Helmuth Tünker wrote several books on building organs, sound effects, rhythm machines and synthesizers. The second part of his book ‘Electronic pianos and synthesizers’ is about building a synthesizer with easy (obtainable) components. Including wiring schemes and PCB layouts that can be cloned onto experimentation board. The book I have was published by Dutch ‘Kluwer Electronica bibliotheek’ but there is an original German book, also it has been published in Italy and, maybe, more countries. Until now we were not able to find an English version or digital English version, so we scanned our Dutch book, OCR’d and asked Google to translate it for us.
Below you will find the translated text of Part 2 of the book (starting with Chapter 3 – The Synthesizer). Images of the single pages (Dutch version, including all schematics, layouts and component lists) and we also included a pdf (Dutch version) with all these pages. We hope to improve this work by creating a post with the schematics and figures at the right places. Maybe you can be of help? Also we are looking for people that have build (parts of) this synthesizer or have pictures for us.
There are probably no music lovers today who have never admired the sound of a synthesizer. Musically interested technicians and experimental musicians often have a great interest in this completely different instrument. Larger synthesizers are not musical instruments in the usual sense of the word. In studios they are used exclusively for producing musical effects. The playing technique is fundamentally different from that of electronic organs. The extensive recordings of synthetic sound images are usually created via an in-dub system. Every effect and every sound combination is carefully tested in advance and built into the planned composition. A synthesizer for studio applications is therefore never “played singly”. The versatility of the synthesizer demands a lot of “feel” and gives pleasure when experimenting yourself. Despite these properties, the synthesizer is still an instrument for the musical “enjoyer”. However, constructions that have been put together in an ingenious way can contain different units, which are ready to play with just a few handles, just like with a sound organ. Such instruments are ideal for use in orchestras, etc. For the do-it-yourselfer, the synthesizer offers a wide range of new combination possibilities. It is not important whether the new effect is already known or not. Anything that sounds nice is allowed! One can start with a few inexpensive units and expand the instrument according to one’s musical taste.
3.1. Sound synthesis – Synthetic sound
At first glance, the concepts of “sound synthesis” and “synthetic sound” seem closely related. However, confusing the terms often gives a completely wrong picture of the musical possibilities of the synthesizer. We will therefore explain the concepts in a simple way.
Sound synthesis is the joining of different partial tones into a harmonic sound. Harmony only exists when the 72 mixed tones are in a fixed frequency ratio to each other. A typical example of sound synthesis is the sound control possibility with “drawbars” of an electronic “sine organ”. One foot measure sounds very calm, since the sine tones have no overtones. However, the drawbars are such that you can set the desired sound combinations yourself. This can be clearly observed with the aid of an oscilloscope. For example, set the following amplitudes: 16′ = 100%, 8′ = 50%, 51/3′ = 331/3%, 4′ = 25%, 22// = 162/3%, 2′ = 12ó% and 1′ = 6.%. The result is a sawtooth vibration! Sound synthesis is that simple. However, the well-known hammond sound can also be traced back to other factors such as a little cross modulation, vibrato using the scanner (mechanical method of generating vibrato), etc. Those who want such an instrument that can be played polyphonically will need a large electronic organ with many effects.
With synthetic sounds it is possible to express oneself musically, in a way that usually cannot be realized with traditional instruments. This is the specific field of larger synthesizers . Of course, all known sound colors can also be generated with these extensive devices. However, their main job is to produce very special effects. Such an instrument, however, can only be played monophonically, but with polyphonic playing technique, since it would not be possible to use voltage control when using a polyphonic generator set. For an electronic organ, the different footprints are therefore only put together behind the generator set . Synthesizers again open up enormous possibilities for combining the different units. Generators can drive other generators, affect the waveform, etc. To make this clear, the main stages of a synthesizer are described below.
Fig. 3-1 shows a block circuit of a synthesizer. The international designations have been deliberately used here, because in this way the interested reader can also find his way in foreign publications .
Control panel (control board)
We only find a series of registers on small synthesizers, which often resemble a sound organ. Larger synthesizers contain mutually independent units with their own faceplate. All connections are made with cables of different lengths. Keyboard (keyboard control) An important playing aid is a normal keyboard , which, unlike an organ keyboard, supplies control voltages in linear order. The exponential gradient is obtained using the function generator. For enveloping effects and driving filters, this voltage can be reversed (inverted). Often several, independent control options are available.
