March 1986

UK £ 1-20

USA $ 3.60IR £1-92

(incl. VAT)

8 mm videoSystem of the future.

Photonics

yHF filtersBohm synthesizer

MSX extensions (3)

1144

EE 111March 1986

LMFARI cs CPU CRYSTALS INTERFACES ICS74

7407401746760740474674667407

7409746

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062-60090060.701.601.10

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1 7111122-20 01113193 111.11616 941371.50 84139_0.70

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4.504503.5036ISO3-20320090

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ATTENTION'ALL PRICES ARE

SUBJECT TO CHANGEWITHOUT NOTICE

SCRS LOW PROFILE ORSOcILETS BY TELLS

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CRT9727 1893CR7645 9.03EF9361 13.100E73356 75.03Ef9336 60056367 63101.1Ci'645 6.501.t1366SP 650MC647 6.50SFF96364 8.0311,354119 603

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18924p3E930P75990903p4094097513

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50-32513

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Subwooferp. 28

15 Editorial16

LettersNews and views

45

'

ELECTRONICSTECHNOLOGY

21 MIDI Expander-add 98 extra voices toyour organ

36 8 mm video -will this become the videosystem of the future?

46 Photonics -a brief look at how infor-mation is conveyed by photons with par-ticular reference to optical fibre cable

61 Inductors in practice -an attempt atsimplifying the design and construction ofinductors

64 Light work for submarine cables -these cables are entering a new era withthe application of photonics

PROJECTS28 Subwoofer -flat frequency response

from 100 Hz down to 30 Hz from an80 -litre speaker system

50 RF circuit design -this second of ashort series of articles looks at VHF filters

55 MSX extensions -the third article in thepresent series deals with an add-on busboard

67 Graphics card 7-the concluding articledescribes the software

We regret that it has been necessary to shift thefirst article describing a Printer Buffer to ourApril issue.

PhotonicsR46

INFORMATION42 New literature; 43 Corrections; 44 Make your ownPCBs; 70 New Products; 81 Infocard; 82 ReadersServices

GUI E LINES75 Switchboard; 76 Buyers guide; 78 Appointments;84 Classified ads; 84 Index of advertisers

MIDI expander11 21

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March 1986Volume 12Number 131ISSN 0268/4519

04

/---In ourAprilissue: Printer buffer (1) Satellite loud-

speakers Dual variable

power supply Digital colour

palette Mixing panel (1) RF circuit

design: VHFpre -amplifier

EEMarch 1986

Back numbers of Elektor ElectronicsFebruary 1978Infra -red Light Gate/ThrowingSome Light on LEDs/Formant -the Bektor Music Synthesiserlel/Slow ori/off /CMOS FunctionGenerator/Zeiler/Tester/Develop-mem timer/Experimenting withthe SC/MP 141.

June 197854 GHz Counter/Constant rtunp6.hide Squatewave to SawtoothConvener / Servo Polaritychanger / Monopoly Dice / MiniCounter / Digital clock Using theSC/MP/Programmable Call Gen-erator / TV Sound Modulator/Automatic Stereo Switch/ TrafficLight controler.Easy Music.

October 1979Touch Tuning/Battery Savo/Im-pedance Bridge/New Programsfor the SC/MP/Digital Rev Coun-ter/Digitated/Short-interval LightSwitch/PCB for Variable FuzzBox/Gate-dipper/Sean (-wive /IPlayed TV Games/ProgrammableSequencer.

November 1979Topamps/ Flash Sequencer/Bec-tronnics the Easiest Way/Remotecontrol Motor Switch/HomeTrainer/fuel Economiser/1 PlayedTV Games 121/Shortwave con-vener/Ionosphere/Low VoltageDirtmere I See your Point/Servo-controlled Motor.

February 1980Aerial Booster/Fit Opamps in theFormant / TV Interference Sup-pression / Bektor VocoderAerial Amplifiers / Digisplay/Analogue Delay Technology / Ex -rending the I: GHz Counter/Digital Thermometer.

September 19808K RAM ÷ 4.8 or 16K EPROM ona Single Card/Precision PowerUnit /Electronic Linear Ther-mometer/The Josephson CormputeriVOX Printed Circuit Board/Efektor: Measuring Muhipath/High Speed Readout for Bekter-minal/Musicat Box/Electrolyto-logy/Curve Tracer/Using theVocoder.

October 1980Programmable Slide Fader/TouchDoorbell/Switched Capacitors/More TV Games/The Junior Com-puter Memory Card/Remote Con-trol Slide Projector/Video PatternGenerator/LCD Tuning Scale!Dual Slide Faders.

November 1980An r.p.m. Indicator as an Econ-omy Guide/Draught Detector/How to Recycle Dry Cell Batteries/Energy Seeing Know-how/Simplefuel Economy Meter/AutomaticPump Control/Long Life Tech-nique in Light Bulbs/Automatic

Curtain Control/Fridge Alarm/Know the iris and outs of yourCentral Heating system/EnergySaving Motor Control/CoffeeMachine Switch/OperationalHours Counter.

December 1980Canned Circuits: 23 of the best en-tries which include Midnight RaidDetector/A 'Flash in the Care/Canomereti Canine Defence.

February 1981Audio Power Meter/Noise Reduc-tion/Process Timer/High voltagefrom 723/Juniors Growing Up!The Voiced/Unvoiced Detec-tor/Emergency Brake for thePower Supply/150 W DC to DCConverter for the Car/Low Noise 2Metre Pre-Amp/21i Digit DVM/Wagnephon.

April 1981Transistor Match-maker/UniversalPower Supply/Interekt/HumiditySensor/Logic Analyser II/Crystal-controlled Stroboscope/JuniorCookbook.

May 1981Camping Clock/ FrequencyDoubler/The Fully Fledged JuniorComputer/Talk to Computers/Choke Alarm/Bar Codes/LogicAnalyser/Waveform Generator/Sophisticated software for theJunior Computer/Reading BarCodes.

September 1982Gas Detector/ Rapid LoadingGarnesiThe Bektor Connection/Inductive Sensor/Darkroom Com-puter Pan 1/Appleratorl HomeTelephone System/SynthesisedSound Animation/Tine Receiverfor the Rugby MSF/Three PhaseTester.

October 1982DSB Demodulator/L.C.D. Ther-mometer/Ultra Sonic DistanceMeasurement/ Electrolytics RunDry/Darkroom Computer Part2/Short Wave Band Shifting forSSB Receiver/ 16 Channels withonly Five ICs/Pre-amp for the SSBReceiver/Active Aerial/ Transistorand IC Data.

January 1983Mielohrnmeterraccessories for theCrescendo power amplifier/Dark-room computer tips/Chips fordigital audio / 3 A computersupply/Traffic-tight control sys-tem / Tomorrows music / Upperand lower case on the Seiner -mina'.

February 1983Prelude pan 1/VAM - video/audio modulator/Main beam dm-mer/Prerude class A headphone

rotifer/ Fuse protector/Acoustictelephone tie...)em/Double doe/Chips for digital audio part 2_

Apnl 1983Low power digital thermometer/MC/MM pram) preen-ea/Mem.brace switches/Interlude/RCequalizer / Telay timer / con-troller/Junior program tester!Prelude (part 31/Programmabledarkroom Omer/Talking clock ex-tension.

May 1983WattmeterIASCII keyboard/Pre(ode p.siMultitester/Maestrolean 11/What is power?/Parallelserial keyboard converter/Morseconvener/78i voltage regulators...and 791/Morse decoding withthe ZBIA.

July/August 1983Summer Circuits Double Issuecontaining over 100 projects.

September 1963Video Graphics/Autotest/ 64k onthe 16k Dynamic RAM Card/high-speed CMOS/VDU Card/PersonalFM/Precision Voltage Divider/alarm Extension/Junior Syn-thesizer/Simple MOSFET Test_

October 1983Basicode-2 / Mint Ouantisizer/Solid-state Dee -n lighting/High -voltage P.e; _ Anem-ometer / Pro_----- - PowerSupply/Basicoe: _ -ace forthe Junior ElectronicVoltage Regulator r BatteryEbminatoraransistor Selec-tor/ FSKleaner EPROMrner usingthe Junior Computer.

November 1983Doorbell -or telephone - oper-ated flashlight/Power Controllerfor Model Ra9ways/Decoupling inDigital Circuits/CPU Card/Decimal to Binary Converter/Movement Detector/Electronicneo-tone Metronome/PseudoStereo:Universal Terrnnat / Ultrasonic; Infrared Barrier !Trick beeterie Crescendo revisited.

December 198364 -way 2eferiensional BusBoard/MF/HF USB Marine Re-ceiver/ LED Ornaments!Symmetri-cal Power Supply/VideoAmplifier; Locomotive HeadlampReverser/Frost Warning Device/Disco Phaser/Banking Program/NOV-RAM: Data Storage withourBatteries/Bus Extension/ .Cumulative index 1983.

