All rights reserved. We advise readers to check that all parts are still available before commencing any project.

Transcription

1 opyright 2008, Wimborne Publishing td (Sequoi House, 398 Ringwood Rod, Ferndown, Dorset BH22 9AU, UK) nd TechBites Interctive Inc., (PO Box 857, Mdison, Albm 35758, USA) All rights reserved. The mterils nd wors contined within EPE Online which re mde vilble by Wimborne Publishing td nd TechBites Interctive Inc re copyrighted. TechBites Interctive Inc nd Wimborne Publishing td hve used their best efforts in prepring these mterils nd wors. However, TechBites Interctive Inc nd Wimborne Publishing td me no wrrnties of ny ind, expressed or implied, with regrd to the documenttion or dt contined herein, nd specificlly disclim, without limittion, ny implied wrrnties of merchntbility nd fitness for prticulr purpose. Becuse of possible vrinces in the qulity nd condition of mterils nd wormnship used by reders, EPE Online, its publishers nd gents disclim ny responsibility for the sfe nd proper functioning of reder constructed projects bsed on or from informtion published in these mterils nd wors. In no event shll TechBites Interctive Inc or Wimborne Publishing td be responsible or lible for ny loss of profit or ny other commercil dmges, including but not limited to specil, incidentl, consequentil, or ny other dmges in connection with or rising out of furnishing, performnce, or use of these mterils nd wors. READERS TEHNIA ENQUIRIES We re unble to offer ny dvice on the use, purchse, repir or modifiction of commercil equipment or the incorportion or modifiction of designs published in the mgzine. We regret tht we cnnot provide dt or nswer queries on rticles or projects tht re more thn five yers old. We re not ble to nswer technicl queries on the phone. PROJETS AND IRUITS All resonble precutions re ten to ensure tht the dvice nd dt given to reders is relible. We cnnot, however, gurntee it nd we cnnot ccept legl responsibility for it. A number of projects nd circuits published in EPE employ voltges tht cn be lethl. You should not build, test, modify or renovte ny item of mins powered equipment unless you fully understnd the sfety spects involved nd you use n RD dptor. OMPONENT SUPPIES We do not supply electronic components or its for building the projects fetured; these cn be supplied by dvertisers in our publiction Prcticl Everydy Electronics. Our web site is locted t We dvise reders to chec tht ll prts re still vilble before commencing ny project. To order you copy for only $18.95 for 12 issues go to

2 onstructionl Project SIMPE AUDIO IRUITS Prt 3 Power Supplies, oudspeers, rossover Networs nd Filters F I RAYMOND HAIGH A selection of pic-n-mix low-cost udio circuits from premplifier to speer! modest output from one of the smller power mplifiers (My 02) is ll tht is required, dry btteries represent suitble power supply. However, when the output is expected to exceed the hlf-wtt level for sustined periods, mins power unit is more pproprite. Svings in the cost of btteries will quicly cover expenditure on components. ompromises, inherent in the design of loudspeers, give rise to limittions which re normlly overcome by the use of two or more units nd crossover. Power supplies, loudspeers nd ssocited networs re the topics to be covered this month. SUPPY REGUATION A simple mins power supply comprising full-wve rectifier nd cpcitor input filter will deliver n off-lod voltge of round 1 4 times the trnsformer secondry voltge. With secondry rted t 12V.c., the off-lod d.c. output voltge will, therefore, be lmost 17V. If the power supply output is close to the mximum sfe operting voltge of the mplifier i.c., there is dnger tht, under no-signl conditions, the device will be ruined. When fully loded, the d.c. output voltge will fll to round 14V with n dequtely rted trnsformer; lower when the trnsformer specifiction hs been simped. Voltge will, therefore, be low t the very moments when the power mplifier is being clled upon to deliver high output. These voltge vritions re cuse of distortion nd impir the performnce of the power mplifier. Moreover, when highgin premplifiers or rdio tuners re fed from the sme supply, the vritions cn lso result in instbility, even when substntil decoupling is provided. POWER SUPPY These problems cn be voided by regulting the output of the power supply, nd verstile circuit, which cn be dpted Simple i.c. Power Amp. modules (left-to-right, topto-bottom) from My 02 issue. B Single TDA2003 Amp B Twin TDA2003 Amp B TDA7052 Amp B TBA820M Amp B M380N Amp B M386N-1 Amp for single or stereo pirs of ny of the mplifiers described in Prt 1 (My 02), is given in Fig.1. The mins voltge is stepped down by trnsformer T1, nd full-wve bridge rectifier