Evaton technologies SDIY MDRONE Manuel utilisateur

Introduction

Thanks for purchasing the SDIY1MDRONE kit from Evaton Technologies! The

SDIY MDRONE kit is a battery-powered standalone tabletop drone synth that

can be built in just a few evenings. The SDIY MDRONE kit is available as just

parts and PCB (build your own case), or as a complete parts + PCB + pre-drilled

enclosure, for those who wish to get up and running right away2.

The SDIY MDRONE voice architecture consists of three independent square-

wave oscillators, which are mixed in a ﬁxed summing mixer. The mixer output

is then fed to a semi-resonant bandpass ﬁlter, with adjustable center frequency

and bandwidth. A “Grit” setting allows overdriving the ﬁlter for dirtying-up the

sound and making a more hard-hitting timbre.

Output is a 1/4” mono (TS) line-level audio jack.

Skill Level

The SDIY MDRONE kit, while not necessarily aimed at the complete novice,

can be built by anyone with some soldering experience. All components are

standard, readily-available thru-hole components. The spacing of the

components on the circuit board is generous, so that no special tools are

required to install. These instructions assume you already know how to solder,

and cut and strip wires.

Precautions

Soldering irons are HOT! Be careful not to touch the business end of your

soldering iron at any time. Also note that components that have been soldered

will remain hot for a few moments. If you need to hold something to solder it, it

is recommended NOT to use your ﬁngers. Wear long pants and long sleeves to

avoid solder splash from burning exposed skin.

1Synthesizer Do-It-Yourself

2If you purchased this kit as a complete parts + PCB + enclosure kit, additional instructions for the

enclosure will be included in your shipment.

SDIY MDRONE

Assembly Manual

Revision A - Parts & PCB Kit

200 School St

Pittsburgh, PA 15220-2718

http://www.evatontechnologies.com/

Tools Required

A few basic electronic assembly tools are needed to complete the assembly

of the circuit board. If you are building your own case, some additional tools

are required to drill holes.

Tools Required - PCB assembly:

•Soldering iron. Minimum 25 watt pencil iron; preferred temperature-

controlled, but not necessary.

•Small wire cutter

•Wire stripper

•Electronic solder. 60/40 lead/tin or 63/37 lead/tin, or lead-free. Use rosin-

core solder. Do NOT use acid-core3(plumbing) solder!

•Pair of needle nose pliers (optional) for bending leads and holding

components

•Small bench vise or “helping hands” (optional) for holding the PCB.

•Small adjustable wrench or 10mm deep-well socket, for tightening

potentiometer nuts

•9/32” open-end wrench for tightening toggle switch nuts

•De-soldering braid (optional) for cleaning up mistakes

•Multimeter with ohms and volts setting. Not a necessity, but handy for testing.

Tools Required - Case assembly:

•Phillips screwdriver

•If building your own case, a 9/32”, 13/64”, and 3/8” drills are required, to

drill holes for the potentiometers, toggle switches, and output jack.

Also Required:

•9V battery. Alkaline preferred, but heavy-duty is ﬁne, too. A properly

constructed SDIY MDRONE will run many hours on a single battery.

•1/4” mono patch cord (TS)

Page 2

3Acidcore music is great. Acid core solder is not.

200 School St

Pittsburgh, PA 15220-2718

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Signal Flow

The SDIY MDRONE consists of three square wave generators that feed a

summing mixer. Each oscillator can be turned on and o!with a switch. Each

oscillator’s frequency can be controlled by a front panel knob. The output of

the summing mixer feeds a bandpass ﬁlter. The ﬁlter bandwidth and center

frequency can be controlled with front panel knobs.

Circuit Theory

While it is not necessary to completely understand exactly how the circuits in

the SDIY MDRONE work, a top-level description of the theory is presented here,

for those who’d like to get a little more acquainted with electronics. Please see

the included schematic diagram to follow along4. The schematic is divided up

into a few logical sections: The oscillators, the summing mixer, the virtual

ground reference, and the bandpass ﬁlter.