January 1984Gyrophonellicrer accurate is yourwatch?./ Digital Cassette Re-corder/Audio Signal EmbeffisheriUniversal Active Fiterifrom Ther-mometer to Thermostat/AudioSleuth at work/Wind Direction In-dicator/720 EPROM programmer/Home-made low-cost Wiring Pro-be/Address derfing.

March 1984Petrol Saver/Triac Control BoardUHF Video and Audio ModulatorGET le GO/Babyrinth; e:Protection Circuits / Real Timeanalyser (part 111Appbcator /TapeTimer.

April 1984Optical Memories /Controllng theFloppy -desk Drive Motor/ PulseGenerator/Using the Pulse Gener-ator/Intelligent EPROM Eraser/ZBO simulator/Metronome Exten-sion/Real-tine analyser, part 2/Variable A.C. Power supply/heist/Chip Selekt/Tape Contents Detec-tor.

elektoralectronics

OMUSITESIMMINITI11.11111111111111116

via., dept..*Sown...1r poet.r great*

sap swischimi sappi*-E109. May 1984Noise Squelch/Short-wavePocket Radio/floppy Tester,Switching Power Supply/ Analytical Video Display/Aviary flumenation/How many Watts?/MiniCrescendo/a look at EXOR andEXNOR Gates/EPROM Copier,Digital Cassette Recorder re.visited/Real-tine Analyser.pan 3/RS423 Interface.

June 1984Portable Distress Signal/ X Exten-sions/Disco Drum/DaisywbeetTypewriter Printer Interface/Mari-mum and Minimum MemoryLead -acid Battery Charger/Wire-less Microphone/Merging BASICPrograms/Echo Sounder/Versetae Audio Peak Meter.

September 1984Data Communication by Tete,phone/Active cross -over Flee'Digital Cassette Recorder with theZX81/Flash Meter/Digital Tacho-meter/ D IR PUT / S CART Adapter!Anodizing Aluminium / LampSaver/Double-sided Printed Cir-cuit Boards

October 1984The Sinclair OL - first im-pressions /Basicode-21TuningFork/Balancing TransformersVideo colour Inverter/Programming the 6845.2X81 Caere -erePulse Cleaner/Direct-en-weedModem/Battery Tester: R scentronics ConvenerPre -amplifier_

January 1985Commodore Cassette Inter-tacei VH F / UHF Modulator/ Port-able Guitar Amplifier/30 watt a.f.Output Stage/JSR swap/RumbleDetector/eP-controlled FrequencyMeter/Switching Radio ControlChannels.

February 1985Groftash/ 1.2 GHz Input StageMicrophone PreampefierIRemoteModel Control by MicrocomputerDIY Connector/ProgrammableRhythm Box /EPROM SelectorReceiver Power from Engine Battery / RIC Meter/ Programme leeKeyboard Encoder.

March 1985K.I.T.T. Scanner/ AXL Arnettfier/pH Meter/Turnout (points?Control/New Keyboard for Spec-trum/19 kHz Precision CaliNetter Versatie Counter Cr-cuiti Darkness -sensitive LightSwitch/Mini Active Loudspeaker!Transistor Unnester.

April 1985Light -powered Radio 'RevolutionCounter/ X -Y Plotter/The FurstCuckoo in Spring/Real-tine Clockfor Micros/10 A Power Supply/Stepping Motors.

May 1985A/D and 13,,A Conversien /Pro.grammable Ttmer/Universal I/OBus/an IBM Compauble Microentrol/Cilow Plug Modulator/Digitizer/Programmable ArrayLogic/Automonitor/PanoramaMixer.June 1985Tone Burst Generator/Infra-redMovement Detector/an IBM Com-patible Micro/RAM used asEPROM /Service Interval Timer/Electric Pantograph/Digital Oscil-lators/The Short Search/AI.phanumeric Display/ Solar Bat-tery/Computer Eye_

July/August 1985Summer Circuits Double IssueComae fee o". F7 I Ce e-cee:ss_

September 1985Intruder Alarm/Solid-state Relay/PL301 1 nerspeeker/High-resol-ution Colour Graphics Card/Fre-quency Standard/Cleaning VideoReconlers/RS232 Interface.

October 1985Viewdata in Britain/ClockOsoiators/BectronCs Er Med-eine/ Electronics Select/Hand-heldAnemometer/Marine Computer/High -resolution Graphics Card- 2 / Sound Rotator/StegeLighting

November 1985Zero mod -en connector/Deep-freeze AtzumiStage Lighting -2Sweep Generator/Car F.,--v-firer/Overload Protectie, -Dec Mc Drys/Play Ball eeRektor/Graphics Card-3/Codas.

December 19858-bn I/O Bus/Phone-correctedCross over Fiter/DissipationLimiter/Graphics Card-4/Audo-controlled Loudspeaker Moni-tor/A Star for Christmas/JumboClock /Teeephone Exchange.

January 1986Car Electronics / Voltage -controlled Attenuators / Protec-ting Data from Prying Eyes /Educational Software for the Han.recapped / CAD in practice atRenault / PROJECTS: Solid-stateIgnition / Infra -red Light Switch /Graphics Card - the software /Mobile Audio Power Amplifier /Oren -compensated Oscillator /Variable Fiter for DX / MSX Ex-tensions.

February 1986Electronically controlled cameras- the Minolta 9300 / SatelEte TVReceiving Equipment / The Futurefor Artificial Intelligence / The Ac-cordion Image Sensor / Designinga Closed Loudspeaker Box / PRO-JECTS: DC operated BatteryCharger / Active Aerial with SMDs/ MSX Extensions - part 2 /Graphics Card - Colour EversionBoard / Car Burglar Alarm / RFCircuit Design.

A selection of back numbers of Elektor Electronics currently available is detailed above, with a brief description of their contents.Send for your copies now, using the pre -paid Order Card at the back of this issue.Price are as follows: any one issue (except July/August) £ 1.50

July/August (Summer Circuits) £ 3.00Prices include postage and packing. Overseas orders requiring airmail postage add £ 1.50 per issue (£ 2.00 for July/Augustissue) (Prices subject to change without notice)

Editor: Len SeymourAdvertisement manager: S BrooksPublished by:Glentop Publishers LimitedStandfast HouseBath PlaceHigh Street, BarnetLondon EN5 lEDTelephone:

Editorial:101) 441 4130Advertising: 402271 66106

Telex: 22828A Kluwor Group Company

Overseas editions:Elektuur B.V.Peter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L KersemakersElektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailleul - FranceEditors: D R S Meyer;G C P RaedersdorfElektor Verlag GmbHSiisterfeld-Stralle 25100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E XanthoulisElektor Electronics PVT Ltd.Chotani Building52 C, Proctor Road, Grant Road (ElBombay 400 007 - IndiaEditor: Surendra lyerElektor JCEVia Rosellini 1220124 Milano - ItalyEditor: D FumagalliFerreira Er Bento Lda.R.D. Estefania, 32-101000 Lisboa - PortugalEditor: Jorge GoncalvesIngelek S.A.Av. Alfonso XIII, 141Madrid 16 - SpainEditor: A M FerrerInternational co-ordinatingEt technical manager:K S M WalravenInternational editorial secretariat:M J M Lacroix; G W P WijnenThe circuits are for domestic useonly. The submission of designs orarticles to Elektor Electronics impliespermission to the publishers to alterand translate the text and design,and to use the contents in otherpublications and activities. Thepublishers cannot guarantee toreturn any material submitted tothem. All drawings, photographs,printed circuit boards and articlespublished in Elektor Electronics arecopyright and may not be repro-duced or transmitted in any form orby any means, including photo-copying and recording, in whole orin part without prior written permis-sion of the publishers. Such writtenpermission must also be obtainedbefore any part of these publicationsis stored in a retrieval system of anynature.

Patent protection may exist inrespect of circuits, devices, com-ponents etc. described in thismagazine. The publishers do notaccept responsibility for failing toidentify such patent or other pro-tection.

Distribution:Seymour Press Ltd., 334 BrixtonRoad, London SW9 7AG.Copyright = 1986 Elektuur B.V.

Printed in the Netherlands by NDB,Zoeterwoude_

IABc1

111 EEMarch 1986

March 1986

Industry Year 1986:will it succeed?

Industry Year 1986 was launched because, virtuallyalone in the world, we have an anti -industrial attitude inan industrial nation. The professions and most serviceindustries cannot make one iota of difference to theeconomic growth of this country; only the manufacturingindustries can.

Regrettably, many of our brightest youngsters choose theprofessions over a career in the manufacturing industry.Many others regard the manufacturing industries merelyas providers of a meal ticket, only to be entered as alast resort.