Tape manual ( ribbon control)
A tape manual in its simplest form consists of a resistance wire, which is connected between plus and minus. The “playing electrode” is connected to an adder circuit. Modern constructions also contain a resistance track of conductive rubber, over which a gold-plated band is attached. This strap is insulated against contact and gives the desired tension (also sliding) when pressed in a certain place. XV controller (joystick control) This is a control unit very similar to the joystick used in multi -channel remote control (model making). This interesting control option is particularly valuable for “fast” effects in an orchestra. Foot swelling ( swell shoe control) Normally the foot swelling acts to influence the amplitude. However, with the aid of a potentiometer, it can also supply the required control voltages. There are versions with a logarithmic, exponential, hyperbolic or linear progression.
Addition circuit ( summer )
Adding circuits linearly add up the voltage components of different voltage sources, allowing simultaneous control by several playing aids or generators. There are also pulse adders . Both versions are used.
Reversing stage ( inverter )
Simple transistor stages can generally be used to invert certain control functions and pulses. Larger synthesizers also have switchable amplifiers. With the help of a handle you can choose between inverting and non-inverting.
Function generator ( exponential function generator)
When a linear voltage change is applied to the input, a voltage with exponential variation is produced at the output, which can be used for various purposes.
Key Memory (sample and hold ).
The key memory is controlled by pulses from the keyboard. A played tone also remains when the key is released . It only disappears when another key is pressed. Usually it is also possible to make the tone shift over longer intervals .
Control generator (voltage controlled oscillator)
The voltage controlled oscillators (VCO) are such that the frequency changes linearly with the applied direct (control) voltage. With ” tempered ” playable instruments, a function generator must be interposed . Smaller synthesizers should have at least three of these control generators. In studio versions, depending on the price, a large number of VCOs in different versions are built in.
Sawtooth former (ramp function generator)
A circuit with which exponentially varying voltages can be made linear.
Triangle shaper ( triangle function generator)
This unit forms a triangle waveform from the generated sawtooth voltage, which is mainly used for control purposes.
Square wave shaper (square wave function generator)
Usually a Schmitt trigger is used for this; however, real limiter circuits are also found. pulse shaper ( pulse function generator) A trigger circuit is usually used for impulse formation, followed by a monostable multivibrator . The pulse ratio is adjustable within wide limits. 76 Sine wave function generator An amplifier with a diode network in the negative feedback circuit. A delta voltage is required for control.
Generator ( pulse control)
A pulse is derived from the ever-changing keyboard control voltage with each keystroke and reshaped to control key memory and other stages. Threshold switch (trigger) The Schmitt trigger is well known. It extracts pulses with a precisely defined amplitude from the desired frequencies and waveforms. Retarder (timer) A monostable multivibrator , which is started by the keyboard or by separate keys. For example, after the selected time has elapsed, an envelope control can be started.
Contour generator (wave form generator)
With this circuit, the control voltages for the envelope modulator are generated. The vertical edges of the square wave signal are adjustable. Envelope modulator (voltage controlled amplifier) This unit allows amplitude modulation of the sound signal. The modulator is controlled by the contour generator. A VCA with an adder at the input can also be influenced by other stages, such as VCO, program generator, etc.
Voltage controlled filter (voltage controlled filter)
Depending on their construction , VCFs are high- pass , low-pass or band-pass filters. The filter frequency can be shifted by means of a control voltage. With some filters, the quality factor (Q) can also be changed.
Resonance filters (filter unit)
Passive filters are usually grouped together in large groups as a T or 1r filter . With the described VCF, they are not used for synthesis, but rather for an analysis of the already composed signal.
Ring modulator (ring bridge modulator)
An interesting modulation circuit, which comes from carrier technology. The circuit is usually built with shell core transformers and four diodes (bridge circuit).
Balance modulator ( balanced mixer)
This name is used for various parts. In the simplest case, a differential amplifier for modulation purposes is intended. However, the same name is used for ” transformerless ” ring modulators, which have recently been built with integrated circuits.
Programmable divider (flip-flop unit)
Frequency divider with adjustable frequency division. At least a quadruple binary counter with decoder is built in. This unit allows simple program control and optionally also the multi -choir sound structure of a sound organ.
Program generator ( sequencer )
A particularly versatile unit for automatic extinction effects. The circuit consists of several programmable dividers. The output voltages are combined into voltage jumps with an adjustable sequence via adder circuits.
Electronic tuning fork (440 cps unit)
A particularly important unit of larger synthesizers. Due to the many control options of the synthesizer, the voice tension changes with every new program combination. With the help of the “tuning fork” a very fast correction is possible. In connection with this we point out another peculiarity of the synthesizer. The stability of the oscillators is usually very reliable. However, when a large number of units are connected to the control voltage, the large time constant becomes smaller. However (unlike the electronic organ) this is something that people are happy to accept, since the large number of possibilities is more important.
