Erica Synths mki x es.EDU Manual

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INTRO |

Hey there, thanks for buying this DIY kit! We - Erica Synths and Moritz Klein - have

developed it with one speciﬁc goal in mind: teaching people with little to no prior

experience how to design analog synthesizer circuits from scratch. So what you'll ﬁnd in

the box is not simply meant to be soldered together and then disappear in your rack.

Instead, we want to take you through the circuit design process step by step, explaining

every choice we've made and how it impacts the ﬁnished module. For that, we strongly

suggest you follow along using LABOR , which is a non-permanent circuit prototyping

tool that allows you to experiment and play around with your components. To help you

with this, we've included suggested breadboard layouts in select chapters.

In addition to this, you can also play around with some of the chapter's circuits in a

circuit simulator called CircuitJS. CircuitJS runs in your browser. You'll ﬁnd weblinks in

the footnotes which will direct you to an instance that already has example circuits set up

for you. We strongly encourage you to ﬁddle with the component values and general

structure of those circuits to get a better understanding of the concepts we're laying out.

Generally, this manual is intended to be read and worked through front to back, but there

were a few things we felt should go into a dedicated appendix. These are general

vignettes on electronic components & concepts, tools, and the process of putting the

module together once you're done experimenting. Don't hesitate to check in there

whenever you think you're missing an important piece of information. Most importantly

though: have fun!

CIRCUIT SCHEMATIC .................................................................................... 2

BILL OF MATERIALS ..................................................................................... 3

USAGE WITH MKI x ES LABOR ....................................................................... 6

CIRCUIT DESIGN CLOSE-UP .......................................................................... 8

COMPONENTS & CONCEPTS APPENDIX ....................................................... 43

TOOLS APPENDIX ....................................................................................... 56

MODULE ASSEMBLY APPENDIX ................................................................... 59

SOLDERING APPENDIX ................................................................................ 71

You can also use a standard breadboard, but this will require you to get a little creative when

adapting the suggested layouts. You'll also need to do some additional engineering to get the

diﬀerent supply voltages.

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Summary of Contents for Erica Synths mki x es.EDU

