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DOLBY PRO-LOGIC SURROUND SOUND DECODER; PT.2 Dolby Surround Sound is the biggest thing in hifi in the 90s & now you can have it in your home without spend­ing big dollars. In this second article on our Dolby ProLogic* Surround Sound Decoder, we give the construction details & show how to connect it to your hifi system. By JOHN CLARKE Although the SILICON CHIP Surround Sound Decoder is complex in operation, it is easy to construct and requires no internal adjustments. The unit is built into a plastic case measuring 255 x 80 x 180mm. Virtually all of the circuitry is mounted onto a PC board coded 02311941 and measuring 204 x 151mm. 32  Silicon Chip You can begin construction by checking the PC board against the published pattern. Check that there are no open circuits or shorts between tracks. If there are any, they should be fixed before proceeding further. Note that the appropriate size holes have been drilled to take the power transformer mounting screw, the mounting screw for the mains terminal block, the screws for the two 3-terminal regulators and for the six self-tapping screws to secure the PC board into the case. The component overlay for the PC board is shown in Fig.5. This shows all components as viewed from the top of the board and the tracks are shown as if you were looking through the board from the topside. We suggest you begin the assembly of the board by inserting all the PC stakes required for the wiring to the switches, pots, sockets and other external components. Install the links using tinned copper wire. To produce a neat job, we recommend that the wire be straightened by holding each end of the wire with a pair of pliers and pulling them until the wire is slightly stretched. Cut the wire to a length suitable for each link A single large PC board accommodates most of the parts, so the construction is quite straightforward. Note the heatshrink tubing used to insulate the terminals on the fuseholder. The terminals of the power switch on the front panel must be insulated in similar fashion, to prevent accidental contact with the mains. and bend each link with pliers so that it fits neatly. Now you can install the five ICs, taking care with the orientation of each device. Take particular care when soldering in IC1 (the Dolby decoder), since its pin spacing is much closer than on normal ICs (.07-inch instead of 0.1-inch). Make sure that solder does not bridge between pins. The resistors can be installed next. Use the colour code table to guide you in selecting the resistor values. A digital multimeter can be used if you are in any doubt about the value. Note that the two 1W resistors are mounted above the PC board by about 3mm and their leads are bent inwards to accommodate the hole spacings on the PC board. Now mount the four reed relays, the diodes and transistor Q1. Take care with the orientation of the diodes and note that diode D4 is a different type to D1-D3 and D5. Regulator REG1 requires a heatsink which is secured to the PC board with a 3mm screw and nut, while REG2 (7805 or LM­340T5) bolts directly to the PC board (no heatsink needed). Bend the regulator leads so that they can be inserted into the board holes before securing with the screw and nut. The heatsink for REG1 does not need to be insulated from the regulator but smear a little heatsink compound on its mount­ing surface (the 7812 or Where To Buy A Kit Because of the licensing requirements associated with this design, it is available only as complete kit of parts from Jaycar Electronics Pty Ltd. Please note that the M69032P Dolby Pro Logic decoder IC is not available as a separate item &, for this reason, it is not possible to construct the unit by separately purchasing individual parts. LM340T12 type) before it is mounted. The capacitors can now be installed. Take care to ensure that the correct value capacitor is installed in each position. For the non-electrolytic types, the accompanying table shows the various markings which may be on the capacitor body. For example, a capacitor of .0047µF could be labelled 4n7, 472 or 0.0047. Electrolytic capacitors must be mounted with the polarity shown on the overlay diagram. The 1000µF capacitor is mounted on its side with the leads bent at right angles. We recommend that this capacitor be secured to the PC board with a dab of silicone rubber to prevent its leads from breaking. The toroidal transformer mounts using a long bolt through its centre and a large metal washer at the top. Between the transformer and the metal washer is a neoprene rubber washer and a second neoprene