Fullscreen HTML5Med Res (??MB)HTML4

Check out amplifier headroom & music power Tone burst source for amplifier testing This self-contained test instrument generates the required signals to measure amplifier headroom and music power. It only needs a multimeter to read out the result. By LEO SIMPSON & JOHN CLARKE Whether or not you regard Music Power and Dynamic Headroom as a joke, hifi equipment manufacturers are quoting music power and headroom figures these days. This means means that these parameters should be confirmed when appraising a hifi amplifier. At SILICON CHIP we regularly test commercial amplifiers and our own designs so we wanted to have our own test set-up. Trouble is, we know of no commercial equipment that will do the tests. We also wanted to be able to go further than the standard IHF Music Power tests. We wanted to do longer pulse testing as advocated by manufacturers such as NAD. So what do you when there's no instrument available? You design and make your own - which is just what we did. This strange-looking instrument provides all the facilities needed to perform measurements of music power, dynamic headroom and amplifier overload recovery time. 74 SILICON CHIP We are presenting the resulting design here, not because we think the design will be produced in large numbers (although there are many organisations which could use such an instrument), but because it features a number of interesting circuit techniques. Defining terms Alright, what are the required test signals for the IHF Dynamic Headroom and Music Power? Well, the Dynamic Headroom of a power amplifier is the ratio of the Music Power to the Continuous Power expressed in decibels. So to measure headroom you first have to measure music power. The required signal conditions are set out exactly in the specification IHF-A-202 1978, as published by The Institute of High Fidelity, Inc, USA. While it is common to refer to the signal as being a tone burst, in reality it is a continuous lkHz sinewave which increases in level by 20dB for a duration of 20 milliseconds, twice a second. Or to put it another way, the amplitude of the lkHz sinewave is modulated by a pulse waveform with an "on" period of 20 milliseconds and an "off" period of 480 milliseconds. Further, the transition in level is required to occur at the zero voltage crossing of the sinewave signal. The problem with such a pulse signal is that it is difficult display on most oscilloscopes (because of its very short pulse duty cycle). Second, once the signal is displayed, it is quite difficult to judge when the onset of clipping occurs (which is the level at which the music power is measured). Then, once the exact onset of clipping is established you OSCILLOSCOPE © SYNC~ <at> © VOLTMETER Fig.1: this diagram shows how the Tone Burst Source is connected to a stereo amplifier. The DC reading on the voltmeter is squared and divided by the load resistance to give the amplifier's music ·power output. have to measure the peak-to-peak voltage displayed on the oscilloscope screen. This is difficult to do with any real accuracy since, for a high power amplifier, say with 300 watts music power, the waveform may be 140 volts peak-topeak or more. Once the peak-to-peak voltage is known, it needs to be divided by a factor of 2.828 to convert it to RMS value, then squared and divided by the load resistance to find the music power output. Clearly then, measuring music power output of an amplifier is a fiddly business. Which is why most magazines reviewing high fidelity equipment don't bother to do it.' (Either that, or they don't know how!) And when you want to measure with even longer pulse durations, say up to 300 milliseconds, you really need a storage oscilloscope to do · the job. What we wanted was a selfcontained instrument which would generate the required modulated sinewave signal, measure the power amplifier's output signal and convert it to a DC voltage which can be measured by any voltmeter, digital or analog. The voltage reading is then squared and divided by the load resistance to get the music power output. The result is our IHF Tone Burst Source. Features The IHF Tone Burst Source has a sinewave output which can be switched for continuous or modulated output, in eight burst lengths of 20, 30, 44, 66, 94, 136 and 200 milliseconds. The duty cycle for all burst lengths is fixed at 24: 1. The pulsed or continuous