Unfortunately, they have a point: in the United States andmost West European countries, the leaders of themanufacturing industries and the trade unions, moreoften than not, are science or engineering graduates. InBritain, the reverse is true: the surest way to top manage-ment and the Board Room is via accountancy or law;very few engineers make it there.

The prime aim of Industry Year 1986 is to bring about agreater understanding between the academic worldand the manufacturing industries. Our youngesters mustbe made aware that only if our manufacturing industryis successful will the quality of life improve.

Of course, the manufacturing industry also has a task: itshould be more effective in making known to thepopulation, but more particularly to the younger gener-ation, its part in the welfare of this country. It can do sothrough schools and universities, and through the media.

It is, of course, too much to hope that the attitudes whichhave flourished for generations can be changed in justa year. And, indeed, even if that were possible, ourmanufacturing industry would not miraculously betransformed into a succes story. That requires more thanattitudes.

But unless we get our wealth producers moving in theright direction and give just pride of place to manufac-turing industry as a whole, we could, to quote the Princeof Wales, become a fourth -rate nation.

For all of us engaged in electronics, it is gratifying tonote that prospects in electronics manufacturing are farmore favourable than those in Britain as a whole. BothGovernment and Opposition want electronics to boom,but even in this industry there is a growing shortage ofskilled staff and graduate engineers.

Although Industry Year 1986 will not create miracles in themanufacturing industry, we must all hope that it will suc-ceed in bringing awareness to all that industrial succes isvital to our welfare, and instilling a resolve in all of us towork towards that success.

EE

March 19S616

WS VIEWS NEWS VIEWS NEWS V:Europeanelectronics in1986Final figures for the totalWest European market forelectronic equipment andcomponents in 1985 areforecast to be about US$96billion in the ThirteenthEdition of the Yearbook ofWest European ElectronicsData 1986 produced byBenn Electronics Publi-cations Ltd (BEP). Thisrepresents an increase of6.4 per cent over the 1984total of US$91 billion atconstant 1984 values. Therate of growth is forecastto slow to 4.4 per cent in1986, when the Europeanelectronics market will topUS$100 billion at constant1984 values, but then torecover to give an annualaverage growth rate of6.7 per cent in real termsover the period 1986-89 toreach US$122 billion in1989 (Fig 1).

The fastest growingEuropean market sectorcontinues to be electronicdata processing (EDP),covering mainframe andmini computers, word pro-cessing systems and com-puter peripherals, with anaverage forecast growth of9.9 per cent per annum inreal terms over the period1984-89, taking theEuropean EDP market toUS$42 billion in 1989.The European Consumerelectronics market is ex-pected to be particularlyslow moving, with anoverall projected growthat an annual average rateof 1.9 per cent over theperiod 1984-89. The onlyproduct showing signifi-cant growth prospects iscompact disc players, withan average growth rate invalue terms predicted of55 per cent of annum. TheBEP Yearbook estimatesthat over 2 million com-pact disc player units willbe sold in Europe in 1986.The market for video

1 European Electronics Market By Sector(Constant 1984 Values)

1935

1986

SIC-0.7bn

1989

5122.5bn

TOD - 1984 S96.4bn 34%

S90.7bnEDP

29%31%

BO- 27%

19% COMPONENTS

19%60- 19%20%

11% TELECOMS13% 13%

13%10% CONSUMER

12% 11%It% CONTROL & INST

20 -12% 12%

12%

8% COMM & MIUTARY94 8% 8%. 4% 3% 3% OFFICE EQUIPMENT3% 3 3% MEDICAL & INDUSTRIAL

84^, Fiectro,cs Lt1

The Active componentsector grew particularlystrongly in 1984, with atrue rate of growth of over30 per cent, mainly due tothe increase in the marketfor integrated circuits.However, BEP predict thatthe European Active com-ponents market after a fallin 1985 will revert to agrowth market in 1986 andshow substantial growth ofover 9 per cent per annumover the period 1986-89.

recorders grew verystrongly in the early 1980s,but has now stabilizedand is projected to growat an average rate of only5.4 per cent per annumup to 1989. In the UK, VCRsales dropped appreci-ably in 1984 from 2.4million units in 1983 to only1.6 million units in 1984 asthe rental boom subsided.The Office Equipmentmarket is also slow movingwith a projected average

growth rate of 2.1 per centper annum. A contributingfactor to the slow growthin 1985 and 1986 is theprice drop in electronictypewriters, where theaverage price will fallfrom $270 in 1984 to $230in 1986.Other sectors covered inthe BEP Yearbook 1986 areControl and Instrumen-tation, which is expectedto expand at 5.0 per centper annum 1984-89, Tele-communications Equip-ment, which is predictedto grow at 4.8 per cent perannum, Communicationsand Military equipmentforecast to increase at4.5 per cent per annumand Passive and AudioComponents with growthrates of 4.5 per cent and3.0 per cent per annum re-spectively.Of the major Europeancountries, West Germanyand the UK are forecast togrow a little faster, at6.9 per cent per annumand 6.4 per cent per an-num respectively over theperiod 1984-89, than Italyand France (5.6 per centper annum and 5.5 percent per annum respect-ively) thus increasing theirshare of the Europeanmarket (Fig 2). The UK willenjoy the highest growthin 1985 of any of thecountries surveyed but willthen falter in later years.The reverse is the case forFrance where 1985 is ex-pected to be a very pooryear but which is forecastto recover in 1986.

The only country in Europeto have a trade surplus inelectronic equipment andcomponents is WestGermany, US$0.7 billion in1983 and US$0.4 billion in1984. However, the UKdeficit has reduced fromUS$4.1 billion in 1983 toUS$3.7 billion in 1984.France also reduced herdeficit, from US$1.8 billionto US$1.6 billion, but inmost other countries thedeficit increased to give atotal European deficit ofUS$11.2 billion. Italy faredparticularly badly with adeficit of US$2.0 billion in1984, up US$0.6 billion.Since 1979, Europe'strading position in elec-tronics products hasworsened considerably(Fig 3), all expressed incurrent prices and ex-change rates.

European Ulan. ofTrade la Electronics P.O..,6666666066 Yews Impa,66)

6,66 6 6....6..ke 66:rs

2 European Electronics Market By Country(Constant 1984 Exchange Rates)

1984590.7bn

Rest of WestEurope Germany27.9% 22.8%

UnitedKingdom

France 20.8%17.3%

19895122.5bn

Rest ofEurope27.9%

Italy

France16.7%

te I ertn Ltd

WestGermany

23.5%

UnitedKingdom

21.0%

EEMarch 1986

WS VIEWS NEWS VIEWS NEWS V:The UK is increasing itsshare of European pro-duction of electronicequipment and compo-nents (Fig 4). In 1979 the UKhad 17.7 per cent of thetotal, which has increasedto 18.6 per cent by 1983and is forecast to furtherimprove to 19.9 per cent in1986. West Germany andFrance are both experi-encing a decrease intheir shares, Germanydown from 28.2 per cent in1979 to 26.5 per cent in1983 and 26.1 per cent in1986, France down from19.8 per cent in 1979 to18.6 per cent in 1983 andforecast at 17.8 per cent in1986. Italy remains con-stant at around 10 percent while the rest ofEurope accounts for aconstant 26 per cent1983-86, having improvedfrom 23 per cent in 1979.Around 65 per cent of thetotal European electronics

market was supplied byimports in 1984. Francehad the lowest proportionof its market supplied byimports at 49 per cent, fol-lowed by Italy with 57 percent, West Germany with61 per cent and the UKwith 65 per cent. However,in the smaller countriesimports accounted for86 per cent of the market.In terms of product sectorsthe proportion variedwidely from 12 per cent ofthe telecommunicationsequipment market to89 per cent of the cornpo-nents market supplied byimports (Table 1).The Thirteenth Edition ofthe Yearbook of WestEuropean Electronics Data1986 is priced US$495 percopy and is availablefrom Benn ElectronicsPublications Ltd, P.O. Box28, Luton LU2 OBD, EnglandTel: (0582) 417438 Telex:827648

4 European Production Of Electronic Products(1979-54 at Current Values; 1985-6 at Constant 1984 Values)

100

80578.1bn

525.6bn

S88.3bn

W.GERMANY26.1%

29.5%26.5%

17.8% FRANCE

19.6% 18.6%

19.9% U.K.

17.8% 18.6%

20 10_2%10.1% 10.2% FTALY.....