Oscillators

The three oscillators are the type known as a “relaxation oscillator.” In a

relaxation oscillator, a capacitor is slowly charged up from zero volts until the

voltage across the capacitor passes a certain threshold, at which time, the

circuit begins to discharge the capacitor. Once the capacitor voltage falls below

Page 3

4Or skip ahead to the next section; there won’t be an exam on this material!

200 School St

Pittsburgh, PA 15220-2718

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a certain voltage, the circuit again begins charging the capacitor. The charge

and discharge rate is determined by the resistance of the control knob on the

front panel.

If we look at the schematic, OSC 1 is formed by the capacitor C6, resistor

R17, and variable resistor (potentiometer) R16, and is controlled by the 40106

Schmitt Trigger chip. A Schmitt trigger circuit outputs zero volts when the input

is above a certain voltage. It outputs 9 volts when the input is below a certain

voltage. So, looking at the voltage on C6, it starts at zero volts, so the output of

IC1A is 9 volts. That 9 volts gets fed back onto C6, and it starts to charge.

Once C6’s voltage gets high enough, IC1A switches its output from 9 volts

to zero volts. C6 now begins to discharge. This repeats over and over again,

making an oscillation!

IC1B takes this rising and falling voltage and turns it into an on/o!signal (a

square wave!). Adjusting R16 (the front panel knob) adjusts how quickly C6

charges and discharges, thus setting the frequency.

OSC 2 and OSC 3 work the same way.

Summing Mixer

U1A is an operational ampliﬁer (op-amp). It adds together the three signals

coming through R2, R4, and R18. An op-amp connected in this conﬁguration is

called a Summing Ampliﬁer.

Virtual Ground Source

R5, R6, and U1D form a bu!ered voltage divider. 9 volts goes through R5

and R6 to ground. Because R5 and R5 are equal in value, the voltage at pin 12

on U1D is exactly half that voltage, or 4.5 volts. U1D is conﬁgured as a “unity

gain follower,” meaning that the output at pin 14 is exactly the same voltage as

the input on pin 12, but it can drive a bigger load without the voltage being

a!ected.

The “virtual ground” of 4.5 volts is required because the SDIY MDRONE

operates from a single 9V supply. Most op-amp circuits require a positive

voltage supply and a negative voltage supply to operate. We can “fake out” the

op-amps by creating this “virtual ground” that is exactly half the battery

voltage, and then pretend that the 0 volts terminal of the battery is actually

“negative 4.5 volts with respect to virtual ground”. Then the +9V terminal of the

battery is “positive 4.5 volts with respect to virtual ground.”

Page 4

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Bandpass Filter

The bandpass ﬁlter is an active ﬁlter that uses two op-amps and capacitors

and resistors to ﬁlter out signals that are outside of its “pass band”.

Frequencies of sound that are below the ﬁlter’s pass band are removed, and

frequencies that are higher than the pass band are also removed, but

frequencies that fall inside the pass band are passed through to the output. The

width of the pass band (the di!erence between the highest frequency that can

pass and the lowest frequency that can pass) is called the ﬁlter bandwidth.

The frequency that falls exactly halfway between the lowest frequency that

can pass and the highest frequency that can pass is called the center frequency

of the ﬁlter, or FC. R23 adjusts the bandwidth of the ﬁlter, and R13 adjusts the

FC.

While this is a very basic description of the ﬁlter operation, a more thorough

description of how the ﬁlter does this is beyond the scope of this manual.

Further reading is suggested if you want to gain a better understanding of op-

amp ﬁlters5.

Kit Contents

•A bare printed circuit board (PCB) and 18-foot (6m) spool of wire

•2x 0.01 µF 16V capacitors

•3x 0.1 µF 16V capacitors

•3x 1.0 µF 16V capacitors

•1x 470Ωresistor

•2x 1.1kΩresistor

•4x 4.7kΩresistors

•9x 10.0kΩresistors

•1x 47kΩresistor

•4x 100kΩlinear potentiometers

•1x 100kΩaudio potentiomer (Frequency Pot)

•1x 5kΩaudio potentiometer (Volume Pot)

•2x 14-pin DIP IC sockets

•1x LM324 op-amp IC

•1x CD40106 Hex Schmitt Trigger IC

•5x DPDT switches

•9V battery snap and battery holder

•1/4” mono audio output jack

Page 5

5While there are many good books on the subject, an internet search of “active ﬁlter design” will also

yield some very useful datasheets and application notes from various op-amp vendors that are quite

thorough. The ﬁlter in the MDRONE is a dual-ampliﬁer passband design.

