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Building The Our state-of-the-art portable public address amplifier Last month, we introduced this compact and powerful portable PA amplifier based on the Philips TDA1562Q 70W class-H power IC. This month, we conclude with the description of the power supply, cabinet and PC board construction and the parts list. A S NOTED last month, the power supply is effectively a battery charger with the 7 amp-hour SLA battery permanently connected. Since the charger has other uses and could be used in any situation where a float charger is required, we are describing its circuit operation and construction separately, on pages 64 and 65. We’re also detailing the box construction separately – you’ll find this on pages 66 and 67. While we give detailed dimensions, this is not the only approach possible. We’re sure some readers will come up with completely different ideas for the enclosures. Construction The PortaPAL PA Amplifier is housed in a timber cabinet measuring 480 x 280 x 240mm which is covered in speaker carpet. Corner protectors, a speaker grille, a speaker stand socket and a handle are included. The electronics is accommodated on four PC boards: the microphone PC board coded 01103032 (64 x 73mm), the auxiliary PC board coded 01103033 (109 x 35mm) and the main PC board coded 01103031 (199 x 90mm). These are mounted on an L-shaped metal bracket, the reverse of which becomes the front panel. The charger PC board coded 01103034 (132 x 66mm) mounts on the side of the box with its indicating LEDs protruding through the front panel. You can begin construction by checking the PC boards for shorted tracks or any breaks in the copper patterns. Also check that the holes are drilled to the correct sizes to suit the components. In particular, check the 56  Silicon Chip siliconchip.com.au PortaPAL FEAT P RO J U R E ECT PART 2: BY JOHN CLARKE & LEO SIMPSON corner mounting hole sizes and the holes for the pots, RCA, 6.35mm jack and XLR sockets. Microphone board Assembling the microphone PC board is simple, as shown in Fig.1. Begin by installing the LM833 op amp (IC1), together with all the resistors and capacitors. Use the resistor colour code and capacitor code tables to guide you in selecting the correct values, and/or check the resistor values with a digital multimeter. Also, the electrolytic capacitors need to be oriented with the polarity shown. Note that the 10kΩ resistors and 10µF capacitor marked with an asterisk (*) are optional for powering electret microphones. These components are not needed for dynamic microphones but will not do any harm to a dynamic mic if you regularly swap microphones. There are a couple of PC stakes required to be installed for test points TP1 and TP2. Next, insert the 90° 6-way pin header into the PC board as shown. Before mounting the two XLR sockets, screw the M3 x 10mm screws into the mounting pillars from the back of the socket and then secure the M3 tapped 6mm long spacers from the front side of the sockets. Then mount the XLR sockets directly into the PC board holes provided. Main PC board The main PC board accommodates all the potentiometers and the TDA1562Q power amplifier module. Its component layout is shown in Fig.2. siliconchip.com.au Apart from the charger/supply board, everything mounts on an L-shaped bracket, the opposite side of which also acts as the front panel. Here everything is assembled, ready for placing inside the enclosure. Aaah . . . the enclosure. Did we forget to mention you have to build that too? You can start its assembly by installing all the links, the resistors and then the ICs but not the TDA1562Q. The 2.2Ω 1W resistors need to have an over-wind of 16 turns of 0.5mm diameter enamelled copper wire. These windings are shown on the circuit published last month, as L1 & L2. Start with a short length of 0.5mm copper wire, strip and tin one end and solder it to one end of the 2.2Ω resistor. Then wind on 16 turns. Strip and tin the other end and solder it to the other end of the resistor. Repeat the process for the second 2.2Ω resistor. Then solder each resistor into the PC board. Insert all the PC stakes used for the test points and also the PC-mount spade connectors. Mount the capacitors