sinewave signal is variable in output level from zero to 2 volts RMS. So that the output waveform of the amplifier under test can be displayed on an oscilloscope, a 15V square wave sync pulse is provided. Fig.1 shows how an amplifier would be connected to the Tone Burst Source to perform a measurement of Music Power. The oscilloscope is desirable but not absolutely mandatory for the test, as we shall see later. Besides the oscilloscope and Tone Burst Source, you need a DC voltmeter (which can be a digital or analog multimeter) and a switchable dummy load which can be set to provide the rated load resistances for the amplifier under test. For most amplifiers, this means that the dummy load will have to provide 4 and 8-ohm loads at the very least, as well as 2-ohm loads for more stringently rated amplifiers. Naturally, the resistive loads need power ratings to cope with the amplifier's full output power. Depending on which channel of the amplifier is being monitored, the left or right channel output is connected to a pair of binding post terminals on the Tone Burst Source, as well as to the dummy load. JULY 1988 . 75 PARTS LIST 1 PCB, code SC4-1 -488, 130 x 103mm 1 Scotchcal front panel, 195 x 1 10mm plastic utility case, 198 x 113 x 60mm (Altronics Cat No H-0 102 or equivalent) 1 15V or 12 .6V mains transformer (see text) 1 push-on/push-off mains switch 3 DPDT miniature toggle switches 1 single-pole 8-position rotary switch (Jay car SR-1 21 0 or equivalent) 1 stereo 6. 5mm jack socket 4 banana jack sockets (two red, two black) 4 panel-mount RCA sockets 1 mains cord and plug 1 cordgrip grommet 3 knobs Inside the Tone Burst Source, the amplifier's output signal is fed to the internal signal monitoring circuitry and to an RCA socket for oscilloscope monitoring. This signal is divided down from the amplifier signals by a factor of 10 or 100, to enable the oscilloscope to correctly display the signal. We have provided this order of signal division because we are assuming that the signal will be connected directly to the CRO instead of via a 10: 1 divider probe and because most CROs have a minimum (calibrated) sensitivity of only 5 volts/div. In addition, the amplifier output signal is fed to a headphone socket which has an associated volume control. With practice, you can judge the onset of clipping "by ear" to within one or two percent. This means that it is possible to dispense with the oscilloscope although, ideally, you should have it anyway to do the test properly. The DC output voltage from the Tone Burst Source is calibrated to provide the DC equivalent of the RMS voltage for two ranges. These are the x3 and x10 ranges. To calculate the IHF power the DC voltage is multiplied by the range, then squared and divided by the load resistance for the amplifier: 76 SILICON CHIP 1 4 1 4 5mm LED and bezel 6mm standoffs solder lug rubber feet Semiconductors 2 555 timers 1 401 3 dual D flipflop 1 4066 quad analog switch 1 TL07 2 dual JFET op amp 1 CA3130 op amp 1 7815 3-terminal regulator 5 1N4002 diodes 1 1N4148, 1 N914 diode Capacitors 1 470µ,F 25VW PC electrolytic 1 4 7 µ,F 1 6VW PC electrolytic 1 15µ,F 1 6VW PC electrolytic 3 1Oµ,F 16VW PC electrolytic 1 6.8µ,F 16VW PC electrolytic 1 4 . 7 µ,F 16VW PC electrolytic 1 3 .3µF 16VW PC electrolytic 2 2. 2µ,F 16VW PC electrolytic PmF = (V x Range) 2/R1 The DC output is also available when the tone burst is disabled so that continuous RMS power can be measured at 1kHz. Using it Having connected the Tone Burst Source as shown in Fig.1, the test for Music Power is straightforward. Feed the burst signal to the amplifier and display the output waveform on the oscilloscope screen. Increase the signal amplitude until the waveform just begins to flatten at the peaks (this is the clipping point) and then back off slightly to obtain an undistorted waveform. Take the meter reading and do the power calculation as outlined above. It's as easy as that. One other test which this instrument can perform is the overload recovery time of an amplifier. The same signal is used but this time it is set so that the amplifier is overloaded by 10dB during the burst times. Most amplifiers will then take a number of cycles (at 1kHz) to recover their equilibium. The overload recovery time is then measured simply by counting the number of cycles at 1kHz so the time can be quoted in milliseconds. 1 3 4 1 1 1 1. 