rrngement, D1 to D4, produces the d.c. output. Reservoir cpcitor 5 reduces supply ripple. Voltge regultors I1 nd I2 virtully eliminte ny voltge swings cused by lod vritions. The regultors lso remove ny residul 100Hz ripple on the supply voltge rils nd permit the use of lower vlue reservoir cpcitor (5). ow level electricl noise, extending into the r.f. spectrum, is present in the output of the i.c.s, nd bypss cpcitors, 6, 7, 8 nd 9, shunt this to the 0V ril. The voltges required by mplifiers, premplifiers nd uxiliry equipment re often different, nd provision is mde for two regulted outputs. Alterntively, ech output cn supply seprte chnnel of stereo system in order to double the current rting. The switching ction of the rectifier diodes (D1 to D4) modultes ny r.f. (rdio frequencies) present in the mins input. This modulted r.f. cn be piced up by rdio receivers connected to the supply nd it mnifests itself s 100Hz hum which only ppers when sttion is tuned in. pcitors 1 to 4, connected cross the diodes, suppress this interference, which is nown s modultion hum. If rdio tuners re to be powered from this circuit, these cpcitors must be fitted. OMPONENT RATINGS Fuse It is good prctice to protect the equipment with n internl fuse of the lowest possible rting. Becuse of the nture of the lod, this should be of the nti-surge or slow-blow type, nd component rted t one mp (1A) would be suitble for power supplies serving the mplifiers described in this series of rticles. Trnsformer The rectified d.c. voltge cross the reservoir cpcitor (5) must be t lest 3V more thn the regultor output when 500 Everydy Prcticl Electronics, July 2002

3 mximum current is being drwn from the supply. Further, the mximum input voltge to the regultor i.c., which is usully 35V for devices with 2A rting, must not be exceeded. It is lso desirble for the voltge drop cross it to be no more thn 10V or so, or power dissiption within the chip will be incresed nd more elborte hetsining will be required. These requirements cn best be met if the mins trnsformer secondry voltge is 3V more thn the regulted d.c. output. To determine the required current rting of the secondry winding, dd together the demnds of the mplifiers nd ncillry equipment to be connected to the power supply, nd increse this by t lest 25 per cent to llow for the rective lod presented by the reservoir cpcitor (5). The current requirements of the power mplifiers were given in Prt 1. For convenience, they re repeted here in Tble 2. Mnufcturers usully indicte the current delivering cpcity of their mins trnsformers by quoting VA rting. This is, of course, the secondry output voltge multiplied by the mximum current which the trnsformer cn supply. In Europe, mins trnsformers often hve two 115V primry windings nd two identicl secondry windings. The primry windings must be series or prllel connected to suit the locl supply voltge, nd the secondry connected to deliver the desired output. Prllel connecting the secondry will, of course, double the current vilble. onnect the windings in phse or the trnsformer will be short circuited. MAINS TRANSFORMER PRIMARY TO SUIT SUPPY VOTAGE. SEE TABE 1 FOR DETAIS OF SEONDARY 1A TIME DEAY (SOW BOW) FUSE P N E EURO STYE MAINS INET PUG Rectifiers With cpcitor input filter, the rectifiers (D1 to D4) must hve p.i.v. (pe inverse voltge) rting t lest three times the secondry voltge of the mins trnsformer. Their current rting should be t lest 50 per cent greter thn the mximum lod on the power supply. Reservoir pcitor The vlue of the reservoir cpcitor, in microfrds (mf), should be t lest 2500 times the mximum lod current in mps when the supply is regulted, nd double this vlue when unregulted. The woring voltge should be t lest double the secondry voltge of the mins trnsformer. Regultors The current rting of the voltge regultors (I1 nd I2) must, of course, be equl to or greter thn the mximum current demnd on the power supply. The mximum input voltge rting (usully 30V to 35V) must be t lest 1 5 times the secondry voltge of the mins trnsformer. Regultor i.c.s re vilble in rnge of output voltges suitble for the udio mplifiers (My 02) nd premplifiers (June 02) described in this series. Mximum current rtings re 5A for 12V nd 3A for 15V units, but chips rted t more thn 2A cn be difficult to obtin. When the current demnd exceeds 2A; e.g. when two, bridge-connected, pirs of TDA2003 udio power mplifier modules re used in stereo combintion, fit 2A regultor to ech output of the power supply nd use one for ech stereo chnnel. Suppressor pcitors The woring voltge of cpcitors 1 to 4, connected cross the rectifier diodes, should be t lest four times the secondry voltge of the mins trnsformer. Bypss cpcitors 6, 7, 8 nd 9, should hve woring voltge t lest 1 5 times the trnsformer secondry voltge to protect them in the event of regultor filure. Everydy Prcticl Electronics, July D1 1N4002 D2 1N4002 Tble 2: Power Amplifier urrent Requirements Power Amp Speer Imp Supply volts urrent drin Power output I.. Ohms V d.c. A W M386N M386N TDA TDA TBA820M TBA820M M380N M380N TDA TDA TDA2003 x TDA2003 x urrent drin nd power output mesured just before the onset of clipping. 