as shown with the electrolytics marked as polarised with the correct orientation. Electrolytics marked BP (ie, non-polarised) can be inserted either way. March 2003  57 The main PC board shown here without the heatsink attached. Note the inductors wound over the resistors (near IC9). Note also that the 10µF capacitor near IC2 must be bent over the top of IC2. This is to allow clearance when the microphone PC board is plugged into the header socket. Insert the 6-way and 8-way headers, as shown. Transistor Q1, diodes D1 and D2 and the power amplifier (IC9) can be inserted. IC9 is positioned with the centre-line of its mounting holes exactly 12mm above the top face of the PC board. Be sure to solder all the pins of the amplifier and take care not to have any of the pins shorted. Diode D3 is mounted onto a 6mm spacer and secured with a nylon screw and another 6mm tapped spacer on the underside of the PC board. The nylon screw is required to prevent the tab of the diode shorting to the metal panel when it is finally assembled. The two LEDs are mounted using LED mounts. The LEDs are inserted into the mounts from the front and the leads bent over at 90° within the mount before being inserted into the PC board. Be sure that the 58  Silicon Chip orientation is correct before bending the leads. Finally, the potentiometers can be installed – take care to place each one in its correct position. The potentiometer bodies are all tied together with a length of 0.8mm tinned copper wire soldered to the top of each body. It is difficult to solder to the passivated metal, so you will need to scrape away the passivation coating (with a knife or screwdriver) before soldering the wire. The wire is then connected to the PC stake adjacent to the 330nF earthing capacitor. Place a dab of red paint or nail polish next to the positive spade lug near the 22Ω resistor and the TP GND PC stake. Fig.1: PC board overlay and same-size photo of the microphone input board. siliconchip.com.au shown. Finally, install the PC stake for the test point, TP3. Support bracket The bracket which supports the amplifier also doubles as the front panel. It is made from 195 x 240 x 1.5mm aluminium, bent at 90° to form an L-shape. The dimensions of the panel, hole positioning and sizes are shown in Fig.4. The panel can be drilled and the larger holes cut before the panel is bent and the label attached. We expect that if you purchase a kit, the panel will already be drilled and bent and will come screen printed. Those building from scratch will need to prepare the panel as shown. The dress panel artwork (like the PC board artwork) can be downloaded from the SILICON CHIP website, siliconchip.com.au and printed, then glued to the aluminium panel. Place nuts on all the pot bushes for the main board and then mount the board on M3 tapped 6mm standoffs, with M3 x 6mm screws and star washers. The standoff beneath D1 is secured in place with an M3 nut and star washer. Secure the pots with nuts on the outside of the panel. Drilling the heatsink Fig.2: install the parts on the PC board as shown on this wiring diagram. Note how the potentiometer bodies are linked together and earthed at a single point. This is for easy identification when connecting the supply wires. Auxiliary board The auxiliary PC board carries the four RCA sockets and the jack sockets. Its component layout is shown in Fig.3. siliconchip.com.au First, install all the resistors and the TL071 (IC3) op amp. Then insert the capacitors, again taking care with the polarity of the electrolytic capacitors. The 6.35mm jack sockets and the stereo RCA sockets are directly mounted onto the PC board. An 8-way pin header is mounted with the orientation The holes in the main heatsink can be drilled as shown in Fig.6. Apply a smear of heatsink compound on the face of the power amplifier and attach the heatsink to the baseplate with M6 screws into the heatsink mounting screw points. Then attach the amplifier to the heatsink with two M3 x 15mm screws, two flat washers and two nuts. Attach the auxiliary board to the front panel by first fitting fibre washers onto the 6.35mm jack socket bushes and then mating them up the relevant panel holes; secure with the nuts. The RCA stereo sockets are