolts used to mount the print of the 'Really Good VCO' and thus add a Sinewave output to that VCO. You can tap the Trianglewave straight from pin 10 of the AS3340 (or CEM3340) chip or from pin 12 of the TL074 quad opamp chip. I think that will be even easier. On those pins the Trianglewave is not yet given a +5V offset voltage so it is still +/-5Vpp and therefore doesn't need to go through the 1µF electrolytic capacitor on the layout of the Triangle- to Sinewave converter. 

Okay that's the new version of this article done. If you have any questions please put them in the comments below or on the EddyBergman Facebook Group page.

Btw, all the comments below upto August 2020 refer to the original Tri- to Sinewave converter article and not to this one. So please disregard those comments.

Synthesizer Build part-2: THE VCO

A word in advance: this article deals with the first VCO I've ever built and is based on the datasheet schematic combined with the LookMumNoComputer lay-out for the CEM or AS3340 chip. I personally had great trouble getting this VCO tuned over a wide range of octaves.  I could also never get really deep notes from this design. I have since found a much better VCO design so if you want to build a simple but excellent working and tunable VCO on stripboard I refer you to Synthesizer Build part-18: A Really Good VCO design.

I'm keeping this article up for my own archive and as a warning for those just starting out not to build this VCO!!!

Here's the original text for the first VCO build:
After having constructed the power supply and the power bus system it is time to move on to the next step. The Voltage Controlled Oscillator. I'm not going to go into details as to how it works etc. There's plenty info online about that.  In order to make this a complete build, not just the circuit board I needed something to mount the knobs and in- and outputs on. So I ordered a sheet of Aluminium, 200 x 1000 X 1.5 mm and powder coated gray/black on one side. That is fantastic stuff to make panels out off and I highly recommend it. You can saw off panels of the right width using an electric jigsaw with a fine toothed metal saw. Make sure you guide the saw with a straight piece of wood or metal to get nice straight panels.

For my VCO I chose the AS3340 chip which is a complete 1 volt per Octave VCO in a chip. It's a clone of the CEM3340 which were used in the 80's in synths like the Prophet 5 the Roland SH101 and many others.
The VCO we're building here will have almost all the options that the AS3340 chip has to offer and those we didn't include are not worth having anyway ;)
The schematic I used is pretty much just the schematic that comes on the datasheet.

This is the one I used:

I used the layout made by Sam Battle, from LookMumNoComputer and did a few enhancements on it. (Look to the one on the right).

For one, his layout is meant for the CEM3340 which uses a 10K pulldown resistor on pin 4, the squarewave output. For the AS chip, that's supposed to be a 51K resistor although I'm reliably informed it doesn't make a blind bit of difference what you use here. There was also a mistake in his design, namely the 10K resistor in the bottom left near the TL072. It is switched in parallel with the 10K on pin 4 making the overall resistance 5K. Just leave the bottom 10 K resistor out.
The 10K trimmer potmeter at the top left of the 3340 needs to be a multiple turn potmeter so you can set it very accurately.

Sam's layout doesn't include the High Frequency Tracking but you really need to include it in your VCO. I first build it without and at first it seemed to work fine but after having completed the whole synthesizer I couldn't get really deep bass tones out of it. That is until I included the High Frequency Tracking. Seems a paradox that something meant for High Frequency adjustments can have so much influence on the bass notes but if you look at the schematics you can see that it pulls the CV voltage on pin 15 down to ground a bit through the 20K potmeter. I kept out the 360K resistor between +15V and CV input because that kicks the VCO into really high notes. I don't know why that resistor is there but it really screws up the frequencies. I left it out but maybe I should have experimented further with that resistor in place. Anyway...
The HF adjustment pot only adjusts about half a note over its full throw so when you first test it it might look as though it doesn't work but it does when you start tuning the higher octaves of the VCO.

Furthermore I gave the buffer for the triangle wave a gain of 2 by adding two 100K resistors to the TL072. That gets the level of the triangle output up to 10V peak-to-peak, in line with the output voltages of the other two waveforms. Btw, you can use any resistor value between 50K and 1M for this purpose as long as both resistors have the same value.