230V FS1 0V T1 SEE OMPONENT D3 1N4002 IST D4 1N µ SEE NOTE SEE TABE 1 FOR DETAIS OF VOTAGE REGUATORS I1 AND I2 IN OM I1 IN OUT OM I2 6 8 OUT REGUATED OUTPUT µ REGUATED OUTPUT µ Fig.1. ircuit digrm for Dul Output Regulted Power Supply. Tble 1: omponent Rtings Regulted Output Trnsformer Sec. Regultor I.. 5 V d.c. V r.m.s. (1A mx output) Woring Voltge NOTES: (1) To determine the trnsformer current rting, dd together the current demnds of pre nd power mplifiers nd ny ncillry equipment, then increse the totl by t lest 25% to llow for the rective lod presented by 5. (2) A bridge-connected pir of TDA2003 i.c.s with 4 ohm lod will drw 1 7A from 15V supply nd the rtings of the rectifiers, regultor nd reservoir cpcitor must be incresed. Use 1N5401 rectifiers, n 78S15 regultor nd 4700mF cpcitor for 5 (35V woring). (3) For two, bridge-connected pirs of TDA2003 i.c.s in stereo combintion, fit 10000mF (or two 4700mF) 35V reservoir cpcitor, two 78S15 regultors, (one for ech stereo chnnel) nd use P600D rectifiers. ompleted power supply bord. V V 0V

4 DUA OUTPUT REGUATED POWER SUPPY pcitors 1 to 4 5 OMPONENTS POWER SUPPY cermic, 100V (4 off) 2200m rdil elect. (see Tble 1) 6, 8 cermic, 50V (2 off) 7, 9 470m rdil elect. 50V (2 off) See SHOP TAK pge Semiconductors D1 to D4 1N4002 rect. diode for 1A mx. output (4 off) 1N5401 rect. diode for 3A mx. output (4 off) P60D rect. diode for 4A mx. output, limited by regultors (4 off) I1, I2 78 series for 1A; 78S series for 2A mximum output. See Tble 1 (2 off) Miscellneous T1 mins trnsformer see text nd Tble 1 FS1 1A 20mm slow-blow fuse to suit holder P Euro fused mins inlet, chssis mounting, plug with line socet Printed circuit bord vilble from the EPE PB Service, code 356 (PSU); metl cse, size nd type to choice; multistrnd connecting wire; mins cble; luminium sheet or proprietry hetsin nd hetsin compound; solder pins; nuts, bolts nd wshers; stnd-off pillrs (4 off); solder etc. Approx. ost Guidnce Only 20 excluding cse FS1 230V 0V T1 D3 D4 3 4 D1 D2 1 2 ONSTRUTION Any reders who hve no experience of building or commissioning mins-powered equipment re reminded tht the voltges involved cn ill! Anyone who feels unsure of his or her bility to complete project of this ind MUST see help nd guidnce from n experienced constructor. The smll components re ssembled on the printed circuit bord (p.c.b.) s illustrted in Fig.2, together with full-size copper foil mster nd the interwiring to off-bord components. This bord is vilble from the EPE PB Service, code 356. ommence construction by first soldering in position on the p.c.b. the rectifier diodes nd non-electrolytic cpcitors. This cn be OUT I1 I2 OM IN OUT 6 8 OM IN OUTPUT 1 REGUATED V SEPARATE EARTH (0V RAI) RETURNS TO PREAMP, POWER AMP, ET. REGUATED V OUTPUT 2 E N SODER TAG HEATSINK 3. 4IN (86. 4mm) P 356 I1 AND I2 ONNETION DETAIS TYPE NUMBER 1. 85IN (47mm) V IN V OUT OMMON Fig.2. Power Supply printed circuit bord, full-size copper mster nd suggested mins trnsformer nd seprte pnel fuseholder interwiring. The 16 s.w.g. luminium hetsin mesures 45mm x 45mm. 502 Everydy Prcticl Electronics, July 2002

5 followed by the lrger electrolytic types nd the voltge regultors I1 nd I2. Finlly, you will need to bolt hetsin to the regultors nd detils of choosing suitble hetsin will be given shortly. Solder pins, inserted t the led-out points, simplify the ts of off-bord wiring. Diodes D1 to D4, the reservoir cpcitor, 5, nd the regultors, I1 nd I2, hve to be chosen to suit the voltge nd current to be delivered by the power supply. The requirements re summrised in Tble 1 nd the ssocited notes. Detils of the modest current needs of the vrious premplifiers were given in Prt 2 of the series, nd the current demnds of the power mplifiers re scheduled in Tble 2. Dimensions nd fixing rrngements for mins trnsformers vry nd this hevy component should be mounted directly into or on the metl equipment cse bottom or chssis pnel. A Euro-style mins inlet plug, with built-in fuseholder for FS1, is strongly recommended. You cn, of course, use seprte pnel-mounting fuseholder if you wish, see Fig.2. Mins Erth should be connected to ny metl cse nd to the core nd cldding of the trnsformer. (A solder tg bolted under one of the mins trnsformer mounting lugs mes good erthing point for the mins Erth led.) Interwiring detils