secured with M3 x 6mm screws tapped into the plastic mounting pillars. Plug the microphone board pin header into the control PC board socket and push the sockets into the front panel holes. Secure with M3 x 6mm screws into the 6mm standoffs already attached to the XLR sockets. Make up a lead that connects the 8-way pin header sockets using 8-way rainbow cable. This connects the auxiliary board to the main board. Make sure the orientation is correct, with no twist in the wiring. March 2003  59 Power switch S1, the fuseholder and the 3-pin DIN socket can now be attached. The DIN socket is secured with M3 x 6mm screws, star washers and nuts. Connecting the boards Fig.3: the auxiliary PC board has the line in/out and guitar input sockets – it connects to the main board via the 8-way header. Fig.5 shows the wiring to the boards, battery and speaker. The battery and speaker connections are run in 7.5A figure-8 wire and crimp plugs. Use the lengths detailed on the diagrams for the charger and Fig.5. Be sure to use blue crimp connectors for the negative lead connections and red connectors for the positive leads. That way, there is less chance of wrong polarity connections. Also note that the amplifier power leads should be connected to piggyback connectors for the battery terminals, so that the charger leads can also be connected to the battery. Making the cabinet The box is made using 16mm Medium Density Fibre board (MDF) or craftwood and 16 x 16mm Meranti for the cleats. Because many home constructors may not have precision Fig. 4: this drilling template should help you with the front panel/amplifier bracket. 60  Silicon Chip siliconchip.com.au Parts List – PortaPAL PA (Main Section) 1 mic input PC board, code 01103032, 64 x 73mm 1 auxiliary input PC board, code 01103033, 109 x 35mm 1 control PC board, code 01103031, 199 x 90mm 2 450 x 900 x 16mm sheets of MDF board or craftwood 1 4m length of 12 x 12mm Meranti 1 195 x 240mm sheet of 1.5mm aluminium for panel 1 aluminium vent strip, 240mm long 15 x 12mm channel with holes or slots (eg, slotted shelf support strip) 1 200mm (8-inch) 4Ω coaxial loudspeaker (Altronics C 2006) 8 speaker box corners, 55 x 35 x 35mm 1 speaker box “top hat” stand socket (Altronics C 3602) 1 200mm speaker grille (Altronics C 3708) 1 strap handle (Altronics C 3660) 1 1m x 1.8m length of speaker box carpet (Altronics C 3530) 1 heavy duty heatsink 110 x 33 x 72mm (Altronics H 0560) 1 M205 fuse holder (Altronics S 5992) 1 7.5A M205 fuse (F1) 4 blue knobs 2 grey knobs 3 16mm PC-mount 10kΩ log pots (VR1-VR3) 1 16mm PC-mount 5kΩ log pot (VR4) 2 16mm PC-mount 100kΩ linear pots (VR5,VR6) 1 SPST 6A rocker switch (S1) 2 6.35mm PC-mount jack sockets (Altronics P 0073) 2 stereo PC-mount RCA sockets (Altronics P-0210) 2 PC-mount XLR/6.35mm jack socket without locking tab (Altronics P-0960) 1 6-way header connector with 90° bend pins (2.54mm spacing) 2 8-way header connectors with straight pins (2.54mm spacing) 2 8-way header sockets (2.54mm spacing) 1 6-way PC-mount header socket (2.54mm spacing) 2 piggy-back 6.3mm crimp connectors 7 red female 6.3mm spade lug crimp connectors 5 blue female 6.3mm spade lug crimp connectors 4 6.3mm spade PC board connectors with 5mm pitch PC lugs (Altronics H 2094) 10 6mm tapped standoffs 10 M3 shakeproof washers 2 M3 flat washers 3 M3 nuts 10 M3 x 6mm screws 2 M3 x 15mm screws (for amplifier to heatsink connection) 4 M3 x 10mm screws (for 6mm standoffs on XLR sockets) 1 M3 x 20mm nylon screw (for diode D3 mounting and PC board mounting point) 2 M6 x 15mm screws (to secure heatsink to baseplate) 6 4G x 16mm countersunk wood screws for securing control panel and charger PC board 4 6G x 10mm cheese-head wood screws for mounting loudspeaker 4 6G x 20mm to mount speaker stand socket 3 6G x 30mm countersunk wood screws to secure MDF battery cover 2 8G x 25mm cheese-head wood screws to mount handle siliconchip.com.au 32 4G x 16mm countersunk wood screws to mount corner protectors 2 5G x 20mm countersunk wood screws to mount aluminium vent strip 1 500mm length of 0.5mm enamel copper wire 1 2m length of 7.5A rated figure-8 wire 1 600mm length of 0.8mm tinned copper wire 1 120mm length of 8-way rainbow cable Semiconductors 3 LM833 op amps (IC1,IC2&IC4) 1 TL072 