22.9% 26.2%26.0% REST OF EUROPE

1979 1980 1981 1982 1983 1984 1985 1986

Sa_st. /km tlectrex.v. hr04elti4.11 1*4

Table 1

Proportion of European Electronics Market Supplied By Imports

Electronic Data Processing 88%Office Equipment 77%Control Er Instrumentation 58%Medical Et Industrial Equipment 51%Communications Et Military Equipment 23%Telecommunications Equipment 12%Consumer Products 68%Components 89%Total Electronics Products 65%

Source: Benn Electronics Publications

InternationalbroadcastingawardThe International Award forOutstanding Work in theField of Broadcasting willbe presented at the Inter-national BroadcastingConvention (IBC) inBrighton from 19 to 23September.The award, first made in1984 to mark the tenth IBC,takes the form of aspecially commissioneddesign in glass with amotif based on the classicGreek Golden Sectionconcept to symbolize thesynthesis of art andtechnology in broad-casting.It is given, together with aprize of £2500, in recog-nition of a significant con-tribution over any periodof time by a person orgroup of persons to allaspects of broadcastingand allied research,design, development,manufacture, operationalpractice, and manage-ment. There is no restric-tion regarding nationalityor country of residence.Nominations are invited foroutstanding work that hasnot already been recog-nized by the presentationof other awards, and willbe assessed by an awardspanel in consultation withfourteen IBC Correspond-ing Members from aroundthe world. Closing date fornominations is May 1986.IBC Secretariat; Institutionof Electrical Engineers;Savoy Place; LondonWC2R OBL.

Anglo-FrenchcomputerBritain and France are tojoin forces in the develop-ment of a computer foruse in science andengineering fields,capable of 500 million op-

erations a second, butcosting less than a tenththat of current machinesof similar power.The three-year develop.ment project is part of theEEC's ESPRIT programme,and half the estimatedcost of £6.5 million will,therefore, be met fromESPRIT funds.At the request of bothFrance and Britain, theRoyal Signals and RadarEstablishment at Malvernwill be the main contrac-tor because of its expertisein this field. Participants inthe project are the univer-sities of Grenoble(Laboratoire de Genie In-formatique - IMAG) andSouthampton, and in-dustrial companies Inmosand Thorn -EMI of Britain,and Telmat SA and Apsisof France.The new computer will beof modular constructionwith each module con-taining sixteen transputers,which are, in effect, com-plete computers on asingle chip. Traditionalcomputers with ordinarychips operate sequen-tially, but the use oftransputers makes it poss-ible for a computer tocarry out a variety of dif-ferent tasks simultaneously.As well as the actualmachine, the Anglo-French teams will alsodevelop the programs forit. (LPS)

Satellite TVreceivingequipmentThe article Satellite TV Re-ceiving Equipment in theFebruary 1986 issue ofEleklor Electronics regret-tably did not give the ad-dress to contact forinformation on the ASTRIDreceiver. This is: MMMicrowave Limited; IngsLane; Kirbymoorside; York-shire YO6 6DW; Telephone:(0751) 31955; Telex: 57920.

EE

March 1986

VIEWS NEWS VIEWS NEWS V:

Prestel:ssuccessfuldevelopmentThe use of Prestel, BritishTelecom's public viewdataservice, has grown bymore than 44 per cent inthe past year, with morethan one million pages aday being accessed andmore than 100 000 elec-tronic mail messages aweek.Specific areas attractingnew customers to the ser-vice included travel, in-surance, microcomputing,city information, farming,home banking, and shop-ping. Messaging, anotherhighly successful oper-ation, now includes fulloutgoing and incomingtelex facilities. Travel in-quiries, for instance, grewfrom 2000 accesses aweek in August 1984 toover 15 000 a week inAugust 1985.When teleshopping waslaunched last year, itgenerated 3000 inquiriesduring the first three days.Since then, teleshoppingfor specific departmentaland mail order stores hasbeen introduced and thisarea is expected to growsignificantly in the future.

More AlveycontractsIntegrated circuittechnology for three con-tracts awarded to STC'sStandard Telecommuni-cations Laboratories andICL is being developedunder the Alvey Pro-gramme. The contracts,from the Ministry ofDefence, involve plannedexpenditure of almost £17million over the next fiveyears. They are among fiveto be presented under thesecond stage of the MOD'sVAD initiative.The VAD programme-Very high performancetegrated circuit Appli-

cation Demonstrator- isan MOD -initiated pro-gramme funded half bythe ministry and half bythe companies involved.Two of the contracts havebeen placed with STC andcover development in ad-vanced radio and elec-tronic counter measures-ECCM. The third hasgone to ICL and covershigh-speed parallel pro-cessing based on ICUsDistributed Array Processorconcept. (LPS)

ICL softwarecentre inBrusselsBritain's leading computerfirm ICL has opened anew centre in Brussels togive its Europeancustomers a much widerchoice of software. The ser-vice offered by theEuropean Software IndustryDevelopment Centre(ESIDC) is part of ICL's con-tribution to an initiativelaunched last February by

a number of majorwestern European com-puter manufacturers topromote common stan-dards of software, knownas the X/Open Group. Theaim of this co-operativeaction is to create soft-ware systems compatiblewith European hardware.ICL sees the ESIDC inBrussels as a means of in-creasing the range of soft-ware to users of its owncomputers. The centre willprovide software houseswith technical andmarketing support. Onemajor service is the oppor-tunity to transfer existingsoftware systems onto ICLcomputers, such as theCLAN supermicro, whichoperates on the UNIX inter-national standard.

New IECstandardsA number of new IEC stan-dards have been an-nounced, including thefollowing.

Keeping communications open in the Highlands in winterweather means taking emergency measures. Here, nearthe hamlet of Culbokia on the Black Isla near Inverness,a British 7blecom engineer climbs a pole to repair anoverhead cable, brought down by blirds. Helicoptersare used by British Tblecom engineers in the Highlandswhen an isolated area is cut off; or lines affecting ahospital or other vital services are damaged.

Publication 169-22: Radio -frequency connectors;Part 22 - RF two -polebayonet coupled con-nectors for use withshielded balancedcables having twin innerconductors (Type BNO).

CISPR Publication 22:Limits and methods ofmeasurement of radio in-terference characteristicsof information technologyequipment.

Publication 94-6: Magnetictape sound recordingand reproducing systems.Part 6: reel-to-reel systems.

Publications 268-13: Soundsystem equipment. Part13: Listening tests onloudspeakers.

Publication 747-111QC750000: Semiconductordevices. Part 11: Sectionalspecification for discretedevices.

Business com-puters doingwellAlthough the home com-puter markets are in thedoldrums and unlikelyever to regain their formerstatus, the market forbusiness computers re-mains buoyant. This hasbeen highlighted by theannouncement of the firstSony computer and of anumber of new models bywell -established suppliers,such as IBM, Apple, Atari,and Amstrad.Although not strictlyaimed at the businessmarket, the newAcorniBBC Master Series isclaimed to be the firstever compatible microseries. It comprises theMaster 128; the 16 -bitMaster 512, which is MS-DOS compatible; theMaster ET, primarily aimedat the educational market;and the 32 -bit Master Sc.,which uses not only BBCBASIC, but also ISOPASCAL, FORTRAN 77, andC and 32016 ASSEMBLER.

19 EEMarch 1986

WS VIEWS NEWS VIEWS NEWS V:

Apricot closesin Germany ..Apricot Computers, whichplunged into a multi-million pound interim losslast year, has closed itsGerman subsidiary. Ac-cording to the company,both their French andGerman companies madeheavy losses, and feel thatthe reasons for the sharpdrop in profits worldwidewere the declining per-sonal computer marketsand some over -ambition.The bulk of the losses iscaused by a stock pro-vision of more than £5million related to the port-able computer, pro-duction of which hasbeen stopped.

...and Com-modore inBritainOwing to poor sales in thehome and personal com-puter markets, Com-modore International isrationalizing its productionoutlets worldwide, as aresult of which it hasclosed its manufacturingcapability in Corby, Nor-thamptonshire. This movehas resulted in some 250people becoming redun-dant. The company'smarketing and service op-erations in the UK have notbeen affected by thesemeasures.

Inmos goingforeign?Inmos, the former state-owned manufacturer of in-tegrated circuits, but nowpart of the Thorn -EMIGroup, may become aforeign -owned or con-trolled company. Eversince its acquisition byThorn -EMI in 1984, the

company has beenoperating at a loss owingto the worldwide declinein the microchip market.Like many others over thepast few years, Thorn -EMIhas found that the invest-ment required for develop-ing integrated circuits istoo high for adequatecommercial rewards.Thorn -EMI is now said tobe discussing a possiblepartnership for Inmos witha number of companies,but it is not likely that anyBritish company will beable (or willing?) to affordthe outlay required.Apart from Inmos, Thorn -EMI is planning to sell offits cable television in-terests, a substantial partof its holding in ThamesTV, and a number ofengineering firms. Theseplanned moves arenecessary to reduce thecompany's debts by about£250 million, and gei itscash -flow under control.