I also added the Positive and Negative Hard Sync options from the Digisound 80 Modular design so that's also available on this VCO.

Here is the layout that I drew and used:

So there we have it. It's become quite a comprehensive VCO with lots of options.
I added a 100K resistor to the +15V input of the Pulse Width Modulation potmeter to get it to work over the complete throw of the potmeter and I added a switch to have the ability to decouple it from the PW Control Voltage if you have PWM controlled by an LFO for instance. You don't have to decouple it but the option is there.

I tested the finished print and everything worked as expected but there was a funny quirck in the squarewave output. Below 1.35kHz there was a strange triangular wave ringing on the downward slope of the square-wave. Here's some pictures of that from my scope:

I opened a discussion about this in the Synth DIY Facebook Group and there were many suggestions but I still haven't figured out the cause. It's not a de-coupling issue anyway.
I suspect that leaving out the High Frequency Tracking I mentioned earlier may be the cause. (Note: I did some more tests and it turns out that it does have a big influence on this issue. Including HF Track with the 360K resistor to +15V almost gets rid of the problem but on low frequencies there still is a bit of ringing on the downward slope but not nearly as much as now.
But as I mentioned before, the 360K resistor really screws up the frequency response so it can not be included. I have heared that there might be batches of chips that have this fault, so it might be the chip. I don't know and don't really care because you don't hear it and everything works fine.

[Edit: In the second VCO I built and now use (see article 18) this ringing is still there but it is much less then in this design. The new VCO has at most 3 spikes in the downward slope of the squarewave. Anyway it has proven to be not a problem what so ever. You can't hear it and it doesn't affect the working of either VCO in any way.]

Although the connection is there in the layout, I did not use the Soft Sync input on my final build. I don't think I'll need it. I did use the FM input. You can connect a second VCO to that for instance.
Here's a look at the finished product, panel and all. The powder coated Aluminium was a great choise and looks so cool. It doesn't scratch easy at all, it's perfect for this project.

I'll explain what's on the panel.
We have the FM input at the top left. The big knob at the top is the Coarse Tune potmeter, below that on the left are the CV1 and CV2 inputs and on the right are the Triangle-, Ramp- or Sawtoothwave and below that the Squarewave outputs. ( I always put inputs on the left and outputs on the right.)
Then there are three inputs to the left of the blue knobs. Those are the Pulse Width Control Voltage input, the blue knob next to it controls its level. Underneath that are the Positive Hard Sync and Negative Hard Sync inputs. The bottom blue knob is the Manual Pulse Width control if you don't use a control voltage. The switch with the diode symbol let's you choose to put a diode in the external Pulse Width input line which de-couples it from the internal PWM control or to bypass that diode and get more range on the PWM control knob. [edit] I have since scrapped this idea and I took out the diode. The switch is now used to turn off or on the manual Pulse Width Modulation potmeter as described above. (It's not necessary but the switch was there so might aswel use it for something). I added one more output which isn't in this picture and that is a "CV out" function to connect the second VCO to the first one. It's simply switched in parallel with the CV-1 input.


Okay, that's it for this one. If you have questions or suggestions please write them in a comment. Next part will be about a filter, probably the Prophet One Low Pass filter.
Stay tuned!

Synthesizer Build part-1: SYMMETRICAL POWER SUPPLY (1,5A) with independent voltage adjustment.

The essential building block for our DIY synth. with outputs for +/- 15V, 12V and 5V at 1.2 Ampères.

Please scroll half way down the article to find the second version (which is modular in set-up) with stripboard layouts

WARNING, THIS PROJECT REQUIRES YOU TO WIRE UP A MAINS TRANSFORMER. BE VERY CAREFUL WHEN HANDLING MAINS POWER. IT CAN BE DEADLY AS YOU PROBABLY KNOW. IF IN DOUBT ASK AN EXPERT OR POST QUESTIONS IN THE FACEBOOK GROUP. DON'T TAKE CHANCES WITH MAINS ELECTRICITY!!