200 School St

Pittsburgh, PA 15220-2718

http://www.evatontechnologies.com/

Assembly Instructions

Note On Assembly Of Front Panel Components

While most of the components on the SDIY MDRONE get soldered directly to

the PCB, the front panel components are ﬁrst soldered to wires, and then the

wires are soldered to the board. Leave long enough wires to allow easy

assembly at the end. While assembling the PCB, it’s best to just solder the front

panel components to long leads (6 to 8 inches), and leave them laying beside

the board. Don’t attempt to install the front panel components into the front

panel until the board is completely assembled.

Preparation

To begin assembly, clear a space on your workbench6. It helps to have good

lighting, and your tools located where they can be easily reached. Plug in your

soldering iron and let it come up to temperature. It helps to have a dampened

sponge nearby, to wipe the solder tip on to keep it clean. Place the bare circuit

board in the middle of your work area, with the white silkscreen legend facing

you.

The next few paragraphs will go step-by-step through the process of

assembling the circuit board. You may wish to check these steps o!as you go,

to keep track of your place.

____ Sockets

First, install the two IC sockets in the locations U1 and U2 on the PCB. There

is a notch at one end of the socket. Line up the notch in the socket with the

notch in the white component outline on the board.

To install the socket, place the socket in the holes on the board for the

socket, and make sure the socket is ﬂat against the board all the way around.

You can use a piece of clear tape to hold the socket in place while you solder

the pins. Remove the tape after soldering.

____ Virtual Ground Resistor Divider

Install two of the 10kΩresistors (brown/black/orange) into locations R5 and

R6 on the board. Carefully bend the leads of the resistors so that they ﬁt

through the two holes in the board at the ends of the component outline. Bend

the leads slightly on the back side of the PCB to hold the resistors in place, and

Page 6

6Hey, that’s my ﬁrst step. My bench is always a complete mess!

200 School St

Pittsburgh, PA 15220-2718

http://www.evatontechnologies.com/

solder the resistors in place. When you are sure you’ve made a good solder

joint on all four pads, cut the excess leads o!.

____ 9V Battery Snap

The 9V battery snap comes with pre-stripped leads. The red lead is the

positive lead, and the black lead is the negative. Solder the black lead to the

hole marked P8 on the PCB. Solder the red lead to the hole marked P7.

____ Power Switch

Get one of the toggle switches out, and solder a 6-

inch wire to one of the center pins. It doesn’t matter

which center pin. Solder another 6-inch wire to

another pin on the same side of the switch. Although

the kit ships with DPDT7switches, we will be using

them as if they were SPST8switches. The switch is

“ON” when the toggle lever is pointing away from the

pair of pins you’ve soldered to.

Now solder the other end of one of those wires to

the hole marked P6 on the PCB. Solder the other wire

to the hole marked P5 on the circuit board.

____ Test Power-Up

At this point, we can perform a simple test of the circuit board, if you have a

multimeter with OHMS and VOLTS settings. First, we’ll check that there is not a

power-to-ground short circuit. Set your meter to the OHMS (Ω) setting.

Put one meter probe on

one contact of the 9V

battery snap, and put the

other probe on the other

contact of the 9V battery

snap. The meter should

read an inﬁnite number of

ohms (open-circuit). If not,

go back and check your

solder joints.

Page 7

7Double-Pole-Double-Throw

8Single-Pole-Single-Throw

200 School St

Pittsburgh, PA 15220-2718

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Now, ﬂip the power switch. The meter should still read inﬁnite resistance

(open-circuit).