Cellular radioresearchCellular radio systems arebeing developed to pro-vide good -quality, andrelatively inexpensive,telecommunications formobile users. However,cellular technology is stilla relative newcomer todomestic use, andresearch at the Universityof Bradford will bringcomputer -controlledsystems into use to makefor cheaper and more ef-ficient radio application.Professor David Howsonand Dr John Gardiner ofthe University's School ofElectrical and ElectronicEngineering have won an£84 000 research contractfrom the SERC -Scienceand Engineering ResearchCouncil.At present, the radiotransmitters that com-municate with the mobiletransceivers (as used incars, for instance) switch

frequency, under the con-trol of a computer, tomaintain good radio con-tact. These transmitters relyon so-called multicouplersto ensure efficient use ofthe aerials for interference -free reception.The research at Bradford isdeveloping a new type ofmulticoupler that can beremotely switched undercomputer control. Thesenew multicouplers willtake cellular radio a stagefurther in efficiency andcost-effectiveness.

Racal andNorsk call ita dayThe joint -venture agree-ment between the RacalElectronics Group andNorway's Norsk Data todevelop advanced com-puter systems for artificialintelligence applications(see Thinking Computers,Elektor Electronics, Oc-tober 1984, p. 21) has beencalled off.According to a spokes-man for Racal, the invest-ment needed to developartificial intelligencesystems, although thesehave good long-term pros-pects, is currently not com-mercially justified.

Pirelli hi -techdriveTwo recently openedplants for the productionof optical fibre and otherspecial cables representan investment of over £14million by Pirelli. Theplants, at Eastleigh,Southampton, are part ofa progressive drive byPirelli into high-technologyproducts aimed at the in-formation industry and atprecision cable markets.One of the plants pro-

duces single -mode opticalfibres with the vapour -phase axial deposition-VAD- process. It is thefirst in Europe to use VADtechnology, and PirelliGeneral is the only UKcable maker to have bothsingle -mode fibre and op-tical fibre cable manufac-ture on the same site.The Pirelli Group is widen-ing its base in the rapidlyexpanding opto-elec-tronics market. In the UK,these activities are carriedout by the OptronicsSystem Centre and byFocom Systems.The principal activities ofthe Optronics SystemCentre are the design,supply, installation, com-missioning, and mainten-ance of optical fibresystems, complete with allterminal equipment,electro-optic interfaces,and installation re-quirements.Focom Systems designsand manufactures digitaldata communicationsequipment that uses op-tical fibre as the trans-mission medium. Theirrange includes opticaltransmitters and receivers,line termination equip-ment, high-speed modemsand multiplexers, andphysical ring networks.Focom is recognized as aUK leader in fibre opticsystems for local connec-tions of terminals andperipherals to computersand a major supplier forother applications.

More sheddingby AcornAcorn Computers Limited,the Cambridge -basedmanufacturer of the BBCMicro and the Electroncomputer, which is now80 per cent owned byOlivetti of Italy, has sold itsleasing subsidiary to theEastern CountiesNewspaper Group.

EEMarch 1986

20

IIATS VIEWS NEWS VIEWS NEWS V:Rotterdamsatellite linkElectronic Data Systems(EDS), the worldwide com-puter company, has be-come British TelecomInternational's (BTI) first full-time customer for itsSatStream Europe small -dish digital satellite ser-vice. This will link EDS's Lon-don and Rotterdam infor-mation processing centreson a 64 Kbit circuit.The link uses the SatelliteMultiservice package car-ried on Eutelsat I -F2,suitable for high -qualitydigital services such asSatStream Europe. BTI aloplans to use the FrenchTelecom 1 satellite forSatStream Europe service.SatStream Europe is one ofa family of digital small -dish satellite services of-fered by BTI. It com-plements SatStream NorthAmerica, which began inFebruary 1984, and BTIplans to introduce aspecialized service for oiland gas platforms thisyear: SatStream Offshore.Each SatStream service of-fers digital satellite links atcircuit speeds rangingfrom 64 Kbit/s to 2 Mbitis.Applications includemultiple site remote print-ing; video conferencing;and integrated voice,data, and text communi-cations.

Simplifiedmicropro-cessorsSince microprocessorswere launched by Intel inthe early 1970s, they havebecome more and morecomplicated; so much sothat many think that thesecomputer brains shouldbe severely simplified. Tothat end, IBM and a smallnumber of other Americanindustrial companies, as

well as some US univer-sities, have developed thereduced -instruction -set -computer (RISC).Although simplicity givesRISC machines theirspeed, they are, at leastfor the time being, aimedprimarily at the scientificand engineering fields: ar-tificial intelligence,number crunching, andgraphics.

Vodafone fordispatch riderOffice boy turned motor-bike courier, Ian Moody, isrevving up into the fastlane as one of thecountry's first dispatchriders to have Vodafonefitted to his motorcycle."As I travel all over thecountry, a 2 -way radio,such as London ridershave, is of no use to me asI would often be out ofradio range. I then tried aradio pager, but, althoughits coverage was good, I

would often ride aroundfor ages before I couldfind a telephone box thatworked. It cost me apacket in petrol andwasted time in mybusiness, and, after all,time is money"."The Vodafone certainlymakes my life a lot easier.Now I can just pull over tothe side of the road andtake the call. If I am awayfrom the bike, I can diverta call to my answeringmachine and then callthe office back':Since it opened on 1stJanuary, 1985, theVodafone service has at-tracted about 20 000subscribers who aremaking over 500 000 callsper week. The network willbe available to 80 percent of the UK populationby the middle of this year.

GE+RCA=BIGThe largest -ever merger inthe electronics industry

was concluded recentlywhen RCA accepted abid of some £5000 millionfrom General Electric. Thiswill create an undertakingthat, with sales of some£30 000 million, will beamong the ten largestcompanies in the world.The move means that,among others, the threelargest television networksin the world have nowchanged hands in the re-cent past (RCA owned thelargest of the three: NCB).

Maritime telexmodernizationTelex messages for ship-ping on the high seas cannow be received andstored, and relayed later-all automatically-through a new computer -based system installed inBritish Telecom's long-range coastal radiostation at Portishead.Previously, storage andlater transmission of telexmessages was donemanually by operators.Now, once a vessel isready to receive the telex,the system will automati-cally transmit. All thatships' operators need do,in advance, is enter theirown watch -keeping ar-rangements to the Por-tishead computer'sdatabase for automatictransmission during pre-determined times. In thisway, messages can be re-ceived onboard withinminutes, almost anywherein the world.The new equipment, whichcame into service inNovember last, marks asignificant stage in themodernization of BritishTelecom International's(BTI) maritime radio com-munications service. BTI isalso planning to introducesimilar automatic telexfacilities on its medium fre-quency radio channels inthe near future.

ei,arch19.6

MIDI EXPANDERFROM B6HM

Until quite recently, no European manufacturerhad ventured to enter the digital

market with a product to compete with the vastnumber of ready-made expander units availablefrom Japanese firms 35hm of Germany have nowtaken this daring step with the introduction of their

polyphonic MIDI -compatible expander which isavailable in kit form only.

An expander is basicallya music synthesizer de-signed to be controlledvia its MIDI (musical instru-ment digital interface) in-put. This type of synthesizeris now gradually becom-ing available in severalversions and price ranges.The advantages and tech-nical characteristics of theMIDI standard have beendiscussed at some lengthin the November 1985issue of Elektor Electronics.The fact that the Bohm ex-pander comes as a kitmakes it of special interestto the reader who has apassion for both musicand applied electronics.After having read thisreview, therefore, he may

judge for himself whetheror not this novel synthesizermay be consideredcapable of rivalry withsimilar ready-made unitsof comparable cost.

12 or 24polyphonicnotesThe basic version of theBohm MIDI expander is adigital, fully program-mable 12 -note polyphonicsynthesizer with 98 presetsounds stored in ROM(read only memory), whileanother 98 may be kept in

a non-volatile RAM (ran-dom access memory) withbattery back-up facility toretain user -defined presetswhen power is switchedoff. For applications thatrequire more than a totalof 196 presets, a cassetterecorder and optional in-terface may be used as amass storage device, inmuch the same manneras v.fith personal com-puters. The extended ver-sion of the expander is a24 -note type to which ananalogue phasing chorusunit may be added. Unfor-tunately, the basic versionof the kit comes without aflat 19 inch case for rackmounting; Bohm, however.offer a suitable pre -drilled

case as an option. As afurther extension to the two98 -preset banks, Bohmhave planned to in-troduce a memory exten-sion to hold up to 392permanently availablepresets. The basic kitcomes with a standard16 -channel MIDI input forthe simultaneous controlof up to 12 notes (or 24 inthe extended version). Inother words, the expandermay simultaneously pro-duce 16 specific sounds,each with its ownenvelope characteristic.Furthermore. a number ofthese programmed soundsmay be used in apolyphonic arrangement(i.e. several notes on a

single MIDI channel), andthis up to a total of 12 or24 notes, divided over 16channels. We found thatthis remarkable feature ofthe Bohm expander en-sures a richness of soundunparalleled by any otherdevice of comparablecost.