5µ,F 16VW PC electrolytic 1µF 16VW PC electrolytic 0 .033µ,F metallised polyester 0 .01 µF metallised polyester 0.00 1µ,F metallised polyester 22pF ceramic Resistors (0 .25W, 5%) 1 x 1.5MO, 1 X 620k0 , 2 X 4 70k0 , 3 x 220k0 , 1 x 180k0, 1 x 1 OOkO, 1 x 68k0, 1 x 4 7k0, 1 x 39k0, 1 x 27k0, 1 x 24k0, 1 x 20k0, 2 x 18k0 1W, 1 x 15k0, 3 x 1 OkO, 4 x 4. 7k0, 1 x 3.3k0 1W, 1 x 1.8k0 , 1 x 1k0, 1 X 22k0 miniature vertical trimpot, 1 x 5k0 linear potentiometer, 1 x 1kO log potentiometer Miscellaneous Hookup wire, rainbow cable , insulating tubing, solder, screws, nuts etc. Circuit features The circuitry for the Tone Burst Source consists of two 555 timers, one 4013 dual D flipflop, one single and one dual op amp package, one 4066 analog gate package plus assorted diodes, passive components and the power supply components. First of all, the circuit is required to generate a clean stable sinewave at precisely 1kHz. We do this in an unconventional way, using 555 timer IC1, D-type flipflop IC3a, and twin-T filter stage IC4a. IC1 is set to produce a 2kHz square wave. This is fed to D-type flipflop IC3a to produce a 1kHz square wave with a duty cycle of exactly 50%. The square wave is then fed to the twin-T filter stage which then produces a clean sinewave with harmonic distortion of less then 2%. That might not sound like a particularly low distortion value but it is low enough for this purpose. The output signal from IC4a is then fed to output level control VR2 and then to output amplifier IC4b. The amplifier either feeds the signal straight through with fixed gain, as for the continuous signal mode, or with gain switched between two levels, for the burst mode. c W!]OD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS .. . WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR Call Geoff for all your instrument needs 20MHz GOS-522 popular Features low cost scope •Sensitivity: SmV/div to SV/div • Bandwidth : , de to 20MHz. • Timebase : 20nS/div to 0.Ss/div $863.10 ex tax $1006.95 inc tax 20MHz GOS-523 with delay and alternate tri ~ 8et: 0 ~ C) 0 ~ Features • Sensitivity : SmV/div to SV/div • Bandwidth : de to 20MHz • Timebase A : 20ns/div to 0.Ss/div (Main) • Timebase B : 20ns/div to 0.Sms/div (Delayed) $1037.60 ex tax $1210.55 inc tax Common Features 40MHz GOS-543 top of the line • Max sensitivity : 1mV/div Features •Modes : Ch1, Ch2, Dual, Ch1±Ch2, • Sensitivity : SmV/div to SV/div X-Y • Bandwidth : de to 40MHz • Swee : Auto, Normal, Sin le • Timebase A: 20ns/div to 0.Ss/div (Main) $1285.10 ex tax • Timebase B : 20ns/d iv to 0.Sms/div (Delayed) $1499.30 inc tax Frequency Counter GFC 801 OF Just In! EPROM Eraser Model LER-121 ~ et: 0 ~ Cl 0 ~ Features • Short Circuit Protected • Auto Constant Voltage • Constant Current Indication • 0.01 % +3mV (typ) Line & Load Regulation • High Quality 4mm Binding Posts • 0.SmV or 1mVrms (typ) Ripple & Noise • Class 2.5 Analog Panel Meters GPR3030 . 0-30V, 0-3A Single Output • V & A analog meters • Fine & Coarse Voltage Control • Hi and Lo Current Ranges $237.60 ex tax $2n.20 inc tax Function Generator GFG-8019 • Multi-Function with BUILT-IN 10MHz Counter • AM, FM Modulation internal or external • Auto/Manual Sweep • 0.2Hz to 2MHz Frequency Range • Sine, Triangle, Square, Pulse and Ramp Waveforms • >20Vp-p open Circuit output, 10Vp-p into son • Variable duty cycle and de offset • VCF gives 1000:1 frequency ratio for 0-1 0V input $554.95 ex tax $643.80 inc tax • Frequency Range from 1Hz to 120MHz • Sensitivity <20mV, 10 to 100MHz, <30mV 100MHz to 120MHz • 8 digit display • 0.1 s, 1s and 10s gate times $307.85 ex tax $359.20 inc tax ~ Reliable Bench Power Supplies Capacity : 9x 24pin or 6x 28pin or . 6x 40pin UV Source : 2537°A, S000µW/cm 2 Tube Life : 3000hours approx Size : 260mm x 86mm x 70mm $95.35 ex tax $110.60 inc tax 23-Pin 'D' Connectors No it's not a misprint - there are now 23-pin connectors on some of the PC's. Geoff of course has 'em! Plugs, sockets and backshell. All $3.50 each GPD3030 2x0-30V, 0Dual Output • Series, Parallel, Independent or Dual Tracking • Four Analog Meters (V & A for both channels) $563.90 ex tax $657.90 inc tax GPQ3030 2x0-30V, 0-3A Dual Output plus Fixed SV • As above but with additional dual fixed +SV, 1A and 3A .supplies • Fixed outputs have LED overload indication $636.77 ex tax $742.90 inc tax Fans We have a furt her small quantity of those quality ITT tangential fans. Made in Germany. High throughput at low pressure across the whole width of the impeller. Noise level is less than a whisper! Self-lubricating sintered bronze sleeve bearings. 