washer is fitted under the transformer to provide a cushioned mounting. Connect the two mains wires of the transformer (two orange) to the mains terminal block as shown on the overlay diagram. Now check your work to make sure January 1995  33 GND S4 47k 180pF 15k 15k 47k 7.5k 7.5k 0.22 0.22 .068 39k 0.1 39k 10uF 180pF 10k 100uF IC2 M65830P 8.2k 8.2k 10k D4 1 X1 10uF 1k 22k 0.1 2.7k 1M 2x100pF 22 25VW VR1 10k 1M 100k D3 RED D2 A 47  1W WHT YEL REG1 47  1W PINK T1 POWER TRANSFORMER 470pF 100uF K 10uF D1 470  8.2k 470pF A 22uF 25VW 1000uF 25VW REG2 LED2 LED1 470  1 IC3 TDA10748A 15k 15k 39k IC5 LM358 0.1 VR3 8.2k 39k IC4 TLO74 1 4.7k 180pF 10k .068 10uF 10uF 0.1 4.7k 1.8k VR2 180pF 1uF .0056 10uF 15k 22uF 100uF 47uF 18k 10uF 10uF 1uF 15k .0056 7.5k 10uF 10uF .0033 .0022 .047 10uF 10uF 10uF 10uF 82  Q1 4.7uF 15k 18k D5 100  0.1 22k 47uF 470pF 0.1 0.22 RELAY 4 25VW 47k .0056 0.1 100  0.22 0.18 47k +4V 0V 4.7uF 10uF RELAY 2 100k 0.1 0.68 100  SURROUND OUT 1 IC1 M69032P 100uF 47k 220uF 0.1 0.1 10uF RELAY 1 100k 10uF LL .0047 2x.022 680pF 330k 100  CENTRE OUT 680pF .047 .047 15k 100k 10M 22uF 15k LEFT OUT 10  10uF RELAY 3 0.1 5.6k 30  100  0.1 0.1 100k 100k 100k 22k 47k 22k 0.1 10uF 22k 22k RIGHT OUT S4 22k 8.2k LEFT IN 10  S5 RIGHT IN 10uF 240VAC Fig.5: install the parts on the PC board exactly as shown here, taking care to ensure that all polarised parts are correctly oriented. Take care also with the transformer connections & note that REG1 is fitted with a small heatsink. that all the components are correctly installed. When you are sure that the PC board assembly so far is correct, the board can be mounted in the base of the case using the self-tapping screws. 34  Silicon Chip Now it may not be immediately apparent but there is a right way and a wrong way of doing this because the case has a slightly larger opening for the front panel than for the rear panel. The correct orientation for the PC board is with the reed relays and power transformer mount­ed above the ventilation slots. Grounding the rear panel Before affixing the front panel label, attach the counter­ sunk earth screw so that it mounts flush with the front EARTH TERMINAL ACTIVE BROWN REAR PANEL FUSE SURROUND OUT LEFT OUT LEFT IN CENTRE OUT RIGHT OUT RIGHT IN EARTH GREEN/YELLOW CLAMP GROMMET BROWN NEUTRAL BLUE 5 7 4 8 6 6 2 1 5 3 4 .001 250VAC S1 EARTH TERMINAL 1 2 0.47 K A LED1 10 C S2 3 K A LED2 A VR3 VR2 VR1 1 S5 7 S3 S4 8 FRONT PANEL Fig.6: be sure to use mains-rated cable for all 240VAC wiring (ie, to the fuseholder, power transformer, mains switch & earth terminals) & note the use of shielded audio cable between the board & potentiometers VR1-VR3. January 1995  35 This close-up view shows how the power switch & its associated .001µF capacitor are insulated using heatshrink tubing. The leads to other components in the vicinity should also be insulated to prevent any possibility of accidental shorts. panel. Now attach the labels to the pre­ punched front and rear panels. The holes can be cut out with a sharp knife, reamer and small file. Now cut the pot shafts and rotary switch shaft to a length suitable for the knobs supplied. This done, install the switches, pots, LEDs (and bezels) and earth terminal on the front panel. On the rear panel, the RCA sockets, the fuse holder and earth termi­nal can be secured in place – see Fig.6 The outer sheath of the mains lead should be stripped back by about 50mm to expose the three wires. Be careful not to cut the wire insulation when doing this. Secure the mains lead into the cord grip grommet and press the grommet into the rear panel hole. The cord should be gripped securely so that it cannot be pulled out of the grommet. Connect the green/yellow (Earth) wire to the solder lug on the rear panel. The brown (Active) wire is terminated at the end lug of the fuseholder but before soldering it in position slip a length of heatshrink tubing over the wire so that the fuse termi­nals can be insulated afterwards. Now solder another brown wire to the side terminal of the fuse holder. Pass this lead through the heatshrink tubing and then push the tubing over the fuse­ hold­er body. Connect the blue (Neutral) mains wire to the mains terminal block on the PC board and another mains wire to the second termi­nal on the terminal block. Again, slip a length of heat­ CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.68µF 680n 684 0.47µF 470n 474 0.22µF 220n 224 0.18µF 180n 184 0.1µF 100n 104 .068µF 68n 683 .047µF 47n 473 .022µF 22n 223 .0056µF 5n6 562 .0047µF 4n7 472 .0033µF 3n3 332 .0022µF 2n2 222 .001µF 1n0 102 680pF 680p 681 470pF 470p 471 180pF 180p 181 100pF 100p 