Noise generator ( white noise generator)
White noise is used in electronic percussion devices to simulate cymbals, cymbals, etc. The VCA allows identical effects in the synthesizer. Noise filter ( colored noise filter) A circuit roughly equivalent to the ” cowtail control ” in some amplifiers. Allows the formation of “colored” noise (red and blue).
Low-pass noise filter ( very low frequency noise filter)
With this switchable filter, the murmur of the wind can be simulated from whisper soft to gale force. The amplitude control takes place via a VCA. Reverberation unit Artificial reverberation is also common in other electronic musical instruments . Suspension systems with driver stage and preamp are usually used.
Mixing unit (audio mixer)
Multiple mixer amplifiers are common in larger instruments. They serve to mix the different sound frequencies and noise voltages. An external signal can also be added in this way.
Mains part (power supply )
Very high demands are placed on the power supply of large synthesizers in terms of constancy. A minimum of two equal, opposite voltages are required as with analog calculators.
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3.2. Synthesizers from the construction set
The design of all the building descriptions presented here is, in accordance with the international idea, that all units can be assembled completely independently of each other. A block diagram for the complete instrument is therefore meaningless. The supply voltage for all units is ± 15 V. The author will also maintain this supply voltage in later designs, so that any expansion is not a problem. Those who recreate the circuitry can use their synthesizer in this way and expand it after many years, without previously made units becoming worthless. Such a universal construction is necessary, because the long-term construction of a large instrument is not exactly cheap. An instrument that only has a VCO is not a synthesizer but a ” one finger jumper”. It is therefore necessary to plan the extensions in advance, taking into account the relatively high costs; the price is higher than that of a large kit of an electronic organ. For later publications are still “Master slave ” VCOs “, extensive program controls and other interesting constructions on the program. However, these are still in a development stage. When this is fully realized, you have an instrument that makes it possible to simulate almost all sound and noise effects. First of all however, we’ll start with relatively simple and easy-to-rebuild units.
All circuits are such that even an inexperienced amateur can achieve a good result with some care. All units can later be replaced by professional units. The integrated circuit TBA221A from Siemens is used in all units. This operational amplifier is very suitable for DIY applications, as its output is symmetrical and also resistant to short circuits. When errors are made in the circuit, there is no immediate need to be afraid of defective ICs . Fig. 3-2 shows the connection of the IC with the connection numbers and symbol used here. These numbers are not used in the circuits, because the symbol is always the same. When deploying the IC , just make sure that the “dot” on the IC is on the right side. The different photos show the units mounted on pertinax plates . The wiring is made with thin flexible wire. A number of shielded cables are required to operate the instrument. These hang on the side of the case so they can be picked up easily. The inputs and outputs each have different plugs and connections, since the outputs may never be directly connected to each other! However, one output can power several inputs. For some units, two or three outputs connected in parallel are therefore very practical.
Larger synthesizers are equipped with special divider fields. One input and three outputs are always available here. Fig. 3-3 gives an example. 3.3. Power Supply Most modern synthesizer units are equipped with operational amplifiers. As a result, a double power supply is always necessary. The supply voltage remains the same for all units. An additional 5 V supply voltage is often found in the larger instruments , as most programming and dividers are made with inexpensive TIL circuitry. Here too, expansion is always possible. Power supply section In most cases, a simple power supply for + and – 15 Ven 2 x 300 mA is sufficient. The block circuit is shown in Fig. 3-4. Fuse and mains switch are built into the housing. T3 and T4 have a common heatsink of 70 x 50 mm. They are mounted with the corresponding mica insulation plates. All other parts are housed on a printed circuit board (fig. 3-5 to 3-8 ). The forward connected diodes D1, D2, D5 and D6 serve for temperature compensation. 3.4. Control voltage from the keyboard This unit provides all the control voltages necessary for using the synthesizer . The block diagram is shown in Fig. 3-9. The keyboard spans five octaves; each button has three contacts (fig. 3-10 to 3-12). The exponential contacts replace the usually very unstable function generator. Voting is discussed in chapter 3.5. The linear control voltages are mainly needed for the effect generators. Later on, the VCO with built-in function generator can also be connected to this.
All effect contacts are connected in parallel . They simply replace a special impulse circuit. The contacts must be set so that the voice contacts close first and then the effect contacts. The structure of the stabilization board is shown in Figs. 3-13 to 3-16. Zener diode D7 is temperature compensated with D8 . P61 is set so that a maximum of 3 V can be measured at output 1 . The second PCB (fig. 3-17 to fig. 3-20) houses three voltage follower circuits, which are switched behind the contacts. All outputs are low-impedance and short-circuit proof.