240V ac operation . Delivers 341itres/second. $49.50 (P&P $10 due to their bulk!) GPQ3030D Dual Supply with Digital Meters • As above but with two 3 1/2digit panel meters with 0.5%+2 digit accuracy $696.95 ex tax $813.12 inc tax IBM Printer Cables 1.75m and with quality connectors on both ends. You couldn't make them for this price! $14.95 GEOFF WOOD ELECTRONICS PTY LTD 229 Burns Bay Road, (Corner Beatrice St.) INC IN Nsw Lane Cove West, N.S:W. P.O. Box 671, Lane Cove N.S.W. 2066 Telephone: (02) 4271676, Fax: (02) 428 5198. 8.30am to 5.00pm Monday to Friday, 8.30am to 12 noon Saturday. Mail Orders add $5.00 to cover postal charges. Next day delivery in Sydney add $5.00. All prices INCLUDE sales tax. · Tax exemption certificates accepted if line value exceeds $10.00. BANKCARD, MASTERCARD, VISA , CHEQUES OR CASH CHEERFULLY ACCEPTED ~ 0 .,, C) 0 )J (") l: ~ +15V is~ti + 1 16VWI: 47k .,. 8 10k 2kHz ADJUST VR1 22k 3 2kHz IC1 555 .,. 11 CK IC3a 4013 ··· 1 1kHz 13 ..n... ':' J'\J\f\Jv''-..._ + 10 16VWI- 14 ,J\J' OUTPUT LEVEL VR2 5k 10k .01l ">'- - - ' - I LEFT RIGHT k .,. 220k ':' 4.7k OUTPUTS .,. .,. 4.7k ...--....--t---.....,_+15V 01 ~ . _,,,, IC3""' b- QF-2_,;;;;-1l......JL=.::;:+::;:15:.:V=-----4...,_-----------~ .,. BURST PERIOD S1 DC OUT TO VOLTMETER + 10 16VWI 22pF T FROM AMPLIFIER OUTPUT 18k 1W f..,. 3.3k 1W OUTPUI VOLUME VR3 1k LOG. HEADPHONES ~ ~ 1k .,. IHF TONE BURST SOURCE SC4·1-488 470 25VW E-~ CASE -~"' I GND The circuit of Tone Burst Source is essentially a pulse modulated oscillator with selectable pulse times, combined with an AC rectifier (D6) and a sample-and-hold circuit (IC6b, IC5) to produce the DC output signal for the external voltmeter. Amplifier monitoring is via headphones or oscilloscope. In the continuous mode, the gain of IC4b is fixed at 2.2 by the associated lOOkO and 220k0 resistors. In the burst mode, the gain is switched between 2.2 and 0.22 by analog switch IC6a. For 480 milliseconds out of each 0.5 second, IC6a shunts the 22okn feedback 78 SILICON CHIP resistor with a 24k0 resistor and thereby reduces the gain of IC4b to 0.22. Thus the required step up in gain of ten times ( + 20dB) is obtained whenever analog switch IC6a closes, in reponse to a pulse signal. The required pulse signal is generated by IC2, another 555 timer which generates a train of pulses with the required 24:1 duty cycle. This is determined by the 620kn and 27k0 resistors which charge and discharge the capacitor connected to pin 6 of the 555. The 24:1 duty cycle is obtained by dividing the sum of the two The wiring inside the Tone Burst Source is a bit of a bird's nest but is fairly straightforward if rainbow cable is used. Don't bind the wires together as this could create crosstalk problems. resistors (ie, 620k0 + 27k0) + 27k0); this gives a result of 23.963 which is within a gnat's whisker of 24:1. Switch S1 changes the capacitor connected to pins 6 and 2 of the 555, to change the pulse duration from a minimum of 20 milliseconds to a maximum of 300 milliseconds. Note that the duty cycle remains constant no matter what pulse length is selected. This means that for a pulse length of 300ms, the time between the end of one pulse and the beginning of the next is 24 x 300ms = 7.2 seconds. Now the pulse signal could have been fed directly to pin 12 of IC6a to control the gain switching of IC4b but this would mean that the transitions in level would not take place at the normal "zero axis points" of the lkHz sine wave. To ensure that this requirement is met, D-type flipflop IC3b is used. The pulse signal from IC2 is fed to IC3b's D (data) input while the CK input is clocked with the 2kHz square wave signal from ICl. This ensures that the pulse signal fed to This is the full-size artwork for the printed circuit board. JULY 1988 79 ____,...-------_______,_~~-2~~ <at> \ POWER TRANSFORMER MAINS CORO CLAMP GROMMET ~ ~ ~ SS K 0 ~LED1 A/ A .__.._ _,.,,-a,.• C OUTPUTS LEFT .7µF 3.3uF .2uF 0 . 