In Oktober 2019 I set myself the task of building my own synthesizer. I started by slowly buying in the components I was going to need, as my budget allowed (and that wasn't much ^__^).
The first thing I needed for this project was a symmetrical power supply to give me positive and negative voltages, because practically everything in a synthesizer runs on a dual powersupply.
I used the LM317 and LM337 for this project because they are easy to work with and fully protected inside against short circuits and over heating. The LM3XX series regulators can deliver up to 1,5 Ampères.
This is the schematic I came up with and it works very well: (click picture for full screen view)

(STRIPBOARD LAYOUT FURTHER DOWN THE ARTICLE!)

I based this schematic on the datasheet schematic for the LM317 and LM337. It calls for a 5K trimpot but I used 10K's because that's what I had and it works fine. Afterall you can trim it down to below 5K just as easy, so no problem there. The values of the electrolytic caps I'm using is way over the top compared to the datasheet but it does help stabilize the voltage especially because some modules, like Sample and Holds or Sequencers can pull a pulsed current from the powersupply. Here's a screenshot of the original schematic from the Texas Instruments datasheet:

The transformer you use for this power supply must be about 2 to 3 Volt higher in output voltage than the needed output voltage of the powersupply. There is going to be some voltage drop over the voltage regulators and the diode rectifiers that must be accounted for. However the voltage will also be higher than the transformer delivers when it comes out the diodes so we must also account for that. I find 2 x 17Vac secondary outputs to be about the sweet spot. You can go a bit higher if you like.

In the schematic above you can see that the output capacitors are 1000µF. They don't have to be this big. 100µF will do nicely too. The caps discharge through the 220 Ohm and 10K potmeter when you switch off.
If you need a power supply that can handle more current, say 10 Ampères for instance, then you can easily adjust this circuit by adding a 2N3055 on the positive side and an MJ2955 on the negative side. You can even put more power transistors in parallel over eachother to get even bigger current specs. Move the capacitors that come after the LM3XX's past the transistors but put an extra 100nF capacitor between the base and the null to suppress transients etc. Use Google to find more specific schematics for that, if you need it.

But for a modular synthesizer those alterations are not needed because the individual modules I'm going to build won't draw much current at all. It's mostly in de 20 to 80 milli amps at most. The only transformer that I had that was big enough for this project didn't have a center tap but it had two independent secundary outputs. One at 21V and one at 17V. This was close enough. I connected one wire from each output together to make a center tap and made a circuit board to build the powersupply on. (Make sure when you connect two secundary windings together like this, that you measure the AC output before proceeding with the next steps. If you connect the wrong wires the 2 voltages will try to cancel eachother out. It won't damage the transformer but you won't get any voltage out.) I didn't have etching fluid anymore so I cut different islands on the copperside of the copperclad circuit board I was using, with a dremmel tool with a milling bit. I had an old 25 Amp. Graetz diode bridge in my collection of components and after I drilled all the holes the build was pretty straight forward.
I used little trimmer potentiometers to set the voltage with. Once you set it, you don't have to touch it again but if you want to make it continuously adjustable you can of course use 10K panel mounted potentiometers with a knob. I put some LED's on the output side to indicate that all is working well. The difference in brightness will indicate if the voltages are set differently from eachother. You could also go the luxurious route and use two panel voltmeters to indicate the voltage but as I intend this to power my synthesizer that will not be necessary.
But if you build this as a stand-alone power supply, it would be a good idea to use two meters on the outputs. Beware with cheap Chinese digital voltmeters. They look great but they put a ton of noise on the voltage rails!! Use analog meters instead if you can. They look even better and are noise free.
The power supply as described above outputs between 1,5 and 25 Volts (dependent on the transformer you use) at a maximum current of 1,5 Ampere. If you want a more powerful version you could use the LM3XX regulators to drive a 2N3055 and a MJ2955 NPN and PNP power transistors as mentioned above and then you can draw up to 10 to 15 Amps. Be aware that the pinouts for the LM regulators differ from eachother. The correct pin numbers are noted on the schematic above.
The ripple is very low on the output. It's actually better than some you buy ready made. Make sure the electrolytic capacitors you use are rated 50 volts or higher. (I used 35V ones and that seems to work fine too but don't go any lower!) and make sure they are oriented the right way. Plus on + on the positive side and plus to ground and minus to negative voltage on the negative side. The voltage at the secundary directly after rectification can go up to 10 volt higher than the AC voltage from the transformer. Don't present more than 35V to the input pin of the regulators and be sure to use big heatsinks on both of them.
I've measured the ripple and noise of the power supply using the method outlined by Dave Jones from the EEVblog on YouTube in his video EEVblog #594 - How To Measure Power Supply Ripple & Noise
I used my simple home build 'brute force power load' described in the article from januari 2017 and under a load of 1 Ampere the Ripple Voltage Vrms was 6mV and Vpeak-to-peak was 10mV. Those are very good results.