Principleof soundproductionThe Bohm expanderfeatures a sound gener-ation process that is gen-erally referred to asadditive; it uses phasemodulation (PM), which isroughly comparable tothe phase distortion (PD)and frequency modula-tion (FM) methods whichare more generally usedin digital synthesizers. It isbeyond the scope of thisarticle, however, to exam-ine the technical charac-teristics of thesemodulation proceduresfurther; the main principleof the additive process isthat any output sound isbasically a combinationof digitally generatedsinusoidal voltages. As op-posed to the subtractivemethod, only those com-ponents are generatedwhich are essential to acertain target outputsound; no filter devicesare present in this ar-rangement. The subtrac-tive method, however,

Main features of the BOhmDYNAMIC 12/24 expander Additive digital synthesis (phase modulation). 4 operators (one with feedback) and 8 algorithms

using 4 envelope generators with touch sensitivityand level scaling features.

12- or 24 -note polyphony depending on version. 98 ROM -stored sounds. 98 programmable sounds in RAM with battery

back-up facility. Large ROM extension planned. Vibrato and vibrato aftertouch. Glide, modulation wheel, aftertouch, touch sensi-

tivity, etc Programmable combination of polyphonic notes

into pairs for beat effects (chords); this halves therequired number of polyphonic notes.

Automatic 440 Hz -based tuningldetuning. Direct programming of 98 presets on the expander;

no auxiliary equipment required. Optional cassette interface. Powerful MIDI interface; simultaneous control of 16

different sounds on the 16 available channels. Parameter readout on 4 front panel mounted

7 -segment displays. 14 function keys; 10 numerical and 4 multi -function

program keys with LED indication. Optional analogue 'ensemble' circuit (bucket

brigade delay). Pedal input for timbre variation. Stereo and mono outputs with front panel volume

adjustment. Mains power supply incorporated. Optional flat 19 inch case available with pre -

drilled and inscribed front panel.

starts from a bulk amountof harmonics, from whichthe undesirable compo-nents are removed byfiltering.In the case of the Bohmexpander, the sound pro-duction process is essen-tially as follows: there are

available four generators(also called operators)which may be user -combined into eightalgorithms (configurations).In each of thesealgorithms, one, unfortu-nately fixed, operator maybe arranged such that it

EE

March 1986

features a certain degreeof feedback to producenoise -like sounds. As fortheir function, theseoperators may be com-pared to the well-knownVCO-VCA-VCF modules,each with their ADSR, aspresent in analogue syn-thesizers; they are de-signed to produce and/ormodulate sound. In mostdigital synthesizers, theLFO function is not re-alized by an actual circuitsection, but by some logicarrangement to the sameeffect. In the November1985 article on the newMIDI standard it wasalready pointed out that,unfortunately, most digitalsynthesizers only feature asingle LFO function, solelyintended for slow pitchmodulation (vibrato effect).In the opinion of manyusers of analogue syn-thesizers, this is a quiteregrettable fact, since theyfeel that there are manyother interesting appli-cations for the LFO func-tion. It is a pity that Brihmhas also provided onlyone LFO ex-pander.The operators in the BOhmexpander are accessiblethrough software only, andthis implies that there areno hardware controls suchas potentiometers orswitches to be set. Instead,a certain number ofparameters are user -defined to obtain thedesired sound effects.These parameters are div-ided into two groups: oneset is common to all

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Parameter Range .--; 1 ,--- 2 ..-.-- 3 :.-. 4

Detuning 0 - 7 00 16 32 48Harmonic 0 - 15 01 17 33 49Level 0 - 99 02 18 34 50Envelope scaling 0 - 3 03 19 35 51Attack 0 - 31 04 20 36 52Decay 0 - 31 05 21 37 53Sustain 0 - 31 06 22 38 54Sustain Level 0 - 15 07 23 39 55Release 1 0 - 15 08 24 40 56Touch sensitivity 0 - 99 09 25 41 57Level scaling + 0 - 99 11 27 43 59Level scaling - 0 - 99 12 28 44 60Release 2 0 - 15 14 30 46 62

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Harmonic 0 64' 32* 16' 8' ..'Harmonic 1 32' 16' 8' 4' 2'Harmonic 2 16' 8' 4' 2' 1'Harmonic 3 10 2/3' 5 1/3' 2 2/3' 1 1/3' 2/3'Harmonic 4 8' 4' 2' 1' 1/2'Harmonic 5 6 2/5' 3 1/5' 1 3/5' 4/5' 2/5'Harmonic 6 5 1/3' 2 2/3' 1 1/3' 2/3' 1/3'Harmonic 7 4 4/7' 2 2/7' 1 1/7' 4/7' 2/7'Harmonic 8 4' 2' 1' 1/2' 1/4'Harmonic 9 3 5/9' 1 7/9' 819' 4/9' 2/9'Harmonic 10 3 1/5' 1 3/5' 4/5' 2/5' 1/5'Harmonic 11 2 10/11' 1 5/11' 8/11' 4/11' 2/11'Harmonic 12 2 2/3' 1 1/3' 2/3' 1/3' 1/6'Harmonic 13 2 6/13' 1 3/13' 8/13' 4/13' 2/13'Harmonic 14 2 2/7' 1 1/7' 4/7' 2/7' 1/7'Harmonic 15 2 2/15' 1 1/15' 8/15' 4/15' 2/15'

Parameter Range

Feedback 0- 7 13Octave 0- 7 45Second Generator 0 - 12 61Connection diagram 0- 7 29Options 0- 7 31Vibrato depth 0-99 10Vibrato frequency 0-99 26Vibrato delay 0-99 42Vibrato after touch 0-99 58

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operators, the other com-prises operator -specificparameters. Among thelatter is the relative pitchparameter, not expressedin units of frequency(Hertz), but in numbers orranges of harmonics, de-rived from a fundamentalnote; this method will bereverted to. Operator out-put amplitude is program-mable between relativevalues 0 and 99; theamount of detuning rela-tive to the othergenerators is also pro-grammable (0 to 7) whilethere are another dozenor so relative parametersto define the envelopeprofile of the signalgenerated by eachoperator.Among the group of com-mon operator parametersis the code number for thedesired internal configur-ation of the expander(algorithm), a parameterfor frequency and intensityof the vibrato effect, aswell as one for the degreeof feedback used withoperator 1.The extended version ofthe Bohm expander offersa choice of two possiblearrangements for the

available 24 notes; de-pending on the valueassigned to the 'secondgenerator' parameter, theuser may select either24 -note polyphony or acombination of the two12 -note groups into asystem with 12 -notepolyphonic characteristics.This unison of two times 12notes, however. in no wayimplies the loss of 12

notes; on the contrary, thisarrangement causes agreat many possible beatnotes in the overall outputspectrum, which results ina 'massive' sound impres-sion. especially with theimitation of strings. The ef-fect thus obtained may becompared to a pianowhich has two or threestrings tuned to the samenote. This seemingly in-

significant detail effec-tively compensates for therelatively few availableoperators.

Pitch definitionSince Bohm has a long-standing reputation in thefield of electronic organsin kit form, it is hardly sur-

prising that they do notdefine pitch in terms of fre-quency (Hertz), but interms of harmonic ranges,relevant to a fundamentalfrequency. This conventionis generally known toorgan players who use theterm fool for this purpose.To set the output pitch ofan operator, the user mustspecify a code number toselect a certain harmonic,which is, of course, de-rived from a fundamentalfrequency, whose pitch isinitially defined with theoctave' parameter com-mon to all operators.Together with the grade ofdetuning specified foreach operator, the out-lined method of pitch con-trol results in highlyinteresting sound effectswhilst ease of program-ming is fully retained.

The completekitThe kit comes with aspecial moulded trans-former, DIN type MIDIsockets, 6.3 mm typesockets for the audio con-nections, 240 V mainscable, dual -fuse mainsreceptacle, push buttonfunction keys and displaysfor front panel mounting,heatsink, all cables andinternal connectors, bat-tery for RAM data reten-tion, and, last but notleast, the whole set ofcomponents to fit onto thePCBs, ranging from ex-cellent quality IC socketsto the microprocessorchip; even solder hasbeen provided to make fora complete kit.The main PCB is a large (4times eurosize!), double -sided and through -platedtype which allows fast andefficient completion. Toprevent short circuits, thesoldering side of this PCBhas been designed suchthat it has no coppertracks running betweentwo IC socket pins. Thereare also separate PCBs forthe expander front panelparts and the input andoutput sockets at the rearof the case.