Page 1: Table Of Contents
INTRO | Hey there, thanks for buying this DIY kit! We – Erica Synths and Moritz Klein – have developed it with one speciﬁc goal in mind: teaching people with little to no prior experience how to design analog synthesizer circuits from scratch. So what you’ll ﬁnd in the box is not simply meant to be soldered together and then disappear in your rack.
Page 2: Circuit Schematic
Here’s an interesting problem: how do you create a delayed duplicate of a sound without recording it to some sort of storage medium? Back in the days before digital signal processing and cheap, abundant memory, this was a prime engineering issue. That’s because at that time, the only practical electronic implementation of an audio delay eﬀect was large, bulky tape echo machines.
Page 3: Bill Of Materials
BILL OF MATERIALS Before we start, please check if your kit contains all of the necessary components. In addition to a PCB, panel and power cable, your box should also contain: An array of resistors. The speciﬁc values (in ohms, which you should check for with a multimeter) are 2M2 x1 100k x9...
Page 4 Some diodes. The speciﬁc model names (which are printed onto their bodies) are 1N4148 (signal) 1N5819 (schottky) x2 A couple transistors. The speciﬁc model names (which are printed onto their bodies) is J113 (N-CH JFET) 78L05 (5V regulator) A handful of potentiometers. Their speciﬁc values (which may be encoded &...
Page 5 A couple chips. Their speciﬁc models (which are printed onto their bodies) are TL072 (dual op amp) V3205SD (BBF 4096) CD4046BE (PLL) A switch. The speciﬁc model is Single pole, double throw You will also ﬁnd a few sockets that are only relevant when assembling the module in the end.
Page 6: Usage With Mki X Es Labor
USAGE WITH MKI x ES LABOR We recommend that you follow this guide using an MKI x ES LABOR prototyping board. LABOR comes equipped with everything you need for testing the circuits we lay out: a standard 830 tie point breadboard, an integrated dual power supply with over current protection, a manual gate/trigger/envelope generator, an LFO, a variable CV source, an output ampliﬁer, and a modular interfacing section where you can insert all of your interfacing components like potentiometers, jack sockets, and switches.
Page 7 Sometimes, this guide will ask you to use external gear like sequencers or LFOs to send CV, audio signals, triggers or gates into your circuit. With Labor, there’s no need for extra equipment – just use the built-in oscillator (audio/LFO), CV source or manual gate/trigger/ envelope generator.
Page 8: Circuit Design Close-Up
ANALOG SAMPLING We’ll start by investigating the ﬁrst stage of a BBD: the analog sampling sub-circuit, which splits the input into transmissible chunks. Okay, but what does that mean, exactly? Well, in electronic circuits, an audio signal is represented as a swinging voltage – like this triangle wave.
Page 9 Next, we pull the gate voltage way below the source, disabling the JFET. This cuts the connection between signal and capacitor, which means that the charge is now trapped inside the cap. This trapped charge is our sample. Okay, but what about a non-static signal? Luckily, it works just the same: we activate the transistor by raising the gate voltage, which causes the voltage above the capacitor to follow the input.
Page 10 input. So we’ll want to automate the sampling process with a fast clock signal – essentially just a high frequency square wave swinging between 0 and -5 V. And while we could generate this clock with any basic square wave oscillator, I’m going to use a 4046 Phase Locked Loop chip instead.
Page 11 Okay. To start oﬀ, we’re feeding LABOR’s sine wave oscillator into our scaling and biasing sub-circuit (connection path 1), before routing it to a J113 JFET followed by a 15 nF capacitor. Then, we connect the clock generator, which receives its -5 V supply from LABOR’s variable voltage source (connection path 0), to the JFET’s gate.
Page 12 SAMPLE TRANSFER Great! Now that we’ve split our signal into samples, we can think about achieving the delay eﬀect itself. The trick here is to take the individual samples and move them through a chain of containers, synchronized with the clock signal. Since each transfer from one container to the next takes a small amount of time –...
Page 13 The solution that they came up with is simple – but not obvious at all. Instead of transferring charge between capacitors, they decided to transfer the charge deﬁcit. It works like this. We ﬁrst add another JFET, which we connect to capacitor two on the left and a 5 V voltage source on the right.
Page 14 Note that to automate this circuit’s operation, we’ll need a second clock signal that is the exact inverse of our existing clock to drive every other JFET. Also note that each cap is only carrying information on every other clock pulse – it is either full (which means it’s not carrying information) or at a charge deﬁcit (which means that it is carrying information).
Page 15 To try this, we’ll add 3 BBD stages to our existing circuit. For the input, we’ll use the same scaled and biased sine wave from before. Please note that some of the components used in this layout are not included in your kit. If you don’t have these extra components in your stash, build the alternate layout below that uses kit components exclusively.
Page 16 In this alternate layout, we use the dedicated BBD chip included in your kit (V3205). We’ll look at its anatomy more in detail later, but this circuit will produce an output very similar to the above circuit. Check out the signal at connection point 2 with your oscilloscope. That voltage should alternate between the full state (2 V relative to ground), which carries no information, and the deﬁcit state, which is moving up and down in a sinusoidal pattern.