Here's the stripboard layout for the powersupply. There are minor differences in values and components because this layout is based on an eBay kit, instead of the above datasheet schematic but it works perfectly, I assure you. You can mount the voltage regulators on a single big heatsink but they must be electrically insulated from the heatsink and eachother.

[NB: 11-Sept-2021 I just built one of these again today using this layout and it worked rightaway.]

You can leave the 10µF electrolytic capacitors over the trimpotmeters out. You don't need to include them. I put them in as an added protection for the LM3** voltage regulators but they are not needed. They are also not included in the schematic above.   

I included an L-Bracket symbol to show which part of the stripboard can be used for mounting behind a panel or in a case. The components are quite spread out so you can put them closer together to make the board smaller, I leave that up to you.

Here are some pictures of the first powersupply . As you can see there's some room left on the circuitboard for extra voltage regulators to get other voltages from the same supply:

I added the inductor coil in series with the Ground or Zero Volt pole to suppress any high frequency noise. It's just something I added as a test but you can leave that out.

It's a week later and I finished the power supply as I need it for my synthesizer project. It now has -15/0/+15V,  -12/0/+12V and -5/0/+5Volt. I looks a bit of a mess as my projects usually do but it works just fine. Here's a picture of the finished psu:

[EDIT: This is future Eddy speaking 5 years later. Having built over 60 synthesizer projects which have all been connected to this powersupply I can say it's a solid design. Many a time I have tested a module and had a short circuit somewhere but the powersupply always survived it.]

Obviously you can't plug in all modules in the same holes so I've build a power bus system to which I can connect every module I build. It's a bit crude and I use a lot of hot-glue to stick it all in place but it works just fine and it will all be invisible once the case is ready.

Below you see the connector I build. The pins carry the following voltages: From top to bottom in the pic below, the top 2 pins are ground or 0V. Then I took out two pins and stuffed the holes in the female connector with hot glue. This is to get an a-symmetrical distribution so you can't put the connector in the wrong way around. Then there's -15, -12 and -5 Volt and then we get +5, +12 and +15 Volt. I kept the plus and minus pins as far away from eachother as possible for safety reasons.

PART TWO. SECOND POWERSUPPLY for stage two of my synthesizer.
So, as I'm writing this we're 6 months on in the synthesizer build and I'm about to add a second stage to go on top of the synthesizer I have already built.
So I need a second power supply. The first design as seen above works so well that I'm repeating it for the second stage with a few minor changes. I'm using multiturn potmeters for the LM317 and 337 voltage regulators so I can set them very accurately. In fact, the one I just built has plus and minus 15.00V that's accurate to 1/100th volt. I'm using all LM3xx regulators for this because I have a lot of them and because their voltage doesn't drop if you pull more current from them which is important because otherwise the VCO's would become out of tune. I'm using the same schematic as above and I made separate stripboards for every stage of the supply. Here's the stripboard layout:

Bridge rectifier board. (Don't forget to cut the copper strip underneath the fuses and to tin all the copper strips that carry current.). You can hang more than one voltage regulator print off of the bridge rectifying board as long as the transformer and rectifying diodes can handle the maximum current of the combined regulator boards.