to off-bord components re lso shown in Fig.2. eds connecting the mins trnsformer to the inlet plug nd the p.c.b., nd ny mins switch wiring, should be tightly twisted to minimise externl fields. Keep the trnsformer t lest 150mm (6in.) wy from signl input wiring. Toroidl trnsformers hve smller externl field thn units with conventionl cores. They re the component of choice when the equipment is prticulrly compct nd/or high gin premplifiers re used. HEATSINKING Unless the current drin is to be very low (sy 20mA or less), the regultor i.c.s must be bolted to hetsin. The 45mm 45mm sheet of 16s.w.g. luminium shown on the drwing (Fig.2) is sufficient for current drins up to 1A when the voltge drop cross the regultors is not too extreme. For lrger current lods it is suggested tht the hetsin be extended nd bolted to the metl cse or chssis of the unit to ensure dequte het trnsfer. Filure to properly dissipte het from the regultors will result in the devices shutting down. OMMISSIONING Once construction hs been completed, chec the p.c.b. for poor soldered joints nd bridged trcs. hec the orienttion of electrolytic cpcitors, diodes nd regultors. Me sure tht the primry windings of the mins trnsformer re connected to suit the locl supply voltge, nd tht the secondry windings re connected, in phse, to deliver the correct voltge to the power supply p.c.b. It is good ide to connect the trnsformer to the mins nd chec the secondry voltge with test meter before lining it to the p.c.b. Extr cre must be ten when crrying out this lst ts. hec the voltge cross the reservoir cpcitor 5, nd tht the voltges delivered by regultors (I1 nd I2) re correct before using the supply to power ny equipment. OUDSPEAKERS oudspeer (speer) designers hve to me compromises. Sensitivity, good trnsient nd good high frequency response cll for lightweight cone nd speech coil ssembly. Power hndling nd n extended low frequency response require lrge, strong (nd hevy) cone nd coil. For good sensitivity, the mgnetic field cutting the voice coil must be intense. Unfortuntely, this increses the impednce t the cone s resonnt frequency. However, this impednce rise cn be controlled by the speer enclosure, nd powerful mgnet is lwys preferble. The reproduction of low frequencies involves lrge cone excursions nd the suspension must be highly complint. High complince lso lowers the cone s resonnt frequency, nd this extends the speer s low frequency response. However, the need to mintin control of the position of the voice coil in the mgnet gp imposes limits on how free the suspension cn be. one movement for given sound output reduces with incresing speer size but, s we hve seen, greter diphrgm mss impirs trnsient nd high-frequency response. HORSES FOR OURSES To void performnce being excessively degrded by these conflicting requirements, domestic hi-fi systems usully combine two or more speers, ech being designed to reproduce prt of the udio frequency spectrum. The low frequency unit, or bss speer, hs comprtively hevy cone nd voice coil with highly complint suspension. lever designers hve mnged to obtin resonble results with smll speers, but n extended low frequency response nd good power hndling re more esy to chieve with speers of 200mm (8in.) or more in dimeter. Mid-rnge units re sometimes provided when the low frequency speer is lrge (300mm to 450mm or 12in. to 18in. dimeter). As one would expect, cones re lighter, the complince is often stiffer, nd the chssis cn form seled enclosure. High-frequency units, or tweeters,hve very smll diphrgm, which is commonly dome shped to improve sound dispersl. Units of this ind lwys hve seled bcs. Whilst moving coil tweeters re the preferred option for hi-fi pplictions, hornloded piezoelectric units re often fitted in the high power speer systems used by musicins. The impednce of these devices rises, nd their power consumption flls lmost to zero, s the pplied frequency is lowered. They do not, therefore, require crossover unit, nd re esy to connect into multiple speer systems. OMMUNIATIONS oudspeers intended primrily for speech reproduction in communictions equipment hve to perform well over restricted frequency rnge, usully round 300Hz to 3000Hz. Inexpensive speers of the type mnufctured for portble receivers re better suited for this purpose, nd, if spce is vilble, 102mm (4in.) dimeter unit is to be preferred. lrity will be impired if low frequencies re llowed to excite the cone of speer of this ind, nd mesures to prevent this were discussed in Prt 1 (My 02). IMPEDANE Speech coil impednce is usully mesured t round 400Hz. At this frequency, the inductnce of the coil hs miniml effect, nd its impednce is only one or two ohms more thn its d.c. resistnce. As frequency rises, the inductnce of