Page 17 MOSFET BUFFER Now, in order to hear how it sounds, we need to add a voltage buﬀer to avoid drawing current from the BBD stage capacitor and distorting the signal. And while we could use an op amp here, BBD chips typically use a MOSFET for a smaller footprint. Lucky for us, we can actually do the same! That’s because voltage buﬀering is a unidirectional use case, which works just ﬁne with a discrete MOSFET.
Page 18 That’s because the activation threshold for a BJT is around 600 mV – which means that the voltage drop between base and emitter is 600 mV as well, shifting the output downwards by that amount and allowing us to buﬀer an input that’s going slightly above our 5 V supply voltage.
Page 19 To test this, we’ll set up a 2N7000 MOSFET as a voltage buﬀer. Please note that some of the components used in this layout are not included in your kit. If you don’t have these extra components in your stash, use the previous alternate layout and use connection point 2 as the circuit’s output.
Page 20 DUAL TAP RECONSTRUCTION If we compare the signal at capacitor 4 to the signal at capacitor 3, you’ll notice that they’re complementary in the sense that whenever cap 4 carries no information, cap 3 does – and vice versa. If we were to combine the two, we should be able to cancel out the clock oscillation, since the signal wouldn’t jump between full and deﬁcit state anymore.
Page 21 If you build and listen to this, you’ll notice that while the amount of clock noise is deﬁnitely reduced, the output does still have a lot of whine in it. This is because ﬁrst, the two signals are not perfectly complementary, so there is no clean handoﬀ between samples.
Page 22 Please note that some of the components used in this layout are not included in your kit. If you don’t have these extra components in your stash, build the alternate layout below that uses kit components exclusively.
Page 23 If you check out the output on your oscilloscope, the waveform should look and sound a little cleaner. It’s not exactly good, but we’ll get back to this later. Because at the moment, our circuit is still pretty useless as a delay, since three transfers at a clock frequency of 10 kHz gives us an eﬀective delay time of just 300 microseconds.
Page 24 MORE STAGES WITH THE V3205 Instead, we’ll use a dedicated BBD chip: the V3205, which implements pretty much the same architecture we have just set up – but with 4096 stages instead of just three. There are two slight diﬀerences that’ll require us to make changes to our existing circuit, though. First, where we used JFETs, the chip exclusively uses MOSFETs.
Page 25 To move our input into that range, we’ll ﬁrst replace the 200k oﬀset resistor with a 47k. This will increase our oﬀset by around 2 V. Next, we’ll have to reduce the input resistance to increase the output’s gain and make use of the available headroom.
Page 26 To test all this, here’s how we’ll set up the V3205. First, it needs to be supplied with 5 V at pin 5 and ground at pin 1. Next, we’ll give it the VGG voltage at pin 8 via a 4k7/56k voltage divider between 5 V and ground.
Page 27 If you have previously built the discrete component version of our BBD using JFETs and 1 nF capacitors, please start with the alternate layout in the Sample Transfer chapter and work your way down to this one to set up the V3205. Once you’ve built this, try turning down the clock frequency.
Page 28 RECONSTRUCTION SAMPLING Traditionally, the way to ﬁx the clock noise bleed problem has been to use a low pass with a much steeper slope than ours. This way, more of the annoying clock whine is cut out – but also more of the input signal’s upper frequency range. And depending on how low we want our clock frequency to go, this would be a signiﬁcant chunk.
Page 29 This means removing one output from the equation and killing the basic low-pass ﬁlter. However, we’ll keep both the AC coupling and the buﬀer to ensure that we don’t run into any headroom issues later on. Next, we’ll set up a general purpose sample & hold circuit. You can check our sample & hold kit’s manual for an in-depth explanation, but there are three main diﬀerences compared to the sampling circuit we set up in the beginning of this manual.
Page 30 So by picking a relatively big capacitor in our sample & hold, we’ll get more of a rough average voltage than a 1:1 reproduction of this downward slope. Third and ﬁnally, there is a non-inverting ampliﬁer at the output with a gain of around 5, restoring the signal to standard eurorack levels –...
Page 31 also notice that you’re getting that typical re-pitching eﬀect as you turn the clock frequency knob. This happens because changing the clock speed alters the playback speed for the samples that are already inside the chip. While those samples are being played back, the pitch changes according to the new playback speed.
Page 32 DRY/WET MIXING Great! But so far, we’re only getting what you would call a fully wet signal from our circuit, meaning that we only hear the delayed sound, not the original one. To change this, we’ll add a simple dry/wet mixing stage. We’ll start by sending the wet (delayed) and dry (unprocessed) signals to opposite sides of a 100k potentiometer.
Page 33 If you turn the dry/wet potentiometer all the way clockwise, you should only hear the wet signal. And if you move it in the other direction, more and more of the dry signal should come in until the wet version completely disappears. Great!
Page 34 FEEDBACK So far, so good. What we have now is what’s commonly known as a slapback delay: a single delayed repeat. But what if we want multiple repeats instead of just one? Thankfully, getting there is really easy. All we have to do is feed the wet signal back into the input via the scaling &...
Page 35 Using the new feedback potentiometer, you should be able to vary the number of repeats from just 1 to so many that the chip goes into wild self oscillation mode. Cool!
