Formant synthesizer home built

[Rick Jansen]

If you're interested in some experiences with building a synthesizer,
read on.

I have built/am still building a modular analog synthesizer. It is
the Elektor Formant designed by C. Chapman (an Englishman?), which
was published in 1977/78 in the European electronics magazine
Elektor. In those days I was still a student, and didn't have the
time or money for the project. So I shelved it, till a later date
when I would have both time and money at the same moment. This rare
combination of factors occurred a few months ago, triggering the
project from hibernation.

The Formant is a conventional Moog-style synthesizer, voltage
controlled with a 1V/octave characteristic. It consists of separate
modules mounted in a rack, six in a row, two racks on top of each
other. Each module is a printed circuit board with a front.
The idea was to put these modules in a 19" rack or something home grown.

The Formant was published in a series of articles in Elektor, and
later as a book with a compilation of the articles. A year later
there was a book with additions and extensions by M. Aigner, an
Austrian.

The first book describes the keyboard and interface, power supply,
VCO, VCF, LFO (consists of 3 LFOs), Noise, ADSR, VCA, COM (output
module), RFM (Resonance Filter Module) and a 24dB VCF. Book 2
contains things like Ring Modulator, Envelope Follower, Mixer, Phase
Shifter, ADSR Controller, VC-LFO's, Sample and Hold, and a few more.
I'll briefly describe the modules here, and how building the Formant
went.


The Modules
===========

Keyboard interface
The keyboard is made with double switches, one switching a resistance
ladder, the other the gate signal.
- inputs: frequency modulation
- controls: portamento, octaves coarse and fine

VCO
The VCO generates sine, triangle, square, sawtooth and spaces
sawtooth waves. The pulse width of the square is adjustable, and even
modulatable.
- inputs: frequency modulation, external control voltage, pulse width
modulation. A LED indicates the pulse width.
- dials for octaves coarse and fine, output level, pulse width, pulse
width modulation and frequency modulation.
- Switches to select each waveform (you can have sine and square at
the same time, the signals are simply added together).
- External control voltage/keyboard voltage selector.

VCF
The VCF is a 12dB/octave voltage controlled filter. You can configure
the filter as Low Pass, High Pass, Band Pass or as a notch filter.
Quite versatile really.
- inputs: Timbre Modulation, external control voltage, external
signal.
- dials for timbre modulation, external signal level, envelope,
octaves, Q (resonance) and output level.
- Switches to select HP, BP, LP and Notch filter function.

ADSR
The ADSR generates the envelope signals for the VCA and the VCF.
Normally you will have two ADSRs in a system, one for the VCA, and
the other for the VCF(s).
- dials for Attack, Decay, Sustain and Release.
- switch to select AD or ADSR envelope
- LED indicator showing the envelope

VCA
The VCA has the following controls:
- inputs for amplitude modulation and external signal.
- dials for AM depth, ES level and Gain.
- Switch for ENV/Off (Off means no ENV control).
- LED to view the input signal level.

LFO
The LFO module consists of 3 LFOs. LFO 1 and 2 are identical,
generating square, triangle and sawtooth (/|/|) waves. LFO 3 is
different, in that it generates triangle and two sawtooths, one being
the inverse of the other. ( /|/| and |\|\). Each LFO has a dial for
the frequency, and a LED that shows the triangular wave amplitude.

Noise
The noise module generates white noise, coloured noise and a random
voltage. The 'speed' of the random voltage is adjustable with a dial
and indicated with a LED.

COM
The Control and Output Module outputs the Formant signal, there are
dials for tone control (Bass, Mid, Treble) and Output level. You can
connect a headphone or external amp to this module. (All outputs of
the Formant you can connect a headphone to.)

24dB VCF
Is basically like the VCF, but 24db/oct.
- inputs: Timbre Modulation (TM), ECV, External Signal (ES).
- dials for TM, ES level, Envelope (ENV), Octaves, Q (resonance) and
output level.
- Switch to select HP/LP, a switch to select VCO's/ES.
- A dB/Oct selector: 6, 12, 18, 24 dB/oct.

RFM
The Resonance Filter Module is used to mimic existing instruments
more naturally, or just as some filter. Another name for an RFM is a
'parametric equalizer'. This is not a voltage controlled filter. The
Formant RFM consists of 3 filters in parallel. Each filter has three
dials for f0, Q and A.