the speech coil hs growing impct nd impednce mounts stedily. The movement of the speech coil in the mgnetic field induces in it voltge which opposes the signl voltge. At the cone s resonnt frequency, very little energy is needed to sustin it in motion, nd it vibrtes redily, over lrger distnces, for comprtively smll power input. These lrger cone excursions generte greter opposing voltge, or bc-e.m.f., nd speech coil impednce, t resonnce, increses by s much s fctor of ten over its nominl vlue. The more powerful the mgnetic field, the more drmtic the rise in impednce. Impednce peing t cone resonnce (between 30Hz nd 100Hz for low frequency speers), nd the grdul rise in impednce with incresing frequency, mes the response of the speer non-liner. (The power which cn be fed to speer system flls s its impednce rises). Fortuntely, the former cn be tmed by good enclosure design, nd the ltter cn be overcome by the use of filter networs nd the ddition of tweeter. re must lwys be ten to ensure tht the rted impednce of speer system is not too low for the power mplifier. Too low n impednce will cuse excessive dissiption in the output trnsistors nd, if there is no overlod protection circuitry, the power mplifier will be ruined. Everydy Prcticl Electronics, July

6 Sfe supply voltge nd speer impednce combintions for the vrious i.c. power mplifiers were given in Prt 1. They re summrised here in Tble 2. ROSSOVERS When two or more speers re used to improve performnce, rrngements must be mde to llocte the udio spectrum between them. The resistnce presented by cpcitors to the flow of lternting current decreses s frequency rises. With inductors, resistnce increses with rising frequency. This frequency-dependnt opposition to current flow is nown s rectnce. pcitors nd inductors cn be combined in simple networs which utilise this phenomenon to llocte frequency bnds to different speers. ircuits nd design dt re given in Fig.3 nd inductor nd cpcitor vlues for common speer impednces, nd rnge of crossover frequencies, re set out in Tble 3. The rectnces of stndrd vlue cpcitors, t A) TREBE FIRST ORDER NETWORK TWO SPEAKER SYSTEM Me rectnce of inductor,, nd cpcitor,, t the crossover frequency, equl to the rted speer impednce. Tble 3: rossover Networ Inductor nd pcitor Vlues rossover frequency Hertz 4 ohm Speer st Order Filter ohm Speer nd Order Filter ohm Speer st Order Filter ohm Speer nd Order Filter Inductnce vlues,, re given in mh (millihenries). pcitor vlues,, re given in mf (microfrds). See text for guidnce on rounding figures up or down to nerest stndrd vlue. vrious udio frequencies, were tbulted in Prt Two. FITER ORDERS The simple first order filters shown in Fig.3 nd Fig.3d re perfectly suitble for domestic systems rted t up to 15W. ) MID RANGE FIRST ORDER NETWORK MID-PASS ARRANGEMENT Me the rectnce of inductor,, nd cpcitor,, t the centre frequency of the pss bnd, equl to the rted speer impednce. Assume bnd centre frequency of 1000Hz when the circuit is being used s bnd-pss filter for speech frequencies. 1 2 ow frequency roll-off bove the crossover frequency is 6dB per octve nd this my not be sufficient to protect some tweeters when higher powered mplifiers re used. In these cses, the second order filters, shown in Fig.3b nd Fig.3e, which produce 12dB roll-off, re sfer options. 1 E) MID RANGE TREBE SEOND ORDER NETWORK THREE SPEAKER SYSTEM (1) lculte inductor nd cpcitor vlues s for the first order three speer networ. B) TREBE D) 2 MID RANGE TREBE (2) Divide the cpcitor vlues by 1 4 nd multiply the inductor vlues by 1 4 to obtin the correct vlues for the second order three speer networ. SEOND ORDER NETWORK TWO SPEAKER SYSTEM (1) lculte inductor nd cpcitor vlues, s for the first order networ. (2) Divide the cpcitor vlues by 1 4 nd multiply the inductor vlues by 1 4 to obtin the correct vlues for the second order two speer networ. Inductors,, re identicl. pcitors,, re identicl. FIRST ORDER NETWORK THREE SPEAKER SYSTEM (1) Me inductor,, nd cpcitor, 1, rectnces, t the bss/midrnge cross-over frequency, equl to the rted speer impednce. (2) Me inductor, 2, nd cpcitor, 2, rectnces, t the mid-rnge/- treble cross-over frequency, equl to the rted speer impednce. Fig.3. ircuit nd design dt for loudspeer crossover networs. Inductor nd cpcitor vlues for common speer impednces nd crossover frequencies re given in Tble 3. omponents with the sme reference numbers hve identicl vlues i.e. nd 2 re two inductors of the sme vlue; 1 nd 2 re cpcitors of the sme vlue. 504 Everydy Prcticl Electronics, July 2002