Voltage regulator board. (Again, make sure to tin all the copper strips that carry current). 

(Last revised: 30-Jan.-2021: Corrected connection of negative voltage indicator LED.)

SOME NOTES ON THE DIFFERENT COMPONENTS TO USE:
Don't get confused by Capacitors being of a different value on the stripboard than on the schematic. The electrolytic caps on the Rectifier board are the big ones. They can be 1000µF to 2200µF or even higher and they do the main ripple suppresion. On the regulator board the electrolytic caps can be smaller, like 100µF because the main ripple suppresion has already been done and these are there to suppress noise and such. 100µF is enough for that.
Diodes also. The diodes around the voltage regulators are simply safety valves. Their purpose is to prevent the output having a higher voltage than the input, which could damage the regulator. The circuit will work fine even if you leave the diodes out. You can use any type of diode you wish 1N4148, 1N4001 upto 1N4007. It doesn't really matter. The diodes on the bridge rectifier however must be types that can handle at least 100V and 1,5 Ampères. You can not compromise on those but there are many different types you can choose from so I didn't specify which type number of diodes to use. You can also use a Graetz Bridge Rectifier, that's 4 big diodes in one case. I saw a 1000V/4Amp one for 50 cents on eBay. Those will work fine and they won't even get warm.
Like I mentioned before, the voltage regulators must be mounted to a heatsink. Either use two separate heatsinks (make sure they can't touch eachother) or use one big one for both regulators but in that case you MUST insulate the regulators electrically from the heatsink otherwise you'll get a very short lived microwave oven with integrated laser lights. ^____^
Naturally the voltage regulators do not have to be mounted on the stripboard itself. You can mount them on the backside of a front panel, using that as a heatsink, or on the side of a metal case you're using and then you can wire them up to the stripboard with normal electrical wire. Use your imagination but do make sure the regulators are not electrically in contact with eachother, otherwise, boom!
The LED's are simply there as a visual indicator that the circuit is under power and they are not critical to the working of the circuit, so you can do without them if you wish. Use 15K current limiting resistors with the LEDs though, because lower values can get hot.

Should you have problems like not getting the right voltages out of the powersupply then check your resistor values. Are you sure the 220 Ohm is not a 220K? This has happened on at least two occasions I know of that's why I'm writing it here as a reminder.

Here are some pictures of the finished power supply. Tinning all the copper strips that carry current is important because they get very thin around the holes in the stripboard. 
I've mounted the whole powersupply on a long piece of MDF ready to accommodate the power-bus system I need to build.

I found some very old vintage diodes with a metal case which I think look very cool and they work fine. They are sturdy too because I had some short circuits in testing and the fuse went 2 times but the diodes didn't mind and I use slow fuses too so they did get some current through them.
Use plenty of heat sink compound on the LM's. The electrolithic caps are 1000µF each; all four of them and that's all the capacitance I put in. 1000µF in the rectifier and 1000µF on the output side of the voltage regulators. The rectifier caps have 10K 1Watt resistors over them to make sure the are drained of voltage when the powersupply is switched off. (It's 2K2 in the picture but they were getting slightly warm so I changed them for 10K's)

SIMPLE FIXED VOLTAGE POWERSUPPLY  using the 7812 and 7912 voltage regulators.

Finally I want to close off this article with a very simple powersupply that uses fixed voltage regulators. The 7812 for positive voltage and the 7912 for negative voltage. These can do up to 1,5 Ampères but I wouldn't use it for more than 1 Amp. otherwise they get very hot even with heatsink.

Btw, you must use these on a heatsink too, just like the previous designs, and you must make sure they don't electrically touch the heatsink if you have both regulators on one heatsink. Otherwise you get a short circuit and a lot of magic smoke. The circuit schematics for this one can be found by clicking here

Here is the layout I made for this PSU. It's very small and can fit anywhere. The LEDs are there to indicate if power is present on the outputs. You can mount those in a panel if you make a panel for your powersupply. I always mount leds like this near the ON/OFF switch for the PSU (Power Supply Unit).