The application possibilities of a synthesizer are largely determined by the number of built-in tone generators . Voltage -controlled oscillators can be built in very different ways and can cost up to about 1000 guilders, depending on the desired properties. Special program generators are even more expensive! The same is true for other units used in the synthesizer. However, simple and reliable circuits are described here, which are also affordable for the young amateur.
Generator (VCO 1) Figs. 3-21 to 3-25 show the structure of a sawtooth generator that is already used in various synthesizers. IC6 forms a linear adder stage with resistors R81, R82 and R83. When a positive control voltage with exponential variation is applied to input I, a ” tempered ” tonal range of five octaves is created. An additional modulation voltage can be connected to input II . The actual generator consists of a sawtooth integrator, which is formed by IC7, C13 and D10. A negative voltage from the adder linearly charges the capacitor until the threshold value of the four- layer diode D10 is reached. C13 discharges dary immediately. The sawtooth signal arrives at output 111W via the circuit of D13, T5 and D14. When a well-tuned comparison tool is available, voting is very easy. First of all, P62, P63 and P64 are turned to the zero position. Point X is set to 3.8 V with P65. Then P62 is turned fully open and input I is connected to output II of the keyboard control (fig. 3-9). Now P64 – with key 61 pressed – is set such that the maximum frequency is 2093.0 Hz (c4 of the comparison instrument). Now the other tones, starting with keys 60 and P60 (fig. 3-10) are also adjusted without beating with the aid of the comparator. Finally, when the maximum frequency (key 61 and P64) is slightly increased, the correct tuning can always be obtained by comparison with a 1 = 440 Hz. be done using P62. The keyboard is tuned in 8′ (eight feet). The a1 of 440 Hz is in the third octave. By lowering the control voltage (at P62), the instrument can be set to 16′ (a1 in the fourth octave) or 32′ (a1 in the fifth octave).
Effect generator (VCO 11)
The triangle generator from Fig. 3-26 to 3-34 is particularly suitable for modulation and percussion effects. With the indicated capacitors one has a frequency range of 0.01 to 130 Hz with linear control by the keyboard. The really extensive circuit is housed on two printed circuit boards. lC 8 and IC9 serve here as ” balanced ” mixer”. The positive signals applied simultaneously to the inputs I and II are added (f1 + f2). If, on the other hand, a larger positive signal (f1) is applied to the input and a smaller positive signal (f2) is applied to input 111 , then the the result is a difference signal (f1 – f2) The positive control voltage at point X charges C18 linearly via the integrator IC10 up to the threshold value of the Schmitt trigger IC11. T6 becomes conductive and places point X at a low potential, until C18 is linearly discharged again. A triangular signal is therefore available at output IV. Its relationship to the zero line can be set with P69. The square-wave signal of the trigger (output V) is fixed at D16, T8 and D17 at a level suitable for outputting the contour generator.
The contour generator (Fig. 3-35) is a universal unit for controlling the envelope modulator. The monostable The multivibrator and the envelope modulator are housed on separate PCBs and combined into a unit using spacers. Figs. 3-36 to 3-39 show the structure of the monostable multivibrator . In resting state, T9 is blocked and T10 is in conduction. A positive voltage jump at input I inverts this starting position. The duration of this state can be set in two ranges with S3 and P70. The output pulse is sent via port 35 to the contour former (Fig. 3-40 to Fig. 3-43). P71, P72 and S4 are used to set the response and decay times. IC12 and IC13 serve as impedance converters. Input II is intended for continuous playing and repeat percussion (repeat percussion). It can be controlled by the keyboard voltage or by the square wave output of the effector. The large control area of the contourer is only fully usable when a key memory is used .
White noise is useful for many musical effects. Fig. 3-44 shows that various rustling percussion instruments such as cymbal, cymbal, etc. can be imitated using a number of units. You can set the targeting and extinction yourself with the contour generator. Figures 3-45 to 3-49 show the structure of a good noise generator. T11 serves as the noise source and should be selected for optimal (sharp) noise . T12 and IC14 amplify the noise signal. The maximum amplitude is set with P73 at approx. 3 Vn set. Output II is adjustable. Noise filters are connected to input 1 .