Page 36 FLANGER MODE But while our current delay time range is working great for, well, delay, I’d like to be able to push it up into ﬂanger territory. A ﬂanger, if you don’t know, is basically just a delay with a very short delay time. Since the delay time depends on the speed of our clock, we can shorten it by increasing the clock frequency.
Page 37 If you set the new switch to short, you should be able to dial in much shorter delay times, which, with a bit of feedback, start to sound really trippy. Great! But you might ask: why not use an even smaller capacitor for even shorter delay times? To answer that, take another look at the triggers driving our reconstruction sample &...
Page 38 DELAY TIME MODULATION Now, an actual ﬂanger is not just a delay with a very short delay time – it also modulates that delay time using an LFO or similar. This modulation gives it that characteristic jet plane sound. To implement this in our circuit, we’ll need to add a control voltage input for the clock frequency.
Page 39 Okay, but what if there is no external signal plugged in at all? In that case, we would blast the 4046’s CV input with 10 V – which it is not able to handle. To ﬁx this, we simply add another variable voltage divider before the external CV input. This solves two problems at once.
Page 40 To test this, ﬁrst try sweeping the delay time knob’s range without any external CV applied. The range should stay roughly the same. Next, connect LABOR’s oscillator to the clock CV input (while using something else for the audio input, of course). You should now be able to dial in diﬀerent amounts of modulation going from subtle to extreme.
Page 41 INHIBIT CV And while our circuit is now pretty much feature complete, there is a pin on the 4046 chip that caught my attention: the INHIBIT pin, which we’ve decided to tie straight to ground previously. As a reminder, the voltage applied to that pin decides whether the chip’s oscillator is running or not.
Page 42 If you now apply a gate sequence to the new inhibit cv input, you should be able to create a fun rhythmic stuttering eﬀect. Great! And with this, our bucket brigade delay is complete. Once you’re done experimenting, dig out the panel and PCB from the kit, heat up your soldering iron and get to building.
Page 43: Components & Concepts Appendix
COMPONENTS & CONCEPTS APPENDIX In this section, we’ll take a closer look at the components and elemental circuit design concepts we’re using to build our module. Check these whenever the main manual moves a bit too fast for you! THE BASICS: RESISTANCE, VOLTAGE, CURRENT There are three main properties we’re interested in when talking about electronic circuits: resistance, voltage and current.
Page 44 USING TWO 9 V BATTERIES AS A DUAL POWER SUPPLY Dual power supplies are great – and if you want to get serious about synth design, you should invest in one at some point. But what if you’re just starting out, and you’d like to use batteries instead? Thankfully that’s totally doable.
Page 45 RESISTORS While a conductive wire is like a very big pipe where lots of water can pass through, a resistor is like a narrow pipe that restricts the amount of water that can ﬂow. The narrowness of that pipe is equivalent to the resistance value, measured in ohms (Ω). The higher that value, the tighter the pipe.
Page 46 CAPACITORS A capacitor is a bit like a balloon that you can attach to the open end of a pipe. If there’s some pressure in the pipe, the balloon will ﬁll up with water until the pressure equalizes. (Since the balloon needs some space to expand into, both of the capacitor’s legs need to be connected to points in your circuit.) Then, should the pressure in the pipe drop, the balloon releases the water it stored into the pipe.
Page 47 DIODES Diodes are basically like one-way valves. Current can only pass through in one direction – from anode to cathode. That direction is indicated by the arrow in the diode symbol and by a black stripe on the diode’s casing. So any current trying to move in the opposite direction is blocked from ﬂowing.
Page 48: Voltage Dividers
VOLTAGE DIVIDERS A voltage divider is really just two resistors set up like this: input on the left, output on the right. If R1 and R2 are of the same value, the output voltage will be half of what the input voltage is. How does it work? Let’s use our analogy again: so we have a pipe on the left, where water is being pushed to the right with a speciﬁc amount of force.
Page 49 POTENTIOMETERS Potentiometers can be used as variable resistors that you control by turning a knob. But, and that’s the handy part, they can also be set up as variable voltage dividers. To see how that works, let’s imagine we open one up. Inside, we would ﬁnd two things: a round track of resistive material with connectors on both ends plus what’s called a wiper.
Page 50 AC COUPLING What is AC coupling – and how does it work? Imagine two adjacent pipes with a balloon between them. Now, no water can get from one pipe into the other, since it’s blocked by the balloon. But, and that’s the kicker, water from one side can still push into the other by bending and stretching the balloon, causing a ﬂow by displacement.
Page 51 OP AMPS Op amps might seem intimidating at ﬁrst, but they’re actually quite easy to understand and use. The basic concept is this: every op amp has two inputs and one output. Think of those inputs like voltage sensors. You can attach them to any point in your circuit and they will detect the voltage there without interfering.
Page 52 OP AMP BUFFERS/AMPLIFIERS Buﬀering, in the world of electronics, means that we provide a perfect copy of a voltage without interfering with that voltage in the process. With an op amp-based buﬀer, the buﬀering process itself works like this. We use the non-inverting input to probe a voltage, while the inverting input connects straight to the op amp’s output.
Page 53 ampliﬁer because the output signal is in phase with the input. For an inverting buﬀer/ampliﬁer, the input signal is no longer applied to the non-inverting input. Instead, that input is tied directly to ground. So it’ll just sit at 0 V the entire time.