(Last revised: 24-Aug-2022: Corrected a mistake where the LEDs were not connected to ground properly, thanks to a observant reader. )

Okay that's it for this one. If you have any questions you can leave them in the comments or post them on our special Facebook Group for this website, where we have a cool little community who will love to help you out.

ELECTRO-MAGNETIC FIELD DETECTOR.

Here is an easy to build EM Field detector with 4 stage LED strength indication and which has a wide range of applications. This circuit will detect electromagnetic fields and also static electricity. It detects the mains hum on a 240 Volt (or 110V) wall socket or cable without having to touch the object. It is enormously sensitive to any changes of the EM field surrounding it so it could be used to detect lightning (proof is in the video below) or maybe even ghosts. (No video proof of that alas! At least not yet  ^__^ ). Please note: this circuit can not be used as a metal detector.

Here is the circuit (click on image to display full screen):

(Last revised: 02-june-2020: Changed 1M potmeter for 20 to 50K potmeter.)

Parts list:

Transistors:
8 x BC547 

Resistors:
1 x 680 Ohm 
4 x 470 Ohm
1 x 220 Ohm 
1 x 4K7 
1 x 3K3 
2 x 2K2 
1 x 100K
1 x 1M 

Potmeter:
1 x 20K or 50K potmeter (use either a trimpotmeter or a panel potmeter if you're building this into a case.) 

LEDs (3mm):
3 x green, 1 x yellow, 1 x red

Diode:
1 x 1N4148

Miscellaneous:
9V battery clip, 1 switch (SPDT Toggle Switch ON-ON), 1 Bullet conncector for antenna. (optional)

Before I go on with the rest of the explanation, here's a video showing this EMF Detector in action in a lightning storm. In the background audio you can hear the crackle of the lightning on an AM radio I had switched on, and you can see that the meter lights up as the radio crackles and lightning occurs. Sometimes it even detects the build up of the electric field in the air before lightning happens. I'm not influencing the meter in any way. I'm just holding it by the 9 volt battery underneath. Here it is:

I designed this because I always found it a shame that these "everything detectors" or 8 Million times amplifiers never had a strength indicator so you could actually see if and how it's working. So I tried combining two pre-existing circuits and see if I could make them work together and it turned out to work very well. The first of these circuits is this 4 LED signal strength indicator

and the second is this circuit which is the actual detector stage, consisting of the 8 million times amplifier.

You can easily build this on a piece of stripboard.
The circuit needs only 8 transistors (BC547 or 2N3904), 5 LEDs and 11 resistors. The extra (5th) LED is there simply to function as a on/off indicator and could be left out if you so wish. I used 3mm LEDs on this project but 5mm will work too. Don't use LEDs that draw a lot of current though like bright white LEDs or blue LEDs. The circuit is fed from a normal 9 Volt battery.

The sensitivity of the circuit can be changed with the 20K or 50K potmeter. If you're using it like me, without a case, you can use a trim-potmeter. If you're building this into a little case then use a panel potmeter for sensitivity. Make sure there's a grounding point when you build it into a case. Some connector from where you can ground it.

The circuit is very sensitive and it reacts to all sorts of things. If you hold this EMF Detector  near any mains cables it will instantly detect the voltage, I noticed that if you hold it near metal it will detect that too and even in an open space it will sometimes indicate a field even if there's nothing visible there but it's not a malfunction because it will keep indicating on the same spot in the room. 

This meter works best if it is grounded properly, either by connecting minus to a metal case in which you build the meter and then holding it in your hand  or by  grounding it to some metal item (do NOT connect to ground of mains power supply!!!)
Here are some pictures of the detector I build:

Enjoy building this awesome little "everything detector" ^____^ oh and hey, while you're here, please leave a comment! That'll be cool! :-)