440 Hz generator
At the beginning of this chapter, we already pointed out the need for a suitable equation generator. However , a crystal -controlled oscillator is far too expensive for a small synthesizer. A sine oscillator, which is from time to time compared to a mechanical tuning fork, is more than sufficient here. The frequency of the generator described here (Fig. 3-50 to 3-54 is determined by a Wien bridge. C43, C44, R130, P76 and P77 are included in the feedback loop of the operational amplifiers IC15 and IC16 . The stabilization takes place in the negative feedback LA 1 acts as a PTC resistor P75 is set so that the output voltage is approximately 3 Vpp Those who do not have an oscilloscope available for this measurement can also use a high – impedance alternating voltage instrument The effective indication of the measuring instrument must be factored in by a factor 2.828 are multiplied The voice generator remains constantly switched on The output is connected during use to a free input of the mixing amplifier 3.6.
Modulators and Filters
All known mixing circuits and modulators are used in synthesizers . However, they rarely serve to obtain a purely filtered intermediate frequency. However, the often undesired sidebands are particularly interesting here for obtaining differential tones. For selective sound shaping, active RC filters and passive LC filters are usually used. Larger instruments also have additional third and octave filters. Noise filter This adjustable filter is very suitable for generating storm effects and the murmur of the surf. The sound and amplitude controls must be varied in the correct intervals for this purpose . The use of long track slide potentiometers simplifies operation considerably. The circuit (Fig. 3-55 to 3-59) largely corresponds to that of the usual active sound controllers. The negative feedback network is optimally adapted here.
Low-pass noise filter
The low-pass noise filter creates a hollow -sounding noise, which is especially suitable when generating wind effects. It is therefore often referred to as “wind filter”. At a small “dosage” , the filter can also be used to simulate the blowing of an organ pipe (fig. 3-60). Figs. 3-61 to 3-65 show the simple structure. The active filter with IC18 contains few parts. C56 and C57 determine the filter frequency. Since the low- frequency parts of the noise are only small, the very weak signal with IC19 must be amplified quite a bit. The entrance must therefore be carefully shielded. Pi filter It has already been mentioned in the introduction that larger instruments, in addition to stages for synthesis, also contain special units for the analysis of the composite signal. The 7T filter described here (Fig. 3-66) can be used in many ways. By switching on different coils and capacitors in the filter, high, low and band filters with a high quality factor can be composed as required. The circuits can be muted with the potentiometers P84 to P86. The circuit is housed on four printed circuit boards. With the exception of a few very small differences, these filter prints are completely identical. All details are indicated in Figs. 3-67 to 3-80.
Envelope Modulator (VCA)
Envelope circuits always operate on the principle of amplitude modulators. In contrast to conventional mixing circuits, however, distortion-free modulation up to approx. zero is possible. Simple ports, which are used as piano ports or as organ sustain contacts , are not sufficient here. In the lower part of the modulation curve they cut off the signal and thereby cause an additional and undesired overtone formation. Such difficulties are also encountered with various mixing devices that are often built into small synthesizers and sound organs. Fig. 3-81 shows the principle of an interesting circuit. Since symmetrical signals are required for both inputs, the DC voltage setting of the prestages is extremely critical. One gains the necessary experience in this one’s own experiments. In the circuit designed by the author (Fig. 3-82 to 3-86) the advantages of a light modulator are used. With careful adjustment, all practical requirements imposed on an envelope modulator are met. An adder with IC23 is used as the driver for the LED (light-emitting diode). It is therefore possible to mix different control signals without any feedback. The actual modulation amplifier contains two stages. Via the adder circuit with IC22 , all signals are reduced in the ratio 10:1. The gain of the second stage (IC24) depends on • the instantaneous resistance of the LOR (photosensitive resistance). In the unexposed state, its resistance is at least 10 Mfi . With R160 as the negative feedback resistor, there is an attenuation of about 1000 times. At maximum modulation, the resistance drops to about 1 kfi . The negative feedback ratio then corresponds to a ten-fold gain. LDR and LED must be mounted light-tight.
Fig. 3-87 shows a circuit of a ring modulator. It looks simple, but the circuit has many drawbacks. However, for those willing to experiment, here are some pointers. Only high-quality shell cores are suitable for the construction of the transformers. The winding data depends on the desired frequency range. Coils with taps must be wound bifilar. The use of a ring modulator is not entirely clear musically, since the usual beating effects (f1 + f 2) can also be obtained with the VCA. Modulations of f1 – f2 are also possible if overdrives are avoided. Fig. 3-88 shows a block diagram.
3.7. Signal Shapers
The units described below make the generator (VCO 1) a universal generator. However, they can also be used for other generators with an approximately equal output amplitude. Individual signal shapers can therefore be used in many ways.