7 ROSSOVER FREQUENY With two-speer systems the crossover frequency is usully between 1Hz nd 4 5Hz, nd the tweeter mnufcturer s recommendtions should be followed. If the unit is of uncertin origin, dopt crossover frequency of round 2 5Hz: this will normlly be stisfctory. When the bss speer is lrge (12 inches dimeter or more), crossover t 1Hz or even lower cn produce more even frequency response. Suitble tweeters tend to be rther costly, but n inexpensive lterntive will be described lter. THREE SPEAKERS Another wy of ensuring more even response when lrge bss speer is used is to instll third, mid-rnge unit. Suitble circuits re given in Fig.3d nd Fig.3e. The bss/mid-rnge crossover point is usully round 500Hz with open chssis mid-rnge speers, nd 1000Hz with seled bc units. The mid-rnge/treble crossover is generlly between 4 5Hz nd 6Hz. Agin, the recommendtions of the speer mnufcturer should be followed. PHASING Prllel connected bss speers must be wired in phse to void cncelltion of the lower udio frequencies. Use 1 5V dry cell to test for phsing on unmred speers by noting the bttery positive connection for the outwrd movement of the cone. rossover networs introduce phse shift, but, s frequency increses, phsing becomes less importnt. Reders cn try reversing the connections to mid-rnge units. However, unless they hve very refined er, they re not liely to detect ny difference. ROSSOVER OMPONENTS Inductors Inductors for home-mde crossovers hve to be hnd wound. The mount of wire, nd the resistive losses, cn be gretly reduced by winding the coils on short lengths of ferrite eril rod. ore sturtion problems should not rise t the power levels encountered in domestic instlltions. Bobbin construction is illustrted in Fig.4. Winding detils for the inductor vlues liely to be encountered re given in Tble 4. The wire should be wound on evenly, nd msing tpe, pplied over ech lyer, will me the ts little esier. onstructors who hve difficulty producing net windings should increse the dimeter of the bobbin ends for the lrger inductnce coils. pcitors The bipolr electrolytic cpcitors used in crossover networs re vilble in limited rnge of vlues. pcitors of this ind cn be formed by connecting two ordinry electrolytics bc-to-bc, nd this mes possible the production of nonstndrd vlues. The detils re given in Fig.5. pcitors rted t 50V woring UT BOBBIN ENDS FROM 3mm HARDBOARD (MASONITE IN USA) USING A HOE SAW IN AN EETRI DRI Tble 4: Inductnce of Ferrite-cored oils Induct mh No. of turns Use 20 s.w.g. (19.w.g.) enmelled copper wire for coils up to 2mH. Use 22 s.w.g. (21.w.g.) enmelled copper wire for 2 5mH to 3 5mH coils. See illustrtion for detils of bobbin nd core. will be suitble for ll of the power mplifiers described in Prt 1. The performnce of electrolytic cpcitors cn become uncertin t high udio frequencies, nd the best crossover networs use components with pper, polyester or polypropylene dielectric. Tolernces Vritions in the composition of ferrite rod will ffect the tbulted inductor vlues shown in Tble 4 by plus or minus 10 per cent or so. Bipolr electrolytics, whether purchsed or homemde, hve tolernce, t best, of plus or minus 20 per cent. Fortuntely, loudspeer crossover networs re very forgiving, nd component spreds even greter thn this produce no udible difference. When clculted vlues re being rounded up or down, it is prudent to err on the high side with inductors nd on the low side with cpcitors. BANDPASS FITERS Mention hs lredy been mde of the desirbility of restricting the udio bndwidth of speers used primrily for speech communiction. An inductor nd cpcitor cn be combined to produce bndpss effect, nd typicl circuit is given in Fig.3c. As strting point, select the inductor nd cpcitor vlues for centre frequency of 1000Hz (1Hz). If more severe ttenution of frequencies below 300Hz nd bove 3000Hz (3Hz) is required, reduce the cpcitor nd increse the inductor vlue. When using this networ with erphones, connect both erpieces in prllel to produce n impednce of 16 ohms, nd perform the clcultions on this bsis. Although extremely simple, this mesure will gretly improve the clrity of speech, especilly when signls re overlid by received or generted noise within the mplifiers. ROSSOVER UNIT The circuit digrm for n inexpensive 8ohm rossover/filter unit suitble for multi-purpose worshop speer is shown Fig.4. Inductor bobbin construction detils. FORMUAE FOR THE REATANE OF INDUTORS AND APAITORS X = f ohms ohms X = f c where f is in Hertz is in millihenries (mh) nd is in microfrds (mf) Everydy Prcticl Electronics, July mm GUE BOBBIN END TO PAPER TUBE ORE 60mm ENGTH OF 9. 5mm DIA FERRITE ROD 50mm mm ROED AND GUED PAPER TUBE 13mm O.D. 2 Fig.5. reting bipolr electrolytic from two cpcitors. 2 FORMUAE FOR OMBINING APAITORS Two cpcitors in series: 1 2 x = 1 2 pcitors in prllel: x = The woring voltge of ech cpcitor should be t lest 1 5 times the pe-to-pe signl voltge developed cross the loudspeer t mximum input.