A basic Formant consists of 3 VCOs, 1 VCF, 2 ADSRs, 1 LFO, 1 Noise
and a COM. So far I have built 3 VCOs, 1VCF, 1 24dB VCF, 2 ADSRs, 1
VCA, 1 LFO, 1 Noise , 1 COM.


Getting the parts
=================

One of the first difficulties when you're going to build a thing that
was designed 15 years ago is getting the components. Most of the
parts used in the Formant are just common opamps, there are no exotic
custom chips used, like the CEM chips.

There are some (three) key components, that are getting pretty hard
to get these days. The following turned out to be 'difficult':
- The exponential generator that converts the linear control voltages
to an exponential voltage in the VCO was made with a uA726 double
transistor from Fairchild. The uA726 is an ideal part, it contains
both a precise double transistor and an oven which keept the
temperature constant. Thus temperature stability is guaranteed. It
never was a commonly used component anyway, and now it is getting
rare. I have been able to get a few still, thanks Georg :) You could
use a modern double transistor though, like a MAT02. Modern
transistors are far more stable, and it might be you can use one
straight away. I haven't tried though. If I would not have gotten
hold of the uA726 I would have used the MAT02, and built a
temperature controlled heater myself (using a powertransistor as a
heater and a temperature sensor to control it).
- The exponential generator in the other voltage controlled modules
(VCF and VCA) were built with another double transistor, a PNP
transistor array in an ic, the CA3084. I have been able to get 10 of
those still. You could use a MAT03 as a replacement though.
- In the VCOs BC107C and BC177C transistors were used. Very simple
and common transistors you'd say. Well, they aren't. I have not been
able to locate a single BC107C. The A and B types are available
though, but it is explicitly stated that a C type is absolutely
crucial. BC108C or BC109C won't do, as they have too low a voltage
rating. I used BC547C and BC557C instead. Those are very common
transistors these days. No idea why there are no BC107Cs available
any more.
The BC's are used in a comparator, converting a sawtooth to square
and in a sawtooth to triangle converter. (Maybe using the BC5..C's is
the reason the square waves are not *very* sharp, but more or less
rounded off a bit. Not that it matters very much to the sound
though.)

All other components are still easy to get. I ordered opamps from a
mail order company, and the things they didn't have from others. It
is vital to keep a list of companies you already phoned and what you
asked for, to avoid the embarrassment of asking someone the same
thing again a few days later. It happened to me only once. Things I
first wanted to have a look at I went to local electronics shops for.


Upgrading to 'modern' standards
===============================

Not a great lot seems to have happened in analog electronics in the
past 15 years. Nearly all parts common then still are common today,
with the exception of the few mentioned above. I have been able
though to upgrade the design very easily by just using some modern
equivalents:
- 741
I have used TL071C opamps instead of the old 741. If you buy a
hundred they're same price, or lower, than the bl**dy old 741. The
TL071C is a FET opamp with very low noise specs. Ideally suited for a
synthesizer or any other low-noise application, like preamps.
- FETs
In many places FET source followers are used as buffers. In those
days FET opamps were not widely available, and very expensive. The
disadvantage of using a FET source follower is that you have to
select suitable FETs and select a resistor with it. I used the metal
can version of the LF356H instead, which, with some bending of its
legs, will fit beautifully in all places FET source followers are
used. No selection necessary, and no R either.
- Rs
Metal film resistors are almost as cheap as carbon film ones these
days. I simply used metal film resistors just everywhere. The
advantage of metal film Rs is that they are low-noise and more
stable. In some places 1% resistors are used, but they were as easy
to get as the normal (10%) ones.


Printed circuit boards
======================

For all modules Elektor published PCB layouts. Back then you could
then also buy the prints from them. Elektor only has prints a limited
period of time, but I found a company that still has the films, and
can produce the PCBs for you. All modules, except the VCO, are
eurocards. The VCO is a double eurocard. Price of the VCO board is
Dfl 61,-, which is ca US$ 30,- if I count two Dfl's to the dollar.
The eurocards cost ca US$ 12,- each. The PCB layout is also in the
book, so you could etch and drill the prints yourself, but I thought
that far too much hassle, and environmentally unfriendly.