op amp (IC5) 2 TL071 op amps (IC3,IC8) 1 LM358 op amp (IC6) 1 7555 CMOS timer (IC7) 1 TDA1562Q power amplifier (IC9) 1 BC337 transistor (Q1) 2 1N914, 1N4148 diodes (D1,D2) 1 15A diode (MUR1550 or similar TO-220 package) (D3) 2 5mm high brightness red LEDs (LED1,LED2) 2 PC board LED mounts (Altronics H 1543) Capacitors 2 4700µF 16V PC electrolytic 1 2200µF 25V PC electrolytic 2 100µF 16V PC electrolytic 8 47µF 16V PC electrolytic 14 10µF 16V PC electrolytic 2 2.2µF BP* electrolytic 1 2.2µF 16V PC electrolytic 4 1µF 16V PC electrolytic 5 1µF BP* electrolytic 1 330nF MKT polyester 4 220nF MKT polyester 1 100nF MKT polyester 2 15nF MKT polyester 2 1.5nF MKT polyester 1 680pF ceramic 1 560pF ceramic 2 390pF ceramic 3 330pF ceramic 2 220pF ceramic 4 150pF ceramic 1 39pF ceramic 1 22pF ceramic 1 10pF ceramic Resistors (0.25W, 1%) 1 10MΩ 1 1MΩ 1 47kΩ 1 39kΩ 4 15kΩ 21 10kΩ 8 1kΩ 5 150Ω * BP (bipolar) capacitors are also known as NP (non-polarised) 3 470kΩ 2 22kΩ 4 4.7kΩ 2 2.2Ω 1W 5 100kΩ 2 18kΩ 5 2.2kΩ Miscellaneous PVA (timber) adhesive, contact adhesive, black paint, Bag of TEK particle board screws (for box assembly) Optional: 3-pin mains socket, panel mounting – not connected but mounts inside bottom of box to act as a storage holder for plugpack when not in use. March 2003  61 Fig.5: when you have all the boards assembled, connecting them together is as simple as following this diagram. Parts List – PortaPAL SLA Float Charger 1 SLA battery charger PC board coded 01103034, 132 x 66mm 1 16VAC 1.5A plugpack 3-wire earthed type (Altronics M 9332) 1 PC board fin heatsink 84 x 24 x 28mm (Altronics H 0668) 1 12V relay with 6A contacts (RELAY1) (Altronics S 4160A) 1 3-pin 180° DIN plug 1 3-pin 180° DIN chassis socket 2 5mm high brightness red LEDs (LED3, 4) 2 PC board LED mounts (Altronics H 1543) 4 6.3mm spade PC board connectors with 5mm pitch PC lugs (Altronics H 2094) 2 M3 x 6mm screws (for DIN socket) 2 M3 x 10mm screws (for heatsink) 4 M3 nuts 4 3mm star washers 1 50mm length of 0.8mm tinned copper wire 62  Silicon Chip 4 4G x 16mm countersunk wood screws for securing charger PC board Semiconductors 1 LM317T regulator (REG1) 2 BC337 transistors (Q2,Q3) 9 1N4004 1A diodes (D4-D12) Capacitors 1 4700µF 25V PC electrolytic 1 4700µF 16V PC electrolytic 1 470µF 25V PC electrolytic 2 10µF 16V PC electrolytic Resistors (0.25W, 1%) 2 2.2kΩ 3 1kΩ 3 470Ω 1 220Ω 0.5W, 5% 1 1Ω 5W wirewound 1 500Ω horizontal trimpot (VR7) 1 120Ω siliconchip.com.au Resistor Colour Codes      No. p 1 p 1 p 3 p 5 p 1 p 1 p 2 p 2 p 4 p 21 p 4 p 7 p 11 p 3 p 1 p 5 p 1 p 2 Value       4-Band Code (1%)        5-Band Code (1%) 10MΩ brown black blue brown brown black black green brown 1MΩ brown black green brown brown black black yellow brown 470kΩ yellow violet yellow brown yellow violet black orange brown 100kΩ brown black yellow brown brown black black orange brown 47kΩ yellow violet orange brown yellow violet black red brown 39kΩ orange white orange brown orange white black red brown 22kΩ red red orange brown red red black red brown 18kΩ brown grey orange brown brown grey black red brown 15kΩ brown green orange brown brown green black red brown 10kΩ brown black orange brown brown black black red brown 4.7kΩ yellow violet red brown yellow violet black brown brown 2.2kΩ red red red brown red red black brown brown 1kΩ brown black red brown brown black black brown brown 470Ω yellow violet brown brown yellow violet black black brown 220Ω red red brown brown red red black black brown 150Ω brown green brown brown brown green black black brown 120Ω brown red brown brown brown red black black brown 2.2Ω red red gold brown red red black silver brown woodworking equipment (nor skills!) we have described the box construction in detail overleaf. Once the box is completed you can install the speaker in its rebated hole in the front panel. We used some self-adhesive foam tape underneath the speaker to make it an airtight seal. Fit the speaker grille over the front of the speaker and screw in the four mounting screws. The grille may seem like overkill because the speaker cone is so far back from the front panel – but if you don’t fit one it won’t be long before you wished you did! Testing Before installing the assembly into the box, you