SYUNWAVE * Sounds from swirling sea to cymbal and wood block Easy to build and play *Dual trigger operation - percussive/external trigger *Touch sensitive Design - Mike Beecher Development - Robert Penfold he Synwawe continues aur ‘sans of small projec that Drodiion sounds ‘or ase in slectre-rmasit by percussive cn trol, Tre minimury number at Senin home been selected 1a give = side rarge of zen wave! Pounds, ln addition, eifarent et tings ofthe controts wll padre sein, cpriaal and woedlack Like the Syria preyect show elseahere inthis issue, the tnt cam be tingeted by teoping ‘he case or by string 2 drum on which the Syrucine routed). These projects ave also iaeal tor Ieiggering ram an _ external souree (eg. a Sequences syrten Siser br micro) ants asecones ‘rade of aperatan can befrarn an electronic trigger using a positive oing edge of about J to LS wots in smaliiude. Interaction of the feo erodes of use Is acssible $0 that compen rhythms cat be nase from asteagy eterna tig. gered’ beat maed wih hand ar druin lace praviding symcopaton, The feu contols are Volum ern anzaft saitch), for setting output level: Gecay - eciusts the ‘takes far the sound 09 ie Pitch ~ sets the ‘requarcy range cf roise framulow te veh, Sa rasenanen conrad thst nar rows ane high ints the pik range eeloctec Circuit “The bleek diagram of Fisure 1 shows the general srrannerent ised the Byewave. Araneae shawer can be operated by either - cree H | Ne aw a — | en internal micrephone oar Exe! tigger sgn an both | The envelope shapar has 3 las! | stack and slow doc, with latter being agjustabie fra less than 100m fo about 8 seconds The cutput of the envelane | shaper is fed to the control input of 3 voltage contre’ arnpliier O¥CA) un Butter stage simple ise annerator feeds e bandpass fier which i tum foods the input af the VOM ‘The bandpacs iter ie tunable froin sin hundted hevte to rere tha Iht, and therefore gives cursidersblé contra! over the Sound prosued by the unk. The bardeidth of the titer can be vpried forma verybroadresponse tapvery sharp ceakyresponse by means otted control, an again this perrnns the ouneat sound of the unil to be vatled great. He row consider the tl circu diagram af the Syrave | (Figure 2y, 01, R1.D1, B2,and Re | brocess the trigger sigrel 30 tnat | fh ts rising (pereive) ace abit Desi putee of abet 7 wots in ahiplituda is supplind tothe base: cof TRL. TRL and TR2 farm @ Dar- Tington pair ernlter follower | ing the brie! inst alse ta TRI RS one RII pews # uischarae path for C2, aod the setting of AVL ottermines the discharge time of C2 (and therefore sne lerath of the nut sige HRerystn microphone 41 is ub jected te strong vipratiens ‘ti lve an output fevel of several ‘alls peak 10 peak, and postive goeng output half eycieswill result in G2 being rapidly charged. The ssutgat sigral hovel ard Irence Ihe charge produced an C2 deperids tan hw hard the unit oe se dean | input o ta which it ie attached is sluick, ‘and this gues a degree oF to sensi, ‘The signal across C2 must be only lightly loaded ae the OBcay time wl be greally shortened by the cnarge curmert leskad away ‘birough the cosine c-Four, TAS therefore used ag en eriiter fo lomer buffer stage whieF couples the cutnit trom G2 tothe canal YOR, The WGA wis @ CASOHO transconductance am | plitier, and it gives a love! of gain ‘hat is proparticnal tothe cantral rises rapidly to its peak hs then decays relatively skoaly. in sympathy with fhe ex age across C2, The VGA is coupled te eutpul sockat hy way of youre wantral F¥2, Dual halenced supplies are requires by the VGA cia try ane 2 terial OV rail effect vely Breguces by FIO, R12 end C5 18 15 uged a the ree ere erator and R12 apolies 2 mevmrse Bias to 1 basen’ iunction This junction beraves rales ike a dene’ ounde and 'ke a Zener Grade presucrs meee seshes. This arrargeme ns preferable 10 se ing a Zener uigse thaugr. a= altos a ghee audit al audic Evencies The bah becusrty Euplit of th noise generator isexcessive, and so C11 is used to give high’ frequency attenuation to correct this. ‘A twin T filter is used as the basis of the bandpass filter, butas a twin T network gives @ natch at its centre frequency rather than 3 peak, the filter network is con: nected to give negative feedback over a common emitter amplifier. This amplifier features TR4 in a Conventional configuration. TR's emitter circuitry enables certain amount of negative feedback to be applied to the amplifier and the amount of feedback is con- trolled by RV4. With the slider of RV4 at or near the lower track connection there is little or no feedback; giving the circuita high @ value and a narrow, peaky response. Moving the wiper of RV4 towards the upper end of its track gives increased feedback and @ consequent reduction in Q ‘together with a broader, flatter re- sponse. 