The designers at Bohmhave obviously takenpains to avoid a largenumber of alignmentpoints in their circuit; oncecompleted, there are onlyfour presets to adjust, andthese pertain only to thecassette and phaser ex-tensions.The time spent on the con-struction of this complexkit depends to a large ex-tent on individual skill andexperience, but it wouldseem advisable to allowat least fifteen hours. If thestep by step constructionprocedure is followed asoutlined in the kit manual,even the least experi-enced user will stand agood chance of first-timesuccessful completion,provided, of course, thatthe necessary (simple)tools are to hand.After a thorough visualcheck of the completedPCBs, power may be ap-plied for the first time. Donot run into trouble, as we

did, by fitting the Type6809 microprocessor thewrong way about...Thereare some 50 ICs on themain PCB, 9 of which are40 -pin types. These are allmounted in the samedirection, except for...theCPU! After having cor-rected this trifling mistake(happily, the 6809 sur-vived), the expander wasat once fully functional.With an amplifier and aset of loudspeakers con-nected, the first chordsmay be sounded with aMIDI keyboard, anotherMIDI -compatible syn-thesizer, or a micropro-cessor system with suitablesoftware supplying serialdata to the relevant inputon the Bohm expander.

15 function keysOperating the expander isremarkably simple, since

EEMarch 1986

the user need merelydecide on his choice ofpreset to go with one ormore MIDI channels,which may be controlledby the above mentionedpossible sources. Datareception at the expanderMIDI input is signalled bya LED, and two 7 -segmentdisplays indicate the cur-rent MIDI channel; twofurther displays show thepreset code relevant tothat MIDI channel. Thecode may be set by press-ing the keys marked 0 to 9,and selection of anotherchannel is effected bydepressing the CHANNELkey which shows the wholerange of channel -presetcombinations. This simplearrangement of selectionkeys and displays hasproved ideal for effectiveprogramming of the ex-pander unit.To create one's ownsounds and timbres, the 98ROM -resident presets mayfirst be copied into RAMby pressing the EDIT keyduring power -up. Note thatthe B6hm expanderfeatures a RAM data reten-tion and protection facilityto prevent loss of user-programmed presets; thiswill be appreciated, nodoubt, by musicians per-forming live on stage andcomposing at home. TheROM to RAM copy routinemay be run whenever it isdesirable to start fromscratch, that is, from the 98presets defined by Bohm.Copying takes less thantwo seconds while thedisplays read 'init'.This review does not coverthe actual programmingprocedures, as this is ex-plained and exemplifiedat considerable depth inthe manual supplied withthe kit.

SoundcoverageAmong the vast amount ofROM -stored sounds aresynthesized imitations of abandoneon, Hawaiianguitar, pipe organ, severaltypes of electronic organ,

EEMarch 1986

a brass section, thehuman voice, string instru-ments, etc. Among the per-cussion instruments arefound a quite successfulvibraphone, xylophoneand marimba, as well asa glockenspiel andtubular bells, which soundquite impressive. Apartfrom these imitations, thereis, of course, an extensiverange of modern syn-thesizer sounds which areever so easily 'puttogether' by trial and errorparameter programming.A noteworthy aspect of theexpander parameters isthat they are readily learntby heart; after only a fewdays' use of the expander,the preset codes table isonly required to look upthe less usual sound ar-rangements.

26

Bohm DYNAMIC12/24 com-pared withYamaha TX7To appreciate the relativequalities of the Bohm ex-pander, it is useful to com-pare it with the well-knownYamaha TX7. The TX7 waschosen because it is func-tionally similar to theDYNAMIC 12 24 (bothdevices have been de-signed to function as anextension to other elec-trophonic instruments: theTX7 to the popular DX7digital synthesizer, and theDYNAMIC 12 24 to B6hmorgans. Moreover, the unitsare offered at about thesame price. Finally, theTX7 is considered as akind of standard by many.It should be noted that ourcomparison is by nomeans intended to be atest.The first noticeable differ-ence between the twounits is that the DYNAMIC12 24 is programmed en-tirely and direct via itsfront panel controls with-out the need of any auxili-ary equipment, whereasthe TX7 can only be oper-ated in conjunction with

the DX7 (or similar) syn-thesizer.A further difference comesabout in the use of theMIDI interface and the as-sociated protocol.Whereas the TX7 has beendesigned for a fixed ar-rangement of one soundper MIDI channel, thestandard 12 -note version ofthe BOhm expander iscapable of simultaneous12 -channel MIDI reception(or even 16 in the 24 -noteextended version); at thesame time these 12 or 16(or even 24) notes mayhave 16 distinct sounds.This obviously puts theGerman expander in anadvantageous position.

Psycho -acousticsSince there is no accoun-ting for taste, any judgement of the overall outputsound produced by theexpanders is bound to besubjective. Nevertheless,some remarks need to bemade concerning thissubject.From a musical point ofview, the PM and FM syn-thesis methods are six ofone and half a dozen ofthe other, so this will notbe examined any further.The six operators and 32algorithms offered by theYamaha TX7 may seem toexceed the possibilities ofthe Bohm expander, but tosay that the presets on theTX7 are 'better' than thoseon the DYNAMIC 12 24would be too bold; theyare simply... different, ex-otic, charming. The largenumber of availableoperators in the TX7 allowsa rich output sound, es-pecially in the attackparts. Their brilliant,(almost flashy qualityshows that the designersat Yamaha have clearlyunderstood the relative im-portance of the attackcharacteristic in the defi-nition of a vocal or in-strumental sound. However,in the end, the continuousemphasis on the attacksmay well cause a certain

fatigue in the listener; itseems that the high fre-quency components inthe output spectrum areexcessively accentuatedduring attack. Quite con-trary to this, the Bohm ex-pander features asmoother, warmer soundby virtue of its selectiveaccent on the low andlower medium fre-quencies.It is certainly quite clearthat the sounds of the twoexpanders have beenshaped in different con-tinents of the world, andyet, they are wonderfullycomplementary to oneanother.The touch sensitivityqualities of the B6hm ex-pander are certainly lessconvincing than those ofthe TX7, but it is not clearwhether this is a matter ofbadly chosen program-ming parameters (eitherby us or by Bohm) or,perhaps, of a real short-coming on the DYNAMIC12 24. However, in our opi-nion, touch sensitivity ishardly ever up to thedesired standard, despitethe fact that mostmanufacturers makerather a fuss about it.

DeceptivefiguresAn actual count of thenumber of notes availablefor polyphonic ar-rangements shows the TX7superior to the DYNAMIC12124, since the formerhas 16 -note polyphony, thelatter only 12 (basic ver-sion). This difference is notas important as it wouldseem, however, since theBohm expander featurespolyphony of sounds, i.e.not a mere 12 distinctnotes, but 12 polyphonicinstrumental sounds. The24 -note version of theBohm expander no doubtoutclasses the TX7 evenfurther in this respect.Another rather essentialdifference involves thenumber of ROM -stored(pre-programmed) sounds:98 in the BOhm, 32 in theYamaha. Again, the rela-tive importance of thesenumbers should not be ex-aggerated, because thereare effective levelling fac-tors such as ROM exten-sionsicartridges, acassette interface, and dif-ferent MIDI interface con-ventions. This goes to showthat from a musical pointof view, the debate aboutthe highest numbers isquite beside the point.

ErgonomicsIt is true that the simple7 -segment displays on theBohm unit are only usefulfor coded indications, butthey have the advantageover the LCD display onthe TX7 of being legibleunder the most adverselighting conditions. As forthe front panel controls,both units do equally wellin this respect. The stereooutput on the Bohm ex-pander is likely to be ap-preciated as much as theheadphone socket on theTX7. The 'ensemble' exten-sion of the Bohm ex-pander undeniablyensures a rich outputsound and compensatesfor the relatively fewoperators, but as such it

EE

March 1986

does not constitute amajor advantage over theJapanese unit. Quiteregrettably, the DYNAMIC12/24 lacks a control forfast and automatic in-crease of the preset -parameter displayreading. The level scalingcharacteristics of the unitsappear to be about thesame, just as their after -touch qualities, but itshould be noted that theBohm expander allowssimultaneous specificationof 16 different values ofthese parameters, as op-posed to a single one onthe TX7.These are the most essen-tial points of comparison,but it should beremembered also that theBohm expander comes inkit form, true to the tradi-tion of this firm, whereasthe Yamaha TX7 comesready-made. However, thejoy of putting together agood electronic kit will beone of the strongarguments in favour ofBohm, except perhaps inthe eyes of non -technicalmusicians.

Faites cos jeuxEach of the expandershere compared will nodoubt have its staunchsupporters, who will stickto 'their rig' through thickand thin. Obviously, theTX7-DX7 combinationdeserves our esteem andadmiration, but we feelmore sympathetic towards

the Bitihm DYNAMIC 12/24when it comes to buyinga state-of-the-art digital ex-pander.This comparison, which isno doubt more or less sub-jective, has tried to showthat both expanders havenot only their specificmerits, often cunninglypresented in sales ploys,but also their deficiencies,carefully hushed up bythe manufacturers. Boththe negative and positivepoints, however, are boundto become apparent oncethe potential buyer hassubjected all units offeredwithin a certain pricerange to critical analysisand comparison.