can test the circuit by applying power using the battery. At switch-on, the power LED should flash at a one-second rate. Check that there is power to the op amps by testing for 12V between pins 4 and 8 of the LM833, TL072 and LM358 op amps (IC1, IC2, IC4, IC5, IC6) and at pins 4 and 7 for the TL071 op amps (IC3, IC8). IC7 should have 12V between pins 1 and 8. The output of IC4b (pin 7) should be at half supply, at around +6V. Similarly, the outputs of IC1a (pin 1), IC1b (pin 7), IC2a (pin 1), IC2b (pin 7), IC3 (pin 6), IC4a (pin 1), IC5a (pin 1), IC5b (pin 7) and IC8 (pin 6) should be also at about +6V. Check that the circuit works by consiliconchip.com.au Capacitor Codes Value 330nF 220nF 100nF 15nF 1.5nF 680pF 560pF 390pF 330pF 220pF 150pF 39pF 22pF 10pF IEC Code 330n 220n 100n 15n 1n5 680p 560p 390p 330p 220p 150p 39p 22p 10p EIA Code 334 224 104 153 152 681 561 391 331 221 151 39 22 10 the cleat frame with 4G x 16mm long screws. The battery leads for the amplifier and charger pass through from the rear of the battery compartment . The battery cover is secured with three 6G x 30mm countersunk screws. With the dimensions shown, the battery should be a snug fit but if necessary, pack some pieces of foam into the compartment to stop it moving around in transit. Finally, a chassis-mounting 3-pin mains socket, screwed to the inside bottom of the case but not connected to anything, makes an ideal plugpack holder when the plugpack is not being used to charge or power the SC PortaPAL. necting the loudspeaker and applying an audio signal to one of the inputs. Turn up the volume and the speaker should begin to produce sound. The power LED should light continuously when not muted. Check operation of the charger by connecting the output leads to the piggyback battery terminals (make sure the polarity is correct) and connecting the DIN socket to the AC input on the charger. Switch on power to the plugpack and the charger LED should light and possibly the charging LED will light depending on battery charge. Mount the charger board on the inside of the cabinet, making sure that the two LEDs align and protrude through their respective holes in the control panel. Use 4G x 16mm screws to attach it in place. We used a small rubber grommet cut in half to lift the two front mountings of the PC board off the cleats by about 1mm. The L-shaped amplifier bracket/panel is installed into the box by sliding it into the 2mm Fig.6: this template can be used to ensure your drill gap and securing it to holes on the heatsink are in exactly the right place! March 2003  63 MAKING THE BOX One of the areas where home constructors come unstuck is in the cutting-out of speaker box panels. It is essential that the edges are not only straight and square but opposite panels also need to be exactly the same size – otherwise the box may be crooked or there may be air gaps. For a typical part-time woodworker using typical home workshop tools (as distinct from a pro who does it all the time!), achieving perfectly straight, smooth and square cuts with a hand saw or any type of hand-held power saw is difficult. Yes, it can be done – but it is difficult. However, there is a delightfully easy way to ensure that at least three sides of each panel have perfectly straight and parallel sides/right angles – and that is to use sheets of pre-cut board. (If the manufacturers can’t get it straight and square then we are all in trouble!) For this reason, we have elected to use two sheets of 16mm, 450 x 900mm craftwood (MDF would also be suitable). We have made the three vertical panels (ie front and both sides) 450mm high. Originally we had planned to use a single sheet of 900 x 900mm board but fortunately couldn’t find any in our local hardware store. So we purchased two 450mm wide sheets and suddenly realised what an advantage that was! Cut the two sides (240mm wide) from the top of each sheet and the front (247mm wide) from the bottom of one of the sheets (as shown on the cutting diagram) and you’ll have three edges on each panel perfectly square. The fourth edge depends on how accurately you cut. The identical top and bottom pieces (240 x 280mm) and the various bits and pieces which form the battery holder, etc, can be cut from what is