There are several circuits that convert a sawtooth signal into a symmetrical delta voltage. The circuit of Figs. 3-89 to 3-93 uses the principle of a modified phase shifter with equal emitter and collector resistances. The emitter of T16 receives an additional negative bias via R 162. In the first period of the sawtooth signal, the circuit acts as a normal phase shifter . During the second positive period of the sawtooth, the base-collector diode is conductive. As a result, the signal is no longer reversed (inverted}. The reversal point can be set exactly with P91. No measuring device is required for this. The setting is done by ear, in such a way that as few overtones as possible are audible. P92 and IC25 are used for the level shift.
This unit allows meri to convert the output voltage of the triangle shaper into a sinusoidal signal. No frequency dependent components are required for this. The circuit can therefore be used over a large pitch range. Fig. 3-94 shows as an example the combination of different units with which sinus percussion can be obtained. Figs. 3-95 to 3-99 show the structure of the sinusoidal waveformer. The pairs of diodes in the counter couple must be selected for reverse and forward resistance. An oscilloscope is required to set the operating point (P93). Level (P94) and symmetry (P92 in Fig. 3-89) are externally adjustable.
The block former is connected to the output of the control generator (VCO 1). It converts the sawtooth signal into a symmetrical or asymmetrical square wave voltage. Together with the triangle and the sine shapers (fig. 3-89 to fig. 3-99) , a universal generator is thus obtained, which generates all common fundamental waveforms . A block circuit is shown in Fig. 3-100. The simple limiting circuits are not very useful here. A Schmitt trigger (Fig. 3-101 to Fig. 3-105) is more suitable here. Due to the high gain of the operational amplifier IC 28, steep edges are obtained. The pulse ratio can be set within wide limits with P95 .
In every large synthesizer you need a number of simple amplifiers that can also be used as inverters . In addition, at least one mixing amplifier is required. A circuit with high- and low-impedance inputs makes it possible to connect other musical instruments; a microphone can also be connected. Universal amplifier The unit shown in Figs. 3-106 to 3-110 can really be used in many ways. It is not only the amplifier (input x 10), but also an attenuator (input x 0, 1). Signal voltages that are too high and too low can therefore be adjusted to a large extent. In addition, an entrance x 1 is available; the signal amplitude remains constant in this case. When a positive voltage is applied to this input, a negative voltage is available at the inverting output IV. At the non-inverting output V, the signal with IC30 is inverted again.
With the aid of the mixer amplifier , if two tape devices are available, ” in-dub ” recording is possible in a simple manner . The block diagram is given in Fig. 3-111. Compared to conventional devices, this “two-band method” has the advantage that the reproducing tape can always be changed in the case of extensive compositions . In addition, passages once recorded can be repeated as many times as desired ( endless cassette ). In any case, the synthesizer signal must be fed through the mixing amplifier (Fig. 3-112 to 3-116), as it contains the required isolation capacitors. All inputs are completely free of retroactive effect. Special Inputs Using the universal units of a synthesizer, other instruments can also be influenced in sound. Fig. 3-117 shows an example of an extra repeat percussion with a sound-shaping part behind it. Own ideas are also always easy to realize. Figures 3-118 through 3-122 show the layout of the input amplifier. The gain is determined by R198 and R199. They should therefore be 3.9.
Use and extension
Built with independent units, the synthesizer is extremely versatile. The combination possibilities increase with each new unit by the factor 2n-1. Taking into account the numerous controls, it will also be clear to the layman that a detailed description of all applications would become a very extensive book. This is also the reason that thick manuals have been developed over time for larger studio synthesizers, which include combination examples and setting instructions for effects. Such a “trick list” is also very practical for amateur instruments. The following examples are therefore only intended as a guide. Each unit must be set so that the desired effect is heard. A synthesizer can be expanded almost indefinitely; however, the development of new units is still in progress. New developments in integrated circuits have already reached the point where they can be used in new units in the foreseeable future. Possibilities that the technician and the musician currently only dream about. The author will return to this development in his building description service (chapter 4).