Next, change your multimeter to the VOLTS

setting. If it is a manual-range meter, make

sure it is set up to read at least 9 volts full

scale. Many meters will have a 0-20V setting.

Put the positive (red) probe of the

multimeter on the positive (smaller) terminal of

your 9V battery. Put the negative (black) probe

on the negative (larger) terminal of the 9V

battery. The multimeter should read

somewhere between 9 and 10 volts.

Congratulations! Your battery is good!

Now, for our ﬁrst functional test of the board. Plug

the battery into the 9V snap. Touch the negative

probe of the multimeter to pin 7 of the socket in

U2. Touch the positive probe to the lead of R6 that

is nearest the edge of the PCB. Turn the power

switch ON. The multimeter should read 9 volts.

Now, with the negative lead of the multimeter still

touching pin 7 of the U2 socket, touch the positive

probe to the other end of R6. The meter should

read approximately 4.5 volts. If not, unplug the

battery, and go back and check your work. If

everything worked out, turn o!the power switch,

and unplug the battery from the 9V snap before

continuing assembly.

____ 0.1 µF Bypass Capacitors

Now, install the three 0.1 µF bypass capacitors into C3, C4, and C5 locations

and solder into place. It does not matter which direction these three capacitors

are installed. After soldering, trim the leads. You may wish to repeat the Test

Power-Up section again after installing these three capacitors, just to verify

there are no short-circuits.

Page 8

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____ 10kΩResistors

Install the remaining 10kΩresistors into locations R2, R4, R7, R8, R10, R18,

and R22.

____ 1.1kΩResistor

Install a 1.1kΩresistor in location R14. There will be another 1.1kΩresistor

left over; we’ll talk about this a little later.

____ 4.7kΩResistors

Install 4.7kΩresistors into locations R3, R17, and R19. There will be one

4.7kΩresistor left over; we’ll talk about this a little later.

____ 47kΩResistor

Install the 47kΩresistor into location R9.

____ 470ΩResistor

Install the 470Ωresistor into location R24.

____ 0.01 µF (10,000 pF) Capacitors

Install the 10,000 pF capacitors into locations C2 and C8. It does not matter

which way you install them.

____ 1.0 µF Capacitors

The 1.0µF capacitors are polarized electrolytic capacitors. These are the

timing capacitors for the three oscillators. Because they are polarized, you must

pay attention to which direction you install them. The capacitor has a gray

stripe on one side. The lead next to this stripe is the negative lead. The other

lead is the positive lead. Make sure the positive lead (the lead opposite the gray

stripe) is installed in the hole marked with a plus sign (+) on the board. Install

the 1.0 µF capacitors in locations C1, C7, and C6. You may have to bend C6 just

slightly in order to clear the chip socket.

___ Take a break!

At this point, nearly all the thru-hole components have been soldered to the

board. Only a 4.7k resistor and a 1.1k resistor remain. The rest of the

Page 9

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components are front-panel components. Take a break for a moment9, and re-

check your solder joints; make sure all the components you installed so far

have good joints.

And Now, A Few Words About Potentiometers

The next steps of assembling your SDIY MDRONE involve wiring up the

front-panel components. As mentioned earlier, it’s best to wire the front panel

components, and lay them out beside the board, rather than attempting to

mount the front panel components ﬁrst and then wiring.

There are six potentiometers included with the kit. Four of them are 100kΩ

linear potentiometers, one is a 100k audio-taper pot, and one is a 5kΩaudio-

taper potentiometer.

The PCB outline for the potentiometers has three numbered pads. These

correspond to the three legs of the potentiometers, as labelled in the photo on

the left. Wire pin 1 to the leftmost pin, pin 2 to the center, and pin 3 to the

rightmost pin on the potentiometer. If your knobs seem to turn backwards of

what you expect, reverse pins 1 and 3. (This may be the case for the Bandwidth

knob -- if you prefer to think of it as a Resonance knob, you may wish to

reverse pins 1 and 3).

Page 10

9It was at this very moment that I also took a break from writing this assembly manual. Whew!

200 School St

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http://www.evatontechnologies.com/

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