8 SK1 SK2 TERMINAS 1 10m FROM AMPIFIER BIPOAR EETROYTI S1 POSITIONS 1) WIDE RANGE 2) OW PASS 3) HIGH PASS 4) MID RANGE ROSSOVER/AUDIO FITER P S FINISH 200 TURNS 8 S1b 7 P 6 5 TAP 100 TURNS S1 8Ω START S2 8Ω SPEAKER TREBE SPEAKER Fig.6. ircuit digrm for the oudspeer rossover/audio Filter IN (49. 5mm) FINISH START TAP 1 S1 2 3 A 4 TREBE SPEAKERS B ROSSOVER/AUDIO FITER pcitors 1 Inductor Miscellneous S1 OMPONENTS 10m bipolr rdil elect. 50V (Alterntively, two 22m stndrd elect. connected bc-to-bc see text nd Fig.5) 9 5mm (3/8in.) di. ferrite rod, length 63mm See (2½in.); crd, hrdbord nd glue for bobbin. Enmelled copper wire: rossover only 100 turns 20 s.w.g. (19.w.g.). rossover nd Filter 200 turns 22 s.w.g. (21.w.g.). See Fig.4 nd text 3-pole 4-wy rotry switch (only two poles used) SK1, SK2 4mm screw terminl post/socet (2 off) SHOP TAK pge Printed circuit bord vilble from the EPE PB Service, code 357 (rossover/filter); multistrnd nd connecting wire; plstic control nob; speer terminls; solder pins; solder etc. Approx. ost Guidnce Only 9 excluding speers IN (74 9mm) Fig.7. rossover/audio Filter printed circuit bord component lyout, interwiring to off-bord components nd full-size copper foil mster. The completed crossover is shown in the bove photogrph. 506 Everydy Prcticl Electronics, July 2002

9 in Fig.6. The first order filter serves s bsic crossover when the speer is being used for testing or listening to hi-fi equipment. Switching out the Treble speer nd connecting the inductor in series with the Bss speer gives low-pss (top cut) effect. onnecting the cpcitor in series with the speer provides high-pss (bss cut) rrngement. With the inductor nd cpcitor in series with the speer, response to speech frequencies is emphsised, ming the unit suitble for use with communictions receiver or for surveillnce wor. Rotry switch S1 selects the required function, nd the inductor is tpped to provide pproprite vlues for the crossover nd speech filter. ONSTRUTION onstruction of the rossover/filter Unit is bsed on smll single-sided printed circuit bord (p.c.b.). This bord is vilble from the EPE PB Service, code 357. The topside component lyout, full-size copper foil mster nd off-bord wiring detils re illustrted in Fig.7. Agin, solder pins t the led-out points will simplify off-bord wiring. The p.c.b. mes provision for series nd prllel combintions of cpcitors, nd wire lin must be inserted Infr-Red Autoswitch As the Infr-Red Autoswitch project is mins powered, ll the components hve been specilly selected to fit directly on the smll printed circuit bord (p.c.b.). If lterntive, non-bord mounting components, such s the mins trnsformer nd rely, re used you mus te extr cre when building nd testing this unit. In this cse, it is very importnt tht the p.c.b. nd ny offbord prts be mounted in its cse before testing nd tht seprte bttery supply is used for checing its opertion, prior to mins connection. The specil Shrp IS471F infr-red sensor/detector cme from RS omponents nd crries the order code They lso supplied the p.c.b. mounting, short-circuit proof, mins trnsformer with twin 9V 0 027A (0 5VA totl) secondries, code These components cn be ordered from ny bon-fide RS stocists, including some of our dvertisers. You cn order direct (credit crd only) on P or on the web t rswww.com. A post nd hndling chrge will be mde. The 12V d.c. low-profile rely, with 12A 250V.c. rted single-pole chngeover contcts, used in the model ws purchsed from Rpid Electronics (P or electronics.co.u), code We understnd tht RS (see bove) lso stoc similr rely, code The specified low-profile cse cme from P (credit crd only), P , code EN A post nd pcing chrge is mde on ll orders under 30. The Autoswitch printed circuit bord is vilble from the EPE PB Service, code 358 (see pge 539). Tech-In 2002 b 9 Once gin, it s only the sensor nd semiconductor devices clled for in this month s Tech-In 2002 b Wor tht will give some reders sourcing grief. Strting with the Nemoto NAP-7AU gs sensor/compenstor pir, these were obtined from Mplin (P or code FM87U nd re sold s pir. We hve found two listings for the precision low off-set op.mp type OP177 nd it cn be ordered from Rpid Electronics (P or