Page 54 BIPOLAR JUNCTION TRANSISTORS Bipolar junction transistors (or BJTs for short) come in two ﬂavors: NPN and PNP. This refers to how the device is built internally and how it’ll behave in a circuit. Apart from that, they look pretty much identical: a small black half-cylinder with three legs. Let’s take a look at the more commonly used NPN variant ﬁrst.
Page 55 collector current. (At least not without some unwanted side eﬀects.) Third, also unlike a resistor, a BJT is not a linear device. Meaning that a change in collector voltage will not aﬀect the collector current. And fourth, the collector current is aﬀected by the transistor’s temperature! The more it heats up, the more current will ﬂow.
Page 56: Tools Appendix
TOOLS APPENDIX There are two types of tools that will help you tremendously while designing a circuit: multimeters and oscilloscopes. In this appendix, we’ll take a quick look at each of these and explore how to use them. MULTIMETERS Multimeters come in diﬀerent shapes and sizes, but the most common type is probably the hand-held, battery powered variant.
Page 57 OSCILLOSCOPES While multimeters are fairly cheap and compact, oscilloscopes are usually somewhat pricey and bulky. If you’re willing to make the investment, they are a huge help with the troubleshooting process, though. Using one is, again, surprisingly straightforward – if you manage to work your way through the sometimes quite convoluted UI, especially on digital models.
Page 58 BUILD GUIDE...
Page 59: Module Assembly Appendix
MODULE ASSEMBLY APPENDIX Before we start building, let’s take a look at the complete mki x es.edu BBD schematics (see next page) that were used for the final module’s design and PCB fabrication. Most compo- nents on the production schematics have denominations (a name – like R1, C1, VT1, VD1, etc.) and values next to them.
Page 60 Capacitors C5 – C8 and C21, C22 are additional decoupling capacitors. If you inspect the PCB, you’ll see that these are placed as close to the power supply pins of the ICs as possible. For well-designed, larger PCBs you will find decoupling capacitors next to each IC. Like the others, their job is to simply compensate for any unwanted noise in the supply rails.
Page 62 Before you start soldering, we highly recommend printing out the following part placement diagrams with designators and values. Because some of our PCBs are rather densely popu- lated, this will help you to avoid mistakes in the build process.
Page 63 Place the BBD PCB in a PCB holder for soldering or simply on top of some spacers (I use two empty solder wire coils here). I usually start populating PCBs with lower, horizontally placed components. In this case, these are few resistors, switching diodes and the power protection diodes.
Page 64 Next, insert the first DIP socket, hold it in place and solder one of the pins. Continue with the next DIP socket. Make sure the DIP sockets are oriented correctly – the notch on the socket should match the notch on the PCB’s silkscreen. Now, turn the PCB around and solder all remaining pins of the DIP sockets.
Page 65 In order to save space on the PCB, some of our projects, including the BBD, have verti- cally placed resistors. The next step is to place & solder those. Let’s start with 100k, 22k, 10k and 470ohm resistors. Bend a resistor’s legs so that its body is aligned with both legs and insert it in its designated spot.
Page 66 Now, proceed with remaining resistors. Next up: inserting & soldering the 5V voltage regulator the transistor. Make sure you align those components in TO-92 case with the marked outline on the silkscreen – orien- tation is critically important here. Also, insert film capacitors and solder them.
Page 67 Then complete the component side of the BBD PCB by soldering the PSU socket. Make sure the orientation of the socket is as shown in the picture below – the arrow pointing to the first pin is aligned with a notch on the silkscreen.
Page 68 Insert the jack sockets and the green B100k potentiometer and solder them. Insert other potentiometers, but don’t solder them yet! Fit the front panel and make sure that the potentiometer shafts are aligned with the holes in the panel – and that they’re able to rotate freely.
Page 69 The LONG/SHORT switch requires spe- cial attention. Insert the switch in the rele- vant place on the PCB, place the front panel, fix it with few nuts on the potenti- ometer and jack sockets, then fix the switch with its nut (do not overtighten it) and then solder the switch.
Page 70 Congratulations! You have completed the assembly of the mki x es.edu BBD module! It does not need any calibration and, if assembly is correct, it should work straight away. Con- nect it to your eurorack power supply and switch it on. If there’s no "magic smoke”, it’s a good sign that your build was successful.
Page 71: Soldering Appendix
SOLDERING APPENDIX If you’ve never soldered before – or if your skills have become rusty – it’s probably wise to check out some THT (through-hole technology) soldering tutorials on YouTube. The main thing you have to remember while soldering is that melted solder will flow towards higher temperature areas.
Page 72 DIY electronics is a great (and quite addictive) hobby, therefore we highly recommend you invest in good tools. In order to really enjoy soldering, you’ll need: A decent soldering station. Top-of-the-line soldering stations (brands like Weller) will cost 200€ and above, but cheaper alternatives around 50€...
Page 73 A solder suction pump. No matter how refined your soldering skills are, you will make mistakes. So when you’ll inevitably need to de-solder components, you will also need to remove any remaining solder from the solder pads in order to insert new components.

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