ConclusionThe qualities of the Bohmexpander make it apowerful newcomer on thesynthesizer market, whichis heavily dominated byJapanese firms. TheGerman firm has suc-ceeded in producing ahighly sophisticated, state-of-the-art music generatorwhose unique features,low price, and availabilityin kit form ensure a worthycomparison with far moreexpensive ready-madeunits of other makes. DM

Definitions used in this articleSound is the result of vibrations of the air (which setup similar vibrations of the ear drum); a sound ismusical if the vibrations are regular, and unmusical ifthe vibrations are irregular.

Timbre is the characteristic quality of a sound pro-duced by a particular voice of instrument, depend-ing on the number and character of the harmonics.

Pitch is the quality of a sound determined by thenumber of vibrations by which the sound is caused.

A note (shown by little oval characters on a sheet ofmusic) defines the pitch of a pure musical sound, i.e.one lacking any harmonics. Notes are named afterthe first seven letters of the alphabet: A, B, C, D, E,and G.

A lone defines the distance of pitch from a line (orspace) to the space (or line) next above or below iton a sheet of music, that is, the distance between thenotes A and B, C and D, D and E, F and G, and Gand A. The distance between notes B and C and Eand F is called a semitone, which is the smallest div-ision of pitch recognized in modern music.

Bandoneon = an Argentinian type of accordion.There is no keyboard, merely buttons. And the left-hand buttons produce not chords but single notes, sothat to produce chords several buttons must bedepressed (0.C. to Music).

VCO = voltage -controlled oscillator

VCA = voltage -controlled amplifier

VCF = voltage controlled filter

ADSR = attack -decay -sustain -release

CFO = low frequency oscillator

LCD = liquid crystal display

EE

March 198628

The subwoofer described in this article can be used toextend any existing loudspeaker system. It has beendesigned to obtain a frequency response within ±-1 dBover the frequency range 30-100 Hz with an enclosurevolume of only 85 litres.

ACTIVESUBWOOFER

The faithful reproduction of very lowaudio frequencies in normal livingrooms poses a number of problems.The first is that the lowest frequency,I. that can be reproduced depends

Technical characteristics

System:Net volume:Crossover network:

Frequency range:Recommendedamplifier output:

Maximum soundpressure:

Sensitivity:

active closed box85 litreselectronic; 24 dB: octave;Bessel filter30-100 Hz (see Fig. 1b)

50-100 W

>100 dB (50-100 Hz)87.5 dB (1 watt at 1 metre)

The system has been provided with a presettable outputpower limiter

on the lencrih.1, of the room:

= c 2/ Hz-_

where c is the velocity of soundwaves in metres per second at nor-mal atmospheric pressure and at20 CC.In a 6 -metre long room, therefore,the lowest frequency that can bereproduced without distortion isabout 28 Hz. In practice. other prob-lems, such as the vibrating of doors,windows, cupboards. glassware,and so on. become evident longbefore this frequency has beenreached.A more important problem concernsthe dimensions of the enclosure. Fora reasonably faithful reproduction at30 Hz and full volume. the enclosureshould normally have a volume ofnot less than 100 litres. andpreferably about 200 litres. Two

such large boxes required for astereo installation are often unaccep-table in a normal living room.Fortunately, there is an alternativewhich offers much the same bassperformance and has a much moremodest space requirement. It usesonly one enclosure for the low fre-quencies, even in stereo operation.For the middle and high fre-quencies, one loudspeaker systemper channel remains required.The alternative solution is madepossible by the human ear havingvirtually no sense of direction at fre-quencies below about 200 Hz. Thismeans that if frequencies below.say, 100 Hz. are reproduced by onecentral subwoofer, and the re-mainder of the audio spectrum byso-called satellite loudspeakers,there is no discernible impairmentof the stereo effect. Note that thesatellite speakers can be kept small

29 EEMarch 1986

because they are required toreproduce frequencies above100 Hz only. The design and con-struction of these satelliteloudspeakers will be described innext month's issue of Elektor Elec-tronics.Table 1 shows some types of loud-speaker system and their most im-portant characteristics. It is clear thatthe closed box generally offers thebest performance, were it not for its

inability to reproduce very lowaudio frequencies when its volumeis modest to small. The bass reflexand transmission -line types aresuperior in this respect, but thesesuffer from an inferior frequencyresponse characteristic and a muchworse step response. The horn andtransmission -line types are, further-more, rather difficult to build.This leaves, in practical terms, theactive closed box. The properties of

this type depend to a large extent onits specific design, which can be ap-proached from different directions.The questions that immediately cropup are: "how low should the -3 dBpoint be?", and "what are the ac-ceptable dimensions of the enclos-ure?". The lower the frequency atthe -3 dB point for a certain volume,or the smaller the dimensions for agiven -3 dB point, the more elec-tronic correction will be necessary.

Type of system Dimensions Sensitivity Step response Characteristic Lower -3 dBpoint

Horn very large very high reasonable very irregular fairly highBass reflex large high reasonable irregular lowTransmission line large low poor irregular lowClosed box large fair good tapering highActive closed box small reasonable* good* smooth* low*

* Depends to a large extent on the system set-up.

Table I Someprominent typesof loudspeakersystem and theirmost importantproperties.

Fig. Ia. Fre-quency responsecharacteristic ofthe Dynaudio30W54 drive unitin an 80 -litreclosed box with-out any filtering.

Fig lb. Fre-quency responsecharacteristic ofthe Dynaudio30W54 drive unitin an 80 -litreclosed box withelectroniccrossover net-work and correc-tion filter.

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EEMarch 1986

30

Fig. 2. Blockschematic of theactive subwoofersystem. Anygood 50-100 Wpower amplifiermay be used asoutput amplifier.

Fig: 3. TheDynaudio 30W54drive unit.

But this correcting cannot be takentoo far, otherwise the sensitivity aswell as the step response will suffer;also, distortion will increase andpower handling will be reduced.The present system was designed togive a reasonable performance with-out any electronic help first, andthen some electronic circuits wereadded to extend the frequencyrange downwards.The frequency response of the sub -woofer in an 80 I enclosure is givenin fig. 1: lb clearly shows the effectof the added filters, particularly thelowering of the -3 dB point fromabout 50 Hz to 30 Hz.

Set-upThe system is arranged as shownschematically in Fig. 2, and is seen toconsist of the loudspeaker in itsenclosure, an output amplifier, andan electronic circuit. The outputamplifier will not be discussed here,because any good type may beused, as long as it is capable ofdelivering at least 50 W into 8 ohms.The enclosure is simple to build asdescribed under Construction. Theloudspeaker used in the prototypewas a Dynaudio (Denmark) type30W54 -see Fig. 3. This is a robust300 mm drive unit on a light metalframe with high peak power hand-ling capability, good step response,and a suitable frequency response(see Fig. Ia).The electronic circuit consists of twoparts: the filters and the output

limiter. There are three filters: asteep -skirted anti -rumble type withits change -over point at 20 Hz; a cor-rection filter for the very low audiofrequencies from 50 Hz downwards;and a crossover filter with change-over point at 100 Hz and a slope of24 dB/octave. The combination ofthese filters results in the frequencyresponse shown in Fig. lb.The output limiter is, strictly speak-ing, not essential but very useful,particularly where full volume isused habitually. It has been added toallow for the decreasing powerhandling capability of the drive unitbelow 50 Hz. The coming into oper-ation of the limiter is indicated by thelighting of an LED.

Subwoofer andsatellite speakersIn principle, the subwoofer can be

used as an addition to any loud-speaker system that has unsatisfac-tory performance at low fre-quencies. If, however, a new loud-speaker system is planned, thedesign of the satellite speakersshould take account of the sub -woofer. These units need reproducefrequencies above 100 Hz only, sothat the volume of their enclosurescan be kept to about 10 litres. Asalready stated, suitable satellitespeakers will be dealt with in nextmonth's issue.The various units should be intercon-nected as shown in Fig. 4. Thesimplest and least expensive way isshown in Fig. 4a: the subwoofersystem, including the output ampli-fier and filters is simply connected tothe loudspeaker terminals of theexisting amplifier. Capacitors C forma 6 dB filter to protect the satellitespeakers high low -frequency outputpower. The necessary level match-ing between the subwoofer and thesatellite speakers may be effectedwith a preset on the filter PCB.Where the pre -amplifier an outputamplifier are separate units, inter-connections may be made as il-lustrated in Fig. 4b. In this way, eachloudspeaker has its own outputamplifier, so that filtering can takeplace between the pre -amplifier andthe output amplifiers. The set-up inFig. 4b is preferable to that in Fig. 4a.The question may be asked why thesatellite speakers are filtered at only6 dB/octave from 100 Hz, whereas thesubwoofer has a skirt roll -off of24 dB/octave. The answer is that thesatellite speakers (in a closed box)have an inherent fall -off of about12 dB/octave. Together with the a