101 shrink tubing over the wires, ready to shroud the front panel power switch, S1. Now solder the .001µF 250VAC capacitor across S1’s terminals, then solder the two mains wires to their respective terminals and cover the switch with the heatshrink tubing. RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  2 ❏  1 ❏  7 ❏  6 ❏  4 ❏  7 ❏  2 ❏  9 ❏  4 ❏  5 ❏  3 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 ❏  2 ❏  5 ❏  1 ❏  2 ❏  1 ❏  2 36  Silicon Chip Value 10MΩ 1MΩ 330kΩ 100kΩ 47kΩ 39kΩ 22kΩ 18kΩ 15kΩ 10kΩ 8.2kΩ 7.5kΩ 5.6kΩ 4.7kΩ 2.7kΩ 1.8kΩ 1kΩ 470Ω 100Ω 82Ω 47Ω 1W 5% 30Ω 10Ω 4-Band Code (1%) brown black blue brown brown black green brown orange orange yellow brown brown black yellow brown yellow violet orange brown orange white orange brown red red orange brown brown grey orange brown brown green orange brown brown black orange brown grey red red brown violet green red brown green blue red brown yellow violet red brown red violet red brown brown grey red brown brown black red brown yellow violet brown brown brown black brown brown grey red black brown yellow violet black gold orange black black brown brown black black brown 5-Band Code (1%) brown black black green brown brown black black yellow brown orange orange black orange brown brown black black orange brown yellow violet black red brown orange white black red brown red red black red brown brown grey black red brown brown green black red brown brown black black red brown grey red black brown brown violet green black brown brown green blue black brown brown yellow violet black brown brown red violet black brown brown brown grey black brown brown brown black black brown brown yellow violet black black brown brown black black black brown grey red black gold brown not applicable orange black black gold brown brown black black gold brown Use cable ties to bind the mains wiring & the wiring to the front panel, as shown here. All ICs, including IC1 (the Dolby Pro Logic decoder), can be soldered direct to the PC board. Make sure that the mains cord is securely anchored. Both the fuse­holder and switch heatshrink tubing can now be shrunk down with a hot-air gun. The front panel is earthed to the rear panel using a length of green/yellow earth wire terminated into the solder lugs at front and rear (see Fig.6). Do not leave this lead out – it is necessary to ensure electrical safety. Take care when wiring up the rotary switch S3 since there are many connections to be made. Use hook-up wire for this. We used rainbow cable for wiring the LEDs and from S5 and S4 to the three PC pins on the board near the relays. Standard hook-up wire was used for the remaining connections. There is no need to use shielded cable for the connections to the rear panel RCA sockets. Shielded cable, however, must be used for the wiring to pots VR1, VR2 and VR3. Voltage checks Now check all your wiring carefully against the diagram of Fig.6. When complete, the Surround Sound Decoder is ready for testing. Before plugging into the mains, insert the 250mA fuse into the fuse holder if you have not already done so. Connect the negative lead of your multimeter to the 0V test point near IC1 (see Fig.5). Apply power and check that the power LED lights. Check that the output voltages of REG1 and REG2 are +12V and +5V, respectively. Actually, for REG1, the voltage should lie between +11.5V and +12.5V and for REG2, between +4.8V and +5.2V. If the voltage is low or not present, turn off the power and find the fault before switching on again. Check that there is +12V at pin 37 of IC1, pin 11 of IC3, pin 4 of IC4 and pin 8 of IC5. There should be +5V at pins 1 and 24 of IC2. Check also for +4V at pins 43 and 44 of IC1, and for +6V at pin 8 of IC3. Check that the relays operate about 10 seconds after power is applied. This can be checked by measuring the voltage at the collector of Q1. Initially, the voltage should be about +16V and when the relays switch on, the collector vol­tage should fall to less than +0.5V. Noise tests Switch on the noise test switch, S2, *Trademarks & Program Requirements Note 1: “Dolby”, “Pro Logic” and the Double-D symbol are trade­marks of Dolby Laboratories Licensing Corporation, San Francisco, CA 941034813 USA. Note 2: this Surround Sound Decoder requires a stereo program source such as a stereo television or hifi stereo VCR. For sur­round sound, the program must be Dolby Surround encoded as indi­cated in the movie credits by the Dolby Double-D symbol. For unencoded stereo signals, the Dolby 3-stereo selection will provide the centre front channel. The decoder will not operate from a mono signal. January 1995  