left over. The vertical panels sit between (ie, inside) the top and bottom pieces, making the overall height of the box 482mm (450+16+16). One reason for placing the vertical panels inside the top and bottom, rather than vice-versa, is for strength. As made, the box will easily handle someone using it as a seat (as will inevitably happen). The front panel and the various rear pieces are recessed – the front back far enough to accommodate the speaker grille, while the rear is even further recessed. Recessing both front and back will allow the box to fall over and not break or damage the speaker itself, pot knobs or other controls. It might appear that 247mm is wrong for the front panel: if the base is 280mm wide and the two sides are 16mm wide, surely it should be 248mm (28016-16)? That extra 1mm off allows the front panel to be a snug, but not too tight fit. We cut suitable lengths of 16 x16mm meranti (which we happened to have on hand – just about any softwood will be OK) for the cleats – all around the front inside of the box for the box front (speaker baffle) to attach to and in strategic locations on the rear inside as shown by our drawings. Before assembling the box proper, we 64  Silicon Chip glued’n’screwed the cleats in position. The “L”-shaped aluminium plate holding most of the amplifier electronics screws to these cleats. After the cleats were done, the top, bottom and two side box panels were glued and clamped together, and allowed to dry overnight. The (unglued) front panel was placed in position as formwork to keep the whole thing square, When dry, we pushed out the front panel and on it marked and cut (with a jigsaw) a 185mm circle right in the centre. Naturally enough, this is where the speaker mounts – but first, the hole needs a 7mm deep, 10mm rebate all around from the front (using a router) to allow the speaker to sit flush. A 200mm metal speaker grille goes over the speaker later on to protect it. The final bit of woodwork is the mounting of the various bits of craftwood (or MDF) which hold the battery and other components in place. These mount as shown in our detailed drawing opposite. The finished box, measuring 280(w) x 240(d) x 482mm(h), can be painted, veneered, or as we have done, covered in speaker “carpet”. A lot of pro audio gear is covered in this stuff because it helps it absorb knocks and scrapes on the job or in transit. It also hides any “sins” you might have created along the way. The carpet is glued on with contact adhesive, making sure it is stretched nice and tight over and around the box. Edges are trimmed with a sharp knife and also glued. We also completely covered the inside of the box (and even the back of the speaker magnet) with the carpet to act as a sound deadening and resonance-reducing agent. siliconchip.com.au It looks schmick, too! All these pieces need to be cut to the appropriate size before gluing in place. Eight plastic speaker box corners were fitted on all corners (top and bottom) to protect them from damage. For ease of transportation we added a flexible carry handle. As we mentioned before, a metal speaker grille is fitted over the front of the speaker cone to protect it. In perhaps a bit of overkill, we added a “top hat” stand mount to the bottom of the box. This allows the box to be mounted “up high” on a standard 35mm speaker stand (or even a length of 35mm OD water pipe driven into the ground). Raising the box above the heads of an audience dramatically improves the sound “throw”, allowing greater coverage without the use of a second box or extension. Finally, the “aluminium air vent” shown above is simply an offcut from a length of U-shaped slotted aluminium channel used for shelf support verticals (the kind that brackets clip into to hold shelves). This should be available at any hardware store. It even comes with the slots pre-cut for you! These three shots, along with the diagram above, give a pretty good idea of how we constructed our box. Of course, other approaches may be just as valid – and because it is for PA (not hifi) use, dimensions are not particularly critical with the exception of the speaker cutout, battery compartment and, of course, the amplifier mounting arrangement. siliconchip.com.au March 2003  65