1p . OC OUT TO + VOLTMETER - 0 o:1~J P S3 ~ OUTPUT FROM AMPLIRER OUTPUT TOCRO T HEADPHONES S ~ II \ ~ If I The wiring diagram of the Tone Burst Source uses letter coding to show the various interconnections. Note that eight capacitors are wired around switch S1. Take care with the mains wiring and use plastic sleeving to cover exposed mains connections. pin 12 of IC6a is exactly synchronised with each positive edge of the 2kHz square wave and therefore with the zero axis points of the sinewave from IC4a. Switch S2 disables flipflop IC3b so that its Q output is permanently low. This maintains IC6a in the open-circuit condition so that the gain of IC4b is fixed at 2.2. The output of IC4b is fed via a lµF capacitor to a pair of RCA sockets, for the left and right inputs of a stereo amplifier. IC4a and IC4b are biased to half the supply voltage by a voltage divider con80 SILICON GHIP sisting of two 10k0 resistors bypassed with a lOµF capacitor. The half-supply output of this divider is fed to the non-inverting inputs, pins 5 and 3, of IC4a and IC4b, respectively. The Q-bar output of flipflop IC3b provides the sync signal for an oscilloscope. Well, the description so far has detailed how the sinewave is generated and how it is switched between two levels with a duty cycle of 24:1. Now let's have a look at how the output signal from the amplifier under test is processed. Power amplifier output As noted above, the (left or right channel) output from the amplifier under test is connected via attentua tors to provide monitoring signals for headphones and an oscilloscope, as well as the signal to be measured and processed. VR3 provides the headphone signal, with quite a lot of attenuation in consideration of the high power levels likely to be involved, while the oscilloscope signal comes from the voltage divider associated with switch S3. This gives two division ratios, + 10 and + 100, so the 111, 1.11 -==:-:.:::=-=--• 10 I .. ...... Normally $7.95 ,a ~ 1.9 2s 1 $4.95ea $4.25ea $3.95ea QUALITY 3mm LEDS Cat. No . Col. 1-9 Z 10140 Red $0.1 5 Z 10141 Grn $0.20 Z 10 143 Ylw $0.20 z 10145 o,a $0.20 10 100 I 1 $0.12 $0.15 $0.15 $0.15 $0.10 $0.12 $0.12 $0.12 Equiv (Bourns 3540S, Beckman A14100 R14 110 R14120 A 14 130 R14 140 R14080 1K R14090 1·9 2K SK 10K 20K SOK 100K 10 + $9.95 $9.50 100 + $ 3.50 $ 4.95 $ 5.50 .... $ 7.90 .. . $ 8.90 .. .. $ 9.95 .. $1 0.95 ... $10.95 ... $11 .95 ... $12.95 .. . $26.95 $0.09 $0.08 $0.12 $0.10 $0.1 2 $0.1 0 H10525 105 x 75mm .. .. .. H 10529 105 x 100mm .... H 10534 105 x 140m m H 10535 105 x 150mm x 170mm H 10542 105 x 195mm ---,==r·- - - - i::a-cn--- Dials to suit 16-1-11, 18-1-11, 21-1-11. SOR 100R 200R S00A ~ !!li~~~l~Hi~i:~;~nts of heat for Designe~ by Rod Irving . H10538 105 7256) A14050 R14055 R1 4060 A1 4070 I [l' I H 10543 105 x 200mm H10546 105x 225mm H 10549 105x300mm H10560 105 x 600mm I I I . !'I RCA GOLD PLATED PLUGS AND SOCKETS ' WIRE WRAP IC SOCKETS Black anodised with a thick base plate, this radial fin heatsink can H 10520 105 x 30mm ..... QUALITY 5mm LEDS 10 + HIGH EFFICIENCY RADIAL FIN HEATSINK (!., ~ <%H::l ~ <%H ~ --====at Cat. No . Col. 1-9 Z 10 150 Red $0.10 Z 10151 Grn $0.15 Z 101 52 Ylw $0.15 10 TURN WIRE WOUND POTENTIOMETER Spec:trol Model 534 ¼ " shaft. J ~ \ ... ~ .., These quality 3·1evel wire wrap sockets are tin-plated phosphor bronze. Cat.No. Description 1-9 1O+ P10579 8 pin $1.50 $1.40 P10580 14 pin $1.85 $1 .70 P10585 16 pin $1.95 $1.80 18 pin $1.95 $1.80 P 10587 P 10590 20 pin $2.95 $2.70 P 10592 22 pin $2.95 $2.70 P10594 24 pin $3.95 $3.50 P10596 28 pin $3.95 $3.50 P 10598 40 pin $4.95 $4.50 We have m llllons of d iodes In stock! + 100 + 1000 + IN4148 Small signal Cat. 21 01 35 Je 2½e 3½e Overall : 63mm across, Srnm high . 2e LEDs: 10 x Smmx 1mm Cat.No. 1-9 3e Z101 80 IN4004 400V 1A Cat. 2 101 07 4e HIGH INTENSITY RED LED BAR GRAPH Dimension s: $2.95 10 + $2.75 Save a fort~f~~~~ nalve throw away batteries w ith t hese quality Nlcad s and Rechargers l Size Oes c. 1·9 10+ 100+ AA 450 mA.H. $2.95 $2.75 $2.50 C 1.2 A. H. $9.95 $9.50 $8.95 D 1.2 A .H . S9.95 $9. 50 $8.95 WELLER WTCPN SOLDERING STATION DIODE SPECIALS 1-99 For those who need the ultimate in connection. Essential for laser disc players to get that fantastic sound quality. Plug Cat. P10 15 1 $2.95 Socket Cat P1Qt 50 $2.25 ELECTRET MIC INSERTS With pins for easy board insertion. Cat. C10170 1·9 10+ 100 + $1.20 $1.00 S0.90 The WTCPN Features: • Power Unit 240 V AC • Temperature controlled iron , 24 VAC • Flexible silicon lead for ease of use • Can be left on without fear of damaged tips! The best is always worth having. Ca1. T1 2500 .... .... .. ... R.R.P. $149 SPECIAL, ONLY $129 THIS MONTH ON LY! SUPER DELUXE BATTERY CHARGER • Charges from 1 to 10 O, C, AA, AAA, N, and up to 3 x 9V batteries at the same time . • Dual-colour LED in first three compartments to designate 1·SV or 9V. • 240V AC/SOHz. • Approval No. N10637 Cat. M23525 ROD IRVING ELECTRONICS IS AUSTRALIA'S COMPLETE ELECTRONICS STORE. □- · ··• ~ TRIGGER TRANSFORMERS .. .. .. .... .. ... ..... $1.45 • SAVE$30 O,ECAST ,o,es D1ecast boxes are excellent for RF shleld lng, and s1'ength. ~~re ~rii;o v6dxeg ~~ eaih 14 5 5 H1 1452 110 x60 x30mm . S 6.50 H114531 20 x65x40mm $ 6.95 H 11461 120 x9 4 x53mm $11 .50 H11462 188 x 120 x 78mm ... $13. 