Keyboard and housing
====================

Building a synthesizer is not simply soldering parts onto printed
circuit boards. The total effort involved is more than *twenty* times
the effort of the plain soldering. Most of this effort and
frustration is invested in mechanical things like the keyboard and
the housing.

The keyboard is just a plain electronic-organ keyboard. There is a
double switch for each key, and those switches have to close
simultaneously. Such switches are made by a company called Kimber-
Allen in England. The mechanical interface between key and switch is
a *lot* of work. The original idea was that under each key there is a
T-shaped piece of plastic that will close the two switches at the
same time. I have not been able to get a keyboard with those T-shaped
'pushers'. My keyboard just had a piece of plastic, with two hooks in
it, as used in electronic organs. I had to find my own solution, so
for each switch I drilled two tiny holes in the piece of plastic
attached to the key. I have a 5 octave keyboard, with 61 keys, so I
had a marvellous weekend.

The housing of the Formant turned out to be an awful lot of work too,
and very costly as well. The Formant consists of eurocards and double
eurocards. All pictures in the book get the idea across that
everything fits neatly in a 19" rack, six modules in a row. The truth
is not so simple. The pictures show a 19" rack, divided in 6HE and
3HE. The modules with the bigger fronts, like VCO and VCF are in the
lower part, the smaller modules in the upper 3HE part. And here
things go wrong. The VCO is a double eurocard, but the VCF is a
single eurocard. A double eurocard does *not* fit in a 6HE 19" rack.
As you see, this is a complete mess, you cannot put VCO and VCF
prints in rails in a standard 19" 6HE rack. I ended up with extra alu
profiles, and mounting the eurocard on a piece of aluminium the size
of a double eurocard.
Add to this that my pcb manufacturer did not cut the epoxy material
really very precisely the 10 centimeter width of a eurocard, but a
few millimeters extra, that I had to grind off using sandpaper. Of
course I only found out after having already soldered all components
in place. I have called the good man some very bad names.

The fronts of the modules have given me headaches. Elektor has given
a design for them, too. You can copy those on 0.5 mm thick adhesive
photosensitive aluminium, as made by 3M. My pcb-making company could
also do that for me. What fun, as the fronts turned out to be some 5
millimeters larger than 6HE. Also, the markers for the drill-holes on
the fronts do not match the spacing of a 19" rack at all. So, I ended
up with fronts with screws in the corners, and the marks very
visible. Furthermore the result was quite fuzzy, the lines and
figures being far from sharp. I guess during the years the films got
scratched, and so my fronts also looked rather scratched. Another
things is that I use knobs for the dials with a plexiglass clear
disk. In the original design the figures are then obscured by the
plexiglass disc, making them unreadable. You can see them, but as the
clear plexiglass disc is curved its more like looking through a lens.
Awful.

Thus I was not pleased with the fronts at all, and designed new ones
myself on a Macintosh. My idea was to print them on film with a 600
dpi printer and use the same 3M alu front stuff. Alas, the printing
would cost me US$ 10 per A4 (two big fronts or 4 small ones). Plus
US$ 15 per A4 sheet 3M alu foil. I thought that a bit steep. And then
having to process it all... nah. I printed my designs onto overhead
sheets, which I simply glue onto a piece of aluminium with
transparent 2-component glue. Looks great!

Oh, I haven't mentioned yet that you need to drill a *lot* of holes
in the alu fronts for potentiometers, connectors, switches, LEDs and
the lot, have I? Well, you have to drill a lot of holes in the alu
fronts for potentiometers, connectors, switches, LEDs and the lot.
About a hundred holes in total. And you think drilling holes in 1.5
mm aluminium is easy? Very funny. It is not. The holes for switches
and 3.5 connectors are still easy, but the bigger (ca. 10mm) holes
for potmeters are a pain. You cannot simply drill those, for you will
end up with a triangular hole. Instead, you have to use a conical
drilling tool that I don't know the english word for now, but I'd
call it a 'widener' :-)

Next fun thing is, you have to connect the prints and potmeters and
switches and all with pieces of wire. Many hundreds in total, each of
which I neatly soldered and protected with the insulating shrinking
stuff the English word for which eludes me right now. It is all a lot
of work. Especially as not all directions from the book are clear. I
ended up with quite a few potmeters connected in reverse, so you'd
turn up something and it would in fact go down. Very confusing if you
don't know what you're doing.


