The Formant in it's cabinet

If you're interested in some experiences with home-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 The Netherlands called Elektuur). 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 in October '92, 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, which I mounted in a rack. Each module is a printed circuit board with a front.

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.


The VCO generates sine, triangle, square, sawtooth and spaced sawtooth waves. The pulse width of the square is adjustable, and even modulatable (PWM).

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. 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).

The VCA has the following controls:

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.

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.

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.

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.

Basic Formant

A basic Formant consists of 3 VCOs, 1 VCF, 2 ADSRs, 1 LFO, 1 Noise and a COM. So far I have built 6 VCOs, 2 VCFs, 2 24dB VCFs, 4 ADSRs, 2 VCAs, 2 LFO, 1 Noise, 1 COM, 1 RFM, 1 Sample&Hold, 1 Ringmodulator, 4 ADSR Controllers and 2 Mixers.

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':

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:

Printed circuit boards

For all modules Elektor published PCB layouts. Back then you could 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.

The prints from book 2 were never published in Elektor, but they are printed in book 2 of course. I had the company mentioned above just take them from the book.

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 in the book 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, nor does a single eurocard. 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 both eurocards and double eurocards on a piece of aluminium as to fit in a 6HE rack. Add to this that my pcb manufacturer did not cut the epoxy material really very precisely the 10 centimeter width of a eurocard (3HE), 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. (Image flipped, with the toner on the inside of course.) 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 3.5mm 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 exactly what you're doing. You'll learn though.

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 nightmares of the electronics lab where we had to make a simple single transistor work as an emitter follower or something as like 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. Sometimes directions are open for more than one interpretation even. You definitely need an oscilloscope, frequency counter and a digital volt meter for the final adjustment of the VCOs.


*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. Nothing beats 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.)


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 our management after 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 definitely 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.

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. Sometimes directions are open for more than one interpretation even. You definitely 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. (Note the error in the ringmodulator print, where pin 2 and 3 of the ringmodulator ic aren't connected.)


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.

Book 2

The past future has now begun. I have now built some modules from book 2: sample&hold, ringmodulator, ADSR controller and a ring modulator.

Ring modulator

The ring modulator module contains a ring modulator and an envelope follower, which is also a sensitive input to connect a microphone. Book 2 contains a eurocard format ring modulator print. The same circuit was published in book 1, but not as a eurocard. After soldering all the parts and assembling the module... it didn't work. After a few hours of happily (ahem!) bug-searching it appeared pin 2 and 3 of the ringmodulator ic erroneously weren't connected on the print. A little piece of wire and a blob of solder fixed this.


The Sample&Hold is fun! Simply connect a few slow LFO signals and control a VCO with the result, and it plays silly little melodies. Or use the (slow) random voltage from the Noise module to control it. The S&H has two inputs (Sample and Trigger) and one output. A dial sets the trigger level. There is a C at the sample input. To be able to use slow LFO signals you should omit this C and put in a wire instead. No need for AC coupling. This is a bug, in my opinion.


The mixer is a 6-input mixer. One of the inputs has a high sensitivity, to connect a microphone or other external signal to the Formant. The inputs are AC coupled with a rather big capacitor (680nF). You better leave this C out, i.e. mount a piece of wire instead, else slow LFO signals don't work. It works fine without anyway. Rather nice to construct complex control signals from the LFOs.

ADSR Controller

Normally the gate signal directly drives the ADSR module(s). If you want to hook up a sequencer or an LFO instead there now is a way to do it: with the ADSR Controller. The ADSR Controller lets you select an external gate signal. Also it allows keyboard repeat, i.e. the external gate signal is only fed through if a key is pressed. Another feature is Delay. A dial for Delay lets you delay a gate signal from 0 to 5 seconds.

There is a bug in the circuit. Keyboard repeat doesn't work, unless you change R21 from 10k to 22k.

Some more pictures:

Close-up of the fronts


Front layout

Rick Jansen,