50 H11464188x 188 x 64mm .. . $29.50 g~;S 5~ 09,s CO•NECTOR SPECIALS! • W e have just lmpoeed 50,000 . So you get to save a small fortune ! DB25 MALE (P109001 1-9 10 + $1 .00 160 + $0.90 $0.80 DB25 FEMALE (P10901) 10 + 1-9 $1 .20 l OO + $1 .00 $0.90 CANNON TYPE CONNECTORS MULTIMETER Thi s instrument Is a compact, ruaged, battery operated, hand held 31".12 digit multimeter for measuring DC and AC voltage, DC and AC current. Resistance and Diode, for 1-9 10 < P10960 3 PIN LI NE MALE . $3.90 ...................... $3.50 P10962 3 PIN CHAS IS MALE ~~:~i~i~ t~~g~~~ ~~~t~~~r.:i~~e $3.00 ...................... $2.50 CORDLESS RECHARGEABLE SOLDERING IRON • Built in solder point illumination • Easy replacement of solder tip • Protective stand which also functions as chargi ng unit • Sponge pad attach to stand • Plug pack power adaptor • Includes Nicad battery • lnstructtion manual • 12 months warranty Cat. Tt 2480 ....... Normally $79.95 P10964 3 PIN LI NE FEMALE $4.50 ...................... $3.90 P10966 3 PI N CHASI S FEMALE $4.95 ...................... $3.95 n SPECIAL, $69.95 "NO'E!RAND" DISKS !! .!~~to~.t~1~? Now you can buy absolute top qu~lity disks that are also the cheapest 1n Australi a! They even come with a lifetime warranty! So why pay 2-3 times the pnce for the same quality ? Packs of 10, DIS DID without boxes, or brand name, just their white paper jacket, and index labels. (5 V 4 " disks includes write protects) . • t ~t~a~~ti~ r~~~es without short circuit except 200 ohm Range which shows " 000 or 001 ". • ~ ~~~~Jle/oltage protection • Diode testing with 1 mA fixed current. • Audible Continuity Test. • Transistor hFE Test. SPECIFICATIONS .Maximum Display: 1999 counts SPECI AL$79 • MELBOURNE : 48 A 'Beckett St . Pho ne (03) 663 6151 NO RTHCOTE:425High St. Pho ne(03) 4898866 CLAYTON : 56 Renver Rd . Pho ne (03) 543 7877 SOUTH AUSTRALI A: Elec1, o nl c Dlscou nte,s PIL , 305 Morphett St, ADELAID E ~g~~:~~~~Js2~~/Ja~Jin1e1sta1edue 10 3800 ~Jritgi~l :i~~~ automatic Indication Method : LCD display. Measuring Method : Dual-slope in A-0 converter system . Over.range Indic ation: " 1 " Figure only in the display . Temperature Ranges: Operating OoC to +40oC Power Su pply: one 9 volt battery (006P or FC- 1 type of equivalent) Cat. 091530 Normally $109 • Rod Irving Electronics lretght costs) METEX A-D Converter uses C-MOS technology for auto-zeroing, polarity selection and over-range indication. Full overload is provided. It is an ideal instrument for use in the field, laboratory, workshop, hobby and home applications. Features ... • Push-button ON/OFF power switch . • Single 30 position easy to use rotary switch for FUNCTION and RANGE selection. • 1.12" high contrast LCD. • Automatic over-range indication with the " 1" displayed. • Automatic polari ty indication on DC ranges . . . · .. . r1:e · 5¼" DISK STORAGE 5¼" "NO BRAND" DISKS DOUBLE SIDED/DOUBLE DENSITY 10+DISKS 100+DISKS 1.000 +DISKS Efficient ant~Pa~,~ ~otect your disks from being damaged or lost ! Features ... • 100 x s ·1; 4" disk capacity • Smoked plastic hinged lid • Lockable (2 keys supplied) • High impact ABS plastic base. • Contemporary design c1so20 .. .. .... ... .. .. only $17.95 $8-95., $8·50°0 $7·80°0 (ALL PR IC ES PER 10 DIS KS ) 3½" "NO BRAND" DISKS DOUBLE SIDED/DOUBLE DENSITY 10+DI SKS 100 +DISKS 1.000+0ISKS $27 $26 $24 (ALL PRICES PER 10 DISKS) MAIL ORDER : Loca l Orders : (03) 543 7877 Interst ate Orders: (008) 33 5757 All Inquiries : (03) 543 7877 CORRESPONDENCE : P.O. B ox 620, CL AYTON 3168 Telex : AA 151938 Fax: (03) 543 2648 - MAIL ORDER HOnlNE 008 335757 ITOLLFREEJ (STRICTLY O RDERS O N LY) LOCAL ORDERS &INQUIRIES (031 543 7877 POSTAGE RATE S: $1 S9.99 .. ... $10 $24.99 $25 $49.99 $50 $99.99 $ 100 $199 $200 $499 $500 plu s $2 .00 S3.00 $4.00 $5.00 $7.50 $10.00 $1 2.50 The above postage rates are for b asic postage only. Road Freight, b ulky and f ragile Items w ill be cha rged at different rates. All sa les tax exempt orders and wholesale inquiries to : RITRONICS WHOLESALE , 56 Renver Rd , Clayton . Ph. (03) 543 2166 (3 tines) Errors and omissions excepted. Prices and specifications sub1ec1to change :~~:-:a~~s~T;n~;r~a~~en~~~~~~~~s Machines · Apple 1s a registered trademark · Deno1es registered tr admarks of th eir respective owners llla3Z rlndNI 1:131:1l1dWV 1nd1no o~o 7 en w z 0 :::c Q. C") >< 0 0 ,.... 