Radio play effects
The simple combinations of Fig. 3-123 to Fig. 3-126 are very suitable for making sound in radio plays and films. If the frequency of VCO Il is increased by approx. 12 . in the siren circuit, hertz increases sounds a floating “space effect”. The “locomotive effect” is for simulating a passing train. The settings of the noise colors and the amplitude controls should be changed as slowly as possible. Simple Instruments The units described here are not only for generating unconventional effects, they can be used to simulate virtually any known sound. A block diagram for sustained voices (long tones) is given in Fig. 3-127. The universal 1T filter makes it possible to use numerous variants of the selective sound shaping. The vibrato frequency depends on the pitch played, since VCO II is affected by the linear output of the keyboard control unit. The tone inset is determined by the contour generator. Fig. 3-128 shows a more elaborate combination that can simulate different pipe organ registers. Selective and additive sound shaping is used here. Noise generator and low-pass noise filter provide a faint murmur that can be heard on a pipe organ when the pipes are blown. Multi-voice playing The simultaneous use of several VCOs makes a synthesizer truly universal, since the tuning ranges can be shifted relative to each other as desired. The already mentioned “master-si ave VCO” makes it possible to keep the frequency ratio constant even over a longer period of time. Each output of the keyboard controller is capable of powering up to five inputs. However, this possibility can be easily doubled. The circuit for this is shown in Fig. 3-129. The two ICs are connected as a voltage follower (buffer). Please note that with larger instruments a power supply that can deliver more power is also necessary.
Figs. 3-130 through 3-132 show three simple combinations with percussion properties. A square wave signal is suitable for imitation of a xylophone. VCO Il takes care of the repetitive attack. The fundamental of the metallophone is a sinusoidal signal. The square wave signal is added only very weakly – to form harmonics. For imitating a vibraphone, the setup is a bit more complicated. VCO 1 (1) gives the fundamental tone via the triangle and sine shaper. VCO 1 (2) provides the overtone-rich attack. The vibrato (VCO 11) should have only a small frequency swing. TIL circuits Since the square wave outputs of the effect generator and square shaper described above are TIL-compatible, the field of application of the synthesizer can be expanded significantly in a simple way. The supply voltage is obtained using a stabilized mains voltage supply of 5 volts. The negative terminal of this is connected to zero (0). For larger instruments, the installation of a standardized print connector is also recommended. The standardized plug-in PCBs for TIL circuits can then be plugged into this . Unfortunately, extensive combination circuits are not possible within the scope of this book. However , the principle is clearly shown in the following sections .
Fig. 3-133 shows the combination for a four -choir (four footages) square wave organ with the binary counter FLJ181. A 1r filter is fitted for every two foot sizes. The square wave sawtooth formation of a sound organ (see Electronics and music) is also easy to realize, since VCO I generates a linear sawtooth signal.
Fig. 3-134 shows the construction of a simple rhythm unit. Each pulse from the VCO II (2) strikes a noise instrument via the VCA (2). The timbre can be adjusted to your liking with the controls of the noise filter. Via the divider FLJ181, a drum beat is given at every fourth beat. This is simulated with VCO II (1) and VCA ( 1) . Of course , very complex rhythms can also be generated. For extensive pulse generators, the entire TIL program with divisors, monostable multivibrators and ports available.
The following paragraphs should not be skipped. The tempered tuning is discussed and a synthesizer voltage table is also included. Furthermore, an overview is included of gramophone records of synthesizers. The literature overview gives an impression of the publications on electronic musical instruments known to the author. Some titles are no longer available from the publisher; however, some major bookstores still have them in stock. A number of electronics books have also been specified, with which one can expand the knowledge if necessary. The theoretically interested reader will certainly be interested in the books on operational amplifiers, analog computing devices and active filters. The science of designing synthesizers is also covered mathematically herein.
4.1. Building description service
Books that appear in large print runs usually only contain themes that are still interesting even after a few years. Current affairs should be published in a different way. If the building description is not too extensive, the “sound” of the season can always be published in a magazine. Moreover, there are also many effects and musical instruments that are only sought after by a few specialists. Numerous letters from readers have given the author the idea of establishing a building description service specifically for electronic musical instruments . In this context, more extensive instruments and units in which the professional musician is particularly interested can be treated. All building descriptions are such that reconstruction is possible without any problems and a list is also included of all necessary materials
4.2. Equal Tempered Tuning
Electronic musical instruments with generators and frequency dividers are really very easy to tune when a suitable comparison tool is available. The tuning method has already been discussed on page 63. However, a tonal comparison is only possible if the comparison instrument is also tuned in a tempered manner. Ideal is the use of an electronic organ. With monophonic instruments, one has to resort to other aids, since the human ear cannot sufficiently compare high tones. The table included here lists the common frequencies for all electronic musical instruments that use equal temperament tempered are tuned. When tuning with a digital frequency meter, the pulse time must be at least ten seconds. Below 100 Hz, a pulse time of 100 s is required. In the table, the 12 tones of an octave are noted vertically. The associated frequencies are indicated horizontally after each tone in hertz.