code , or RS omponents (P or on the web t rswww.com), code Expect to py hndling nd postge chrge. If reders experience ny difficulty in finding locl source for the 4093 qud 2-input NAND Schmitt trigger (Rpid ) nd the AD bit nlogue-to-digitl chip (Mplin QQ00A or RS ) they should contct the bove mentioned compnies. The relevnt code numbers re shown in brcets. The iner Technology T1062N8 5th order switched cpcitor lowpss filter i.c., used in the Anti-lising Filter (b 9.5), ppers to be listed only by RS (see bove), code EPE Stylopic A couple of items proved hrd to find when trcing down prts for the EPE StyloPI project. The Ntionl Semiconductor M13600 trnsconductnce mplifier i.c. nd the SGS-Thompson 272 dul power op.mp i.c. only pper to be listed by RS, codes nd respectively. You cn order if cpcitor 1 is single, bipolr electrolytic. onstructors interested only in hi-fi pplictions cn ignore the switching rrngements nd simply connect 100- turn (0 5mH) inductor nd the cpcitor s shown in Fig.3. Next Month: The finl prt will del with speer enclosures nd include low-cost, high-performnce design ow Frequency Oscilltor for loudspeer resonnce checing. which incorportes this month s rossover/filter unit. The construction of simple nd inexpensive oscilltor nd resonnce detector, which cn be used to mtch ny speer to n enclosure nd optimise performnce, will lso be described. them direct from RS (credit crd only) on P or on the web t rswww.com. A post nd hndling chrge will be levied. The bove compny supplied the Texs T7524N 8-bit digitl-to-nlogue converter chip, code It is lso currently listed by Rpid (P or code , but double chec it is the 16-pin device being supplied. For those reders unble to progrm their own PIs, redy-progrmmed PI16F microcontroller cn be purchsed from Mgent Electronics (P or for the inclusive price of 10 ech (overses dd 1 p&p). It is the 20MHz version you require. The softwre is vilble on 3 5in. P-comptible dis (EPE Dis 5) from the EPE Editoril Office for the sum of 3 ech (UK), to cover dmin costs (for overses chrges see pge 539). It is lso vilble Free from the EPE web site: ftp://ftp.epemg.wimborne.co.u/pub/pi/stylopi. The printed circuit bord/eybord is vilble from the EPE PB Service, code 359 (see pge 539). Simple Audio ircuits 3 Most of our components dvertisers should be ble to supply ll the prts needed to construct the circuits in this month s instlment of the Simple Audio ircuits. A suitble Bulgin fused Euro-style mins inlet, chssis mounting, plug (code MK18U or FT37S) together with n insultion, rer tg, protective cover (code JK67X) nd line socet (U6S) is listed by Mplin (P or They lso list the 6A 200V P600D rectifier diode for one version of the Power Supply Unit, code UK60Q. If problems re experienced in obtining ferrite rod for the rossover unit, we understnd, from the uthor, tht one is obtinble from JAB, PO Box 5774, Birminghm, B44 8PJ (mil order only), nd J. Birett (P ).You will need to cut the rod down to size (te cre, it is brittle!). These two firms cn lso supply 50g (2oz) reels of enmelled copper wire for the rossover. The two printed circuit bords re vilble from the EPE PB Service, codes 356 (PSU) nd 357 (rossover) see pge 539. Rotry ombintion oc Probbly the most expensive item when purchsing components for the Rotry ombintion oc project is liely to be the hevy-duty power solenoid. The one in the model cost bout 15 nd cme from RS (P or rswww.com) nd is their 12V d.c. stndrd pull ction, spring return type, code They lso supplied the Omron 12V d.c. ultrmin., p.c.b. mounting rely, code The two printed circuit bords re vilble from the EPE PB Service, code 260 (oc) nd 361 (Interfce). PEASE TAKE NOTE.E.D. Sequencer (Ingenuity Unlimited) June 02 Pge 406. To prevent the i.c. outputs (I2, I3) from dversely ffecting ech other, 1N4148 signl diodes should be inserted between ech i.c. pin nd the respective l.e.d. The node on the pin nd cthode on the l.e.d. World mp June 02 Where it is sid tht VR1 should be turned clocwise, this should red nti-clocwise, nd where nti-clocwise, clocwise. Toolit TK3 Updted files for V1.2 re now on our FTP site. Only files Dis 1 nd Dis 3 re ffected. Everydy Prcticl Electronics, July