Calibrating procedures
======================

An analog synthesizer has to be adjusted and calibrated. And again,
this is a lot of work. Plus, you need to know what you are doing. Now
I'm an electro engineer, but I work as a systems programmer so I
don't have much experience in the field of practical electronics,
which I was never very good at at all in the first place. (I still
remember nightmare of the electronics lab where we had to make a
simple single transistor work as an emitter follower or something as
simple as that, and nothing seemed to work. Least of all the
oscilloscope, that had about as many dials and trigger options as my
synthesizer has now, which would show nothing but an oscillating
emitter follower. Aaaaargh!) Well anyway, not all directions and
procedures are very clear, and you have to fill in a lot
yourself.JSometimes directions are open for more than one
interpretation even. You definately need an oscilloscope and a
digital volt meter for the final adjustment of the VCOs.


Cost
====

*important note*
If you think that building a synthesizer yourself is a cheap way of
getting a synthesizer, here is what you must do: forget it.

The Formant has cost me a *lot* of money. I could have bought, for
example, a Waldorf microWave plus an Atari, or maybe even a Macintosh
LC. But, no regrets. There's no such thing as twiddling your own
knobs (no pun intended here) and knowing the ins and outs of your
synthesizer.

Most expensive single items are the 19" racks. The rest is not very
expensive per se, only you need a lot of things. A potmeter and a
knob aren't very deer, but if you need a hundred it all adds up to
quite an amount. Same goes for the switches (also about 50), and 3.5
mm connectors. Also you need tools. I bought an electric drill,
drills (amazing!), saws, what not.

In total, very roughly speaking, the Formant has cost me about US$
2500,-. (Including tools and parts already bought for future use.)


Time
====

I had time off from work last year for 5 weeks in a row in the
autumn, time I had to take off or lose it. Being rather fed up with
work on our Visualization Center (computer animations of scientific
data, video equipment and the lot) I decided to take it :-) It cost
me a full week to get more or less all the most important parts. I
spent much of the remaining 4 weeks fulltime putting it all together.
Planning is vital here, nothing is more frustrating than not having
bought just one silly tiny resistor. So, if you have to build a
Formant just in the evenings and weekend, be prepared to work on it
some time.


Playing it
==========

Well, after spending so much time and money I found out what I knew
before. I can play with it, but not really play it very well yet.
I've had music lessons as a kid, and even learned how to play a
recorder. The wooden type, not the tape type. I never learned to play
a keyboard. Only a few weeks ago I found out how to play scales. Not
that it matters much, I'll interface it to midi and a computer one
day and be my own Kraftwerk. Or I could practise and learn how to
play, really. I'm definately having fun with it anyway.

I already have been able to reproduce some sounds Tomita used on
Pictures at an Exhibition, I know how to do the Popcorn sound, and I
have found how to make the thin high-pitched sound in the background
of Kraftwerk's Spacelab, and how to do the deng-deng-deng-deng-... of
old Radioactivity. Wow.


Who can build a Formant?
========================

Building a machine like this is not something to undertake lightly.
It costs a lot of money, it takes a lot of time, and requires a lot
of mechanical skills and not least some insight in electronics. An
analog synthesizer has to be adjusted and calibrated. And again, this
is a lot of work. Plus, you need to know what you are doing. Well
anyway, not all directions and procedures are very clear, and you
have to fill in a lot yourself.JSometimes directions are open for
more than one interpretation even. You definately need an
oscilloscope and a digital volt meter for the final adjustment of the
VCOs.

I have been lucky that I haven't made many errors while soldering the
boards, but I have made some. Those can be a big puzzle, and you
*will* have to solve them.

If you have never built anything electronic before: don't do it.
If you don't have the money: don't do it.
If you don't have *plenty* of time: don't do it.
If you don't have the mechanical tools: get them first.
If you have neighbours who don't like synthesizer sounds: get rid of
them first, or buy a pair of headphones.


Future
======

Well, there still are new modules to build and play with, like the
extensions from book 2 (ring modulator etc). I want a sequencer, the
simple analog type with just a few potmeter dials for pitch and
duration. I will design and build it myself, its rather an easy thing
really.


Rick Jansen
e-mail: ri...@sara.nl

Amsterdam, February 1993

--
ri...@sara.nl

"She's a Module and she's looking good"