0 ~ >< :::::, ,.... >< 0 0 C >< :::c <( ,.... 0 w Q. ~ :::::, 0 C -o/ ' 0 0 (.) w (.) + z > en :ii! :::::, ...I 0 > 0 a: (.) ~ ~ LL LL ...I :::c C, -o, ii: / ~ LL w ...I ~ :::::, cc C") Q. ,.... ~ :::::, 0 ~ 0) cc cc • • 0 0 w > w ...I z en 0~ al ,,, 0 0 N ....... 0 0 C") --//\ 0 ~ ~ 0 C") 0 N en E C 0 ii: w Q. ~ en a: :::::, a:i w 0 a: ::::, 0 a: w 3:: en Ien 0 Q. ::::, a: m w z 0 I- L LL - :c This is the full-size artwork for the front panel of the Tone Burst Source. resulting display on the CRO needs to be multiplied by 10 or 100 to give the true value. Diode D6 rectifies the signal from the amplifier and feeds it via switch S4 and its associated resistors to analog switch IC6b which, together with IC5, forms a 82 SILICON CHIP "sample and hold" circuit. Each time the sinewave signal from IC4b increases in value by 20dB, analog switch IC6b closes and feeds the rectifier output from D6 to the lOµF capacitor at pin 3 of IC5. The lOµF capacitor stores and holds the charge until the next time IC6b closes, when it takes a new voltage sample. IC5 is a CA3130 Mosfet input op amp arranged as a voltage follower. This op amp has an extremely high input impedance which means that the 10µF capacitor experiences virtually no loading at all from the op amp input. IC5 feeds the voltage from the 10µF capacitor to the output for the DC voltmeter. Diode D5 is a voltage clamp which prevents input voltages to IC6b and IC5 from exceeding + 15.6 volts. This means that for output voltages of more than about 12 .volts or so, the attenuator switch S4 should be switched from the x3 range to the xlO. The resistor values associated with DC output switch S4 are arranged so that the DC voltage at the output terminals is equal to the RMS value of the AC voltage from the amplifier's speaker terminals, when in the continuous mode. For example, in the continuous mode (ie, switch S2 set to disable the burst mode), if 20 volts RMS is fed into the AC input terminals and the DC output switch is set to xlO, the voltage across the DC output terminals will be 2.00 volts. Similarly, for the same input conditions, if the DC output switch is set to x3 , the DC output will be 6.67 volts. In the burst mode, the DC output voltage is equivalent to the music power output voltage from the amplifier. The circuit is powered from a small 15VAC transformer which feeds a bridge rectifier, Dl to D4, and a 470µF filter capacitor. The smoothed DC is regulated to + 15 volts with a 7815 3-terminal regulator. Construction We housed our Tone Burst Source test set in a standard black plastic case measuring 198 x 113 x 60mm, with most of the circuit components mounted on a printed circuit board measuring 130 x 103mm (code SC4-1-488). The power transformer and the printed board is mounted on the metal lid of the plastic case. The lid then becomes the baseplate of the instrument. All the controls are then mounted on the top of the case while most of the input and output terminals are mounted on the sides. We used a 15V 1A transformer but since the current drain of the whole circuit is low, you could save a few dollars by going to a 12.6V 150mA transformer (such as the Altronics Cat. No. MM-2006). Asse_mbly of the PCB is a straightforward job. Install the links, resistors and diodes first, followed by the capacitors and integrated circuits. All the connections to the board are made via lengths of ribbon cable. The capacitors for the burst period switch are wired around the switch itself. Note that the wiring diagram shows most of the interconnecting wires with letter codes. For example, point K on the printed circuit board is joined to point K on VR3, the headphone level control. The case can be drilled for all the controls using the Scotchcal panel as a template. Then it is simply a matter of installing all the hardware and completing the wiring. Setting up You will need a frequency meter or