37 The rear panel carries the left & right input sockets, plus sockets for left out (L), right out (R), surround out (S) & centre out (C). STEREO AMPLIFIER 1 L STEREO TV OR VCR PRO-LOGIC DECODER R FRONT LOUDSPEAKERS L L R R S STEREO AMPLIFIER 2 REAR LOUDSPEAKERS LEFT SURROUND RIGHT SURROUND Fig.7: the easy way of connecting the Surround Sound Decoder to your hifi system is to use a phantom centre channel. All you need, apart from the source, is another stereo amplifier & an extra pair of loudspeakers. STEREO AMPLIFIER 1 Connecting the system L L R R L STEREO TV OR VCR PRO-LOGIC DECODER FRONT LOUDSPEAKERS MONO AMPLIFIER C C R STEREO AMPLIFIER 2 REAR LOUDSPEAKERS LEFT SURROUND S RIGHT SURROUND Fig.8: this is the preferred method of installing the Surround Sound Decoder. In this case the centre channel is used & a total of five power amplifiers (& five loudspeakers) is required. 38  Silicon Chip and check that LED 2 lights. If all these tests show no problems, the decoder is ready for a listening test using the noise signal. To do this, connect an amplifier and loudspeaker to the left channel output and check that noise is present when S2 is switched on and the left channel is selected with S3. Make sure that the surround mode is selected with S5. Check the volume control operation from minimum to maximum rotation. At minimum volume, nothing should be heard from the loudspeaker while at maximum volume the noise signal should be quite loud. This done, do the same checks for the centre, right and surround channel outputs. If all is well, you can connect up to your stereo TV or stereo VCR. In general, there are two ways in which you can use the SILICON CHIP Dolby Surround Sound Decoder in your system. The easiest way is to use a phantom centre channel so that no centre channel loudspeaker or amplifier is required. This setup is shown in Fig.7 and essentially all you need, apart from a stereo TV or VCR as the source, is two stereo amplifiers and four loudspeakers. The left and right channel outputs from the decoder connect to a pair of line inputs (ie, tuner, aux) on a stereo amplifier. The rear channel signal then connects to the second stereo amplifier which is switched to mono mode so that both channels get the same signal. The rear channel amplifier does not need to be a high power unit – a unit rated at 10 watts per channel or more will be adequate. Similarly, the rear speakers can be quite modest and do not need to be full range units. Centre channel options SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ The second way to wire the system is to use the setup shown in Fig.8. In this case the centre channel is used and a total of five power amplifiers will be required. The extra power amplifier is for the centre channel and it can drive a full range loud­speaker which should ideally be of similar quality to the left and right channel speakers. This is the preferred option and for this you set the centre channel switch (S4) to “wide band”. Alternatively, you can choose to have a small centre channel speaker which has a restricted bass response. For this option, you set the centre channel switch to “normal”. This rolls off the centre channel signals below 100Hz but they are not lost and are added to the left and right channels. Warning! If a centre loudspeaker is used, do not place it on top of or underneath your TV set unless you are sure that the loudspeak­er magnets are shielded. Severe colour distortion and loss of purity will result from placing a normal speaker near a television screen or monitor. We should mention a third option which can involve two stereo amplifiers and still drive the centre channel. In this case, one power amplifier is used to drive both rear speakers which are simply connected in parallel. This prevents you from easily changing the balance between the rear speakers but this would normally not be a problem. Once the system has been installed, balance adjustments will need to be made so that the sound output is equal in all channels. This is done with the noise switch on. Start by select­ing the left channel output and the surround sound mode, and adjust the volume to a comfortable level. Now select the right channel and adjust the balance in the stereo amplifier so that the left channel and right channel outputs are the same. This done, select the centre channel and adjust the centre trim con­trol for the same sound level as the left channel, then do the same for the surround channel. That concludes the setting up. Switch off the noise test and your Dolby Pro-Logic Surround Sound Decoder SC is ready for use. January 1995  39