'RV3 is part of the twin T net- work, and varying the setting of this Component alters the centre frequency of the filter. Ideally all ‘three resistive elements in the filter should be varied when tun- ing the fitter, but this ts nat really Comnteted Greuit board practical, This simple system works quite well though, and the only minor drawback is that the Q cof the filter varies somewhat with ‘changes in the settingofthe pitch ‘control. At some settings of RV3 it may be found that setting RV4 for a very high Q causes the filter to oscillate at its centre frequency. If desired, this can be avoided by adding a resistor of about 150 ohms in value between the posi: tive terminal of C9 and the upper track connection of RV4, How. ever, as this would limit maxi mum Q available, especially at the highest and lowest pitch con: trol settings, it wauld reduce the effectiveness ofthe unit andisnot really worth while, C13 is needed to prevent the fitter becoming unstable due to Figure 2_The circuit diagram ot the Symware. stray high frequency feedback. C4 couples the output of the filter to the input of the ¥CA. The current consumption of the cir- is only about 1.5mA.. or a little higher than this when it is triggered. Pr view mryz3, Bewor DL BFWBRCTYE Construction Details Except for C9 all the resistors, capacitors, and semiconductors are fitted onto a printed circuit board. Fit the semiconductors last, and make quite sure that the electrolytic capacitors and semi conductors are connected the right way round. The printed ci cuit board fits into the mount- ing rails ofthe specified case, but this leaves insufficient roam for Jeads to be taken around the board to the controls, battery clip, microphone, and sockets. This makes it necessary to fit Veropins to the board at the points where:it nnectstothese components, or preferred, these leads can sim: ply be soldered direct to the copper tracks. Details of the printed circuit board are provided in Figure 3 The removable lid of the case is used as the rear panel in this application, and the two sockets are mounted on this panel. The front panel is drilled to take the four potentiometers and the mi- crophone is mounted on the right side of the case (as viewed from the front). The microphone isFigure 3. PCB Wack. component and wiring Get Figure &. Cae and bracket contruction. | actually @ crystal earphone hav: ing the earpip unscrewed, The | senall ecrew at the rear of theesr: | phone is removed, and this i hen used to fix the earphone to | the case. Figure 4, shows te drilling of the case, and it is advisable to follow this as accu rately a3 possible since there is nat a great deal of excess space inside the case and it might etherwise be found that all the parts cannot be fitted into the case. Next C9 is connected to RV4 and the other wiring to the off board components is completed Figure 3 gives details of all this wiring. The printed circuit board fits into the upper set of mount: ing rails in the case with the | component side uppermost. The battery fits vertically into the case | in the space between the two sockets and the microphone, A iece of foam material can be glued ta the rear panet ofthe case to keepthe battery firmly in place It the Synwave is to be fitted ‘onta a drum it is necessary to fit ‘the unit with a mounting bracket, This can consist of 8 piece of25mm aluminium channel sec- tion which is fixed to the case using a couple of 6mm M4 bolts. A large bolt is used to clamp the Synwave onto the drum, and the bracket is drilled and threadedon one side. to take this bolt. A | handwheel bolt is ideal for use in | this application, but an ordinary type can be used of course. It is advisable to fit a small pad of rubber on the part of the bracket ‘Opposite the mounting bolt as this will help to prevent the rim of the drum from becoming scratched when the Synwave is fitted in place. To complete your project use our smart brushed aluminium panel with electric blue legend and sticky back as shown. Testing and Use Connect the Synwave to an amplifier via SK2 and switch on with the Volume control set to midway. Set Decay to maximum, Pitch to minimum and Q to mid- way. Give the unit a sharp tap or usé a suitable trigger signal (applied to SK1) and a ‘seawave" should be heard. Using short Decay and high Pitch and Q, the woodblock saund can be obtained. Cymbal effects | fequire high Pitch and @ with slightly longer Decay. Sos aed complete kit (LW87L) of all parts listed P&P. The kit does not include batteries, In addition, the Q control can put the filter into oscillation and Pitch will then vary the fre- quency. Of course, this effect may not be desirable, especially asthe volume increases substantially, and is simply removed by reduc- ing the Q contral or inserting a resistor as mentioned garlier. A little experimentation with 1 £10 26 inc. VAT ane \s available fram Maplin Electronic Supplies ata price of the controls will soon give an idea of the wide range of useful effects that can be produced | Sgtwave external view with bracket. SYNTOM continued from page 25.