4.3. Voltage table
As has already been described in detail above, it can be seen that the frequency of a VCO linearly follows the externally supplied control voltage. However, since tuning according to the tempered scale requires an exponential gradient, the keyboard voltage divider must be adjusted. The table below gives the required control voltage for each key at the output II of the keyboard control unit. When designing an exponential converter, the table can also be used for function checking. 4.4. New Synthesizer Units The development of modern synthesizer units parallels the development of integrated technology. This development will hardly come to an end in the coming years. After finishing this book, the author already had a series of new circuits at his disposal, which, however, can only be published in later editions. However, we will mention the most interesting units here.
- Rhythm unit. Freely programmable percussion controlled by a multi-stage ring counter. Guidance generator. A VCO that simultaneously generates triads that can be played across the entire keyboard.
- Chorus generator.
- polychoral generator set, which is synchronized by a “high-speed” VCO.
- Tone converter. A circuit that derives an external signal control voltage from pitch and loudness.
- Digital key memory . This allows any key to be programmed digitally; repetition is possible as long as one wishes .
4.5. Overview of gramophone records
Those who want to build a bigger synthesizer should definitely listen to some gramophone records, which express, better than the written word, the numerous musical possibilities of the instrument. Walter Carlos, who has interpreted the various pieces of music on these records, has been friends with Robert Moog for many years. With the ” Switched -on Rock” record, pay special attention to all the rhythm effects produced by the synthesizer. ” The Well – Tempered Synthesizer” includes new choral effects and vocal tones. Switched -On Bach. CBS S 63501 Switched -On Bach ll. CBS S 65974 Switched -On Rock/The Moog Machine. CBS S 63807 The Well- Tempered Synthesizer. CBS S 63656
4.6. Notes on the Dutch edition
The book Electronics and Music mentioned in this edition is published by Kluwer Technische Boeken BV and can be bought in bookshops or possibly directly from the publisher (PO Box 23, Deventer). The Valvo shell cores mentioned in this book do not have an air gap. They can be replaced by other types if the number of turns is adjusted so that the inductance value is correct: For building preamplifier (page 58), mains supply (page 60) and stabilization and voltage follower (page 87) use the appropriate circuitry, as some minor errors have crept into the PCBs and component arrangements. The connecting lines of the electronic piano contacts should be at a distance of 4 to 5 mm. The usual contact sets on the market for use in electronic organs are therefore not suitable. By submitting two international reply coupons, you can receive the latest corrections and a list from the author’s building plan service. Ordering address: Helmuth Tünker , D 433 Mülheim / Ruhr , Heidkamp 2, FRG.
4.7. Literature overview
Bergtold , Schaltungen mit Operationsverstärkern , 2 Bände (R. Oldenbourg – Verlag, Munich ) Bergtold , Umgang mit Operationsverstärkern (R. Oldenbourg -Verlag, Munich ) Böhm , Electronic Organn und ihr Selbstbau ( Franzis -Verlag, Munich ) Dort, Electronic Musical Instruments Forcht , Trickschaltung und Tonband ( Telekosmos- Verlag, Stuttgart) Goddijn , Electronic Organs for DIY (De Muiderkring NV, Bussum) Goddijn , Large Electronic Organ Book (Kluwer Technische Boeken BV, Deventer-Antwerp) Goddijn , Electronics in pop music (Kluwer Technische Boeken BV, Deventer- Antwerp) Heinlein /Holmes, Active Filters tor Integrated Circuits (R. Oldenbourg – Verlag, Munich ) Judd , Electronic Music – Musik aus der Retorte ( Franzis -Verlag, Munich ) • Lange, Digital- Analog -, Analog -Digital- Wandlung (R. OldenbourgVerlag , Munich ) Martin, La musique électronique Meijer/ Heggie , Electronic Musical Instruments (De Muiderkring NV, Bussum) Pressman, Digitale Schaltungen mit Transistoren (Verlag Berliner Union, Stuttgart) Sabrowsky , Sinus-, Rechteck – und pulse generators ( Franzis -Verlag, Munich ) Schmidt, Die physikalische Grundlagen der Musik ( Franzis -Verlag, Munich ) Sutaner , Das Spulenbuch ( Franzis -Verlag, Munich ) Tünker , Electronics and music (Kluwér Technische Boeken BV, Deventer-Antwerp) Tünker , Wir bauen electronic Musikinstrumente ( Telekosmos – Verlag, Stuttgart) Vahldiek , Operationsverstärker ( Telekosmos – Verlag, Stuttgart) Wilk , Rechenverstärker (Verlag Frech , Stuttgart -Bottnang ) Winckel , Klangstruktur der Musik (Verlag für Radio- Foto- Kinotechnik GmbH, Berlin)