oscilloscope to set up the instrument. After applying power and checking the 15V supply rail, adjust trimpot VR1 to obtain a frequency of 2kHz from pin 3 of IC1. This done, check that tkHz is obtained from pin 13 of IC3, then check the sinewave at pin 7 of IC4. Trimpot VR1 can be tweaked to obtain the cleanest sinewave but make sure the lfrequency is still close to tkHz. dheck that the continuous and burst modes can be obtained at the appropriate settings of switch S2. Check that the burst length varies in accordance with the setting of switch St. Finally, the DC output at pin 6 of IC5 can be adjusted to equal the continuous RMS AC voltage (with burst disabled) from the amplifier output. This can be done by trimming the resistor values associated with switch S4. To trim the xto setting, the 1.5MO resistor can be changed or shunted with higher values to obtain the correct reading. Similarly, the x3 setting can be trimmed by changing or shunting the 20k0 resistor with higher values. ~ T-2500MFP, Philips BT137F-600 or General Electric SC142M. The Discolight ctd from page 63 So the MOC3021s provide very high voltage isolation between all the low voltage control circuitry and the 240V AC circuitry to the Triacs. In series with each IC8 output to the MOC3021s is a LED and these are mounted on the front panel so that they give an indication of the behaviour of the Triac driven lamps. Associated with each Triac is an inductor (Lt to L4) and a 0.tµF 250VAC capacitor. These two components form an RF suppression network for each Triac so that radio interference is reduced when the Triacs are in the phase control mode (for the 4-Band Modulated and Modulated settings of S4). Note that we have specified Triacs with an isolated tab so that they can be mounted directly onto the rear panel without any need for mica washers, insulating bushes and so on. The types specified are Motorola MAC218A8FP, Motorola ~~ Power supply Power for the low voltage circuitry is provided by a 12.6V transformer feeding two half-wave rectifiers, D20 and D21, and two 470µF capacitors. The resulting unregulated positive and negative rails are fed to 3-terminal regulators to give ± 12V DC supply rails. The additional toµF and 1µF capacitors connected at the output of the regulators provide decoupling and bypassing of high frequency "hash". Note that the power switch (S6) connects mains power to the transformer only and not to the Triac output circuitry. The Active AC supply lead to the Triacs is fed directly to their anodes via the 10A front panel fuse. That completes the circuit description of the Discolight. Next month we'll present the constructional information, set-up routine and troubleshooting procedure. ~ SPECTACULAR ELEASE ..-- vifci NEWSA-100 SPEAKER KIT f,:t:i1il~ Since the introduction of VIFA speaker kits in Australia in 1985, thousands of speakers have been built with superb results. VIFA is now proud to release four new speaker kits ranging from a mere $399 to $1199 per pair including cabinets. Never before have speaker kits been so popular in Australia than after the heavy devaluation of the dollar. Similar fully imported quality loudspeakers are today typically 2-2½ times more expensive. And these speakers may very well be using Danish VIFA drivers anyway, as VIFA supply more than 50 of the world's most respected loudspeaker manufacturers with drivers. But why the big savings? Because fully imported speakers suffer from 25% import duty, 20-30% freight, 30% sales tax and 28% handling charges (typically). So if you would rather put your money into better quality than in other people's pockets, VIFA 1 sp::~~:~sd~:1::~t~: ~:~~;o;~·the kits are supplied with all parts needed including fully built crossovers and pre-cut flatpack cabinets ready to assemble. No soldering or carpentry skills are needed, just a Phillips head screwdriver, some simple hand tools and a few hours of your leisure time. Are they as good as people say? Read the reviews, listen and compare with any other speakers twice the price or more. Need we say anymore? VIFA for the quality conscious audiophile. For full details please contact Sole Australian Distributor: SCAN AUDIO Pty. Ltd. P.O. Box 242, Hawthorn 3122. Fax (03)4299309 Phone: (03! 4292199 (Melbourne) (02 5225697 (Sydney) (07 3577433 (Brisbane) (09) 3224409 (Perth) Stocked by leading stores throughout Australia :-:-:-:❖:•:•:•:-. JULY 1988 83